Inline tui as helix-tui fork.

We only rely on some of the rendering primitives and implement our
Cursive-style compositor on top.

Cargo.lock

@@ -330,6 +330,7 @@ dependencies = [
  "fuzzy-matcher",
  "helix-core",
  "helix-lsp",
+ "helix-tui",
  "helix-view",
  "ignore",
  "log",
@@ -340,7 +341,18 @@ dependencies = [
  "serde_json",
  "tokio",
  "toml",
- "tui",
+]
+
+[[package]]
+name = "helix-tui"
+version = "0.1.0"
+dependencies = [
+ "bitflags",
+ "cassowary",
+ "crossterm",
+ "serde",
+ "unicode-segmentation",
+ "unicode-width",
 ]
 
 [[package]]
@@ -351,12 +363,12 @@ dependencies = [
  "crossterm",
  "helix-core",
  "helix-lsp",
+ "helix-tui",
  "once_cell",
  "serde",
  "slotmap",
  "tokio",
  "toml",
- "tui",
  "url",
 ]
 
@@ -955,19 +967,6 @@ dependencies = [
  "regex",
 ]
 
-[[package]]
-name = "tui"
-version = "0.15.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "861d8f3ad314ede6219bcb2ab844054b1de279ee37a9bc38e3d606f9d3fb2a71"
-dependencies = [
- "bitflags",
- "cassowary",
- "crossterm",
- "unicode-segmentation",
- "unicode-width",
-]
-
 [[package]]
 name = "unicase"
 version = "2.6.0"

Cargo.toml

@@ -3,6 +3,7 @@ members = [
   "helix-core",
   "helix-view",
   "helix-term",
+  "helix-tui",
   "helix-syntax",
   "helix-lsp",
 ]

helix-term/Cargo.toml

@@ -21,7 +21,7 @@ once_cell = "1.4"
 
 tokio = { version = "1", features = ["full"] }
 num_cpus = "1"
-tui = { version = "0.15", default-features = false, features = ["crossterm"] }
+tui = { path = "../helix-tui", package = "helix-tui", default-features = false, features = ["crossterm"] }
 crossterm = { version = "0.19", features = ["event-stream"] }
 clap = { version = "3.0.0-beta.2 ", default-features = false, features = ["std", "cargo"] }
 

helix-term/src/compositor.rs

@@ -67,7 +67,7 @@ pub trait Component: Any + AnyComponent {
 use anyhow::Error;
 use std::io::stdout;
 use tui::backend::CrosstermBackend;
-type Terminal = crate::terminal::Terminal<CrosstermBackend<std::io::Stdout>>;
+type Terminal = tui::terminal::Terminal<CrosstermBackend<std::io::Stdout>>;
 
 pub struct Compositor {
     layers: Vec<Box<dyn Component>>,

helix-term/src/main.rs

@@ -4,7 +4,6 @@ mod application;
 mod commands;
 mod compositor;
 mod keymap;
-mod terminal;
 mod ui;
 
 use application::Application;

helix-tui/.gitignore

@@ -0,0 +1,6 @@
+target
+Cargo.lock
+*.log
+*.rs.rustfmt
+.gdb_history
+.idea/

helix-tui/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "helix-tui"
+version = "0.1.0"
+authors = ["Blaž Hrastnik <blaz@mxxn.io>"]
+description = """
+A library to build rich terminal user interfaces or dashboards
+"""
+edition = "2018"
+
+[features]
+default = ["crossterm"]
+
+[dependencies]
+bitflags = "1.0"
+cassowary = "0.3"
+unicode-segmentation = "1.2"
+unicode-width = "0.1"
+crossterm = { version = "0.19", optional = true }
+serde = { version = "1", "optional" = true, features = ["derive"]}

helix-tui/README.md

@@ -0,0 +1,6 @@
+# helix-tui
+
+This library is a fork of the great library
+[tui-rs](https://github.com/fdehau/tui-rs/). We've mainly relied on the double
+buffer implementation and render diffing, side-stepping it's widget and
+layouting.

helix-tui/src/backend/crossterm.rs

@@ -0,0 +1,221 @@
+use crate::{
+    backend::Backend,
+    buffer::Cell,
+    layout::Rect,
+    style::{Color, Modifier},
+};
+use crossterm::{
+    cursor::{Hide, MoveTo, Show},
+    execute, queue,
+    style::{
+        Attribute as CAttribute, Color as CColor, Print, SetAttribute, SetBackgroundColor,
+        SetForegroundColor,
+    },
+    terminal::{self, Clear, ClearType},
+};
+use std::io::{self, Write};
+
+pub struct CrosstermBackend<W: Write> {
+    buffer: W,
+}
+
+impl<W> CrosstermBackend<W>
+where
+    W: Write,
+{
+    pub fn new(buffer: W) -> CrosstermBackend<W> {
+        CrosstermBackend { buffer }
+    }
+}
+
+impl<W> Write for CrosstermBackend<W>
+where
+    W: Write,
+{
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        self.buffer.write(buf)
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        self.buffer.flush()
+    }
+}
+
+impl<W> Backend for CrosstermBackend<W>
+where
+    W: Write,
+{
+    fn draw<'a, I>(&mut self, content: I) -> io::Result<()>
+    where
+        I: Iterator<Item = (u16, u16, &'a Cell)>,
+    {
+        let mut fg = Color::Reset;
+        let mut bg = Color::Reset;
+        let mut modifier = Modifier::empty();
+        let mut last_pos: Option<(u16, u16)> = None;
+        for (x, y, cell) in content {
+            // Move the cursor if the previous location was not (x - 1, y)
+            if !matches!(last_pos, Some(p) if x == p.0 + 1 && y == p.1) {
+                map_error(queue!(self.buffer, MoveTo(x, y)))?;
+            }
+            last_pos = Some((x, y));
+            if cell.modifier != modifier {
+                let diff = ModifierDiff {
+                    from: modifier,
+                    to: cell.modifier,
+                };
+                diff.queue(&mut self.buffer)?;
+                modifier = cell.modifier;
+            }
+            if cell.fg != fg {
+                let color = CColor::from(cell.fg);
+                map_error(queue!(self.buffer, SetForegroundColor(color)))?;
+                fg = cell.fg;
+            }
+            if cell.bg != bg {
+                let color = CColor::from(cell.bg);
+                map_error(queue!(self.buffer, SetBackgroundColor(color)))?;
+                bg = cell.bg;
+            }
+
+            map_error(queue!(self.buffer, Print(&cell.symbol)))?;
+        }
+
+        map_error(queue!(
+            self.buffer,
+            SetForegroundColor(CColor::Reset),
+            SetBackgroundColor(CColor::Reset),
+            SetAttribute(CAttribute::Reset)
+        ))
+    }
+
+    fn hide_cursor(&mut self) -> io::Result<()> {
+        map_error(execute!(self.buffer, Hide))
+    }
+
+    fn show_cursor(&mut self) -> io::Result<()> {
+        map_error(execute!(self.buffer, Show))
+    }
+
+    fn get_cursor(&mut self) -> io::Result<(u16, u16)> {
+        crossterm::cursor::position()
+            .map_err(|e| io::Error::new(io::ErrorKind::Other, e.to_string()))
+    }
+
+    fn set_cursor(&mut self, x: u16, y: u16) -> io::Result<()> {
+        map_error(execute!(self.buffer, MoveTo(x, y)))
+    }
+
+    fn clear(&mut self) -> io::Result<()> {
+        map_error(execute!(self.buffer, Clear(ClearType::All)))
+    }
+
+    fn size(&self) -> io::Result<Rect> {
+        let (width, height) =
+            terminal::size().map_err(|e| io::Error::new(io::ErrorKind::Other, e.to_string()))?;
+
+        Ok(Rect::new(0, 0, width, height))
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        self.buffer.flush()
+    }
+}
+
+fn map_error(error: crossterm::Result<()>) -> io::Result<()> {
+    error.map_err(|e| io::Error::new(io::ErrorKind::Other, e.to_string()))
+}
+
+impl From<Color> for CColor {
+    fn from(color: Color) -> Self {
+        match color {
+            Color::Reset => CColor::Reset,
+            Color::Black => CColor::Black,
+            Color::Red => CColor::DarkRed,
+            Color::Green => CColor::DarkGreen,
+            Color::Yellow => CColor::DarkYellow,
+            Color::Blue => CColor::DarkBlue,
+            Color::Magenta => CColor::DarkMagenta,
+            Color::Cyan => CColor::DarkCyan,
+            Color::Gray => CColor::Grey,
+            Color::DarkGray => CColor::DarkGrey,
+            Color::LightRed => CColor::Red,
+            Color::LightGreen => CColor::Green,
+            Color::LightBlue => CColor::Blue,
+            Color::LightYellow => CColor::Yellow,
+            Color::LightMagenta => CColor::Magenta,
+            Color::LightCyan => CColor::Cyan,
+            Color::White => CColor::White,
+            Color::Indexed(i) => CColor::AnsiValue(i),
+            Color::Rgb(r, g, b) => CColor::Rgb { r, g, b },
+        }
+    }
+}
+
+#[derive(Debug)]
+struct ModifierDiff {
+    pub from: Modifier,
+    pub to: Modifier,
+}
+
+impl ModifierDiff {
+    fn queue<W>(&self, mut w: W) -> io::Result<()>
+    where
+        W: io::Write,
+    {
+        //use crossterm::Attribute;
+        let removed = self.from - self.to;
+        if removed.contains(Modifier::REVERSED) {
+            map_error(queue!(w, SetAttribute(CAttribute::NoReverse)))?;
+        }
+        if removed.contains(Modifier::BOLD) {
+            map_error(queue!(w, SetAttribute(CAttribute::NormalIntensity)))?;
+            if self.to.contains(Modifier::DIM) {
+                map_error(queue!(w, SetAttribute(CAttribute::Dim)))?;
+            }
+        }
+        if removed.contains(Modifier::ITALIC) {
+            map_error(queue!(w, SetAttribute(CAttribute::NoItalic)))?;
+        }
+        if removed.contains(Modifier::UNDERLINED) {
+            map_error(queue!(w, SetAttribute(CAttribute::NoUnderline)))?;
+        }
+        if removed.contains(Modifier::DIM) {
+            map_error(queue!(w, SetAttribute(CAttribute::NormalIntensity)))?;
+        }
+        if removed.contains(Modifier::CROSSED_OUT) {
+            map_error(queue!(w, SetAttribute(CAttribute::NotCrossedOut)))?;
+        }
+        if removed.contains(Modifier::SLOW_BLINK) || removed.contains(Modifier::RAPID_BLINK) {
+            map_error(queue!(w, SetAttribute(CAttribute::NoBlink)))?;
+        }
+
+        let added = self.to - self.from;
+        if added.contains(Modifier::REVERSED) {
+            map_error(queue!(w, SetAttribute(CAttribute::Reverse)))?;
+        }
+        if added.contains(Modifier::BOLD) {
+            map_error(queue!(w, SetAttribute(CAttribute::Bold)))?;
+        }
+        if added.contains(Modifier::ITALIC) {
+            map_error(queue!(w, SetAttribute(CAttribute::Italic)))?;
+        }
+        if added.contains(Modifier::UNDERLINED) {
+            map_error(queue!(w, SetAttribute(CAttribute::Underlined)))?;
+        }
+        if added.contains(Modifier::DIM) {
+            map_error(queue!(w, SetAttribute(CAttribute::Dim)))?;
+        }
+        if added.contains(Modifier::CROSSED_OUT) {
+            map_error(queue!(w, SetAttribute(CAttribute::CrossedOut)))?;
+        }
+        if added.contains(Modifier::SLOW_BLINK) {
+            map_error(queue!(w, SetAttribute(CAttribute::SlowBlink)))?;
+        }
+        if added.contains(Modifier::RAPID_BLINK) {
+            map_error(queue!(w, SetAttribute(CAttribute::RapidBlink)))?;
+        }
+
+        Ok(())
+    }
+}

helix-tui/src/backend/mod.rs

@@ -0,0 +1,25 @@
+use std::io;
+
+use crate::buffer::Cell;
+use crate::layout::Rect;
+
+#[cfg(feature = "crossterm")]
+mod crossterm;
+#[cfg(feature = "crossterm")]
+pub use self::crossterm::CrosstermBackend;
+
+mod test;
+pub use self::test::TestBackend;
+
+pub trait Backend {
+    fn draw<'a, I>(&mut self, content: I) -> Result<(), io::Error>
+    where
+        I: Iterator<Item = (u16, u16, &'a Cell)>;
+    fn hide_cursor(&mut self) -> Result<(), io::Error>;
+    fn show_cursor(&mut self) -> Result<(), io::Error>;
+    fn get_cursor(&mut self) -> Result<(u16, u16), io::Error>;
+    fn set_cursor(&mut self, x: u16, y: u16) -> Result<(), io::Error>;
+    fn clear(&mut self) -> Result<(), io::Error>;
+    fn size(&self) -> Result<Rect, io::Error>;
+    fn flush(&mut self) -> Result<(), io::Error>;
+}

helix-tui/src/backend/test.rs

@@ -0,0 +1,151 @@
+use crate::{
+    backend::Backend,
+    buffer::{Buffer, Cell},
+    layout::Rect,
+};
+use std::{fmt::Write, io};
+use unicode_width::UnicodeWidthStr;
+
+/// A backend used for the integration tests.
+#[derive(Debug)]
+pub struct TestBackend {
+    width: u16,
+    buffer: Buffer,
+    height: u16,
+    cursor: bool,
+    pos: (u16, u16),
+}
+
+/// Returns a string representation of the given buffer for debugging purpose.
+fn buffer_view(buffer: &Buffer) -> String {
+    let mut view = String::with_capacity(buffer.content.len() + buffer.area.height as usize * 3);
+    for cells in buffer.content.chunks(buffer.area.width as usize) {
+        let mut overwritten = vec![];
+        let mut skip: usize = 0;
+        view.push('"');
+        for (x, c) in cells.iter().enumerate() {
+            if skip == 0 {
+                view.push_str(&c.symbol);
+            } else {
+                overwritten.push((x, &c.symbol))
+            }
+            skip = std::cmp::max(skip, c.symbol.width()).saturating_sub(1);
+        }
+        view.push('"');
+        if !overwritten.is_empty() {
+            write!(
+                &mut view,
+                " Hidden by multi-width symbols: {:?}",
+                overwritten
+            )
+            .unwrap();
+        }
+        view.push('\n');
+    }
+    view
+}
+
+impl TestBackend {
+    pub fn new(width: u16, height: u16) -> TestBackend {
+        TestBackend {
+            width,
+            height,
+            buffer: Buffer::empty(Rect::new(0, 0, width, height)),
+            cursor: false,
+            pos: (0, 0),
+        }
+    }
+
+    pub fn buffer(&self) -> &Buffer {
+        &self.buffer
+    }
+
+    pub fn resize(&mut self, width: u16, height: u16) {
+        self.buffer.resize(Rect::new(0, 0, width, height));
+        self.width = width;
+        self.height = height;
+    }
+
+    pub fn assert_buffer(&self, expected: &Buffer) {
+        assert_eq!(expected.area, self.buffer.area);
+        let diff = expected.diff(&self.buffer);
+        if diff.is_empty() {
+            return;
+        }
+
+        let mut debug_info = String::from("Buffers are not equal");
+        debug_info.push('\n');
+        debug_info.push_str("Expected:");
+        debug_info.push('\n');
+        let expected_view = buffer_view(expected);
+        debug_info.push_str(&expected_view);
+        debug_info.push('\n');
+        debug_info.push_str("Got:");
+        debug_info.push('\n');
+        let view = buffer_view(&self.buffer);
+        debug_info.push_str(&view);
+        debug_info.push('\n');
+
+        debug_info.push_str("Diff:");
+        debug_info.push('\n');
+        let nice_diff = diff
+            .iter()
+            .enumerate()
+            .map(|(i, (x, y, cell))| {
+                let expected_cell = expected.get(*x, *y);
+                format!(
+                    "{}: at ({}, {}) expected {:?} got {:?}",
+                    i, x, y, expected_cell, cell
+                )
+            })
+            .collect::<Vec<String>>()
+            .join("\n");
+        debug_info.push_str(&nice_diff);
+        panic!("{}", debug_info);
+    }
+}
+
+impl Backend for TestBackend {
+    fn draw<'a, I>(&mut self, content: I) -> Result<(), io::Error>
+    where
+        I: Iterator<Item = (u16, u16, &'a Cell)>,
+    {
+        for (x, y, c) in content {
+            let cell = self.buffer.get_mut(x, y);
+            *cell = c.clone();
+        }
+        Ok(())
+    }
+
+    fn hide_cursor(&mut self) -> Result<(), io::Error> {
+        self.cursor = false;
+        Ok(())
+    }
+
+    fn show_cursor(&mut self) -> Result<(), io::Error> {
+        self.cursor = true;
+        Ok(())
+    }
+
+    fn get_cursor(&mut self) -> Result<(u16, u16), io::Error> {
+        Ok(self.pos)
+    }
+
+    fn set_cursor(&mut self, x: u16, y: u16) -> Result<(), io::Error> {
+        self.pos = (x, y);
+        Ok(())
+    }
+
+    fn clear(&mut self) -> Result<(), io::Error> {
+        self.buffer.reset();
+        Ok(())
+    }
+
+    fn size(&self) -> Result<Rect, io::Error> {
+        Ok(Rect::new(0, 0, self.width, self.height))
+    }
+
+    fn flush(&mut self) -> Result<(), io::Error> {
+        Ok(())
+    }
+}

helix-tui/src/buffer.rs

@@ -0,0 +1,745 @@
+use crate::{
+    layout::Rect,
+    style::{Color, Modifier, Style},
+    text::{Span, Spans},
+};
+use std::cmp::min;
+use unicode_segmentation::UnicodeSegmentation;
+use unicode_width::UnicodeWidthStr;
+
+/// A buffer cell
+#[derive(Debug, Clone, PartialEq)]
+pub struct Cell {
+    pub symbol: String,
+    pub fg: Color,
+    pub bg: Color,
+    pub modifier: Modifier,
+}
+
+impl Cell {
+    pub fn set_symbol(&mut self, symbol: &str) -> &mut Cell {
+        self.symbol.clear();
+        self.symbol.push_str(symbol);
+        self
+    }
+
+    pub fn set_char(&mut self, ch: char) -> &mut Cell {
+        self.symbol.clear();
+        self.symbol.push(ch);
+        self
+    }
+
+    pub fn set_fg(&mut self, color: Color) -> &mut Cell {
+        self.fg = color;
+        self
+    }
+
+    pub fn set_bg(&mut self, color: Color) -> &mut Cell {
+        self.bg = color;
+        self
+    }
+
+    pub fn set_style(&mut self, style: Style) -> &mut Cell {
+        if let Some(c) = style.fg {
+            self.fg = c;
+        }
+        if let Some(c) = style.bg {
+            self.bg = c;
+        }
+        self.modifier.insert(style.add_modifier);
+        self.modifier.remove(style.sub_modifier);
+        self
+    }
+
+    pub fn style(&self) -> Style {
+        Style::default()
+            .fg(self.fg)
+            .bg(self.bg)
+            .add_modifier(self.modifier)
+    }
+
+    pub fn reset(&mut self) {
+        self.symbol.clear();
+        self.symbol.push(' ');
+        self.fg = Color::Reset;
+        self.bg = Color::Reset;
+        self.modifier = Modifier::empty();
+    }
+}
+
+impl Default for Cell {
+    fn default() -> Cell {
+        Cell {
+            symbol: " ".into(),
+            fg: Color::Reset,
+            bg: Color::Reset,
+            modifier: Modifier::empty(),
+        }
+    }
+}
+
+/// A buffer that maps to the desired content of the terminal after the draw call
+///
+/// No widget in the library interacts directly with the terminal. Instead each of them is required
+/// to draw their state to an intermediate buffer. It is basically a grid where each cell contains
+/// a grapheme, a foreground color and a background color. This grid will then be used to output
+/// the appropriate escape sequences and characters to draw the UI as the user has defined it.
+///
+/// # Examples:
+///
+/// ```
+/// use helix_tui::buffer::{Buffer, Cell};
+/// use helix_tui::layout::Rect;
+/// use helix_tui::style::{Color, Style, Modifier};
+///
+/// let mut buf = Buffer::empty(Rect{x: 0, y: 0, width: 10, height: 5});
+/// buf.get_mut(0, 2).set_symbol("x");
+/// assert_eq!(buf.get(0, 2).symbol, "x");
+/// buf.set_string(3, 0, "string", Style::default().fg(Color::Red).bg(Color::White));
+/// assert_eq!(buf.get(5, 0), &Cell{
+///     symbol: String::from("r"),
+///     fg: Color::Red,
+///     bg: Color::White,
+///     modifier: Modifier::empty()
+/// });
+/// buf.get_mut(5, 0).set_char('x');
+/// assert_eq!(buf.get(5, 0).symbol, "x");
+/// ```
+#[derive(Debug, Clone, PartialEq)]
+pub struct Buffer {
+    /// The area represented by this buffer
+    pub area: Rect,
+    /// The content of the buffer. The length of this Vec should always be equal to area.width *
+    /// area.height
+    pub content: Vec<Cell>,
+}
+
+impl Default for Buffer {
+    fn default() -> Buffer {
+        Buffer {
+            area: Default::default(),
+            content: Vec::new(),
+        }
+    }
+}
+
+impl Buffer {
+    /// Returns a Buffer with all cells set to the default one
+    pub fn empty(area: Rect) -> Buffer {
+        let cell: Cell = Default::default();
+        Buffer::filled(area, &cell)
+    }
+
+    /// Returns a Buffer with all cells initialized with the attributes of the given Cell
+    pub fn filled(area: Rect, cell: &Cell) -> Buffer {
+        let size = area.area() as usize;
+        let mut content = Vec::with_capacity(size);
+        for _ in 0..size {
+            content.push(cell.clone());
+        }
+        Buffer { area, content }
+    }
+
+    /// Returns a Buffer containing the given lines
+    pub fn with_lines<S>(lines: Vec<S>) -> Buffer
+    where
+        S: AsRef<str>,
+    {
+        let height = lines.len() as u16;
+        let width = lines
+            .iter()
+            .map(|i| i.as_ref().width() as u16)
+            .max()
+            .unwrap_or_default();
+        let mut buffer = Buffer::empty(Rect {
+            x: 0,
+            y: 0,
+            width,
+            height,
+        });
+        for (y, line) in lines.iter().enumerate() {
+            buffer.set_string(0, y as u16, line, Style::default());
+        }
+        buffer
+    }
+
+    /// Returns the content of the buffer as a slice
+    pub fn content(&self) -> &[Cell] {
+        &self.content
+    }
+
+    /// Returns the area covered by this buffer
+    pub fn area(&self) -> &Rect {
+        &self.area
+    }
+
+    /// Returns a reference to Cell at the given coordinates
+    pub fn get(&self, x: u16, y: u16) -> &Cell {
+        let i = self.index_of(x, y);
+        &self.content[i]
+    }
+
+    /// Returns a mutable reference to Cell at the given coordinates
+    pub fn get_mut(&mut self, x: u16, y: u16) -> &mut Cell {
+        let i = self.index_of(x, y);
+        &mut self.content[i]
+    }
+
+    /// Returns the index in the Vec<Cell> for the given global (x, y) coordinates.
+    ///
+    /// Global coordinates are offset by the Buffer's area offset (`x`/`y`).
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use helix_tui::buffer::Buffer;
+    /// # use helix_tui::layout::Rect;
+    /// let rect = Rect::new(200, 100, 10, 10);
+    /// let buffer = Buffer::empty(rect);
+    /// // Global coordinates to the top corner of this buffer's area
+    /// assert_eq!(buffer.index_of(200, 100), 0);
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// Panics when given an coordinate that is outside of this Buffer's area.
+    ///
+    /// ```should_panic
+    /// # use helix_tui::buffer::Buffer;
+    /// # use helix_tui::layout::Rect;
+    /// let rect = Rect::new(200, 100, 10, 10);
+    /// let buffer = Buffer::empty(rect);
+    /// // Top coordinate is outside of the buffer in global coordinate space, as the Buffer's area
+    /// // starts at (200, 100).
+    /// buffer.index_of(0, 0); // Panics
+    /// ```
+    pub fn index_of(&self, x: u16, y: u16) -> usize {
+        debug_assert!(
+            x >= self.area.left()
+                && x < self.area.right()
+                && y >= self.area.top()
+                && y < self.area.bottom(),
+            "Trying to access position outside the buffer: x={}, y={}, area={:?}",
+            x,
+            y,
+            self.area
+        );
+        ((y - self.area.y) * self.area.width + (x - self.area.x)) as usize
+    }
+
+    /// Returns the (global) coordinates of a cell given its index
+    ///
+    /// Global coordinates are offset by the Buffer's area offset (`x`/`y`).
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use helix_tui::buffer::Buffer;
+    /// # use helix_tui::layout::Rect;
+    /// let rect = Rect::new(200, 100, 10, 10);
+    /// let buffer = Buffer::empty(rect);
+    /// assert_eq!(buffer.pos_of(0), (200, 100));
+    /// assert_eq!(buffer.pos_of(14), (204, 101));
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// Panics when given an index that is outside the Buffer's content.
+    ///
+    /// ```should_panic
+    /// # use helix_tui::buffer::Buffer;
+    /// # use helix_tui::layout::Rect;
+    /// let rect = Rect::new(0, 0, 10, 10); // 100 cells in total
+    /// let buffer = Buffer::empty(rect);
+    /// // Index 100 is the 101th cell, which lies outside of the area of this Buffer.
+    /// buffer.pos_of(100); // Panics
+    /// ```
+    pub fn pos_of(&self, i: usize) -> (u16, u16) {
+        debug_assert!(
+            i < self.content.len(),
+            "Trying to get the coords of a cell outside the buffer: i={} len={}",
+            i,
+            self.content.len()
+        );
+        (
+            self.area.x + i as u16 % self.area.width,
+            self.area.y + i as u16 / self.area.width,
+        )
+    }
+
+    /// Print a string, starting at the position (x, y)
+    pub fn set_string<S>(&mut self, x: u16, y: u16, string: S, style: Style)
+    where
+        S: AsRef<str>,
+    {
+        self.set_stringn(x, y, string, usize::MAX, style);
+    }
+
+    /// Print at most the first n characters of a string if enough space is available
+    /// until the end of the line
+    pub fn set_stringn<S>(
+        &mut self,
+        x: u16,
+        y: u16,
+        string: S,
+        width: usize,
+        style: Style,
+    ) -> (u16, u16)
+    where
+        S: AsRef<str>,
+    {
+        let mut index = self.index_of(x, y);
+        let mut x_offset = x as usize;
+        let graphemes = UnicodeSegmentation::graphemes(string.as_ref(), true);
+        let max_offset = min(self.area.right() as usize, width.saturating_add(x as usize));
+        for s in graphemes {
+            let width = s.width();
+            if width == 0 {
+                continue;
+            }
+            // `x_offset + width > max_offset` could be integer overflow on 32-bit machines if we
+            // change dimenstions to usize or u32 and someone resizes the terminal to 1x2^32.
+            if width > max_offset.saturating_sub(x_offset) {
+                break;
+            }
+
+            self.content[index].set_symbol(s);
+            self.content[index].set_style(style);
+            // Reset following cells if multi-width (they would be hidden by the grapheme),
+            for i in index + 1..index + width {
+                self.content[i].reset();
+            }
+            index += width;
+            x_offset += width;
+        }
+        (x_offset as u16, y)
+    }
+
+    pub fn set_spans<'a>(&mut self, x: u16, y: u16, spans: &Spans<'a>, width: u16) -> (u16, u16) {
+        let mut remaining_width = width;
+        let mut x = x;
+        for span in &spans.0 {
+            if remaining_width == 0 {
+                break;
+            }
+            let pos = self.set_stringn(
+                x,
+                y,
+                span.content.as_ref(),
+                remaining_width as usize,
+                span.style,
+            );
+            let w = pos.0.saturating_sub(x);
+            x = pos.0;
+            remaining_width = remaining_width.saturating_sub(w);
+        }
+        (x, y)
+    }
+
+    pub fn set_span<'a>(&mut self, x: u16, y: u16, span: &Span<'a>, width: u16) -> (u16, u16) {
+        self.set_stringn(x, y, span.content.as_ref(), width as usize, span.style)
+    }
+
+    #[deprecated(
+        since = "0.10.0",
+        note = "You should use styling capabilities of `Buffer::set_style`"
+    )]
+    pub fn set_background(&mut self, area: Rect, color: Color) {
+        for y in area.top()..area.bottom() {
+            for x in area.left()..area.right() {
+                self.get_mut(x, y).set_bg(color);
+            }
+        }
+    }
+
+    pub fn set_style(&mut self, area: Rect, style: Style) {
+        for y in area.top()..area.bottom() {
+            for x in area.left()..area.right() {
+                self.get_mut(x, y).set_style(style);
+            }
+        }
+    }
+
+    /// Resize the buffer so that the mapped area matches the given area and that the buffer
+    /// length is equal to area.width * area.height
+    pub fn resize(&mut self, area: Rect) {
+        let length = area.area() as usize;
+        if self.content.len() > length {
+            self.content.truncate(length);
+        } else {
+            self.content.resize(length, Default::default());
+        }
+        self.area = area;
+    }
+
+    /// Reset all cells in the buffer
+    pub fn reset(&mut self) {
+        for c in &mut self.content {
+            c.reset();
+        }
+    }
+
+    /// Merge an other buffer into this one
+    pub fn merge(&mut self, other: &Buffer) {
+        let area = self.area.union(other.area);
+        let cell: Cell = Default::default();
+        self.content.resize(area.area() as usize, cell.clone());
+
+        // Move original content to the appropriate space
+        let size = self.area.area() as usize;
+        for i in (0..size).rev() {
+            let (x, y) = self.pos_of(i);
+            // New index in content
+            let k = ((y - area.y) * area.width + x - area.x) as usize;
+            if i != k {
+                self.content[k] = self.content[i].clone();
+                self.content[i] = cell.clone();
+            }
+        }
+
+        // Push content of the other buffer into this one (may erase previous
+        // data)
+        let size = other.area.area() as usize;
+        for i in 0..size {
+            let (x, y) = other.pos_of(i);
+            // New index in content
+            let k = ((y - area.y) * area.width + x - area.x) as usize;
+            self.content[k] = other.content[i].clone();
+        }
+        self.area = area;
+    }
+
+    /// Builds a minimal sequence of coordinates and Cells necessary to update the UI from
+    /// self to other.
+    ///
+    /// We're assuming that buffers are well-formed, that is no double-width cell is followed by
+    /// a non-blank cell.
+    ///
+    /// # Multi-width characters handling:
+    ///
+    /// ```text
+    /// (Index:) `01`
+    /// Prev:    `コ`
+    /// Next:    `aa`
+    /// Updates: `0: a, 1: a'
+    /// ```
+    ///
+    /// ```text
+    /// (Index:) `01`
+    /// Prev:    `a `
+    /// Next:    `コ`
+    /// Updates: `0: コ` (double width symbol at index 0 - skip index 1)
+    /// ```
+    ///
+    /// ```text
+    /// (Index:) `012`
+    /// Prev:    `aaa`
+    /// Next:    `aコ`
+    /// Updates: `0: a, 1: コ` (double width symbol at index 1 - skip index 2)
+    /// ```
+    pub fn diff<'a>(&self, other: &'a Buffer) -> Vec<(u16, u16, &'a Cell)> {
+        let previous_buffer = &self.content;
+        let next_buffer = &other.content;
+        let width = self.area.width;
+
+        let mut updates: Vec<(u16, u16, &Cell)> = vec![];
+        // Cells invalidated by drawing/replacing preceeding multi-width characters:
+        let mut invalidated: usize = 0;
+        // Cells from the current buffer to skip due to preceeding multi-width characters taking their
+        // place (the skipped cells should be blank anyway):
+        let mut to_skip: usize = 0;
+        for (i, (current, previous)) in next_buffer.iter().zip(previous_buffer.iter()).enumerate() {
+            if (current != previous || invalidated > 0) && to_skip == 0 {
+                let x = i as u16 % width;
+                let y = i as u16 / width;
+                updates.push((x, y, &next_buffer[i]));
+            }
+
+            to_skip = current.symbol.width().saturating_sub(1);
+
+            let affected_width = std::cmp::max(current.symbol.width(), previous.symbol.width());
+            invalidated = std::cmp::max(affected_width, invalidated).saturating_sub(1);
+        }
+        updates
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn cell(s: &str) -> Cell {
+        let mut cell = Cell::default();
+        cell.set_symbol(s);
+        cell
+    }
+
+    #[test]
+    fn it_translates_to_and_from_coordinates() {
+        let rect = Rect::new(200, 100, 50, 80);
+        let buf = Buffer::empty(rect);
+
+        // First cell is at the upper left corner.
+        assert_eq!(buf.pos_of(0), (200, 100));
+        assert_eq!(buf.index_of(200, 100), 0);
+
+        // Last cell is in the lower right.
+        assert_eq!(buf.pos_of(buf.content.len() - 1), (249, 179));
+        assert_eq!(buf.index_of(249, 179), buf.content.len() - 1);
+    }
+
+    #[test]
+    #[should_panic(expected = "outside the buffer")]
+    fn pos_of_panics_on_out_of_bounds() {
+        let rect = Rect::new(0, 0, 10, 10);
+        let buf = Buffer::empty(rect);
+
+        // There are a total of 100 cells; zero-indexed means that 100 would be the 101st cell.
+        buf.pos_of(100);
+    }
+
+    #[test]
+    #[should_panic(expected = "outside the buffer")]
+    fn index_of_panics_on_out_of_bounds() {
+        let rect = Rect::new(0, 0, 10, 10);
+        let buf = Buffer::empty(rect);
+
+        // width is 10; zero-indexed means that 10 would be the 11th cell.
+        buf.index_of(10, 0);
+    }
+
+    #[test]
+    fn buffer_set_string() {
+        let area = Rect::new(0, 0, 5, 1);
+        let mut buffer = Buffer::empty(area);
+
+        // Zero-width
+        buffer.set_stringn(0, 0, "aaa", 0, Style::default());
+        assert_eq!(buffer, Buffer::with_lines(vec!["     "]));
+
+        buffer.set_string(0, 0, "aaa", Style::default());
+        assert_eq!(buffer, Buffer::with_lines(vec!["aaa  "]));
+
+        // Width limit:
+        buffer.set_stringn(0, 0, "bbbbbbbbbbbbbb", 4, Style::default());
+        assert_eq!(buffer, Buffer::with_lines(vec!["bbbb "]));
+
+        buffer.set_string(0, 0, "12345", Style::default());
+        assert_eq!(buffer, Buffer::with_lines(vec!["12345"]));
+
+        // Width truncation:
+        buffer.set_string(0, 0, "123456", Style::default());
+        assert_eq!(buffer, Buffer::with_lines(vec!["12345"]));
+    }
+
+    #[test]
+    fn buffer_set_string_zero_width() {
+        let area = Rect::new(0, 0, 1, 1);
+        let mut buffer = Buffer::empty(area);
+
+        // Leading grapheme with zero width
+        let s = "\u{1}a";
+        buffer.set_stringn(0, 0, s, 1, Style::default());
+        assert_eq!(buffer, Buffer::with_lines(vec!["a"]));
+
+        // Trailing grapheme with zero with
+        let s = "a\u{1}";
+        buffer.set_stringn(0, 0, s, 1, Style::default());
+        assert_eq!(buffer, Buffer::with_lines(vec!["a"]));
+    }
+
+    #[test]
+    fn buffer_set_string_double_width() {
+        let area = Rect::new(0, 0, 5, 1);
+        let mut buffer = Buffer::empty(area);
+        buffer.set_string(0, 0, "コン", Style::default());
+        assert_eq!(buffer, Buffer::with_lines(vec!["コン "]));
+
+        // Only 1 space left.
+        buffer.set_string(0, 0, "コンピ", Style::default());
+        assert_eq!(buffer, Buffer::with_lines(vec!["コン "]));
+    }
+
+    #[test]
+    fn buffer_with_lines() {
+        let buffer =
+            Buffer::with_lines(vec!["┌────────┐", "│コンピュ│", "│ーa 上で│", "└────────┘"]);
+        assert_eq!(buffer.area.x, 0);
+        assert_eq!(buffer.area.y, 0);
+        assert_eq!(buffer.area.width, 10);
+        assert_eq!(buffer.area.height, 4);
+    }
+
+    #[test]
+    fn buffer_diffing_empty_empty() {
+        let area = Rect::new(0, 0, 40, 40);
+        let prev = Buffer::empty(area);
+        let next = Buffer::empty(area);
+        let diff = prev.diff(&next);
+        assert_eq!(diff, vec![]);
+    }
+
+    #[test]
+    fn buffer_diffing_empty_filled() {
+        let area = Rect::new(0, 0, 40, 40);
+        let prev = Buffer::empty(area);
+        let next = Buffer::filled(area, Cell::default().set_symbol("a"));
+        let diff = prev.diff(&next);
+        assert_eq!(diff.len(), 40 * 40);
+    }
+
+    #[test]
+    fn buffer_diffing_filled_filled() {
+        let area = Rect::new(0, 0, 40, 40);
+        let prev = Buffer::filled(area, Cell::default().set_symbol("a"));
+        let next = Buffer::filled(area, Cell::default().set_symbol("a"));
+        let diff = prev.diff(&next);
+        assert_eq!(diff, vec![]);
+    }
+
+    #[test]
+    fn buffer_diffing_single_width() {
+        let prev = Buffer::with_lines(vec![
+            "          ",
+            "┌Title─┐  ",
+            "│      │  ",
+            "│      │  ",
+            "└──────┘  ",
+        ]);
+        let next = Buffer::with_lines(vec![
+            "          ",
+            "┌TITLE─┐  ",
+            "│      │  ",
+            "│      │  ",
+            "└──────┘  ",
+        ]);
+        let diff = prev.diff(&next);
+        assert_eq!(
+            diff,
+            vec![
+                (2, 1, &cell("I")),
+                (3, 1, &cell("T")),
+                (4, 1, &cell("L")),
+                (5, 1, &cell("E")),
+            ]
+        );
+    }
+
+    #[test]
+    #[rustfmt::skip]
+    fn buffer_diffing_multi_width() {
+        let prev = Buffer::with_lines(vec![
+            "┌Title─┐  ",
+            "└──────┘  ",
+        ]);
+        let next = Buffer::with_lines(vec![
+            "┌称号──┐  ",
+            "└──────┘  ",
+        ]);
+        let diff = prev.diff(&next);
+        assert_eq!(
+            diff,
+            vec![
+                (1, 0, &cell("称")),
+                // Skipped "i"
+                (3, 0, &cell("号")),
+                // Skipped "l"
+                (5, 0, &cell("─")),
+            ]
+        );
+    }
+
+    #[test]
+    fn buffer_diffing_multi_width_offset() {
+        let prev = Buffer::with_lines(vec!["┌称号──┐"]);
+        let next = Buffer::with_lines(vec!["┌─称号─┐"]);
+
+        let diff = prev.diff(&next);
+        assert_eq!(
+            diff,
+            vec![(1, 0, &cell("─")), (2, 0, &cell("称")), (4, 0, &cell("号")),]
+        );
+    }
+
+    #[test]
+    fn buffer_merge() {
+        let mut one = Buffer::filled(
+            Rect {
+                x: 0,
+                y: 0,
+                width: 2,
+                height: 2,
+            },
+            Cell::default().set_symbol("1"),
+        );
+        let two = Buffer::filled(
+            Rect {
+                x: 0,
+                y: 2,
+                width: 2,
+                height: 2,
+            },
+            Cell::default().set_symbol("2"),
+        );
+        one.merge(&two);
+        assert_eq!(one, Buffer::with_lines(vec!["11", "11", "22", "22"]));
+    }
+
+    #[test]
+    fn buffer_merge2() {
+        let mut one = Buffer::filled(
+            Rect {
+                x: 2,
+                y: 2,
+                width: 2,
+                height: 2,
+            },
+            Cell::default().set_symbol("1"),
+        );
+        let two = Buffer::filled(
+            Rect {
+                x: 0,
+                y: 0,
+                width: 2,
+                height: 2,
+            },
+            Cell::default().set_symbol("2"),
+        );
+        one.merge(&two);
+        assert_eq!(
+            one,
+            Buffer::with_lines(vec!["22  ", "22  ", "  11", "  11"])
+        );
+    }
+
+    #[test]
+    fn buffer_merge3() {
+        let mut one = Buffer::filled(
+            Rect {
+                x: 3,
+                y: 3,
+                width: 2,
+                height: 2,
+            },
+            Cell::default().set_symbol("1"),
+        );
+        let two = Buffer::filled(
+            Rect {
+                x: 1,
+                y: 1,
+                width: 3,
+                height: 4,
+            },
+            Cell::default().set_symbol("2"),
+        );
+        one.merge(&two);
+        let mut merged = Buffer::with_lines(vec!["222 ", "222 ", "2221", "2221"]);
+        merged.area = Rect {
+            x: 1,
+            y: 1,
+            width: 4,
+            height: 4,
+        };
+        assert_eq!(one, merged);
+    }
+}

helix-tui/src/layout.rs

@@ -0,0 +1,534 @@
+use std::cell::RefCell;
+use std::cmp::{max, min};
+use std::collections::HashMap;
+
+use cassowary::strength::{REQUIRED, WEAK};
+use cassowary::WeightedRelation::*;
+use cassowary::{Constraint as CassowaryConstraint, Expression, Solver, Variable};
+
+#[derive(Debug, Hash, Clone, Copy, PartialEq, Eq)]
+pub enum Corner {
+    TopLeft,
+    TopRight,
+    BottomRight,
+    BottomLeft,
+}
+
+#[derive(Debug, Hash, Clone, PartialEq, Eq)]
+pub enum Direction {
+    Horizontal,
+    Vertical,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum Constraint {
+    // TODO: enforce range 0 - 100
+    Percentage(u16),
+    Ratio(u32, u32),
+    Length(u16),
+    Max(u16),
+    Min(u16),
+}
+
+impl Constraint {
+    pub fn apply(&self, length: u16) -> u16 {
+        match *self {
+            Constraint::Percentage(p) => length * p / 100,
+            Constraint::Ratio(num, den) => {
+                let r = num * u32::from(length) / den;
+                r as u16
+            }
+            Constraint::Length(l) => length.min(l),
+            Constraint::Max(m) => length.min(m),
+            Constraint::Min(m) => length.max(m),
+        }
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct Margin {
+    pub vertical: u16,
+    pub horizontal: u16,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum Alignment {
+    Left,
+    Center,
+    Right,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct Layout {
+    direction: Direction,
+    margin: Margin,
+    constraints: Vec<Constraint>,
+}
+
+thread_local! {
+    static LAYOUT_CACHE: RefCell<HashMap<(Rect, Layout), Vec<Rect>>> = RefCell::new(HashMap::new());
+}
+
+impl Default for Layout {
+    fn default() -> Layout {
+        Layout {
+            direction: Direction::Vertical,
+            margin: Margin {
+                horizontal: 0,
+                vertical: 0,
+            },
+            constraints: Vec::new(),
+        }
+    }
+}
+
+impl Layout {
+    pub fn constraints<C>(mut self, constraints: C) -> Layout
+    where
+        C: Into<Vec<Constraint>>,
+    {
+        self.constraints = constraints.into();
+        self
+    }
+
+    pub fn margin(mut self, margin: u16) -> Layout {
+        self.margin = Margin {
+            horizontal: margin,
+            vertical: margin,
+        };
+        self
+    }
+
+    pub fn horizontal_margin(mut self, horizontal: u16) -> Layout {
+        self.margin.horizontal = horizontal;
+        self
+    }
+
+    pub fn vertical_margin(mut self, vertical: u16) -> Layout {
+        self.margin.vertical = vertical;
+        self
+    }
+
+    pub fn direction(mut self, direction: Direction) -> Layout {
+        self.direction = direction;
+        self
+    }
+
+    /// Wrapper function around the cassowary-rs solver to be able to split a given
+    /// area into smaller ones based on the preferred widths or heights and the direction.
+    ///
+    /// # Examples
+    /// ```
+    /// # use helix_tui::layout::{Rect, Constraint, Direction, Layout};
+    /// let chunks = Layout::default()
+    ///     .direction(Direction::Vertical)
+    ///     .constraints([Constraint::Length(5), Constraint::Min(0)].as_ref())
+    ///     .split(Rect {
+    ///         x: 2,
+    ///         y: 2,
+    ///         width: 10,
+    ///         height: 10,
+    ///     });
+    /// assert_eq!(
+    ///     chunks,
+    ///     vec![
+    ///         Rect {
+    ///             x: 2,
+    ///             y: 2,
+    ///             width: 10,
+    ///             height: 5
+    ///         },
+    ///         Rect {
+    ///             x: 2,
+    ///             y: 7,
+    ///             width: 10,
+    ///             height: 5
+    ///         }
+    ///     ]
+    /// );
+    ///
+    /// let chunks = Layout::default()
+    ///     .direction(Direction::Horizontal)
+    ///     .constraints([Constraint::Ratio(1, 3), Constraint::Ratio(2, 3)].as_ref())
+    ///     .split(Rect {
+    ///         x: 0,
+    ///         y: 0,
+    ///         width: 9,
+    ///         height: 2,
+    ///     });
+    /// assert_eq!(
+    ///     chunks,
+    ///     vec![
+    ///         Rect {
+    ///             x: 0,
+    ///             y: 0,
+    ///             width: 3,
+    ///             height: 2
+    ///         },
+    ///         Rect {
+    ///             x: 3,
+    ///             y: 0,
+    ///             width: 6,
+    ///             height: 2
+    ///         }
+    ///     ]
+    /// );
+    /// ```
+    pub fn split(&self, area: Rect) -> Vec<Rect> {
+        // TODO: Maybe use a fixed size cache ?
+        LAYOUT_CACHE.with(|c| {
+            c.borrow_mut()
+                .entry((area, self.clone()))
+                .or_insert_with(|| split(area, self))
+                .clone()
+        })
+    }
+}
+
+fn split(area: Rect, layout: &Layout) -> Vec<Rect> {
+    let mut solver = Solver::new();
+    let mut vars: HashMap<Variable, (usize, usize)> = HashMap::new();
+    let elements = layout
+        .constraints
+        .iter()
+        .map(|_| Element::new())
+        .collect::<Vec<Element>>();
+    let mut results = layout
+        .constraints
+        .iter()
+        .map(|_| Rect::default())
+        .collect::<Vec<Rect>>();
+
+    let dest_area = area.inner(&layout.margin);
+    for (i, e) in elements.iter().enumerate() {
+        vars.insert(e.x, (i, 0));
+        vars.insert(e.y, (i, 1));
+        vars.insert(e.width, (i, 2));
+        vars.insert(e.height, (i, 3));
+    }
+    let mut ccs: Vec<CassowaryConstraint> =
+        Vec::with_capacity(elements.len() * 4 + layout.constraints.len() * 6);
+    for elt in &elements {
+        ccs.push(elt.width | GE(REQUIRED) | 0f64);
+        ccs.push(elt.height | GE(REQUIRED) | 0f64);
+        ccs.push(elt.left() | GE(REQUIRED) | f64::from(dest_area.left()));
+        ccs.push(elt.top() | GE(REQUIRED) | f64::from(dest_area.top()));
+        ccs.push(elt.right() | LE(REQUIRED) | f64::from(dest_area.right()));
+        ccs.push(elt.bottom() | LE(REQUIRED) | f64::from(dest_area.bottom()));
+    }
+    if let Some(first) = elements.first() {
+        ccs.push(match layout.direction {
+            Direction::Horizontal => first.left() | EQ(REQUIRED) | f64::from(dest_area.left()),
+            Direction::Vertical => first.top() | EQ(REQUIRED) | f64::from(dest_area.top()),
+        });
+    }
+    if let Some(last) = elements.last() {
+        ccs.push(match layout.direction {
+            Direction::Horizontal => last.right() | EQ(REQUIRED) | f64::from(dest_area.right()),
+            Direction::Vertical => last.bottom() | EQ(REQUIRED) | f64::from(dest_area.bottom()),
+        });
+    }
+    match layout.direction {
+        Direction::Horizontal => {
+            for pair in elements.windows(2) {
+                ccs.push((pair[0].x + pair[0].width) | EQ(REQUIRED) | pair[1].x);
+            }
+            for (i, size) in layout.constraints.iter().enumerate() {
+                ccs.push(elements[i].y | EQ(REQUIRED) | f64::from(dest_area.y));
+                ccs.push(elements[i].height | EQ(REQUIRED) | f64::from(dest_area.height));
+                ccs.push(match *size {
+                    Constraint::Length(v) => elements[i].width | EQ(WEAK) | f64::from(v),
+                    Constraint::Percentage(v) => {
+                        elements[i].width | EQ(WEAK) | (f64::from(v * dest_area.width) / 100.0)
+                    }
+                    Constraint::Ratio(n, d) => {
+                        elements[i].width
+                            | EQ(WEAK)
+                            | (f64::from(dest_area.width) * f64::from(n) / f64::from(d))
+                    }
+                    Constraint::Min(v) => elements[i].width | GE(WEAK) | f64::from(v),
+                    Constraint::Max(v) => elements[i].width | LE(WEAK) | f64::from(v),
+                });
+            }
+        }
+        Direction::Vertical => {
+            for pair in elements.windows(2) {
+                ccs.push((pair[0].y + pair[0].height) | EQ(REQUIRED) | pair[1].y);
+            }
+            for (i, size) in layout.constraints.iter().enumerate() {
+                ccs.push(elements[i].x | EQ(REQUIRED) | f64::from(dest_area.x));
+                ccs.push(elements[i].width | EQ(REQUIRED) | f64::from(dest_area.width));
+                ccs.push(match *size {
+                    Constraint::Length(v) => elements[i].height | EQ(WEAK) | f64::from(v),
+                    Constraint::Percentage(v) => {
+                        elements[i].height | EQ(WEAK) | (f64::from(v * dest_area.height) / 100.0)
+                    }
+                    Constraint::Ratio(n, d) => {
+                        elements[i].height
+                            | EQ(WEAK)
+                            | (f64::from(dest_area.height) * f64::from(n) / f64::from(d))
+                    }
+                    Constraint::Min(v) => elements[i].height | GE(WEAK) | f64::from(v),
+                    Constraint::Max(v) => elements[i].height | LE(WEAK) | f64::from(v),
+                });
+            }
+        }
+    }
+    solver.add_constraints(&ccs).unwrap();
+    for &(var, value) in solver.fetch_changes() {
+        let (index, attr) = vars[&var];
+        let value = if value.is_sign_negative() {
+            0
+        } else {
+            value as u16
+        };
+        match attr {
+            0 => {
+                results[index].x = value;
+            }
+            1 => {
+                results[index].y = value;
+            }
+            2 => {
+                results[index].width = value;
+            }
+            3 => {
+                results[index].height = value;
+            }
+            _ => {}
+        }
+    }
+
+    // Fix imprecision by extending the last item a bit if necessary
+    if let Some(last) = results.last_mut() {
+        match layout.direction {
+            Direction::Vertical => {
+                last.height = dest_area.bottom() - last.y;
+            }
+            Direction::Horizontal => {
+                last.width = dest_area.right() - last.x;
+            }
+        }
+    }
+    results
+}
+
+/// A container used by the solver inside split
+struct Element {
+    x: Variable,
+    y: Variable,
+    width: Variable,
+    height: Variable,
+}
+
+impl Element {
+    fn new() -> Element {
+        Element {
+            x: Variable::new(),
+            y: Variable::new(),
+            width: Variable::new(),
+            height: Variable::new(),
+        }
+    }
+
+    fn left(&self) -> Variable {
+        self.x
+    }
+
+    fn top(&self) -> Variable {
+        self.y
+    }
+
+    fn right(&self) -> Expression {
+        self.x + self.width
+    }
+
+    fn bottom(&self) -> Expression {
+        self.y + self.height
+    }
+}
+
+/// A simple rectangle used in the computation of the layout and to give widgets an hint about the
+/// area they are supposed to render to.
+#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq)]
+pub struct Rect {
+    pub x: u16,
+    pub y: u16,
+    pub width: u16,
+    pub height: u16,
+}
+
+impl Default for Rect {
+    fn default() -> Rect {
+        Rect {
+            x: 0,
+            y: 0,
+            width: 0,
+            height: 0,
+        }
+    }
+}
+
+impl Rect {
+    /// Creates a new rect, with width and height limited to keep the area under max u16.
+    /// If clipped, aspect ratio will be preserved.
+    pub fn new(x: u16, y: u16, width: u16, height: u16) -> Rect {
+        let max_area = u16::max_value();
+        let (clipped_width, clipped_height) =
+            if u32::from(width) * u32::from(height) > u32::from(max_area) {
+                let aspect_ratio = f64::from(width) / f64::from(height);
+                let max_area_f = f64::from(max_area);
+                let height_f = (max_area_f / aspect_ratio).sqrt();
+                let width_f = height_f * aspect_ratio;
+                (width_f as u16, height_f as u16)
+            } else {
+                (width, height)
+            };
+        Rect {
+            x,
+            y,
+            width: clipped_width,
+            height: clipped_height,
+        }
+    }
+
+    pub fn area(self) -> u16 {
+        self.width * self.height
+    }
+
+    pub fn left(self) -> u16 {
+        self.x
+    }
+
+    pub fn right(self) -> u16 {
+        self.x.saturating_add(self.width)
+    }
+
+    pub fn top(self) -> u16 {
+        self.y
+    }
+
+    pub fn bottom(self) -> u16 {
+        self.y.saturating_add(self.height)
+    }
+
+    pub fn inner(self, margin: &Margin) -> Rect {
+        if self.width < 2 * margin.horizontal || self.height < 2 * margin.vertical {
+            Rect::default()
+        } else {
+            Rect {
+                x: self.x + margin.horizontal,
+                y: self.y + margin.vertical,
+                width: self.width - 2 * margin.horizontal,
+                height: self.height - 2 * margin.vertical,
+            }
+        }
+    }
+
+    pub fn union(self, other: Rect) -> Rect {
+        let x1 = min(self.x, other.x);
+        let y1 = min(self.y, other.y);
+        let x2 = max(self.x + self.width, other.x + other.width);
+        let y2 = max(self.y + self.height, other.y + other.height);
+        Rect {
+            x: x1,
+            y: y1,
+            width: x2 - x1,
+            height: y2 - y1,
+        }
+    }
+
+    pub fn intersection(self, other: Rect) -> Rect {
+        let x1 = max(self.x, other.x);
+        let y1 = max(self.y, other.y);
+        let x2 = min(self.x + self.width, other.x + other.width);
+        let y2 = min(self.y + self.height, other.y + other.height);
+        Rect {
+            x: x1,
+            y: y1,
+            width: x2 - x1,
+            height: y2 - y1,
+        }
+    }
+
+    pub fn intersects(self, other: Rect) -> bool {
+        self.x < other.x + other.width
+            && self.x + self.width > other.x
+            && self.y < other.y + other.height
+            && self.y + self.height > other.y
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_vertical_split_by_height() {
+        let target = Rect {
+            x: 2,
+            y: 2,
+            width: 10,
+            height: 10,
+        };
+
+        let chunks = Layout::default()
+            .direction(Direction::Vertical)
+            .constraints(
+                [
+                    Constraint::Percentage(10),
+                    Constraint::Max(5),
+                    Constraint::Min(1),
+                ]
+                .as_ref(),
+            )
+            .split(target);
+
+        assert_eq!(target.height, chunks.iter().map(|r| r.height).sum::<u16>());
+        chunks.windows(2).for_each(|w| assert!(w[0].y <= w[1].y));
+    }
+
+    #[test]
+    fn test_rect_size_truncation() {
+        for width in 256u16..300u16 {
+            for height in 256u16..300u16 {
+                let rect = Rect::new(0, 0, width, height);
+                rect.area(); // Should not panic.
+                assert!(rect.width < width || rect.height < height);
+                // The target dimensions are rounded down so the math will not be too precise
+                // but let's make sure the ratios don't diverge crazily.
+                assert!(
+                    (f64::from(rect.width) / f64::from(rect.height)
+                        - f64::from(width) / f64::from(height))
+                    .abs()
+                        < 1.0
+                )
+            }
+        }
+
+        // One dimension below 255, one above. Area above max u16.
+        let width = 900;
+        let height = 100;
+        let rect = Rect::new(0, 0, width, height);
+        assert_ne!(rect.width, 900);
+        assert_ne!(rect.height, 100);
+        assert!(rect.width < width || rect.height < height);
+    }
+
+    #[test]
+    fn test_rect_size_preservation() {
+        for width in 0..256u16 {
+            for height in 0..256u16 {
+                let rect = Rect::new(0, 0, width, height);
+                rect.area(); // Should not panic.
+                assert_eq!(rect.width, width);
+                assert_eq!(rect.height, height);
+            }
+        }
+
+        // One dimension below 255, one above. Area below max u16.
+        let rect = Rect::new(0, 0, 300, 100);
+        assert_eq!(rect.width, 300);
+        assert_eq!(rect.height, 100);
+    }
+}

helix-tui/src/lib.rs

@@ -0,0 +1,134 @@
+//! [tui](https://github.com/fdehau/tui-rs) is a library used to build rich
+//! terminal users interfaces and dashboards.
+//!
+//! ![](https://raw.githubusercontent.com/fdehau/tui-rs/master/assets/demo.gif)
+//!
+//! # Get started
+//!
+//! ## Adding `tui` as a dependency
+//!
+//! ```toml
+//! [dependencies]
+//! tui = "0.15"
+//! crossterm = "0.19"
+//! ```
+//!
+//! The same logic applies for all other available backends.
+//!
+//! ## Creating a `Terminal`
+//!
+//! Every application using `tui` should start by instantiating a `Terminal`. It is a light
+//! abstraction over available backends that provides basic functionalities such as clearing the
+//! screen, hiding the cursor, etc.
+//!
+//! ```rust,no_run
+//! use std::io;
+//! use helix_tui::Terminal;
+//! use helix_tui::backend::CrosstermBackend;
+//!
+//! fn main() -> Result<(), io::Error> {
+//!     let stdout = io::stdout();
+//!     let backend = CrosstermBackend::new(stdout);
+//!     let mut terminal = Terminal::new(backend)?;
+//!     Ok(())
+//! }
+//! ```
+//!
+//! You may also refer to the examples to find out how to create a `Terminal` for each available
+//! backend.
+//!
+//! ## Building a User Interface (UI)
+//!
+//! Every component of your interface will be implementing the `Widget` trait. The library comes
+//! with a predefined set of widgets that should meet most of your use cases. You are also free to
+//! implement your own.
+//!
+//! Each widget follows a builder pattern API providing a default configuration along with methods
+//! to customize them. The widget is then rendered using the [`Frame::render_widget`] which take
+//! your widget instance an area to draw to.
+//!
+//! The following example renders a block of the size of the terminal:
+//!
+//! ```rust,no_run
+//! use std::io;
+//! use crossterm::terminal;
+//! use helix_tui::Terminal;
+//! use helix_tui::backend::CrosstermBackend;
+//! use helix_tui::widgets::{Widget, Block, Borders};
+//! use helix_tui::layout::{Layout, Constraint, Direction};
+//!
+//! fn main() -> Result<(), io::Error> {
+//!     terminal::enable_raw_mode()?;
+//!     let stdout = io::stdout();
+//!     let backend = CrosstermBackend::new(stdout);
+//!     let mut terminal = Terminal::new(backend)?;
+//!     terminal.draw(|f| {
+//!         let size = f.size();
+//!         let block = Block::default()
+//!             .title("Block")
+//!             .borders(Borders::ALL);
+//!         f.render_widget(block, size);
+//!     })?;
+//!     Ok(())
+//! }
+//! ```
+//!
+//! ## Layout
+//!
+//! The library comes with a basic yet useful layout management object called `Layout`. As you may
+//! see below and in the examples, the library makes heavy use of the builder pattern to provide
+//! full customization. And `Layout` is no exception:
+//!
+//! ```rust,no_run
+//! use std::io;
+//! use crossterm::terminal;
+//! use helix_tui::Terminal;
+//! use helix_tui::backend::CrosstermBackend;
+//! use helix_tui::widgets::{Widget, Block, Borders};
+//! use helix_tui::layout::{Layout, Constraint, Direction};
+//!
+//! fn main() -> Result<(), io::Error> {
+//!     terminal::enable_raw_mode()?;
+//!     let stdout = io::stdout();
+//!     let backend = CrosstermBackend::new(stdout);
+//!     let mut terminal = Terminal::new(backend)?;
+//!     terminal.draw(|f| {
+//!         let chunks = Layout::default()
+//!             .direction(Direction::Vertical)
+//!             .margin(1)
+//!             .constraints(
+//!                 [
+//!                     Constraint::Percentage(10),
+//!                     Constraint::Percentage(80),
+//!                     Constraint::Percentage(10)
+//!                 ].as_ref()
+//!             )
+//!             .split(f.size());
+//!         let block = Block::default()
+//!              .title("Block")
+//!              .borders(Borders::ALL);
+//!         f.render_widget(block, chunks[0]);
+//!         let block = Block::default()
+//!              .title("Block 2")
+//!              .borders(Borders::ALL);
+//!         f.render_widget(block, chunks[1]);
+//!     })?;
+//!     Ok(())
+//! }
+//! ```
+//!
+//! This let you describe responsive terminal UI by nesting layouts. You should note that by
+//! default the computed layout tries to fill the available space completely. So if for any reason
+//! you might need a blank space somewhere, try to pass an additional constraint and don't use the
+//! corresponding area.
+
+pub mod backend;
+pub mod buffer;
+pub mod layout;
+pub mod style;
+pub mod symbols;
+pub mod terminal;
+pub mod text;
+pub mod widgets;
+
+pub use self::terminal::{Terminal, TerminalOptions, Viewport};

helix-tui/src/style.rs

@@ -0,0 +1,281 @@
+//! `style` contains the primitives used to control how your user interface will look.
+
+use bitflags::bitflags;
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
+pub enum Color {
+    Reset,
+    Black,
+    Red,
+    Green,
+    Yellow,
+    Blue,
+    Magenta,
+    Cyan,
+    Gray,
+    DarkGray,
+    LightRed,
+    LightGreen,
+    LightYellow,
+    LightBlue,
+    LightMagenta,
+    LightCyan,
+    White,
+    Rgb(u8, u8, u8),
+    Indexed(u8),
+}
+
+bitflags! {
+    /// Modifier changes the way a piece of text is displayed.
+    ///
+    /// They are bitflags so they can easily be composed.
+    ///
+    /// ## Examples
+    ///
+    /// ```rust
+    /// # use helix_tui::style::Modifier;
+    ///
+    /// let m = Modifier::BOLD | Modifier::ITALIC;
+    /// ```
+    #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
+    pub struct Modifier: u16 {
+        const BOLD              = 0b0000_0000_0001;
+        const DIM               = 0b0000_0000_0010;
+        const ITALIC            = 0b0000_0000_0100;
+        const UNDERLINED        = 0b0000_0000_1000;
+        const SLOW_BLINK        = 0b0000_0001_0000;
+        const RAPID_BLINK       = 0b0000_0010_0000;
+        const REVERSED          = 0b0000_0100_0000;
+        const HIDDEN            = 0b0000_1000_0000;
+        const CROSSED_OUT       = 0b0001_0000_0000;
+    }
+}
+
+/// Style let you control the main characteristics of the displayed elements.
+///
+/// ```rust
+/// # use helix_tui::style::{Color, Modifier, Style};
+/// Style::default()
+///     .fg(Color::Black)
+///     .bg(Color::Green)
+///     .add_modifier(Modifier::ITALIC | Modifier::BOLD);
+/// ```
+///
+/// It represents an incremental change. If you apply the styles S1, S2, S3 to a cell of the
+/// terminal buffer, the style of this cell will be the result of the merge of S1, S2 and S3, not
+/// just S3.
+///
+/// ```rust
+/// # use helix_tui::style::{Color, Modifier, Style};
+/// # use helix_tui::buffer::Buffer;
+/// # use helix_tui::layout::Rect;
+/// let styles = [
+///     Style::default().fg(Color::Blue).add_modifier(Modifier::BOLD | Modifier::ITALIC),
+///     Style::default().bg(Color::Red),
+///     Style::default().fg(Color::Yellow).remove_modifier(Modifier::ITALIC),
+/// ];
+/// let mut buffer = Buffer::empty(Rect::new(0, 0, 1, 1));
+/// for style in &styles {
+///   buffer.get_mut(0, 0).set_style(*style);
+/// }
+/// assert_eq!(
+///     Style {
+///         fg: Some(Color::Yellow),
+///         bg: Some(Color::Red),
+///         add_modifier: Modifier::BOLD,
+///         sub_modifier: Modifier::empty(),
+///     },
+///     buffer.get(0, 0).style(),
+/// );
+/// ```
+///
+/// The default implementation returns a `Style` that does not modify anything. If you wish to
+/// reset all properties until that point use [`Style::reset`].
+///
+/// ```
+/// # use helix_tui::style::{Color, Modifier, Style};
+/// # use helix_tui::buffer::Buffer;
+/// # use helix_tui::layout::Rect;
+/// let styles = [
+///     Style::default().fg(Color::Blue).add_modifier(Modifier::BOLD | Modifier::ITALIC),
+///     Style::reset().fg(Color::Yellow),
+/// ];
+/// let mut buffer = Buffer::empty(Rect::new(0, 0, 1, 1));
+/// for style in &styles {
+///   buffer.get_mut(0, 0).set_style(*style);
+/// }
+/// assert_eq!(
+///     Style {
+///         fg: Some(Color::Yellow),
+///         bg: Some(Color::Reset),
+///         add_modifier: Modifier::empty(),
+///         sub_modifier: Modifier::empty(),
+///     },
+///     buffer.get(0, 0).style(),
+/// );
+/// ```
+#[derive(Debug, Clone, Copy, PartialEq)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
+pub struct Style {
+    pub fg: Option<Color>,
+    pub bg: Option<Color>,
+    pub add_modifier: Modifier,
+    pub sub_modifier: Modifier,
+}
+
+impl Default for Style {
+    fn default() -> Style {
+        Style {
+            fg: None,
+            bg: None,
+            add_modifier: Modifier::empty(),
+            sub_modifier: Modifier::empty(),
+        }
+    }
+}
+
+impl Style {
+    /// Returns a `Style` resetting all properties.
+    pub fn reset() -> Style {
+        Style {
+            fg: Some(Color::Reset),
+            bg: Some(Color::Reset),
+            add_modifier: Modifier::empty(),
+            sub_modifier: Modifier::all(),
+        }
+    }
+
+    /// Changes the foreground color.
+    ///
+    /// ## Examples
+    ///
+    /// ```rust
+    /// # use helix_tui::style::{Color, Style};
+    /// let style = Style::default().fg(Color::Blue);
+    /// let diff = Style::default().fg(Color::Red);
+    /// assert_eq!(style.patch(diff), Style::default().fg(Color::Red));
+    /// ```
+    pub fn fg(mut self, color: Color) -> Style {
+        self.fg = Some(color);
+        self
+    }
+
+    /// Changes the background color.
+    ///
+    /// ## Examples
+    ///
+    /// ```rust
+    /// # use helix_tui::style::{Color, Style};
+    /// let style = Style::default().bg(Color::Blue);
+    /// let diff = Style::default().bg(Color::Red);
+    /// assert_eq!(style.patch(diff), Style::default().bg(Color::Red));
+    /// ```
+    pub fn bg(mut self, color: Color) -> Style {
+        self.bg = Some(color);
+        self
+    }
+
+    /// Changes the text emphasis.
+    ///
+    /// When applied, it adds the given modifier to the `Style` modifiers.
+    ///
+    /// ## Examples
+    ///
+    /// ```rust
+    /// # use helix_tui::style::{Color, Modifier, Style};
+    /// let style = Style::default().add_modifier(Modifier::BOLD);
+    /// let diff = Style::default().add_modifier(Modifier::ITALIC);
+    /// let patched = style.patch(diff);
+    /// assert_eq!(patched.add_modifier, Modifier::BOLD | Modifier::ITALIC);
+    /// assert_eq!(patched.sub_modifier, Modifier::empty());
+    /// ```
+    pub fn add_modifier(mut self, modifier: Modifier) -> Style {
+        self.sub_modifier.remove(modifier);
+        self.add_modifier.insert(modifier);
+        self
+    }
+
+    /// Changes the text emphasis.
+    ///
+    /// When applied, it removes the given modifier from the `Style` modifiers.
+    ///
+    /// ## Examples
+    ///
+    /// ```rust
+    /// # use helix_tui::style::{Color, Modifier, Style};
+    /// let style = Style::default().add_modifier(Modifier::BOLD | Modifier::ITALIC);
+    /// let diff = Style::default().remove_modifier(Modifier::ITALIC);
+    /// let patched = style.patch(diff);
+    /// assert_eq!(patched.add_modifier, Modifier::BOLD);
+    /// assert_eq!(patched.sub_modifier, Modifier::ITALIC);
+    /// ```
+    pub fn remove_modifier(mut self, modifier: Modifier) -> Style {
+        self.add_modifier.remove(modifier);
+        self.sub_modifier.insert(modifier);
+        self
+    }
+
+    /// Results in a combined style that is equivalent to applying the two individual styles to
+    /// a style one after the other.
+    ///
+    /// ## Examples
+    /// ```
+    /// # use helix_tui::style::{Color, Modifier, Style};
+    /// let style_1 = Style::default().fg(Color::Yellow);
+    /// let style_2 = Style::default().bg(Color::Red);
+    /// let combined = style_1.patch(style_2);
+    /// assert_eq!(
+    ///     Style::default().patch(style_1).patch(style_2),
+    ///     Style::default().patch(combined));
+    /// ```
+    pub fn patch(mut self, other: Style) -> Style {
+        self.fg = other.fg.or(self.fg);
+        self.bg = other.bg.or(self.bg);
+
+        self.add_modifier.remove(other.sub_modifier);
+        self.add_modifier.insert(other.add_modifier);
+        self.sub_modifier.remove(other.add_modifier);
+        self.sub_modifier.insert(other.sub_modifier);
+
+        self
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn styles() -> Vec<Style> {
+        vec![
+            Style::default(),
+            Style::default().fg(Color::Yellow),
+            Style::default().bg(Color::Yellow),
+            Style::default().add_modifier(Modifier::BOLD),
+            Style::default().remove_modifier(Modifier::BOLD),
+            Style::default().add_modifier(Modifier::ITALIC),
+            Style::default().remove_modifier(Modifier::ITALIC),
+            Style::default().add_modifier(Modifier::ITALIC | Modifier::BOLD),
+            Style::default().remove_modifier(Modifier::ITALIC | Modifier::BOLD),
+        ]
+    }
+
+    #[test]
+    fn combined_patch_gives_same_result_as_individual_patch() {
+        let styles = styles();
+        for &a in &styles {
+            for &b in &styles {
+                for &c in &styles {
+                    for &d in &styles {
+                        let combined = a.patch(b.patch(c.patch(d)));
+
+                        assert_eq!(
+                            Style::default().patch(a).patch(b).patch(c).patch(d),
+                            Style::default().patch(combined)
+                        );
+                    }
+                }
+            }
+        }
+    }
+}

helix-tui/src/symbols.rs

@@ -0,0 +1,233 @@
+pub mod block {
+    pub const FULL: &str = "█";
+    pub const SEVEN_EIGHTHS: &str = "▉";
+    pub const THREE_QUARTERS: &str = "▊";
+    pub const FIVE_EIGHTHS: &str = "▋";
+    pub const HALF: &str = "▌";
+    pub const THREE_EIGHTHS: &str = "▍";
+    pub const ONE_QUARTER: &str = "▎";
+    pub const ONE_EIGHTH: &str = "▏";
+
+    #[derive(Debug, Clone)]
+    pub struct Set {
+        pub full: &'static str,
+        pub seven_eighths: &'static str,
+        pub three_quarters: &'static str,
+        pub five_eighths: &'static str,
+        pub half: &'static str,
+        pub three_eighths: &'static str,
+        pub one_quarter: &'static str,
+        pub one_eighth: &'static str,
+        pub empty: &'static str,
+    }
+
+    pub const THREE_LEVELS: Set = Set {
+        full: FULL,
+        seven_eighths: FULL,
+        three_quarters: HALF,
+        five_eighths: HALF,
+        half: HALF,
+        three_eighths: HALF,
+        one_quarter: HALF,
+        one_eighth: " ",
+        empty: " ",
+    };
+
+    pub const NINE_LEVELS: Set = Set {
+        full: FULL,
+        seven_eighths: SEVEN_EIGHTHS,
+        three_quarters: THREE_QUARTERS,
+        five_eighths: FIVE_EIGHTHS,
+        half: HALF,
+        three_eighths: THREE_EIGHTHS,
+        one_quarter: ONE_QUARTER,
+        one_eighth: ONE_EIGHTH,
+        empty: " ",
+    };
+}
+
+pub mod bar {
+    pub const FULL: &str = "█";
+    pub const SEVEN_EIGHTHS: &str = "▇";
+    pub const THREE_QUARTERS: &str = "▆";
+    pub const FIVE_EIGHTHS: &str = "▅";
+    pub const HALF: &str = "▄";
+    pub const THREE_EIGHTHS: &str = "▃";
+    pub const ONE_QUARTER: &str = "▂";
+    pub const ONE_EIGHTH: &str = "▁";
+
+    #[derive(Debug, Clone)]
+    pub struct Set {
+        pub full: &'static str,
+        pub seven_eighths: &'static str,
+        pub three_quarters: &'static str,
+        pub five_eighths: &'static str,
+        pub half: &'static str,
+        pub three_eighths: &'static str,
+        pub one_quarter: &'static str,
+        pub one_eighth: &'static str,
+        pub empty: &'static str,
+    }
+
+    pub const THREE_LEVELS: Set = Set {
+        full: FULL,
+        seven_eighths: FULL,
+        three_quarters: HALF,
+        five_eighths: HALF,
+        half: HALF,
+        three_eighths: HALF,
+        one_quarter: HALF,
+        one_eighth: " ",
+        empty: " ",
+    };
+
+    pub const NINE_LEVELS: Set = Set {
+        full: FULL,
+        seven_eighths: SEVEN_EIGHTHS,
+        three_quarters: THREE_QUARTERS,
+        five_eighths: FIVE_EIGHTHS,
+        half: HALF,
+        three_eighths: THREE_EIGHTHS,
+        one_quarter: ONE_QUARTER,
+        one_eighth: ONE_EIGHTH,
+        empty: " ",
+    };
+}
+
+pub mod line {
+    pub const VERTICAL: &str = "│";
+    pub const DOUBLE_VERTICAL: &str = "║";
+    pub const THICK_VERTICAL: &str = "┃";
+
+    pub const HORIZONTAL: &str = "─";
+    pub const DOUBLE_HORIZONTAL: &str = "═";
+    pub const THICK_HORIZONTAL: &str = "━";
+
+    pub const TOP_RIGHT: &str = "┐";
+    pub const ROUNDED_TOP_RIGHT: &str = "╮";
+    pub const DOUBLE_TOP_RIGHT: &str = "╗";
+    pub const THICK_TOP_RIGHT: &str = "┓";
+
+    pub const TOP_LEFT: &str = "┌";
+    pub const ROUNDED_TOP_LEFT: &str = "╭";
+    pub const DOUBLE_TOP_LEFT: &str = "╔";
+    pub const THICK_TOP_LEFT: &str = "┏";
+
+    pub const BOTTOM_RIGHT: &str = "┘";
+    pub const ROUNDED_BOTTOM_RIGHT: &str = "╯";
+    pub const DOUBLE_BOTTOM_RIGHT: &str = "╝";
+    pub const THICK_BOTTOM_RIGHT: &str = "┛";
+
+    pub const BOTTOM_LEFT: &str = "└";
+    pub const ROUNDED_BOTTOM_LEFT: &str = "╰";
+    pub const DOUBLE_BOTTOM_LEFT: &str = "╚";
+    pub const THICK_BOTTOM_LEFT: &str = "┗";
+
+    pub const VERTICAL_LEFT: &str = "┤";
+    pub const DOUBLE_VERTICAL_LEFT: &str = "╣";
+    pub const THICK_VERTICAL_LEFT: &str = "┫";
+
+    pub const VERTICAL_RIGHT: &str = "├";
+    pub const DOUBLE_VERTICAL_RIGHT: &str = "╠";
+    pub const THICK_VERTICAL_RIGHT: &str = "┣";
+
+    pub const HORIZONTAL_DOWN: &str = "┬";
+    pub const DOUBLE_HORIZONTAL_DOWN: &str = "╦";
+    pub const THICK_HORIZONTAL_DOWN: &str = "┳";
+
+    pub const HORIZONTAL_UP: &str = "┴";
+    pub const DOUBLE_HORIZONTAL_UP: &str = "╩";
+    pub const THICK_HORIZONTAL_UP: &str = "┻";
+
+    pub const CROSS: &str = "┼";
+    pub const DOUBLE_CROSS: &str = "╬";
+    pub const THICK_CROSS: &str = "╋";
+
+    #[derive(Debug, Clone)]
+    pub struct Set {
+        pub vertical: &'static str,
+        pub horizontal: &'static str,
+        pub top_right: &'static str,
+        pub top_left: &'static str,
+        pub bottom_right: &'static str,
+        pub bottom_left: &'static str,
+        pub vertical_left: &'static str,
+        pub vertical_right: &'static str,
+        pub horizontal_down: &'static str,
+        pub horizontal_up: &'static str,
+        pub cross: &'static str,
+    }
+
+    pub const NORMAL: Set = Set {
+        vertical: VERTICAL,
+        horizontal: HORIZONTAL,
+        top_right: TOP_RIGHT,
+        top_left: TOP_LEFT,
+        bottom_right: BOTTOM_RIGHT,
+        bottom_left: BOTTOM_LEFT,
+        vertical_left: VERTICAL_LEFT,
+        vertical_right: VERTICAL_RIGHT,
+        horizontal_down: HORIZONTAL_DOWN,
+        horizontal_up: HORIZONTAL_UP,
+        cross: CROSS,
+    };
+
+    pub const ROUNDED: Set = Set {
+        top_right: ROUNDED_TOP_RIGHT,
+        top_left: ROUNDED_TOP_LEFT,
+        bottom_right: ROUNDED_BOTTOM_RIGHT,
+        bottom_left: ROUNDED_BOTTOM_LEFT,
+        ..NORMAL
+    };
+
+    pub const DOUBLE: Set = Set {
+        vertical: DOUBLE_VERTICAL,
+        horizontal: DOUBLE_HORIZONTAL,
+        top_right: DOUBLE_TOP_RIGHT,
+        top_left: DOUBLE_TOP_LEFT,
+        bottom_right: DOUBLE_BOTTOM_RIGHT,
+        bottom_left: DOUBLE_BOTTOM_LEFT,
+        vertical_left: DOUBLE_VERTICAL_LEFT,
+        vertical_right: DOUBLE_VERTICAL_RIGHT,
+        horizontal_down: DOUBLE_HORIZONTAL_DOWN,
+        horizontal_up: DOUBLE_HORIZONTAL_UP,
+        cross: DOUBLE_CROSS,
+    };
+
+    pub const THICK: Set = Set {
+        vertical: THICK_VERTICAL,
+        horizontal: THICK_HORIZONTAL,
+        top_right: THICK_TOP_RIGHT,
+        top_left: THICK_TOP_LEFT,
+        bottom_right: THICK_BOTTOM_RIGHT,
+        bottom_left: THICK_BOTTOM_LEFT,
+        vertical_left: THICK_VERTICAL_LEFT,
+        vertical_right: THICK_VERTICAL_RIGHT,
+        horizontal_down: THICK_HORIZONTAL_DOWN,
+        horizontal_up: THICK_HORIZONTAL_UP,
+        cross: THICK_CROSS,
+    };
+}
+
+pub const DOT: &str = "•";
+
+pub mod braille {
+    pub const BLANK: u16 = 0x2800;
+    pub const DOTS: [[u16; 2]; 4] = [
+        [0x0001, 0x0008],
+        [0x0002, 0x0010],
+        [0x0004, 0x0020],
+        [0x0040, 0x0080],
+    ];
+}
+
+/// Marker to use when plotting data points
+#[derive(Debug, Clone, Copy)]
+pub enum Marker {
+    /// One point per cell in shape of dot
+    Dot,
+    /// One point per cell in shape of a block
+    Block,
+    /// Up to 8 points per cell
+    Braille,
+}

helix-tui/src/terminal.rs

@@ -1,10 +1,5 @@
+use crate::{backend::Backend, buffer::Buffer, layout::Rect};
 use std::io;
-use tui::{
-    backend::Backend,
-    buffer::Buffer,
-    layout::Rect,
-    widgets::{StatefulWidget, Widget},
-};
 
 #[derive(Debug, Clone, PartialEq)]
 /// UNSTABLE

helix-tui/src/text.rs

@@ -0,0 +1,434 @@
+//! Primitives for styled text.
+//!
+//! A terminal UI is at its root a lot of strings. In order to make it accessible and stylish,
+//! those strings may be associated to a set of styles. `tui` has three ways to represent them:
+//! - A single line string where all graphemes have the same style is represented by a [`Span`].
+//! - A single line string where each grapheme may have its own style is represented by [`Spans`].
+//! - A multiple line string where each grapheme may have its own style is represented by a
+//! [`Text`].
+//!
+//! These types form a hierarchy: [`Spans`] is a collection of [`Span`] and each line of [`Text`]
+//! is a [`Spans`].
+//!
+//! Keep it mind that a lot of widgets will use those types to advertise what kind of string is
+//! supported for their properties. Moreover, `tui` provides convenient `From` implementations so
+//! that you can start by using simple `String` or `&str` and then promote them to the previous
+//! primitives when you need additional styling capabilities.
+//!
+//! For example, for the [`crate::widgets::Block`] widget, all the following calls are valid to set
+//! its `title` property (which is a [`Spans`] under the hood):
+//!
+//! ```rust
+//! # use helix_tui::widgets::Block;
+//! # use helix_tui::text::{Span, Spans};
+//! # use helix_tui::style::{Color, Style};
+//! // A simple string with no styling.
+//! // Converted to Spans(vec![
+//! //   Span { content: Cow::Borrowed("My title"), style: Style { .. } }
+//! // ])
+//! let block = Block::default().title("My title");
+//!
+//! // A simple string with a unique style.
+//! // Converted to Spans(vec![
+//! //   Span { content: Cow::Borrowed("My title"), style: Style { fg: Some(Color::Yellow), .. }
+//! // ])
+//! let block = Block::default().title(
+//!     Span::styled("My title", Style::default().fg(Color::Yellow))
+//! );
+//!
+//! // A string with multiple styles.
+//! // Converted to Spans(vec![
+//! //   Span { content: Cow::Borrowed("My"), style: Style { fg: Some(Color::Yellow), .. } },
+//! //   Span { content: Cow::Borrowed(" title"), .. }
+//! // ])
+//! let block = Block::default().title(vec![
+//!     Span::styled("My", Style::default().fg(Color::Yellow)),
+//!     Span::raw(" title"),
+//! ]);
+//! ```
+use crate::style::Style;
+use std::borrow::Cow;
+use unicode_segmentation::UnicodeSegmentation;
+use unicode_width::UnicodeWidthStr;
+
+/// A grapheme associated to a style.
+#[derive(Debug, Clone, PartialEq)]
+pub struct StyledGrapheme<'a> {
+    pub symbol: &'a str,
+    pub style: Style,
+}
+
+/// A string where all graphemes have the same style.
+#[derive(Debug, Clone, PartialEq)]
+pub struct Span<'a> {
+    pub content: Cow<'a, str>,
+    pub style: Style,
+}
+
+impl<'a> Span<'a> {
+    /// Create a span with no style.
+    ///
+    /// ## Examples
+    ///
+    /// ```rust
+    /// # use helix_tui::text::Span;
+    /// Span::raw("My text");
+    /// Span::raw(String::from("My text"));
+    /// ```
+    pub fn raw<T>(content: T) -> Span<'a>
+    where
+        T: Into<Cow<'a, str>>,
+    {
+        Span {
+            content: content.into(),
+            style: Style::default(),
+        }
+    }
+
+    /// Create a span with a style.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// # use helix_tui::text::Span;
+    /// # use helix_tui::style::{Color, Modifier, Style};
+    /// let style = Style::default().fg(Color::Yellow).add_modifier(Modifier::ITALIC);
+    /// Span::styled("My text", style);
+    /// Span::styled(String::from("My text"), style);
+    /// ```
+    pub fn styled<T>(content: T, style: Style) -> Span<'a>
+    where
+        T: Into<Cow<'a, str>>,
+    {
+        Span {
+            content: content.into(),
+            style,
+        }
+    }
+
+    /// Returns the width of the content held by this span.
+    pub fn width(&self) -> usize {
+        self.content.width()
+    }
+
+    /// Returns an iterator over the graphemes held by this span.
+    ///
+    /// `base_style` is the [`Style`] that will be patched with each grapheme [`Style`] to get
+    /// the resulting [`Style`].
+    ///
+    /// ## Examples
+    ///
+    /// ```rust
+    /// # use helix_tui::text::{Span, StyledGrapheme};
+    /// # use helix_tui::style::{Color, Modifier, Style};
+    /// # use std::iter::Iterator;
+    /// let style = Style::default().fg(Color::Yellow);
+    /// let span = Span::styled("Text", style);
+    /// let style = Style::default().fg(Color::Green).bg(Color::Black);
+    /// let styled_graphemes = span.styled_graphemes(style);
+    /// assert_eq!(
+    ///     vec![
+    ///         StyledGrapheme {
+    ///             symbol: "T",
+    ///             style: Style {
+    ///                 fg: Some(Color::Yellow),
+    ///                 bg: Some(Color::Black),
+    ///                 add_modifier: Modifier::empty(),
+    ///                 sub_modifier: Modifier::empty(),
+    ///             },
+    ///         },
+    ///         StyledGrapheme {
+    ///             symbol: "e",
+    ///             style: Style {
+    ///                 fg: Some(Color::Yellow),
+    ///                 bg: Some(Color::Black),
+    ///                 add_modifier: Modifier::empty(),
+    ///                 sub_modifier: Modifier::empty(),
+    ///             },
+    ///         },
+    ///         StyledGrapheme {
+    ///             symbol: "x",
+    ///             style: Style {
+    ///                 fg: Some(Color::Yellow),
+    ///                 bg: Some(Color::Black),
+    ///                 add_modifier: Modifier::empty(),
+    ///                 sub_modifier: Modifier::empty(),
+    ///             },
+    ///         },
+    ///         StyledGrapheme {
+    ///             symbol: "t",
+    ///             style: Style {
+    ///                 fg: Some(Color::Yellow),
+    ///                 bg: Some(Color::Black),
+    ///                 add_modifier: Modifier::empty(),
+    ///                 sub_modifier: Modifier::empty(),
+    ///             },
+    ///         },
+    ///     ],
+    ///     styled_graphemes.collect::<Vec<StyledGrapheme>>()
+    /// );
+    /// ```
+    pub fn styled_graphemes(
+        &'a self,
+        base_style: Style,
+    ) -> impl Iterator<Item = StyledGrapheme<'a>> {
+        UnicodeSegmentation::graphemes(self.content.as_ref(), true)
+            .map(move |g| StyledGrapheme {
+                symbol: g,
+                style: base_style.patch(self.style),
+            })
+            .filter(|s| s.symbol != "\n")
+    }
+}
+
+impl<'a> From<String> for Span<'a> {
+    fn from(s: String) -> Span<'a> {
+        Span::raw(s)
+    }
+}
+
+impl<'a> From<&'a str> for Span<'a> {
+    fn from(s: &'a str) -> Span<'a> {
+        Span::raw(s)
+    }
+}
+
+/// A string composed of clusters of graphemes, each with their own style.
+#[derive(Debug, Clone, PartialEq)]
+pub struct Spans<'a>(pub Vec<Span<'a>>);
+
+impl<'a> Default for Spans<'a> {
+    fn default() -> Spans<'a> {
+        Spans(Vec::new())
+    }
+}
+
+impl<'a> Spans<'a> {
+    /// Returns the width of the underlying string.
+    ///
+    /// ## Examples
+    ///
+    /// ```rust
+    /// # use helix_tui::text::{Span, Spans};
+    /// # use helix_tui::style::{Color, Style};
+    /// let spans = Spans::from(vec![
+    ///     Span::styled("My", Style::default().fg(Color::Yellow)),
+    ///     Span::raw(" text"),
+    /// ]);
+    /// assert_eq!(7, spans.width());
+    /// ```
+    pub fn width(&self) -> usize {
+        self.0.iter().map(Span::width).sum()
+    }
+}
+
+impl<'a> From<String> for Spans<'a> {
+    fn from(s: String) -> Spans<'a> {
+        Spans(vec![Span::from(s)])
+    }
+}
+
+impl<'a> From<&'a str> for Spans<'a> {
+    fn from(s: &'a str) -> Spans<'a> {
+        Spans(vec![Span::from(s)])
+    }
+}
+
+impl<'a> From<Vec<Span<'a>>> for Spans<'a> {
+    fn from(spans: Vec<Span<'a>>) -> Spans<'a> {
+        Spans(spans)
+    }
+}
+
+impl<'a> From<Span<'a>> for Spans<'a> {
+    fn from(span: Span<'a>) -> Spans<'a> {
+        Spans(vec![span])
+    }
+}
+
+impl<'a> From<Spans<'a>> for String {
+    fn from(line: Spans<'a>) -> String {
+        line.0.iter().fold(String::new(), |mut acc, s| {
+            acc.push_str(s.content.as_ref());
+            acc
+        })
+    }
+}
+
+/// A string split over multiple lines where each line is composed of several clusters, each with
+/// their own style.
+///
+/// A [`Text`], like a [`Span`], can be constructed using one of the many `From` implementations
+/// or via the [`Text::raw`] and [`Text::styled`] methods. Helpfully, [`Text`] also implements
+/// [`core::iter::Extend`] which enables the concatenation of several [`Text`] blocks.
+///
+/// ```rust
+/// # use helix_tui::text::Text;
+/// # use helix_tui::style::{Color, Modifier, Style};
+/// let style = Style::default().fg(Color::Yellow).add_modifier(Modifier::ITALIC);
+///
+/// // An initial two lines of `Text` built from a `&str`
+/// let mut text = Text::from("The first line\nThe second line");
+/// assert_eq!(2, text.height());
+///
+/// // Adding two more unstyled lines
+/// text.extend(Text::raw("These are two\nmore lines!"));
+/// assert_eq!(4, text.height());
+///
+/// // Adding a final two styled lines
+/// text.extend(Text::styled("Some more lines\nnow with more style!", style));
+/// assert_eq!(6, text.height());
+/// ```
+#[derive(Debug, Clone, PartialEq)]
+pub struct Text<'a> {
+    pub lines: Vec<Spans<'a>>,
+}
+
+impl<'a> Default for Text<'a> {
+    fn default() -> Text<'a> {
+        Text { lines: Vec::new() }
+    }
+}
+
+impl<'a> Text<'a> {
+    /// Create some text (potentially multiple lines) with no style.
+    ///
+    /// ## Examples
+    ///
+    /// ```rust
+    /// # use helix_tui::text::Text;
+    /// Text::raw("The first line\nThe second line");
+    /// Text::raw(String::from("The first line\nThe second line"));
+    /// ```
+    pub fn raw<T>(content: T) -> Text<'a>
+    where
+        T: Into<Cow<'a, str>>,
+    {
+        Text {
+            lines: match content.into() {
+                Cow::Borrowed(s) => s.lines().map(Spans::from).collect(),
+                Cow::Owned(s) => s.lines().map(|l| Spans::from(l.to_owned())).collect(),
+            },
+        }
+    }
+
+    /// Create some text (potentially multiple lines) with a style.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// # use helix_tui::text::Text;
+    /// # use helix_tui::style::{Color, Modifier, Style};
+    /// let style = Style::default().fg(Color::Yellow).add_modifier(Modifier::ITALIC);
+    /// Text::styled("The first line\nThe second line", style);
+    /// Text::styled(String::from("The first line\nThe second line"), style);
+    /// ```
+    pub fn styled<T>(content: T, style: Style) -> Text<'a>
+    where
+        T: Into<Cow<'a, str>>,
+    {
+        let mut text = Text::raw(content);
+        text.patch_style(style);
+        text
+    }
+
+    /// Returns the max width of all the lines.
+    ///
+    /// ## Examples
+    ///
+    /// ```rust
+    /// use helix_tui::text::Text;
+    /// let text = Text::from("The first line\nThe second line");
+    /// assert_eq!(15, text.width());
+    /// ```
+    pub fn width(&self) -> usize {
+        self.lines
+            .iter()
+            .map(Spans::width)
+            .max()
+            .unwrap_or_default()
+    }
+
+    /// Returns the height.
+    ///
+    /// ## Examples
+    ///
+    /// ```rust
+    /// use helix_tui::text::Text;
+    /// let text = Text::from("The first line\nThe second line");
+    /// assert_eq!(2, text.height());
+    /// ```
+    pub fn height(&self) -> usize {
+        self.lines.len()
+    }
+
+    /// Apply a new style to existing text.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// # use helix_tui::text::Text;
+    /// # use helix_tui::style::{Color, Modifier, Style};
+    /// let style = Style::default().fg(Color::Yellow).add_modifier(Modifier::ITALIC);
+    /// let mut raw_text = Text::raw("The first line\nThe second line");
+    /// let styled_text = Text::styled(String::from("The first line\nThe second line"), style);
+    /// assert_ne!(raw_text, styled_text);
+    ///
+    /// raw_text.patch_style(style);
+    /// assert_eq!(raw_text, styled_text);
+    /// ```
+    pub fn patch_style(&mut self, style: Style) {
+        for line in &mut self.lines {
+            for span in &mut line.0 {
+                span.style = span.style.patch(style);
+            }
+        }
+    }
+}
+
+impl<'a> From<String> for Text<'a> {
+    fn from(s: String) -> Text<'a> {
+        Text::raw(s)
+    }
+}
+
+impl<'a> From<&'a str> for Text<'a> {
+    fn from(s: &'a str) -> Text<'a> {
+        Text::raw(s)
+    }
+}
+
+impl<'a> From<Span<'a>> for Text<'a> {
+    fn from(span: Span<'a>) -> Text<'a> {
+        Text {
+            lines: vec![Spans::from(span)],
+        }
+    }
+}
+
+impl<'a> From<Spans<'a>> for Text<'a> {
+    fn from(spans: Spans<'a>) -> Text<'a> {
+        Text { lines: vec![spans] }
+    }
+}
+
+impl<'a> From<Vec<Spans<'a>>> for Text<'a> {
+    fn from(lines: Vec<Spans<'a>>) -> Text<'a> {
+        Text { lines }
+    }
+}
+
+impl<'a> IntoIterator for Text<'a> {
+    type Item = Spans<'a>;
+    type IntoIter = std::vec::IntoIter<Self::Item>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.lines.into_iter()
+    }
+}
+
+impl<'a> Extend<Spans<'a>> for Text<'a> {
+    fn extend<T: IntoIterator<Item = Spans<'a>>>(&mut self, iter: T) {
+        self.lines.extend(iter);
+    }
+}

helix-tui/src/widgets/block.rs

@@ -0,0 +1,511 @@
+use crate::{
+    buffer::Buffer,
+    layout::Rect,
+    style::Style,
+    symbols::line,
+    text::{Span, Spans},
+    widgets::{Borders, Widget},
+};
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum BorderType {
+    Plain,
+    Rounded,
+    Double,
+    Thick,
+}
+
+impl BorderType {
+    pub fn line_symbols(border_type: BorderType) -> line::Set {
+        match border_type {
+            BorderType::Plain => line::NORMAL,
+            BorderType::Rounded => line::ROUNDED,
+            BorderType::Double => line::DOUBLE,
+            BorderType::Thick => line::THICK,
+        }
+    }
+}
+
+/// Base widget to be used with all upper level ones. It may be used to display a box border around
+/// the widget and/or add a title.
+///
+/// # Examples
+///
+/// ```
+/// # use helix_tui::widgets::{Block, BorderType, Borders};
+/// # use helix_tui::style::{Style, Color};
+/// Block::default()
+///     .title("Block")
+///     .borders(Borders::LEFT | Borders::RIGHT)
+///     .border_style(Style::default().fg(Color::White))
+///     .border_type(BorderType::Rounded)
+///     .style(Style::default().bg(Color::Black));
+/// ```
+#[derive(Debug, Clone, PartialEq)]
+pub struct Block<'a> {
+    /// Optional title place on the upper left of the block
+    title: Option<Spans<'a>>,
+    /// Visible borders
+    borders: Borders,
+    /// Border style
+    border_style: Style,
+    /// Type of the border. The default is plain lines but one can choose to have rounded corners
+    /// or doubled lines instead.
+    border_type: BorderType,
+    /// Widget style
+    style: Style,
+}
+
+impl<'a> Default for Block<'a> {
+    fn default() -> Block<'a> {
+        Block {
+            title: None,
+            borders: Borders::NONE,
+            border_style: Default::default(),
+            border_type: BorderType::Plain,
+            style: Default::default(),
+        }
+    }
+}
+
+impl<'a> Block<'a> {
+    pub fn title<T>(mut self, title: T) -> Block<'a>
+    where
+        T: Into<Spans<'a>>,
+    {
+        self.title = Some(title.into());
+        self
+    }
+
+    #[deprecated(
+        since = "0.10.0",
+        note = "You should use styling capabilities of `text::Spans` given as argument of the `title` method to apply styling to the title."
+    )]
+    pub fn title_style(mut self, style: Style) -> Block<'a> {
+        if let Some(t) = self.title {
+            let title = String::from(t);
+            self.title = Some(Spans::from(Span::styled(title, style)));
+        }
+        self
+    }
+
+    pub fn border_style(mut self, style: Style) -> Block<'a> {
+        self.border_style = style;
+        self
+    }
+
+    pub fn style(mut self, style: Style) -> Block<'a> {
+        self.style = style;
+        self
+    }
+
+    pub fn borders(mut self, flag: Borders) -> Block<'a> {
+        self.borders = flag;
+        self
+    }
+
+    pub fn border_type(mut self, border_type: BorderType) -> Block<'a> {
+        self.border_type = border_type;
+        self
+    }
+
+    /// Compute the inner area of a block based on its border visibility rules.
+    pub fn inner(&self, area: Rect) -> Rect {
+        let mut inner = area;
+        if self.borders.intersects(Borders::LEFT) {
+            inner.x = inner.x.saturating_add(1).min(inner.right());
+            inner.width = inner.width.saturating_sub(1);
+        }
+        if self.borders.intersects(Borders::TOP) || self.title.is_some() {
+            inner.y = inner.y.saturating_add(1).min(inner.bottom());
+            inner.height = inner.height.saturating_sub(1);
+        }
+        if self.borders.intersects(Borders::RIGHT) {
+            inner.width = inner.width.saturating_sub(1);
+        }
+        if self.borders.intersects(Borders::BOTTOM) {
+            inner.height = inner.height.saturating_sub(1);
+        }
+        inner
+    }
+}
+
+impl<'a> Widget for Block<'a> {
+    fn render(self, area: Rect, buf: &mut Buffer) {
+        if area.area() == 0 {
+            return;
+        }
+        buf.set_style(area, self.style);
+        let symbols = BorderType::line_symbols(self.border_type);
+
+        // Sides
+        if self.borders.intersects(Borders::LEFT) {
+            for y in area.top()..area.bottom() {
+                buf.get_mut(area.left(), y)
+                    .set_symbol(symbols.vertical)
+                    .set_style(self.border_style);
+            }
+        }
+        if self.borders.intersects(Borders::TOP) {
+            for x in area.left()..area.right() {
+                buf.get_mut(x, area.top())
+                    .set_symbol(symbols.horizontal)
+                    .set_style(self.border_style);
+            }
+        }
+        if self.borders.intersects(Borders::RIGHT) {
+            let x = area.right() - 1;
+            for y in area.top()..area.bottom() {
+                buf.get_mut(x, y)
+                    .set_symbol(symbols.vertical)
+                    .set_style(self.border_style);
+            }
+        }
+        if self.borders.intersects(Borders::BOTTOM) {
+            let y = area.bottom() - 1;
+            for x in area.left()..area.right() {
+                buf.get_mut(x, y)
+                    .set_symbol(symbols.horizontal)
+                    .set_style(self.border_style);
+            }
+        }
+
+        // Corners
+        if self.borders.contains(Borders::RIGHT | Borders::BOTTOM) {
+            buf.get_mut(area.right() - 1, area.bottom() - 1)
+                .set_symbol(symbols.bottom_right)
+                .set_style(self.border_style);
+        }
+        if self.borders.contains(Borders::RIGHT | Borders::TOP) {
+            buf.get_mut(area.right() - 1, area.top())
+                .set_symbol(symbols.top_right)
+                .set_style(self.border_style);
+        }
+        if self.borders.contains(Borders::LEFT | Borders::BOTTOM) {
+            buf.get_mut(area.left(), area.bottom() - 1)
+                .set_symbol(symbols.bottom_left)
+                .set_style(self.border_style);
+        }
+        if self.borders.contains(Borders::LEFT | Borders::TOP) {
+            buf.get_mut(area.left(), area.top())
+                .set_symbol(symbols.top_left)
+                .set_style(self.border_style);
+        }
+
+        if let Some(title) = self.title {
+            let lx = if self.borders.intersects(Borders::LEFT) {
+                1
+            } else {
+                0
+            };
+            let rx = if self.borders.intersects(Borders::RIGHT) {
+                1
+            } else {
+                0
+            };
+            let width = area.width.saturating_sub(lx).saturating_sub(rx);
+            buf.set_spans(area.left() + lx, area.top(), &title, width);
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::layout::Rect;
+
+    #[test]
+    fn inner_takes_into_account_the_borders() {
+        // No borders
+        assert_eq!(
+            Block::default().inner(Rect::default()),
+            Rect {
+                x: 0,
+                y: 0,
+                width: 0,
+                height: 0
+            },
+            "no borders, width=0, height=0"
+        );
+        assert_eq!(
+            Block::default().inner(Rect {
+                x: 0,
+                y: 0,
+                width: 1,
+                height: 1
+            }),
+            Rect {
+                x: 0,
+                y: 0,
+                width: 1,
+                height: 1
+            },
+            "no borders, width=1, height=1"
+        );
+
+        // Left border
+        assert_eq!(
+            Block::default().borders(Borders::LEFT).inner(Rect {
+                x: 0,
+                y: 0,
+                width: 0,
+                height: 1
+            }),
+            Rect {
+                x: 0,
+                y: 0,
+                width: 0,
+                height: 1
+            },
+            "left, width=0"
+        );
+        assert_eq!(
+            Block::default().borders(Borders::LEFT).inner(Rect {
+                x: 0,
+                y: 0,
+                width: 1,
+                height: 1
+            }),
+            Rect {
+                x: 1,
+                y: 0,
+                width: 0,
+                height: 1
+            },
+            "left, width=1"
+        );
+        assert_eq!(
+            Block::default().borders(Borders::LEFT).inner(Rect {
+                x: 0,
+                y: 0,
+                width: 2,
+                height: 1
+            }),
+            Rect {
+                x: 1,
+                y: 0,
+                width: 1,
+                height: 1
+            },
+            "left, width=2"
+        );
+
+        // Top border
+        assert_eq!(
+            Block::default().borders(Borders::TOP).inner(Rect {
+                x: 0,
+                y: 0,
+                width: 1,
+                height: 0
+            }),
+            Rect {
+                x: 0,
+                y: 0,
+                width: 1,
+                height: 0
+            },
+            "top, height=0"
+        );
+        assert_eq!(
+            Block::default().borders(Borders::TOP).inner(Rect {
+                x: 0,
+                y: 0,
+                width: 1,
+                height: 1
+            }),
+            Rect {
+                x: 0,
+                y: 1,
+                width: 1,
+                height: 0
+            },
+            "top, height=1"
+        );
+        assert_eq!(
+            Block::default().borders(Borders::TOP).inner(Rect {
+                x: 0,
+                y: 0,
+                width: 1,
+                height: 2
+            }),
+            Rect {
+                x: 0,
+                y: 1,
+                width: 1,
+                height: 1
+            },
+            "top, height=2"
+        );
+
+        // Right border
+        assert_eq!(
+            Block::default().borders(Borders::RIGHT).inner(Rect {
+                x: 0,
+                y: 0,
+                width: 0,
+                height: 1
+            }),
+            Rect {
+                x: 0,
+                y: 0,
+                width: 0,
+                height: 1
+            },
+            "right, width=0"
+        );
+        assert_eq!(
+            Block::default().borders(Borders::RIGHT).inner(Rect {
+                x: 0,
+                y: 0,
+                width: 1,
+                height: 1
+            }),
+            Rect {
+                x: 0,
+                y: 0,
+                width: 0,
+                height: 1
+            },
+            "right, width=1"
+        );
+        assert_eq!(
+            Block::default().borders(Borders::RIGHT).inner(Rect {
+                x: 0,
+                y: 0,
+                width: 2,
+                height: 1
+            }),
+            Rect {
+                x: 0,
+                y: 0,
+                width: 1,
+                height: 1
+            },
+            "right, width=2"
+        );
+
+        // Bottom border
+        assert_eq!(
+            Block::default().borders(Borders::BOTTOM).inner(Rect {
+                x: 0,
+                y: 0,
+                width: 1,
+                height: 0
+            }),
+            Rect {
+                x: 0,
+                y: 0,
+                width: 1,
+                height: 0
+            },
+            "bottom, height=0"
+        );
+        assert_eq!(
+            Block::default().borders(Borders::BOTTOM).inner(Rect {
+                x: 0,
+                y: 0,
+                width: 1,
+                height: 1
+            }),
+            Rect {
+                x: 0,
+                y: 0,
+                width: 1,
+                height: 0
+            },
+            "bottom, height=1"
+        );
+        assert_eq!(
+            Block::default().borders(Borders::BOTTOM).inner(Rect {
+                x: 0,
+                y: 0,
+                width: 1,
+                height: 2
+            }),
+            Rect {
+                x: 0,
+                y: 0,
+                width: 1,
+                height: 1
+            },
+            "bottom, height=2"
+        );
+
+        // All borders
+        assert_eq!(
+            Block::default()
+                .borders(Borders::ALL)
+                .inner(Rect::default()),
+            Rect {
+                x: 0,
+                y: 0,
+                width: 0,
+                height: 0
+            },
+            "all borders, width=0, height=0"
+        );
+        assert_eq!(
+            Block::default().borders(Borders::ALL).inner(Rect {
+                x: 0,
+                y: 0,
+                width: 1,
+                height: 1
+            }),
+            Rect {
+                x: 1,
+                y: 1,
+                width: 0,
+                height: 0,
+            },
+            "all borders, width=1, height=1"
+        );
+        assert_eq!(
+            Block::default().borders(Borders::ALL).inner(Rect {
+                x: 0,
+                y: 0,
+                width: 2,
+                height: 2,
+            }),
+            Rect {
+                x: 1,
+                y: 1,
+                width: 0,
+                height: 0,
+            },
+            "all borders, width=2, height=2"
+        );
+        assert_eq!(
+            Block::default().borders(Borders::ALL).inner(Rect {
+                x: 0,
+                y: 0,
+                width: 3,
+                height: 3,
+            }),
+            Rect {
+                x: 1,
+                y: 1,
+                width: 1,
+                height: 1,
+            },
+            "all borders, width=3, height=3"
+        );
+    }
+
+    #[test]
+    fn inner_takes_into_account_the_title() {
+        assert_eq!(
+            Block::default().title("Test").inner(Rect {
+                x: 0,
+                y: 0,
+                width: 0,
+                height: 1,
+            }),
+            Rect {
+                x: 0,
+                y: 1,
+                width: 0,
+                height: 0,
+            },
+        );
+    }
+}

helix-tui/src/widgets/clear.rs

@@ -0,0 +1,36 @@
+use crate::buffer::Buffer;
+use crate::layout::Rect;
+use crate::widgets::Widget;
+
+/// A widget to to clear/reset a certain area to allow overdrawing (e.g. for popups)
+///
+/// # Examples
+///
+/// ```
+/// # use helix_tui::widgets::{Clear, Block, Borders};
+/// # use helix_tui::layout::Rect;
+/// # use helix_tui::Frame;
+/// # use helix_tui::backend::Backend;
+/// fn draw_on_clear<B: Backend>(f: &mut Frame<B>, area: Rect) {
+///     let block = Block::default().title("Block").borders(Borders::ALL);
+///     f.render_widget(Clear, area); // <- this will clear/reset the area first
+///     f.render_widget(block, area); // now render the block widget
+/// }
+/// ```
+///
+/// # Popup Example
+///
+/// For a more complete example how to utilize `Clear` to realize popups see
+/// the example `examples/popup.rs`
+#[derive(Debug, Clone)]
+pub struct Clear;
+
+impl Widget for Clear {
+    fn render(self, area: Rect, buf: &mut Buffer) {
+        for x in area.left()..area.right() {
+            for y in area.top()..area.bottom() {
+                buf.get_mut(x, y).reset();
+            }
+        }
+    }
+}

helix-tui/src/widgets/list.rs

@@ -0,0 +1,249 @@
+use crate::{
+    buffer::Buffer,
+    layout::{Corner, Rect},
+    style::Style,
+    text::Text,
+    widgets::{Block, StatefulWidget, Widget},
+};
+use std::iter::{self, Iterator};
+use unicode_width::UnicodeWidthStr;
+
+#[derive(Debug, Clone)]
+pub struct ListState {
+    offset: usize,
+    selected: Option<usize>,
+}
+
+impl Default for ListState {
+    fn default() -> ListState {
+        ListState {
+            offset: 0,
+            selected: None,
+        }
+    }
+}
+
+impl ListState {
+    pub fn selected(&self) -> Option<usize> {
+        self.selected
+    }
+
+    pub fn select(&mut self, index: Option<usize>) {
+        self.selected = index;
+        if index.is_none() {
+            self.offset = 0;
+        }
+    }
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct ListItem<'a> {
+    content: Text<'a>,
+    style: Style,
+}
+
+impl<'a> ListItem<'a> {
+    pub fn new<T>(content: T) -> ListItem<'a>
+    where
+        T: Into<Text<'a>>,
+    {
+        ListItem {
+            content: content.into(),
+            style: Style::default(),
+        }
+    }
+
+    pub fn style(mut self, style: Style) -> ListItem<'a> {
+        self.style = style;
+        self
+    }
+
+    pub fn height(&self) -> usize {
+        self.content.height()
+    }
+}
+
+/// A widget to display several items among which one can be selected (optional)
+///
+/// # Examples
+///
+/// ```
+/// # use helix_tui::widgets::{Block, Borders, List, ListItem};
+/// # use helix_tui::style::{Style, Color, Modifier};
+/// let items = [ListItem::new("Item 1"), ListItem::new("Item 2"), ListItem::new("Item 3")];
+/// List::new(items)
+///     .block(Block::default().title("List").borders(Borders::ALL))
+///     .style(Style::default().fg(Color::White))
+///     .highlight_style(Style::default().add_modifier(Modifier::ITALIC))
+///     .highlight_symbol(">>");
+/// ```
+#[derive(Debug, Clone)]
+pub struct List<'a> {
+    block: Option<Block<'a>>,
+    items: Vec<ListItem<'a>>,
+    /// Style used as a base style for the widget
+    style: Style,
+    start_corner: Corner,
+    /// Style used to render selected item
+    highlight_style: Style,
+    /// Symbol in front of the selected item (Shift all items to the right)
+    highlight_symbol: Option<&'a str>,
+}
+
+impl<'a> List<'a> {
+    pub fn new<T>(items: T) -> List<'a>
+    where
+        T: Into<Vec<ListItem<'a>>>,
+    {
+        List {
+            block: None,
+            style: Style::default(),
+            items: items.into(),
+            start_corner: Corner::TopLeft,
+            highlight_style: Style::default(),
+            highlight_symbol: None,
+        }
+    }
+
+    pub fn block(mut self, block: Block<'a>) -> List<'a> {
+        self.block = Some(block);
+        self
+    }
+
+    pub fn style(mut self, style: Style) -> List<'a> {
+        self.style = style;
+        self
+    }
+
+    pub fn highlight_symbol(mut self, highlight_symbol: &'a str) -> List<'a> {
+        self.highlight_symbol = Some(highlight_symbol);
+        self
+    }
+
+    pub fn highlight_style(mut self, style: Style) -> List<'a> {
+        self.highlight_style = style;
+        self
+    }
+
+    pub fn start_corner(mut self, corner: Corner) -> List<'a> {
+        self.start_corner = corner;
+        self
+    }
+}
+
+impl<'a> StatefulWidget for List<'a> {
+    type State = ListState;
+
+    fn render(mut self, area: Rect, buf: &mut Buffer, state: &mut Self::State) {
+        buf.set_style(area, self.style);
+        let list_area = match self.block.take() {
+            Some(b) => {
+                let inner_area = b.inner(area);
+                b.render(area, buf);
+                inner_area
+            }
+            None => area,
+        };
+
+        if list_area.width < 1 || list_area.height < 1 {
+            return;
+        }
+
+        if self.items.is_empty() {
+            return;
+        }
+        let list_height = list_area.height as usize;
+
+        let mut start = state.offset;
+        let mut end = state.offset;
+        let mut height = 0;
+        for item in self.items.iter().skip(state.offset) {
+            if height + item.height() > list_height {
+                break;
+            }
+            height += item.height();
+            end += 1;
+        }
+
+        let selected = state.selected.unwrap_or(0).min(self.items.len() - 1);
+        while selected >= end {
+            height = height.saturating_add(self.items[end].height());
+            end += 1;
+            while height > list_height {
+                height = height.saturating_sub(self.items[start].height());
+                start += 1;
+            }
+        }
+        while selected < start {
+            start -= 1;
+            height = height.saturating_add(self.items[start].height());
+            while height > list_height {
+                end -= 1;
+                height = height.saturating_sub(self.items[end].height());
+            }
+        }
+        state.offset = start;
+
+        let highlight_symbol = self.highlight_symbol.unwrap_or("");
+        let blank_symbol = iter::repeat(" ")
+            .take(highlight_symbol.width())
+            .collect::<String>();
+
+        let mut current_height = 0;
+        let has_selection = state.selected.is_some();
+        for (i, item) in self
+            .items
+            .iter_mut()
+            .enumerate()
+            .skip(state.offset)
+            .take(end - start)
+        {
+            let (x, y) = match self.start_corner {
+                Corner::BottomLeft => {
+                    current_height += item.height() as u16;
+                    (list_area.left(), list_area.bottom() - current_height)
+                }
+                _ => {
+                    let pos = (list_area.left(), list_area.top() + current_height);
+                    current_height += item.height() as u16;
+                    pos
+                }
+            };
+            let area = Rect {
+                x,
+                y,
+                width: list_area.width,
+                height: item.height() as u16,
+            };
+            let item_style = self.style.patch(item.style);
+            buf.set_style(area, item_style);
+
+            let is_selected = state.selected.map(|s| s == i).unwrap_or(false);
+            let elem_x = if has_selection {
+                let symbol = if is_selected {
+                    highlight_symbol
+                } else {
+                    &blank_symbol
+                };
+                let (x, _) = buf.set_stringn(x, y, symbol, list_area.width as usize, item_style);
+                x
+            } else {
+                x
+            };
+            let max_element_width = (list_area.width - (elem_x - x)) as usize;
+            for (j, line) in item.content.lines.iter().enumerate() {
+                buf.set_spans(elem_x, y + j as u16, line, max_element_width as u16);
+            }
+            if is_selected {
+                buf.set_style(area, self.highlight_style);
+            }
+        }
+    }
+}
+
+impl<'a> Widget for List<'a> {
+    fn render(self, area: Rect, buf: &mut Buffer) {
+        let mut state = ListState::default();
+        StatefulWidget::render(self, area, buf, &mut state);
+    }
+}

helix-tui/src/widgets/mod.rs

@@ -0,0 +1,53 @@
+//! `widgets` is a collection of types that implement [`Widget`] or [`StatefulWidget`] or both.
+//!
+//! All widgets are implemented using the builder pattern and are consumable objects. They are not
+//! meant to be stored but used as *commands* to draw common figures in the UI.
+//!
+//! The available widgets are:
+//! - [`Block`]
+//! - [`Tabs`]
+//! - [`List`]
+//! - [`Table`]
+//! - [`Paragraph`]
+//! - [`Clear`]
+
+mod block;
+mod clear;
+// mod list;
+mod paragraph;
+mod reflow;
+// mod table;
+
+pub use self::block::{Block, BorderType};
+pub use self::clear::Clear;
+// pub use self::list::{List, ListItem, ListState};
+pub use self::paragraph::{Paragraph, Wrap};
+// pub use self::table::{Cell, Row, Table, TableState};
+
+use crate::{buffer::Buffer, layout::Rect};
+use bitflags::bitflags;
+
+bitflags! {
+    /// Bitflags that can be composed to set the visible borders essentially on the block widget.
+    pub struct Borders: u32 {
+        /// Show no border (default)
+        const NONE  = 0b0000_0001;
+        /// Show the top border
+        const TOP   = 0b0000_0010;
+        /// Show the right border
+        const RIGHT = 0b0000_0100;
+        /// Show the bottom border
+        const BOTTOM = 0b000_1000;
+        /// Show the left border
+        const LEFT = 0b0001_0000;
+        /// Show all borders
+        const ALL = Self::TOP.bits | Self::RIGHT.bits | Self::BOTTOM.bits | Self::LEFT.bits;
+    }
+}
+
+/// Base requirements for a Widget
+pub trait Widget {
+    /// Draws the current state of the widget in the given buffer. That the only method required to
+    /// implement a custom widget.
+    fn render(self, area: Rect, buf: &mut Buffer);
+}

helix-tui/src/widgets/paragraph.rs

@@ -0,0 +1,197 @@
+use crate::{
+    buffer::Buffer,
+    layout::{Alignment, Rect},
+    style::Style,
+    text::{StyledGrapheme, Text},
+    widgets::{
+        reflow::{LineComposer, LineTruncator, WordWrapper},
+        Block, Widget,
+    },
+};
+use std::iter;
+use unicode_width::UnicodeWidthStr;
+
+fn get_line_offset(line_width: u16, text_area_width: u16, alignment: Alignment) -> u16 {
+    match alignment {
+        Alignment::Center => (text_area_width / 2).saturating_sub(line_width / 2),
+        Alignment::Right => text_area_width.saturating_sub(line_width),
+        Alignment::Left => 0,
+    }
+}
+
+/// A widget to display some text.
+///
+/// # Examples
+///
+/// ```
+/// # use helix_tui::text::{Text, Spans, Span};
+/// # use helix_tui::widgets::{Block, Borders, Paragraph, Wrap};
+/// # use helix_tui::style::{Style, Color, Modifier};
+/// # use helix_tui::layout::{Alignment};
+/// let text = vec![
+///     Spans::from(vec![
+///         Span::raw("First"),
+///         Span::styled("line",Style::default().add_modifier(Modifier::ITALIC)),
+///         Span::raw("."),
+///     ]),
+///     Spans::from(Span::styled("Second line", Style::default().fg(Color::Red))),
+/// ];
+/// Paragraph::new(text)
+///     .block(Block::default().title("Paragraph").borders(Borders::ALL))
+///     .style(Style::default().fg(Color::White).bg(Color::Black))
+///     .alignment(Alignment::Center)
+///     .wrap(Wrap { trim: true });
+/// ```
+#[derive(Debug, Clone)]
+pub struct Paragraph<'a> {
+    /// A block to wrap the widget in
+    block: Option<Block<'a>>,
+    /// Widget style
+    style: Style,
+    /// How to wrap the text
+    wrap: Option<Wrap>,
+    /// The text to display
+    text: Text<'a>,
+    /// Scroll
+    scroll: (u16, u16),
+    /// Alignment of the text
+    alignment: Alignment,
+}
+
+/// Describes how to wrap text across lines.
+///
+/// ## Examples
+///
+/// ```
+/// # use helix_tui::widgets::{Paragraph, Wrap};
+/// # use helix_tui::text::Text;
+/// let bullet_points = Text::from(r#"Some indented points:
+///     - First thing goes here and is long so that it wraps
+///     - Here is another point that is long enough to wrap"#);
+///
+/// // With leading spaces trimmed (window width of 30 chars):
+/// Paragraph::new(bullet_points.clone()).wrap(Wrap { trim: true });
+/// // Some indented points:
+/// // - First thing goes here and is
+/// // long so that it wraps
+/// // - Here is another point that
+/// // is long enough to wrap
+///
+/// // But without trimming, indentation is preserved:
+/// Paragraph::new(bullet_points).wrap(Wrap { trim: false });
+/// // Some indented points:
+/// //     - First thing goes here
+/// // and is long so that it wraps
+/// //     - Here is another point
+/// // that is long enough to wrap
+/// ```
+#[derive(Debug, Clone, Copy)]
+pub struct Wrap {
+    /// Should leading whitespace be trimmed
+    pub trim: bool,
+}
+
+impl<'a> Paragraph<'a> {
+    pub fn new<T>(text: T) -> Paragraph<'a>
+    where
+        T: Into<Text<'a>>,
+    {
+        Paragraph {
+            block: None,
+            style: Default::default(),
+            wrap: None,
+            text: text.into(),
+            scroll: (0, 0),
+            alignment: Alignment::Left,
+        }
+    }
+
+    pub fn block(mut self, block: Block<'a>) -> Paragraph<'a> {
+        self.block = Some(block);
+        self
+    }
+
+    pub fn style(mut self, style: Style) -> Paragraph<'a> {
+        self.style = style;
+        self
+    }
+
+    pub fn wrap(mut self, wrap: Wrap) -> Paragraph<'a> {
+        self.wrap = Some(wrap);
+        self
+    }
+
+    pub fn scroll(mut self, offset: (u16, u16)) -> Paragraph<'a> {
+        self.scroll = offset;
+        self
+    }
+
+    pub fn alignment(mut self, alignment: Alignment) -> Paragraph<'a> {
+        self.alignment = alignment;
+        self
+    }
+}
+
+impl<'a> Widget for Paragraph<'a> {
+    fn render(mut self, area: Rect, buf: &mut Buffer) {
+        buf.set_style(area, self.style);
+        let text_area = match self.block.take() {
+            Some(b) => {
+                let inner_area = b.inner(area);
+                b.render(area, buf);
+                inner_area
+            }
+            None => area,
+        };
+
+        if text_area.height < 1 {
+            return;
+        }
+
+        let style = self.style;
+        let mut styled = self.text.lines.iter().flat_map(|spans| {
+            spans
+                .0
+                .iter()
+                .flat_map(|span| span.styled_graphemes(style))
+                // Required given the way composers work but might be refactored out if we change
+                // composers to operate on lines instead of a stream of graphemes.
+                .chain(iter::once(StyledGrapheme {
+                    symbol: "\n",
+                    style: self.style,
+                }))
+        });
+
+        let mut line_composer: Box<dyn LineComposer> = if let Some(Wrap { trim }) = self.wrap {
+            Box::new(WordWrapper::new(&mut styled, text_area.width, trim))
+        } else {
+            let mut line_composer = Box::new(LineTruncator::new(&mut styled, text_area.width));
+            if let Alignment::Left = self.alignment {
+                line_composer.set_horizontal_offset(self.scroll.1);
+            }
+            line_composer
+        };
+        let mut y = 0;
+        while let Some((current_line, current_line_width)) = line_composer.next_line() {
+            if y >= self.scroll.0 {
+                let mut x = get_line_offset(current_line_width, text_area.width, self.alignment);
+                for StyledGrapheme { symbol, style } in current_line {
+                    buf.get_mut(text_area.left() + x, text_area.top() + y - self.scroll.0)
+                        .set_symbol(if symbol.is_empty() {
+                            // If the symbol is empty, the last char which rendered last time will
+                            // leave on the line. It's a quick fix.
+                            " "
+                        } else {
+                            symbol
+                        })
+                        .set_style(*style);
+                    x += symbol.width() as u16;
+                }
+            }
+            y += 1;
+            if y >= text_area.height + self.scroll.0 {
+                break;
+            }
+        }
+    }
+}

helix-tui/src/widgets/reflow.rs

@@ -0,0 +1,534 @@
+use crate::text::StyledGrapheme;
+use unicode_segmentation::UnicodeSegmentation;
+use unicode_width::UnicodeWidthStr;
+
+const NBSP: &str = "\u{00a0}";
+
+/// A state machine to pack styled symbols into lines.
+/// Cannot implement it as Iterator since it yields slices of the internal buffer (need streaming
+/// iterators for that).
+pub trait LineComposer<'a> {
+    fn next_line(&mut self) -> Option<(&[StyledGrapheme<'a>], u16)>;
+}
+
+/// A state machine that wraps lines on word boundaries.
+pub struct WordWrapper<'a, 'b> {
+    symbols: &'b mut dyn Iterator<Item = StyledGrapheme<'a>>,
+    max_line_width: u16,
+    current_line: Vec<StyledGrapheme<'a>>,
+    next_line: Vec<StyledGrapheme<'a>>,
+    /// Removes the leading whitespace from lines
+    trim: bool,
+}
+
+impl<'a, 'b> WordWrapper<'a, 'b> {
+    pub fn new(
+        symbols: &'b mut dyn Iterator<Item = StyledGrapheme<'a>>,
+        max_line_width: u16,
+        trim: bool,
+    ) -> WordWrapper<'a, 'b> {
+        WordWrapper {
+            symbols,
+            max_line_width,
+            current_line: vec![],
+            next_line: vec![],
+            trim,
+        }
+    }
+}
+
+impl<'a, 'b> LineComposer<'a> for WordWrapper<'a, 'b> {
+    fn next_line(&mut self) -> Option<(&[StyledGrapheme<'a>], u16)> {
+        if self.max_line_width == 0 {
+            return None;
+        }
+        std::mem::swap(&mut self.current_line, &mut self.next_line);
+        self.next_line.truncate(0);
+
+        let mut current_line_width = self
+            .current_line
+            .iter()
+            .map(|StyledGrapheme { symbol, .. }| symbol.width() as u16)
+            .sum();
+
+        let mut symbols_to_last_word_end: usize = 0;
+        let mut width_to_last_word_end: u16 = 0;
+        let mut prev_whitespace = false;
+        let mut symbols_exhausted = true;
+        for StyledGrapheme { symbol, style } in &mut self.symbols {
+            symbols_exhausted = false;
+            let symbol_whitespace = symbol.chars().all(&char::is_whitespace) && symbol != NBSP;
+
+            // Ignore characters wider that the total max width.
+            if symbol.width() as u16 > self.max_line_width
+                // Skip leading whitespace when trim is enabled.
+                || self.trim && symbol_whitespace && symbol != "\n" && current_line_width == 0
+            {
+                continue;
+            }
+
+            // Break on newline and discard it.
+            if symbol == "\n" {
+                if prev_whitespace {
+                    current_line_width = width_to_last_word_end;
+                    self.current_line.truncate(symbols_to_last_word_end);
+                }
+                break;
+            }
+
+            // Mark the previous symbol as word end.
+            if symbol_whitespace && !prev_whitespace {
+                symbols_to_last_word_end = self.current_line.len();
+                width_to_last_word_end = current_line_width;
+            }
+
+            self.current_line.push(StyledGrapheme { symbol, style });
+            current_line_width += symbol.width() as u16;
+
+            if current_line_width > self.max_line_width {
+                // If there was no word break in the text, wrap at the end of the line.
+                let (truncate_at, truncated_width) = if symbols_to_last_word_end != 0 {
+                    (symbols_to_last_word_end, width_to_last_word_end)
+                } else {
+                    (self.current_line.len() - 1, self.max_line_width)
+                };
+
+                // Push the remainder to the next line but strip leading whitespace:
+                {
+                    let remainder = &self.current_line[truncate_at..];
+                    if let Some(remainder_nonwhite) =
+                        remainder.iter().position(|StyledGrapheme { symbol, .. }| {
+                            !symbol.chars().all(&char::is_whitespace)
+                        })
+                    {
+                        self.next_line
+                            .extend_from_slice(&remainder[remainder_nonwhite..]);
+                    }
+                }
+                self.current_line.truncate(truncate_at);
+                current_line_width = truncated_width;
+                break;
+            }
+
+            prev_whitespace = symbol_whitespace;
+        }
+
+        // Even if the iterator is exhausted, pass the previous remainder.
+        if symbols_exhausted && self.current_line.is_empty() {
+            None
+        } else {
+            Some((&self.current_line[..], current_line_width))
+        }
+    }
+}
+
+/// A state machine that truncates overhanging lines.
+pub struct LineTruncator<'a, 'b> {
+    symbols: &'b mut dyn Iterator<Item = StyledGrapheme<'a>>,
+    max_line_width: u16,
+    current_line: Vec<StyledGrapheme<'a>>,
+    /// Record the offet to skip render
+    horizontal_offset: u16,
+}
+
+impl<'a, 'b> LineTruncator<'a, 'b> {
+    pub fn new(
+        symbols: &'b mut dyn Iterator<Item = StyledGrapheme<'a>>,
+        max_line_width: u16,
+    ) -> LineTruncator<'a, 'b> {
+        LineTruncator {
+            symbols,
+            max_line_width,
+            horizontal_offset: 0,
+            current_line: vec![],
+        }
+    }
+
+    pub fn set_horizontal_offset(&mut self, horizontal_offset: u16) {
+        self.horizontal_offset = horizontal_offset;
+    }
+}
+
+impl<'a, 'b> LineComposer<'a> for LineTruncator<'a, 'b> {
+    fn next_line(&mut self) -> Option<(&[StyledGrapheme<'a>], u16)> {
+        if self.max_line_width == 0 {
+            return None;
+        }
+
+        self.current_line.truncate(0);
+        let mut current_line_width = 0;
+
+        let mut skip_rest = false;
+        let mut symbols_exhausted = true;
+        let mut horizontal_offset = self.horizontal_offset as usize;
+        for StyledGrapheme { symbol, style } in &mut self.symbols {
+            symbols_exhausted = false;
+
+            // Ignore characters wider that the total max width.
+            if symbol.width() as u16 > self.max_line_width {
+                continue;
+            }
+
+            // Break on newline and discard it.
+            if symbol == "\n" {
+                break;
+            }
+
+            if current_line_width + symbol.width() as u16 > self.max_line_width {
+                // Exhaust the remainder of the line.
+                skip_rest = true;
+                break;
+            }
+
+            let symbol = if horizontal_offset == 0 {
+                symbol
+            } else {
+                let w = symbol.width();
+                if w > horizontal_offset {
+                    let t = trim_offset(symbol, horizontal_offset);
+                    horizontal_offset = 0;
+                    t
+                } else {
+                    horizontal_offset -= w;
+                    ""
+                }
+            };
+            current_line_width += symbol.width() as u16;
+            self.current_line.push(StyledGrapheme { symbol, style });
+        }
+
+        if skip_rest {
+            for StyledGrapheme { symbol, .. } in &mut self.symbols {
+                if symbol == "\n" {
+                    break;
+                }
+            }
+        }
+
+        if symbols_exhausted && self.current_line.is_empty() {
+            None
+        } else {
+            Some((&self.current_line[..], current_line_width))
+        }
+    }
+}
+
+/// This function will return a str slice which start at specified offset.
+/// As src is a unicode str, start offset has to be calculated with each character.
+fn trim_offset(src: &str, mut offset: usize) -> &str {
+    let mut start = 0;
+    for c in UnicodeSegmentation::graphemes(src, true) {
+        let w = c.width();
+        if w <= offset {
+            offset -= w;
+            start += c.len();
+        } else {
+            break;
+        }
+    }
+    &src[start..]
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use unicode_segmentation::UnicodeSegmentation;
+
+    enum Composer {
+        WordWrapper { trim: bool },
+        LineTruncator,
+    }
+
+    fn run_composer(which: Composer, text: &str, text_area_width: u16) -> (Vec<String>, Vec<u16>) {
+        let style = Default::default();
+        let mut styled =
+            UnicodeSegmentation::graphemes(text, true).map(|g| StyledGrapheme { symbol: g, style });
+        let mut composer: Box<dyn LineComposer> = match which {
+            Composer::WordWrapper { trim } => {
+                Box::new(WordWrapper::new(&mut styled, text_area_width, trim))
+            }
+            Composer::LineTruncator => Box::new(LineTruncator::new(&mut styled, text_area_width)),
+        };
+        let mut lines = vec![];
+        let mut widths = vec![];
+        while let Some((styled, width)) = composer.next_line() {
+            let line = styled
+                .iter()
+                .map(|StyledGrapheme { symbol, .. }| *symbol)
+                .collect::<String>();
+            assert!(width <= text_area_width);
+            lines.push(line);
+            widths.push(width);
+        }
+        (lines, widths)
+    }
+
+    #[test]
+    fn line_composer_one_line() {
+        let width = 40;
+        for i in 1..width {
+            let text = "a".repeat(i);
+            let (word_wrapper, _) =
+                run_composer(Composer::WordWrapper { trim: true }, &text, width as u16);
+            let (line_truncator, _) = run_composer(Composer::LineTruncator, &text, width as u16);
+            let expected = vec![text];
+            assert_eq!(word_wrapper, expected);
+            assert_eq!(line_truncator, expected);
+        }
+    }
+
+    #[test]
+    fn line_composer_short_lines() {
+        let width = 20;
+        let text =
+            "abcdefg\nhijklmno\npabcdefg\nhijklmn\nopabcdefghijk\nlmnopabcd\n\n\nefghijklmno";
+        let (word_wrapper, _) = run_composer(Composer::WordWrapper { trim: true }, text, width);
+        let (line_truncator, _) = run_composer(Composer::LineTruncator, text, width);
+
+        let wrapped: Vec<&str> = text.split('\n').collect();
+        assert_eq!(word_wrapper, wrapped);
+        assert_eq!(line_truncator, wrapped);
+    }
+
+    #[test]
+    fn line_composer_long_word() {
+        let width = 20;
+        let text = "abcdefghijklmnopabcdefghijklmnopabcdefghijklmnopabcdefghijklmno";
+        let (word_wrapper, _) =
+            run_composer(Composer::WordWrapper { trim: true }, text, width as u16);
+        let (line_truncator, _) = run_composer(Composer::LineTruncator, text, width as u16);
+
+        let wrapped = vec![
+            &text[..width],
+            &text[width..width * 2],
+            &text[width * 2..width * 3],
+            &text[width * 3..],
+        ];
+        assert_eq!(
+            word_wrapper, wrapped,
+            "WordWrapper should detect the line cannot be broken on word boundary and \
+             break it at line width limit."
+        );
+        assert_eq!(line_truncator, vec![&text[..width]]);
+    }
+
+    #[test]
+    fn line_composer_long_sentence() {
+        let width = 20;
+        let text =
+            "abcd efghij klmnopabcd efgh ijklmnopabcdefg hijkl mnopab c d e f g h i j k l m n o";
+        let text_multi_space =
+            "abcd efghij    klmnopabcd efgh     ijklmnopabcdefg hijkl mnopab c d e f g h i j k l \
+             m n o";
+        let (word_wrapper_single_space, _) =
+            run_composer(Composer::WordWrapper { trim: true }, text, width as u16);
+        let (word_wrapper_multi_space, _) = run_composer(
+            Composer::WordWrapper { trim: true },
+            text_multi_space,
+            width as u16,
+        );
+        let (line_truncator, _) = run_composer(Composer::LineTruncator, text, width as u16);
+
+        let word_wrapped = vec![
+            "abcd efghij",
+            "klmnopabcd efgh",
+            "ijklmnopabcdefg",
+            "hijkl mnopab c d e f",
+            "g h i j k l m n o",
+        ];
+        assert_eq!(word_wrapper_single_space, word_wrapped);
+        assert_eq!(word_wrapper_multi_space, word_wrapped);
+
+        assert_eq!(line_truncator, vec![&text[..width]]);
+    }
+
+    #[test]
+    fn line_composer_zero_width() {
+        let width = 0;
+        let text = "abcd efghij klmnopabcd efgh ijklmnopabcdefg hijkl mnopab ";
+        let (word_wrapper, _) = run_composer(Composer::WordWrapper { trim: true }, text, width);
+        let (line_truncator, _) = run_composer(Composer::LineTruncator, text, width);
+
+        let expected: Vec<&str> = Vec::new();
+        assert_eq!(word_wrapper, expected);
+        assert_eq!(line_truncator, expected);
+    }
+
+    #[test]
+    fn line_composer_max_line_width_of_1() {
+        let width = 1;
+        let text = "abcd efghij klmnopabcd efgh ijklmnopabcdefg hijkl mnopab ";
+        let (word_wrapper, _) = run_composer(Composer::WordWrapper { trim: true }, text, width);
+        let (line_truncator, _) = run_composer(Composer::LineTruncator, text, width);
+
+        let expected: Vec<&str> = UnicodeSegmentation::graphemes(text, true)
+            .filter(|g| g.chars().any(|c| !c.is_whitespace()))
+            .collect();
+        assert_eq!(word_wrapper, expected);
+        assert_eq!(line_truncator, vec!["a"]);
+    }
+
+    #[test]
+    fn line_composer_max_line_width_of_1_double_width_characters() {
+        let width = 1;
+        let text = "コンピュータ上で文字を扱う場合、典型的には文字\naaaによる通信を行う場合にその\
+                    両端点では、";
+        let (word_wrapper, _) = run_composer(Composer::WordWrapper { trim: true }, text, width);
+        let (line_truncator, _) = run_composer(Composer::LineTruncator, text, width);
+        assert_eq!(word_wrapper, vec!["", "a", "a", "a"]);
+        assert_eq!(line_truncator, vec!["", "a"]);
+    }
+
+    /// Tests WordWrapper with words some of which exceed line length and some not.
+    #[test]
+    fn line_composer_word_wrapper_mixed_length() {
+        let width = 20;
+        let text = "abcd efghij klmnopabcdefghijklmnopabcdefghijkl mnopab cdefghi j klmno";
+        let (word_wrapper, _) = run_composer(Composer::WordWrapper { trim: true }, text, width);
+        assert_eq!(
+            word_wrapper,
+            vec![
+                "abcd efghij",
+                "klmnopabcdefghijklmn",
+                "opabcdefghijkl",
+                "mnopab cdefghi j",
+                "klmno",
+            ]
+        )
+    }
+
+    #[test]
+    fn line_composer_double_width_chars() {
+        let width = 20;
+        let text = "コンピュータ上で文字を扱う場合、典型的には文字による通信を行う場合にその両端点\
+                    では、";
+        let (word_wrapper, word_wrapper_width) =
+            run_composer(Composer::WordWrapper { trim: true }, &text, width);
+        let (line_truncator, _) = run_composer(Composer::LineTruncator, &text, width);
+        assert_eq!(line_truncator, vec!["コンピュータ上で文字"]);
+        let wrapped = vec![
+            "コンピュータ上で文字",
+            "を扱う場合、典型的に",
+            "は文字による通信を行",
+            "う場合にその両端点で",
+            "は、",
+        ];
+        assert_eq!(word_wrapper, wrapped);
+        assert_eq!(word_wrapper_width, vec![width, width, width, width, 4]);
+    }
+
+    #[test]
+    fn line_composer_leading_whitespace_removal() {
+        let width = 20;
+        let text = "AAAAAAAAAAAAAAAAAAAA    AAA";
+        let (word_wrapper, _) = run_composer(Composer::WordWrapper { trim: true }, text, width);
+        let (line_truncator, _) = run_composer(Composer::LineTruncator, text, width);
+        assert_eq!(word_wrapper, vec!["AAAAAAAAAAAAAAAAAAAA", "AAA",]);
+        assert_eq!(line_truncator, vec!["AAAAAAAAAAAAAAAAAAAA"]);
+    }
+
+    /// Tests truncation of leading whitespace.
+    #[test]
+    fn line_composer_lots_of_spaces() {
+        let width = 20;
+        let text = "                                                                     ";
+        let (word_wrapper, _) = run_composer(Composer::WordWrapper { trim: true }, text, width);
+        let (line_truncator, _) = run_composer(Composer::LineTruncator, text, width);
+        assert_eq!(word_wrapper, vec![""]);
+        assert_eq!(line_truncator, vec!["                    "]);
+    }
+
+    /// Tests an input starting with a letter, folowed by spaces - some of the behaviour is
+    /// incidental.
+    #[test]
+    fn line_composer_char_plus_lots_of_spaces() {
+        let width = 20;
+        let text = "a                                                                     ";
+        let (word_wrapper, _) = run_composer(Composer::WordWrapper { trim: true }, text, width);
+        let (line_truncator, _) = run_composer(Composer::LineTruncator, text, width);
+        // What's happening below is: the first line gets consumed, trailing spaces discarded,
+        // after 20 of which a word break occurs (probably shouldn't). The second line break
+        // discards all whitespace. The result should probably be vec!["a"] but it doesn't matter
+        // that much.
+        assert_eq!(word_wrapper, vec!["a", ""]);
+        assert_eq!(line_truncator, vec!["a                   "]);
+    }
+
+    #[test]
+    fn line_composer_word_wrapper_double_width_chars_mixed_with_spaces() {
+        let width = 20;
+        // Japanese seems not to use spaces but we should break on spaces anyway... We're using it
+        // to test double-width chars.
+        // You are more than welcome to add word boundary detection based of alterations of
+        // hiragana and katakana...
+        // This happens to also be a test case for mixed width because regular spaces are single width.
+        let text = "コンピュ ータ上で文字を扱う場合、 典型的には文 字による 通信を行 う場合にその両端点では、";
+        let (word_wrapper, word_wrapper_width) =
+            run_composer(Composer::WordWrapper { trim: true }, text, width);
+        assert_eq!(
+            word_wrapper,
+            vec![
+                "コンピュ",
+                "ータ上で文字を扱う場",
+                "合、 典型的には文",
+                "字による 通信を行",
+                "う場合にその両端点で",
+                "は、",
+            ]
+        );
+        // Odd-sized lines have a space in them.
+        assert_eq!(word_wrapper_width, vec![8, 20, 17, 17, 20, 4]);
+    }
+
+    /// Ensure words separated by nbsp are wrapped as if they were a single one.
+    #[test]
+    fn line_composer_word_wrapper_nbsp() {
+        let width = 20;
+        let text = "AAAAAAAAAAAAAAA AAAA\u{00a0}AAA";
+        let (word_wrapper, _) = run_composer(Composer::WordWrapper { trim: true }, text, width);
+        assert_eq!(word_wrapper, vec!["AAAAAAAAAAAAAAA", "AAAA\u{00a0}AAA",]);
+
+        // Ensure that if the character was a regular space, it would be wrapped differently.
+        let text_space = text.replace("\u{00a0}", " ");
+        let (word_wrapper_space, _) =
+            run_composer(Composer::WordWrapper { trim: true }, &text_space, width);
+        assert_eq!(word_wrapper_space, vec!["AAAAAAAAAAAAAAA AAAA", "AAA",]);
+    }
+
+    #[test]
+    fn line_composer_word_wrapper_preserve_indentation() {
+        let width = 20;
+        let text = "AAAAAAAAAAAAAAAAAAAA    AAA";
+        let (word_wrapper, _) = run_composer(Composer::WordWrapper { trim: false }, text, width);
+        assert_eq!(word_wrapper, vec!["AAAAAAAAAAAAAAAAAAAA", "   AAA",]);
+    }
+
+    #[test]
+    fn line_composer_word_wrapper_preserve_indentation_with_wrap() {
+        let width = 10;
+        let text = "AAA AAA AAAAA AA AAAAAA\n B\n  C\n   D";
+        let (word_wrapper, _) = run_composer(Composer::WordWrapper { trim: false }, text, width);
+        assert_eq!(
+            word_wrapper,
+            vec!["AAA AAA", "AAAAA AA", "AAAAAA", " B", "  C", "   D"]
+        );
+    }
+
+    #[test]
+    fn line_composer_word_wrapper_preserve_indentation_lots_of_whitespace() {
+        let width = 10;
+        let text = "               4 Indent\n                 must wrap!";
+        let (word_wrapper, _) = run_composer(Composer::WordWrapper { trim: false }, text, width);
+        assert_eq!(
+            word_wrapper,
+            vec![
+                "          ",
+                "    4",
+                "Indent",
+                "          ",
+                "      must",
+                "wrap!"
+            ]
+        );
+    }
+}

helix-tui/src/widgets/table.rs

@@ -0,0 +1,538 @@
+use crate::{
+    buffer::Buffer,
+    layout::{Constraint, Rect},
+    style::Style,
+    text::Text,
+    widgets::{Block, StatefulWidget, Widget},
+};
+use cassowary::{
+    strength::{MEDIUM, REQUIRED, WEAK},
+    WeightedRelation::*,
+    {Expression, Solver},
+};
+use std::{
+    collections::HashMap,
+    iter::{self, Iterator},
+};
+use unicode_width::UnicodeWidthStr;
+
+/// A [`Cell`] contains the [`Text`] to be displayed in a [`Row`] of a [`Table`].
+///
+/// It can be created from anything that can be converted to a [`Text`].
+/// ```rust
+/// # use helix_tui::widgets::Cell;
+/// # use helix_tui::style::{Style, Modifier};
+/// # use helix_tui::text::{Span, Spans, Text};
+/// Cell::from("simple string");
+///
+/// Cell::from(Span::from("span"));
+///
+/// Cell::from(Spans::from(vec![
+///     Span::raw("a vec of "),
+///     Span::styled("spans", Style::default().add_modifier(Modifier::BOLD))
+/// ]));
+///
+/// Cell::from(Text::from("a text"));
+/// ```
+///
+/// You can apply a [`Style`] on the entire [`Cell`] using [`Cell::style`] or rely on the styling
+/// capabilities of [`Text`].
+#[derive(Debug, Clone, PartialEq, Default)]
+pub struct Cell<'a> {
+    content: Text<'a>,
+    style: Style,
+}
+
+impl<'a> Cell<'a> {
+    /// Set the `Style` of this cell.
+    pub fn style(mut self, style: Style) -> Self {
+        self.style = style;
+        self
+    }
+}
+
+impl<'a, T> From<T> for Cell<'a>
+where
+    T: Into<Text<'a>>,
+{
+    fn from(content: T) -> Cell<'a> {
+        Cell {
+            content: content.into(),
+            style: Style::default(),
+        }
+    }
+}
+
+/// Holds data to be displayed in a [`Table`] widget.
+///
+/// A [`Row`] is a collection of cells. It can be created from simple strings:
+/// ```rust
+/// # use helix_tui::widgets::Row;
+/// Row::new(vec!["Cell1", "Cell2", "Cell3"]);
+/// ```
+///
+/// But if you need a bit more control over individual cells, you can explicity create [`Cell`]s:
+/// ```rust
+/// # use helix_tui::widgets::{Row, Cell};
+/// # use helix_tui::style::{Style, Color};
+/// Row::new(vec![
+///     Cell::from("Cell1"),
+///     Cell::from("Cell2").style(Style::default().fg(Color::Yellow)),
+/// ]);
+/// ```
+///
+/// By default, a row has a height of 1 but you can change this using [`Row::height`].
+#[derive(Debug, Clone, PartialEq, Default)]
+pub struct Row<'a> {
+    cells: Vec<Cell<'a>>,
+    height: u16,
+    style: Style,
+    bottom_margin: u16,
+}
+
+impl<'a> Row<'a> {
+    /// Creates a new [`Row`] from an iterator where items can be converted to a [`Cell`].
+    pub fn new<T>(cells: T) -> Self
+    where
+        T: IntoIterator,
+        T::Item: Into<Cell<'a>>,
+    {
+        Self {
+            height: 1,
+            cells: cells.into_iter().map(|c| c.into()).collect(),
+            style: Style::default(),
+            bottom_margin: 0,
+        }
+    }
+
+    /// Set the fixed height of the [`Row`]. Any [`Cell`] whose content has more lines than this
+    /// height will see its content truncated.
+    pub fn height(mut self, height: u16) -> Self {
+        self.height = height;
+        self
+    }
+
+    /// Set the [`Style`] of the entire row. This [`Style`] can be overriden by the [`Style`] of a
+    /// any individual [`Cell`] or event by their [`Text`] content.
+    pub fn style(mut self, style: Style) -> Self {
+        self.style = style;
+        self
+    }
+
+    /// Set the bottom margin. By default, the bottom margin is `0`.
+    pub fn bottom_margin(mut self, margin: u16) -> Self {
+        self.bottom_margin = margin;
+        self
+    }
+
+    /// Returns the total height of the row.
+    fn total_height(&self) -> u16 {
+        self.height.saturating_add(self.bottom_margin)
+    }
+}
+
+/// A widget to display data in formatted columns.
+///
+/// It is a collection of [`Row`]s, themselves composed of [`Cell`]s:
+/// ```rust
+/// # use helix_tui::widgets::{Block, Borders, Table, Row, Cell};
+/// # use helix_tui::layout::Constraint;
+/// # use helix_tui::style::{Style, Color, Modifier};
+/// # use helix_tui::text::{Text, Spans, Span};
+/// Table::new(vec![
+///     // Row can be created from simple strings.
+///     Row::new(vec!["Row11", "Row12", "Row13"]),
+///     // You can style the entire row.
+///     Row::new(vec!["Row21", "Row22", "Row23"]).style(Style::default().fg(Color::Blue)),
+///     // If you need more control over the styling you may need to create Cells directly
+///     Row::new(vec![
+///         Cell::from("Row31"),
+///         Cell::from("Row32").style(Style::default().fg(Color::Yellow)),
+///         Cell::from(Spans::from(vec![
+///             Span::raw("Row"),
+///             Span::styled("33", Style::default().fg(Color::Green))
+///         ])),
+///     ]),
+///     // If a Row need to display some content over multiple lines, you just have to change
+///     // its height.
+///     Row::new(vec![
+///         Cell::from("Row\n41"),
+///         Cell::from("Row\n42"),
+///         Cell::from("Row\n43"),
+///     ]).height(2),
+/// ])
+/// // You can set the style of the entire Table.
+/// .style(Style::default().fg(Color::White))
+/// // It has an optional header, which is simply a Row always visible at the top.
+/// .header(
+///     Row::new(vec!["Col1", "Col2", "Col3"])
+///         .style(Style::default().fg(Color::Yellow))
+///         // If you want some space between the header and the rest of the rows, you can always
+///         // specify some margin at the bottom.
+///         .bottom_margin(1)
+/// )
+/// // As any other widget, a Table can be wrapped in a Block.
+/// .block(Block::default().title("Table"))
+/// // Columns widths are constrained in the same way as Layout...
+/// .widths(&[Constraint::Length(5), Constraint::Length(5), Constraint::Length(10)])
+/// // ...and they can be separated by a fixed spacing.
+/// .column_spacing(1)
+/// // If you wish to highlight a row in any specific way when it is selected...
+/// .highlight_style(Style::default().add_modifier(Modifier::BOLD))
+/// // ...and potentially show a symbol in front of the selection.
+/// .highlight_symbol(">>");
+/// ```
+#[derive(Debug, Clone, PartialEq)]
+pub struct Table<'a> {
+    /// A block to wrap the widget in
+    block: Option<Block<'a>>,
+    /// Base style for the widget
+    style: Style,
+    /// Width constraints for each column
+    widths: &'a [Constraint],
+    /// Space between each column
+    column_spacing: u16,
+    /// Style used to render the selected row
+    highlight_style: Style,
+    /// Symbol in front of the selected rom
+    highlight_symbol: Option<&'a str>,
+    /// Optional header
+    header: Option<Row<'a>>,
+    /// Data to display in each row
+    rows: Vec<Row<'a>>,
+}
+
+impl<'a> Table<'a> {
+    pub fn new<T>(rows: T) -> Self
+    where
+        T: IntoIterator<Item = Row<'a>>,
+    {
+        Self {
+            block: None,
+            style: Style::default(),
+            widths: &[],
+            column_spacing: 1,
+            highlight_style: Style::default(),
+            highlight_symbol: None,
+            header: None,
+            rows: rows.into_iter().collect(),
+        }
+    }
+
+    pub fn block(mut self, block: Block<'a>) -> Self {
+        self.block = Some(block);
+        self
+    }
+
+    pub fn header(mut self, header: Row<'a>) -> Self {
+        self.header = Some(header);
+        self
+    }
+
+    pub fn widths(mut self, widths: &'a [Constraint]) -> Self {
+        let between_0_and_100 = |&w| match w {
+            Constraint::Percentage(p) => p <= 100,
+            _ => true,
+        };
+        assert!(
+            widths.iter().all(between_0_and_100),
+            "Percentages should be between 0 and 100 inclusively."
+        );
+        self.widths = widths;
+        self
+    }
+
+    pub fn style(mut self, style: Style) -> Self {
+        self.style = style;
+        self
+    }
+
+    pub fn highlight_symbol(mut self, highlight_symbol: &'a str) -> Self {
+        self.highlight_symbol = Some(highlight_symbol);
+        self
+    }
+
+    pub fn highlight_style(mut self, highlight_style: Style) -> Self {
+        self.highlight_style = highlight_style;
+        self
+    }
+
+    pub fn column_spacing(mut self, spacing: u16) -> Self {
+        self.column_spacing = spacing;
+        self
+    }
+
+    fn get_columns_widths(&self, max_width: u16, has_selection: bool) -> Vec<u16> {
+        let mut solver = Solver::new();
+        let mut var_indices = HashMap::new();
+        let mut ccs = Vec::new();
+        let mut variables = Vec::new();
+        for i in 0..self.widths.len() {
+            let var = cassowary::Variable::new();
+            variables.push(var);
+            var_indices.insert(var, i);
+        }
+        let spacing_width = (variables.len() as u16).saturating_sub(1) * self.column_spacing;
+        let mut available_width = max_width.saturating_sub(spacing_width);
+        if has_selection {
+            let highlight_symbol_width =
+                self.highlight_symbol.map(|s| s.width() as u16).unwrap_or(0);
+            available_width = available_width.saturating_sub(highlight_symbol_width);
+        }
+        for (i, constraint) in self.widths.iter().enumerate() {
+            ccs.push(variables[i] | GE(WEAK) | 0.);
+            ccs.push(match *constraint {
+                Constraint::Length(v) => variables[i] | EQ(MEDIUM) | f64::from(v),
+                Constraint::Percentage(v) => {
+                    variables[i] | EQ(WEAK) | (f64::from(v * available_width) / 100.0)
+                }
+                Constraint::Ratio(n, d) => {
+                    variables[i]
+                        | EQ(WEAK)
+                        | (f64::from(available_width) * f64::from(n) / f64::from(d))
+                }
+                Constraint::Min(v) => variables[i] | GE(WEAK) | f64::from(v),
+                Constraint::Max(v) => variables[i] | LE(WEAK) | f64::from(v),
+            })
+        }
+        solver
+            .add_constraint(
+                variables
+                    .iter()
+                    .fold(Expression::from_constant(0.), |acc, v| acc + *v)
+                    | LE(REQUIRED)
+                    | f64::from(available_width),
+            )
+            .unwrap();
+        solver.add_constraints(&ccs).unwrap();
+        let mut widths = vec![0; variables.len()];
+        for &(var, value) in solver.fetch_changes() {
+            let index = var_indices[&var];
+            let value = if value.is_sign_negative() {
+                0
+            } else {
+                value.round() as u16
+            };
+            widths[index] = value;
+        }
+        // Cassowary could still return columns widths greater than the max width when there are
+        // fixed length constraints that cannot be satisfied. Therefore, we clamp the widths from
+        // left to right.
+        let mut available_width = max_width;
+        for w in &mut widths {
+            *w = available_width.min(*w);
+            available_width = available_width
+                .saturating_sub(*w)
+                .saturating_sub(self.column_spacing);
+        }
+        widths
+    }
+
+    fn get_row_bounds(
+        &self,
+        selected: Option<usize>,
+        offset: usize,
+        max_height: u16,
+    ) -> (usize, usize) {
+        let mut start = offset;
+        let mut end = offset;
+        let mut height = 0;
+        for item in self.rows.iter().skip(offset) {
+            if height + item.height > max_height {
+                break;
+            }
+            height += item.total_height();
+            end += 1;
+        }
+
+        let selected = selected.unwrap_or(0).min(self.rows.len() - 1);
+        while selected >= end {
+            height = height.saturating_add(self.rows[end].total_height());
+            end += 1;
+            while height > max_height {
+                height = height.saturating_sub(self.rows[start].total_height());
+                start += 1;
+            }
+        }
+        while selected < start {
+            start -= 1;
+            height = height.saturating_add(self.rows[start].total_height());
+            while height > max_height {
+                end -= 1;
+                height = height.saturating_sub(self.rows[end].total_height());
+            }
+        }
+        (start, end)
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct TableState {
+    offset: usize,
+    selected: Option<usize>,
+}
+
+impl Default for TableState {
+    fn default() -> TableState {
+        TableState {
+            offset: 0,
+            selected: None,
+        }
+    }
+}
+
+impl TableState {
+    pub fn selected(&self) -> Option<usize> {
+        self.selected
+    }
+
+    pub fn select(&mut self, index: Option<usize>) {
+        self.selected = index;
+        if index.is_none() {
+            self.offset = 0;
+        }
+    }
+}
+
+impl<'a> StatefulWidget for Table<'a> {
+    type State = TableState;
+
+    fn render(mut self, area: Rect, buf: &mut Buffer, state: &mut Self::State) {
+        if area.area() == 0 {
+            return;
+        }
+        buf.set_style(area, self.style);
+        let table_area = match self.block.take() {
+            Some(b) => {
+                let inner_area = b.inner(area);
+                b.render(area, buf);
+                inner_area
+            }
+            None => area,
+        };
+
+        let has_selection = state.selected.is_some();
+        let columns_widths = self.get_columns_widths(table_area.width, has_selection);
+        let highlight_symbol = self.highlight_symbol.unwrap_or("");
+        let blank_symbol = iter::repeat(" ")
+            .take(highlight_symbol.width())
+            .collect::<String>();
+        let mut current_height = 0;
+        let mut rows_height = table_area.height;
+
+        // Draw header
+        if let Some(ref header) = self.header {
+            let max_header_height = table_area.height.min(header.total_height());
+            buf.set_style(
+                Rect {
+                    x: table_area.left(),
+                    y: table_area.top(),
+                    width: table_area.width,
+                    height: table_area.height.min(header.height),
+                },
+                header.style,
+            );
+            let mut col = table_area.left();
+            if has_selection {
+                col += (highlight_symbol.width() as u16).min(table_area.width);
+            }
+            for (width, cell) in columns_widths.iter().zip(header.cells.iter()) {
+                render_cell(
+                    buf,
+                    cell,
+                    Rect {
+                        x: col,
+                        y: table_area.top(),
+                        width: *width,
+                        height: max_header_height,
+                    },
+                );
+                col += *width + self.column_spacing;
+            }
+            current_height += max_header_height;
+            rows_height = rows_height.saturating_sub(max_header_height);
+        }
+
+        // Draw rows
+        if self.rows.is_empty() {
+            return;
+        }
+        let (start, end) = self.get_row_bounds(state.selected, state.offset, rows_height);
+        state.offset = start;
+        for (i, table_row) in self
+            .rows
+            .iter_mut()
+            .enumerate()
+            .skip(state.offset)
+            .take(end - start)
+        {
+            let (row, col) = (table_area.top() + current_height, table_area.left());
+            current_height += table_row.total_height();
+            let table_row_area = Rect {
+                x: col,
+                y: row,
+                width: table_area.width,
+                height: table_row.height,
+            };
+            buf.set_style(table_row_area, table_row.style);
+            let is_selected = state.selected.map(|s| s == i).unwrap_or(false);
+            let table_row_start_col = if has_selection {
+                let symbol = if is_selected {
+                    highlight_symbol
+                } else {
+                    &blank_symbol
+                };
+                let (col, _) =
+                    buf.set_stringn(col, row, symbol, table_area.width as usize, table_row.style);
+                col
+            } else {
+                col
+            };
+            let mut col = table_row_start_col;
+            for (width, cell) in columns_widths.iter().zip(table_row.cells.iter()) {
+                render_cell(
+                    buf,
+                    cell,
+                    Rect {
+                        x: col,
+                        y: row,
+                        width: *width,
+                        height: table_row.height,
+                    },
+                );
+                col += *width + self.column_spacing;
+            }
+            if is_selected {
+                buf.set_style(table_row_area, self.highlight_style);
+            }
+        }
+    }
+}
+
+fn render_cell(buf: &mut Buffer, cell: &Cell, area: Rect) {
+    buf.set_style(area, cell.style);
+    for (i, spans) in cell.content.lines.iter().enumerate() {
+        if i as u16 >= area.height {
+            break;
+        }
+        buf.set_spans(area.x, area.y + i as u16, spans, area.width);
+    }
+}
+
+impl<'a> Widget for Table<'a> {
+    fn render(self, area: Rect, buf: &mut Buffer) {
+        let mut state = TableState::default();
+        StatefulWidget::render(self, area, buf, &mut state);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    #[should_panic]
+    fn table_invalid_percentages() {
+        Table::new(vec![]).widths(&[Constraint::Percentage(110)]);
+    }
+}

helix-tui/tests/terminal.rs

@@ -0,0 +1,36 @@
+use helix_tui::{
+    backend::{Backend, TestBackend},
+    layout::Rect,
+    widgets::Paragraph,
+    Terminal,
+};
+use std::error::Error;
+
+#[test]
+fn terminal_buffer_size_should_be_limited() {
+    let backend = TestBackend::new(400, 400);
+    let terminal = Terminal::new(backend).unwrap();
+    let size = terminal.backend().size().unwrap();
+    assert_eq!(size.width, 255);
+    assert_eq!(size.height, 255);
+}
+
+// #[test]
+// fn terminal_draw_returns_the_completed_frame() -> Result<(), Box<dyn Error>> {
+//     let backend = TestBackend::new(10, 10);
+//     let mut terminal = Terminal::new(backend)?;
+//     let frame = terminal.draw(|f| {
+//         let paragrah = Paragraph::new("Test");
+//         f.render_widget(paragrah, f.size());
+//     })?;
+//     assert_eq!(frame.buffer.get(0, 0).symbol, "T");
+//     assert_eq!(frame.area, Rect::new(0, 0, 10, 10));
+//     terminal.backend_mut().resize(8, 8);
+//     let frame = terminal.draw(|f| {
+//         let paragrah = Paragraph::new("test");
+//         f.render_widget(paragrah, f.size());
+//     })?;
+//     assert_eq!(frame.buffer.get(0, 0).symbol, "t");
+//     assert_eq!(frame.area, Rect::new(0, 0, 8, 8));
+//     Ok(())
+// }

helix-tui/tests/widgets_block.rs

@@ -0,0 +1,213 @@
+use helix_tui::{
+    backend::TestBackend,
+    buffer::Buffer,
+    layout::Rect,
+    style::{Color, Style},
+    text::Span,
+    widgets::{Block, Borders},
+    Terminal,
+};
+
+#[test]
+fn widgets_block_renders() {
+    let backend = TestBackend::new(10, 10);
+    let mut terminal = Terminal::new(backend).unwrap();
+    terminal
+        .draw(|f| {
+            let block = Block::default()
+                .title(Span::styled("Title", Style::default().fg(Color::LightBlue)))
+                .borders(Borders::ALL);
+            f.render_widget(
+                block,
+                Rect {
+                    x: 0,
+                    y: 0,
+                    width: 8,
+                    height: 8,
+                },
+            );
+        })
+        .unwrap();
+    let mut expected = Buffer::with_lines(vec![
+        "┌Title─┐  ",
+        "│      │  ",
+        "│      │  ",
+        "│      │  ",
+        "│      │  ",
+        "│      │  ",
+        "│      │  ",
+        "└──────┘  ",
+        "          ",
+        "          ",
+    ]);
+    for x in 1..=5 {
+        expected.get_mut(x, 0).set_fg(Color::LightBlue);
+    }
+    terminal.backend().assert_buffer(&expected);
+}
+
+#[test]
+fn widgets_block_renders_on_small_areas() {
+    let test_case = |block, area: Rect, expected| {
+        let backend = TestBackend::new(area.width, area.height);
+        let mut terminal = Terminal::new(backend).unwrap();
+        terminal
+            .draw(|f| {
+                f.render_widget(block, area);
+            })
+            .unwrap();
+        terminal.backend().assert_buffer(&expected);
+    };
+
+    let one_cell_test_cases = [
+        (Borders::NONE, "T"),
+        (Borders::LEFT, "│"),
+        (Borders::TOP, "T"),
+        (Borders::RIGHT, "│"),
+        (Borders::BOTTOM, "T"),
+        (Borders::ALL, "┌"),
+    ];
+    for (borders, symbol) in one_cell_test_cases.iter().cloned() {
+        test_case(
+            Block::default().title("Test").borders(borders),
+            Rect {
+                x: 0,
+                y: 0,
+                width: 0,
+                height: 0,
+            },
+            Buffer::empty(Rect {
+                x: 0,
+                y: 0,
+                width: 0,
+                height: 0,
+            }),
+        );
+        test_case(
+            Block::default().title("Test").borders(borders),
+            Rect {
+                x: 0,
+                y: 0,
+                width: 1,
+                height: 0,
+            },
+            Buffer::empty(Rect {
+                x: 0,
+                y: 0,
+                width: 1,
+                height: 0,
+            }),
+        );
+        test_case(
+            Block::default().title("Test").borders(borders),
+            Rect {
+                x: 0,
+                y: 0,
+                width: 0,
+                height: 1,
+            },
+            Buffer::empty(Rect {
+                x: 0,
+                y: 0,
+                width: 0,
+                height: 1,
+            }),
+        );
+        test_case(
+            Block::default().title("Test").borders(borders),
+            Rect {
+                x: 0,
+                y: 0,
+                width: 1,
+                height: 1,
+            },
+            Buffer::with_lines(vec![symbol]),
+        );
+    }
+    test_case(
+        Block::default().title("Test").borders(Borders::LEFT),
+        Rect {
+            x: 0,
+            y: 0,
+            width: 4,
+            height: 1,
+        },
+        Buffer::with_lines(vec!["│Tes"]),
+    );
+    test_case(
+        Block::default().title("Test").borders(Borders::RIGHT),
+        Rect {
+            x: 0,
+            y: 0,
+            width: 4,
+            height: 1,
+        },
+        Buffer::with_lines(vec!["Tes│"]),
+    );
+    test_case(
+        Block::default().title("Test").borders(Borders::RIGHT),
+        Rect {
+            x: 0,
+            y: 0,
+            width: 4,
+            height: 1,
+        },
+        Buffer::with_lines(vec!["Tes│"]),
+    );
+    test_case(
+        Block::default()
+            .title("Test")
+            .borders(Borders::LEFT | Borders::RIGHT),
+        Rect {
+            x: 0,
+            y: 0,
+            width: 4,
+            height: 1,
+        },
+        Buffer::with_lines(vec!["│Te│"]),
+    );
+    test_case(
+        Block::default().title("Test").borders(Borders::TOP),
+        Rect {
+            x: 0,
+            y: 0,
+            width: 4,
+            height: 1,
+        },
+        Buffer::with_lines(vec!["Test"]),
+    );
+    test_case(
+        Block::default().title("Test").borders(Borders::TOP),
+        Rect {
+            x: 0,
+            y: 0,
+            width: 5,
+            height: 1,
+        },
+        Buffer::with_lines(vec!["Test─"]),
+    );
+    test_case(
+        Block::default()
+            .title("Test")
+            .borders(Borders::LEFT | Borders::TOP),
+        Rect {
+            x: 0,
+            y: 0,
+            width: 5,
+            height: 1,
+        },
+        Buffer::with_lines(vec!["┌Test"]),
+    );
+    test_case(
+        Block::default()
+            .title("Test")
+            .borders(Borders::LEFT | Borders::TOP),
+        Rect {
+            x: 0,
+            y: 0,
+            width: 6,
+            height: 1,
+        },
+        Buffer::with_lines(vec!["┌Test─"]),
+    );
+}

helix-tui/tests/widgets_list.rs

@@ -0,0 +1,88 @@
+use helix_tui::{
+    backend::TestBackend,
+    buffer::Buffer,
+    layout::Rect,
+    style::{Color, Style},
+    symbols,
+    widgets::{Block, Borders, List, ListItem, ListState},
+    Terminal,
+};
+
+#[test]
+fn widgets_list_should_highlight_the_selected_item() {
+    let backend = TestBackend::new(10, 3);
+    let mut terminal = Terminal::new(backend).unwrap();
+    let mut state = ListState::default();
+    state.select(Some(1));
+    terminal
+        .draw(|f| {
+            let size = f.size();
+            let items = vec![
+                ListItem::new("Item 1"),
+                ListItem::new("Item 2"),
+                ListItem::new("Item 3"),
+            ];
+            let list = List::new(items)
+                .highlight_style(Style::default().bg(Color::Yellow))
+                .highlight_symbol(">> ");
+            f.render_stateful_widget(list, size, &mut state);
+        })
+        .unwrap();
+    let mut expected = Buffer::with_lines(vec!["   Item 1 ", ">> Item 2 ", "   Item 3 "]);
+    for x in 0..10 {
+        expected.get_mut(x, 1).set_bg(Color::Yellow);
+    }
+    terminal.backend().assert_buffer(&expected);
+}
+
+#[test]
+fn widgets_list_should_truncate_items() {
+    let backend = TestBackend::new(10, 2);
+    let mut terminal = Terminal::new(backend).unwrap();
+
+    struct TruncateTestCase<'a> {
+        selected: Option<usize>,
+        items: Vec<ListItem<'a>>,
+        expected: Buffer,
+    }
+
+    let cases = vec![
+        // An item is selected
+        TruncateTestCase {
+            selected: Some(0),
+            items: vec![
+                ListItem::new("A very long line"),
+                ListItem::new("A very long line"),
+            ],
+            expected: Buffer::with_lines(vec![
+                format!(">> A ve{}  ", symbols::line::VERTICAL),
+                format!("   A ve{}  ", symbols::line::VERTICAL),
+            ]),
+        },
+        // No item is selected
+        TruncateTestCase {
+            selected: None,
+            items: vec![
+                ListItem::new("A very long line"),
+                ListItem::new("A very long line"),
+            ],
+            expected: Buffer::with_lines(vec![
+                format!("A very {}  ", symbols::line::VERTICAL),
+                format!("A very {}  ", symbols::line::VERTICAL),
+            ]),
+        },
+    ];
+    for case in cases {
+        let mut state = ListState::default();
+        state.select(case.selected);
+        terminal
+            .draw(|f| {
+                let list = List::new(case.items.clone())
+                    .block(Block::default().borders(Borders::RIGHT))
+                    .highlight_symbol(">> ");
+                f.render_stateful_widget(list, Rect::new(0, 0, 8, 2), &mut state);
+            })
+            .unwrap();
+        terminal.backend().assert_buffer(&case.expected);
+    }
+}

helix-tui/tests/widgets_paragraph.rs

@@ -0,0 +1,220 @@
+use helix_tui::{
+    backend::TestBackend,
+    buffer::Buffer,
+    layout::Alignment,
+    text::{Span, Spans, Text},
+    widgets::{Block, Borders, Paragraph, Wrap},
+    Terminal,
+};
+
+const SAMPLE_STRING: &str = "The library is based on the principle of immediate rendering with \
+     intermediate buffers. This means that at each new frame you should build all widgets that are \
+     supposed to be part of the UI. While providing a great flexibility for rich and \
+     interactive UI, this may introduce overhead for highly dynamic content.";
+
+#[test]
+fn widgets_paragraph_can_wrap_its_content() {
+    let test_case = |alignment, expected| {
+        let backend = TestBackend::new(20, 10);
+        let mut terminal = Terminal::new(backend).unwrap();
+
+        terminal
+            .draw(|f| {
+                let size = f.size();
+                let text = vec![Spans::from(SAMPLE_STRING)];
+                let paragraph = Paragraph::new(text)
+                    .block(Block::default().borders(Borders::ALL))
+                    .alignment(alignment)
+                    .wrap(Wrap { trim: true });
+                f.render_widget(paragraph, size);
+            })
+            .unwrap();
+        terminal.backend().assert_buffer(&expected);
+    };
+
+    test_case(
+        Alignment::Left,
+        Buffer::with_lines(vec![
+            "┌──────────────────┐",
+            "│The library is    │",
+            "│based on the      │",
+            "│principle of      │",
+            "│immediate         │",
+            "│rendering with    │",
+            "│intermediate      │",
+            "│buffers. This     │",
+            "│means that at each│",
+            "└──────────────────┘",
+        ]),
+    );
+    test_case(
+        Alignment::Right,
+        Buffer::with_lines(vec![
+            "┌──────────────────┐",
+            "│    The library is│",
+            "│      based on the│",
+            "│      principle of│",
+            "│         immediate│",
+            "│    rendering with│",
+            "│      intermediate│",
+            "│     buffers. This│",
+            "│means that at each│",
+            "└──────────────────┘",
+        ]),
+    );
+    test_case(
+        Alignment::Center,
+        Buffer::with_lines(vec![
+            "┌──────────────────┐",
+            "│  The library is  │",
+            "│   based on the   │",
+            "│   principle of   │",
+            "│     immediate    │",
+            "│  rendering with  │",
+            "│   intermediate   │",
+            "│   buffers. This  │",
+            "│means that at each│",
+            "└──────────────────┘",
+        ]),
+    );
+}
+
+#[test]
+fn widgets_paragraph_renders_double_width_graphemes() {
+    let backend = TestBackend::new(10, 10);
+    let mut terminal = Terminal::new(backend).unwrap();
+
+    let s = "コンピュータ上で文字を扱う場合、典型的には文字による通信を行う場合にその両端点では、";
+    terminal
+        .draw(|f| {
+            let size = f.size();
+            let text = vec![Spans::from(s)];
+            let paragraph = Paragraph::new(text)
+                .block(Block::default().borders(Borders::ALL))
+                .wrap(Wrap { trim: true });
+            f.render_widget(paragraph, size);
+        })
+        .unwrap();
+
+    let expected = Buffer::with_lines(vec![
+        "┌────────┐",
+        "│コンピュ│",
+        "│ータ上で│",
+        "│文字を扱│",
+        "│う場合、│",
+        "│典型的に│",
+        "│は文字に│",
+        "│よる通信│",
+        "│を行う場│",
+        "└────────┘",
+    ]);
+    terminal.backend().assert_buffer(&expected);
+}
+
+#[test]
+fn widgets_paragraph_renders_mixed_width_graphemes() {
+    let backend = TestBackend::new(10, 7);
+    let mut terminal = Terminal::new(backend).unwrap();
+
+    let s = "aコンピュータ上で文字を扱う場合、";
+    terminal
+        .draw(|f| {
+            let size = f.size();
+            let text = vec![Spans::from(s)];
+            let paragraph = Paragraph::new(text)
+                .block(Block::default().borders(Borders::ALL))
+                .wrap(Wrap { trim: true });
+            f.render_widget(paragraph, size);
+        })
+        .unwrap();
+
+    let expected = Buffer::with_lines(vec![
+        // The internal width is 8 so only 4 slots for double-width characters.
+        "┌────────┐",
+        "│aコンピ │", // Here we have 1 latin character so only 3 double-width ones can fit.
+        "│ュータ上│",
+        "│で文字を│",
+        "│扱う場合│",
+        "│、      │",
+        "└────────┘",
+    ]);
+    terminal.backend().assert_buffer(&expected);
+}
+
+#[test]
+fn widgets_paragraph_can_wrap_with_a_trailing_nbsp() {
+    let nbsp: &str = "\u{00a0}";
+    let line = Spans::from(vec![Span::raw("NBSP"), Span::raw(nbsp)]);
+    let backend = TestBackend::new(20, 3);
+    let mut terminal = Terminal::new(backend).unwrap();
+    let expected = Buffer::with_lines(vec![
+        "┌──────────────────┐",
+        "│NBSP\u{00a0}             │",
+        "└──────────────────┘",
+    ]);
+    terminal
+        .draw(|f| {
+            let size = f.size();
+
+            let paragraph = Paragraph::new(line).block(Block::default().borders(Borders::ALL));
+            f.render_widget(paragraph, size);
+        })
+        .unwrap();
+    terminal.backend().assert_buffer(&expected);
+}
+#[test]
+fn widgets_paragraph_can_scroll_horizontally() {
+    let test_case = |alignment, scroll, expected| {
+        let backend = TestBackend::new(20, 10);
+        let mut terminal = Terminal::new(backend).unwrap();
+
+        terminal
+            .draw(|f| {
+                let size = f.size();
+                let text = Text::from(
+                    "段落现在可以水平滚动了！\nParagraph can scroll horizontally!\nShort line",
+                );
+                let paragraph = Paragraph::new(text)
+                    .block(Block::default().borders(Borders::ALL))
+                    .alignment(alignment)
+                    .scroll(scroll);
+                f.render_widget(paragraph, size);
+            })
+            .unwrap();
+        terminal.backend().assert_buffer(&expected);
+    };
+
+    test_case(
+        Alignment::Left,
+        (0, 7),
+        Buffer::with_lines(vec![
+            "┌──────────────────┐",
+            "│在可以水平滚动了！│",
+            "│ph can scroll hori│",
+            "│ine               │",
+            "│                  │",
+            "│                  │",
+            "│                  │",
+            "│                  │",
+            "│                  │",
+            "└──────────────────┘",
+        ]),
+    );
+    // only support Alignment::Left
+    test_case(
+        Alignment::Right,
+        (0, 7),
+        Buffer::with_lines(vec![
+            "┌──────────────────┐",
+            "│段落现在可以水平滚│",
+            "│Paragraph can scro│",
+            "│        Short line│",
+            "│                  │",
+            "│                  │",
+            "│                  │",
+            "│                  │",
+            "│                  │",
+            "└──────────────────┘",
+        ]),
+    );
+}

helix-tui/tests/widgets_table.rs

@@ -0,0 +1,717 @@
+use helix_tui::{
+    backend::TestBackend,
+    buffer::Buffer,
+    layout::Constraint,
+    style::{Color, Modifier, Style},
+    text::{Span, Spans},
+    widgets::{Block, Borders, Cell, Row, Table, TableState},
+    Terminal,
+};
+
+#[test]
+fn widgets_table_column_spacing_can_be_changed() {
+    let test_case = |column_spacing, expected| {
+        let backend = TestBackend::new(30, 10);
+        let mut terminal = Terminal::new(backend).unwrap();
+
+        terminal
+            .draw(|f| {
+                let size = f.size();
+                let table = Table::new(vec![
+                    Row::new(vec!["Row11", "Row12", "Row13"]),
+                    Row::new(vec!["Row21", "Row22", "Row23"]),
+                    Row::new(vec!["Row31", "Row32", "Row33"]),
+                    Row::new(vec!["Row41", "Row42", "Row43"]),
+                ])
+                .header(Row::new(vec!["Head1", "Head2", "Head3"]).bottom_margin(1))
+                .block(Block::default().borders(Borders::ALL))
+                .widths(&[
+                    Constraint::Length(5),
+                    Constraint::Length(5),
+                    Constraint::Length(5),
+                ])
+                .column_spacing(column_spacing);
+                f.render_widget(table, size);
+            })
+            .unwrap();
+        terminal.backend().assert_buffer(&expected);
+    };
+
+    // no space between columns
+    test_case(
+        0,
+        Buffer::with_lines(vec![
+            "┌────────────────────────────┐",
+            "│Head1Head2Head3             │",
+            "│                            │",
+            "│Row11Row12Row13             │",
+            "│Row21Row22Row23             │",
+            "│Row31Row32Row33             │",
+            "│Row41Row42Row43             │",
+            "│                            │",
+            "│                            │",
+            "└────────────────────────────┘",
+        ]),
+    );
+
+    // one space between columns
+    test_case(
+        1,
+        Buffer::with_lines(vec![
+            "┌────────────────────────────┐",
+            "│Head1 Head2 Head3           │",
+            "│                            │",
+            "│Row11 Row12 Row13           │",
+            "│Row21 Row22 Row23           │",
+            "│Row31 Row32 Row33           │",
+            "│Row41 Row42 Row43           │",
+            "│                            │",
+            "│                            │",
+            "└────────────────────────────┘",
+        ]),
+    );
+
+    // enough space to just not hide the third column
+    test_case(
+        6,
+        Buffer::with_lines(vec![
+            "┌────────────────────────────┐",
+            "│Head1      Head2      Head3 │",
+            "│                            │",
+            "│Row11      Row12      Row13 │",
+            "│Row21      Row22      Row23 │",
+            "│Row31      Row32      Row33 │",
+            "│Row41      Row42      Row43 │",
+            "│                            │",
+            "│                            │",
+            "└────────────────────────────┘",
+        ]),
+    );
+
+    // enough space to hide part of the third column
+    test_case(
+        7,
+        Buffer::with_lines(vec![
+            "┌────────────────────────────┐",
+            "│Head1       Head2       Head│",
+            "│                            │",
+            "│Row11       Row12       Row1│",
+            "│Row21       Row22       Row2│",
+            "│Row31       Row32       Row3│",
+            "│Row41       Row42       Row4│",
+            "│                            │",
+            "│                            │",
+            "└────────────────────────────┘",
+        ]),
+    );
+}
+
+#[test]
+fn widgets_table_columns_widths_can_use_fixed_length_constraints() {
+    let test_case = |widths, expected| {
+        let backend = TestBackend::new(30, 10);
+        let mut terminal = Terminal::new(backend).unwrap();
+
+        terminal
+            .draw(|f| {
+                let size = f.size();
+                let table = Table::new(vec![
+                    Row::new(vec!["Row11", "Row12", "Row13"]),
+                    Row::new(vec!["Row21", "Row22", "Row23"]),
+                    Row::new(vec!["Row31", "Row32", "Row33"]),
+                    Row::new(vec!["Row41", "Row42", "Row43"]),
+                ])
+                .header(Row::new(vec!["Head1", "Head2", "Head3"]).bottom_margin(1))
+                .block(Block::default().borders(Borders::ALL))
+                .widths(widths);
+                f.render_widget(table, size);
+            })
+            .unwrap();
+        terminal.backend().assert_buffer(&expected);
+    };
+
+    // columns of zero width show nothing
+    test_case(
+        &[
+            Constraint::Length(0),
+            Constraint::Length(0),
+            Constraint::Length(0),
+        ],
+        Buffer::with_lines(vec![
+            "┌────────────────────────────┐",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "└────────────────────────────┘",
+        ]),
+    );
+
+    // columns of 1 width trim
+    test_case(
+        &[
+            Constraint::Length(1),
+            Constraint::Length(1),
+            Constraint::Length(1),
+        ],
+        Buffer::with_lines(vec![
+            "┌────────────────────────────┐",
+            "│H H H                       │",
+            "│                            │",
+            "│R R R                       │",
+            "│R R R                       │",
+            "│R R R                       │",
+            "│R R R                       │",
+            "│                            │",
+            "│                            │",
+            "└────────────────────────────┘",
+        ]),
+    );
+
+    // columns of large width just before pushing a column off
+    test_case(
+        &[
+            Constraint::Length(8),
+            Constraint::Length(8),
+            Constraint::Length(8),
+        ],
+        Buffer::with_lines(vec![
+            "┌────────────────────────────┐",
+            "│Head1    Head2    Head3     │",
+            "│                            │",
+            "│Row11    Row12    Row13     │",
+            "│Row21    Row22    Row23     │",
+            "│Row31    Row32    Row33     │",
+            "│Row41    Row42    Row43     │",
+            "│                            │",
+            "│                            │",
+            "└────────────────────────────┘",
+        ]),
+    );
+}
+
+#[test]
+fn widgets_table_columns_widths_can_use_percentage_constraints() {
+    let test_case = |widths, expected| {
+        let backend = TestBackend::new(30, 10);
+        let mut terminal = Terminal::new(backend).unwrap();
+
+        terminal
+            .draw(|f| {
+                let size = f.size();
+                let table = Table::new(vec![
+                    Row::new(vec!["Row11", "Row12", "Row13"]),
+                    Row::new(vec!["Row21", "Row22", "Row23"]),
+                    Row::new(vec!["Row31", "Row32", "Row33"]),
+                    Row::new(vec!["Row41", "Row42", "Row43"]),
+                ])
+                .header(Row::new(vec!["Head1", "Head2", "Head3"]).bottom_margin(1))
+                .block(Block::default().borders(Borders::ALL))
+                .widths(widths)
+                .column_spacing(0);
+                f.render_widget(table, size);
+            })
+            .unwrap();
+        terminal.backend().assert_buffer(&expected);
+    };
+
+    // columns of zero width show nothing
+    test_case(
+        &[
+            Constraint::Percentage(0),
+            Constraint::Percentage(0),
+            Constraint::Percentage(0),
+        ],
+        Buffer::with_lines(vec![
+            "┌────────────────────────────┐",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "└────────────────────────────┘",
+        ]),
+    );
+
+    // columns of not enough width trims the data
+    test_case(
+        &[
+            Constraint::Percentage(11),
+            Constraint::Percentage(11),
+            Constraint::Percentage(11),
+        ],
+        Buffer::with_lines(vec![
+            "┌────────────────────────────┐",
+            "│HeaHeaHea                   │",
+            "│                            │",
+            "│RowRowRow                   │",
+            "│RowRowRow                   │",
+            "│RowRowRow                   │",
+            "│RowRowRow                   │",
+            "│                            │",
+            "│                            │",
+            "└────────────────────────────┘",
+        ]),
+    );
+
+    // columns of large width just before pushing a column off
+    test_case(
+        &[
+            Constraint::Percentage(33),
+            Constraint::Percentage(33),
+            Constraint::Percentage(33),
+        ],
+        Buffer::with_lines(vec![
+            "┌────────────────────────────┐",
+            "│Head1    Head2    Head3     │",
+            "│                            │",
+            "│Row11    Row12    Row13     │",
+            "│Row21    Row22    Row23     │",
+            "│Row31    Row32    Row33     │",
+            "│Row41    Row42    Row43     │",
+            "│                            │",
+            "│                            │",
+            "└────────────────────────────┘",
+        ]),
+    );
+
+    // percentages summing to 100 should give equal widths
+    test_case(
+        &[Constraint::Percentage(50), Constraint::Percentage(50)],
+        Buffer::with_lines(vec![
+            "┌────────────────────────────┐",
+            "│Head1         Head2         │",
+            "│                            │",
+            "│Row11         Row12         │",
+            "│Row21         Row22         │",
+            "│Row31         Row32         │",
+            "│Row41         Row42         │",
+            "│                            │",
+            "│                            │",
+            "└────────────────────────────┘",
+        ]),
+    );
+}
+
+#[test]
+fn widgets_table_columns_widths_can_use_mixed_constraints() {
+    let test_case = |widths, expected| {
+        let backend = TestBackend::new(30, 10);
+        let mut terminal = Terminal::new(backend).unwrap();
+
+        terminal
+            .draw(|f| {
+                let size = f.size();
+                let table = Table::new(vec![
+                    Row::new(vec!["Row11", "Row12", "Row13"]),
+                    Row::new(vec!["Row21", "Row22", "Row23"]),
+                    Row::new(vec!["Row31", "Row32", "Row33"]),
+                    Row::new(vec!["Row41", "Row42", "Row43"]),
+                ])
+                .header(Row::new(vec!["Head1", "Head2", "Head3"]).bottom_margin(1))
+                .block(Block::default().borders(Borders::ALL))
+                .widths(widths);
+                f.render_widget(table, size);
+            })
+            .unwrap();
+        terminal.backend().assert_buffer(&expected);
+    };
+
+    // columns of zero width show nothing
+    test_case(
+        &[
+            Constraint::Percentage(0),
+            Constraint::Length(0),
+            Constraint::Percentage(0),
+        ],
+        Buffer::with_lines(vec![
+            "┌────────────────────────────┐",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "└────────────────────────────┘",
+        ]),
+    );
+
+    // columns of not enough width trims the data
+    test_case(
+        &[
+            Constraint::Percentage(11),
+            Constraint::Length(20),
+            Constraint::Percentage(11),
+        ],
+        Buffer::with_lines(vec![
+            "┌────────────────────────────┐",
+            "│Hea Head2                Hea│",
+            "│                            │",
+            "│Row Row12                Row│",
+            "│Row Row22                Row│",
+            "│Row Row32                Row│",
+            "│Row Row42                Row│",
+            "│                            │",
+            "│                            │",
+            "└────────────────────────────┘",
+        ]),
+    );
+
+    // columns of large width just before pushing a column off
+    test_case(
+        &[
+            Constraint::Percentage(33),
+            Constraint::Length(10),
+            Constraint::Percentage(33),
+        ],
+        Buffer::with_lines(vec![
+            "┌────────────────────────────┐",
+            "│Head1     Head2      Head3  │",
+            "│                            │",
+            "│Row11     Row12      Row13  │",
+            "│Row21     Row22      Row23  │",
+            "│Row31     Row32      Row33  │",
+            "│Row41     Row42      Row43  │",
+            "│                            │",
+            "│                            │",
+            "└────────────────────────────┘",
+        ]),
+    );
+
+    // columns of large size (>100% total) hide the last column
+    test_case(
+        &[
+            Constraint::Percentage(60),
+            Constraint::Length(10),
+            Constraint::Percentage(60),
+        ],
+        Buffer::with_lines(vec![
+            "┌────────────────────────────┐",
+            "│Head1            Head2      │",
+            "│                            │",
+            "│Row11            Row12      │",
+            "│Row21            Row22      │",
+            "│Row31            Row32      │",
+            "│Row41            Row42      │",
+            "│                            │",
+            "│                            │",
+            "└────────────────────────────┘",
+        ]),
+    );
+}
+
+#[test]
+fn widgets_table_columns_widths_can_use_ratio_constraints() {
+    let test_case = |widths, expected| {
+        let backend = TestBackend::new(30, 10);
+        let mut terminal = Terminal::new(backend).unwrap();
+
+        terminal
+            .draw(|f| {
+                let size = f.size();
+                let table = Table::new(vec![
+                    Row::new(vec!["Row11", "Row12", "Row13"]),
+                    Row::new(vec!["Row21", "Row22", "Row23"]),
+                    Row::new(vec!["Row31", "Row32", "Row33"]),
+                    Row::new(vec!["Row41", "Row42", "Row43"]),
+                ])
+                .header(Row::new(vec!["Head1", "Head2", "Head3"]).bottom_margin(1))
+                .block(Block::default().borders(Borders::ALL))
+                .widths(widths)
+                .column_spacing(0);
+                f.render_widget(table, size);
+            })
+            .unwrap();
+        terminal.backend().assert_buffer(&expected);
+    };
+
+    // columns of zero width show nothing
+    test_case(
+        &[
+            Constraint::Ratio(0, 1),
+            Constraint::Ratio(0, 1),
+            Constraint::Ratio(0, 1),
+        ],
+        Buffer::with_lines(vec![
+            "┌────────────────────────────┐",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "│                            │",
+            "└────────────────────────────┘",
+        ]),
+    );
+
+    // columns of not enough width trims the data
+    test_case(
+        &[
+            Constraint::Ratio(1, 9),
+            Constraint::Ratio(1, 9),
+            Constraint::Ratio(1, 9),
+        ],
+        Buffer::with_lines(vec![
+            "┌────────────────────────────┐",
+            "│HeaHeaHea                   │",
+            "│                            │",
+            "│RowRowRow                   │",
+            "│RowRowRow                   │",
+            "│RowRowRow                   │",
+            "│RowRowRow                   │",
+            "│                            │",
+            "│                            │",
+            "└────────────────────────────┘",
+        ]),
+    );
+
+    // columns of large width just before pushing a column off
+    test_case(
+        &[
+            Constraint::Ratio(1, 3),
+            Constraint::Ratio(1, 3),
+            Constraint::Ratio(1, 3),
+        ],
+        Buffer::with_lines(vec![
+            "┌────────────────────────────┐",
+            "│Head1    Head2    Head3     │",
+            "│                            │",
+            "│Row11    Row12    Row13     │",
+            "│Row21    Row22    Row23     │",
+            "│Row31    Row32    Row33     │",
+            "│Row41    Row42    Row43     │",
+            "│                            │",
+            "│                            │",
+            "└────────────────────────────┘",
+        ]),
+    );
+
+    // percentages summing to 100 should give equal widths
+    test_case(
+        &[Constraint::Ratio(1, 2), Constraint::Ratio(1, 2)],
+        Buffer::with_lines(vec![
+            "┌────────────────────────────┐",
+            "│Head1         Head2         │",
+            "│                            │",
+            "│Row11         Row12         │",
+            "│Row21         Row22         │",
+            "│Row31         Row32         │",
+            "│Row41         Row42         │",
+            "│                            │",
+            "│                            │",
+            "└────────────────────────────┘",
+        ]),
+    );
+}
+
+#[test]
+fn widgets_table_can_have_rows_with_multi_lines() {
+    let test_case = |state: &mut TableState, expected: Buffer| {
+        let backend = TestBackend::new(30, 8);
+        let mut terminal = Terminal::new(backend).unwrap();
+        terminal
+            .draw(|f| {
+                let size = f.size();
+                let table = Table::new(vec![
+                    Row::new(vec!["Row11", "Row12", "Row13"]),
+                    Row::new(vec!["Row21", "Row22", "Row23"]).height(2),
+                    Row::new(vec!["Row31", "Row32", "Row33"]),
+                    Row::new(vec!["Row41", "Row42", "Row43"]).height(2),
+                ])
+                .header(Row::new(vec!["Head1", "Head2", "Head3"]).bottom_margin(1))
+                .block(Block::default().borders(Borders::ALL))
+                .highlight_symbol(">> ")
+                .widths(&[
+                    Constraint::Length(5),
+                    Constraint::Length(5),
+                    Constraint::Length(5),
+                ])
+                .column_spacing(1);
+                f.render_stateful_widget(table, size, state);
+            })
+            .unwrap();
+        terminal.backend().assert_buffer(&expected);
+    };
+
+    let mut state = TableState::default();
+    // no selection
+    test_case(
+        &mut state,
+        Buffer::with_lines(vec![
+            "┌────────────────────────────┐",
+            "│Head1 Head2 Head3           │",
+            "│                            │",
+            "│Row11 Row12 Row13           │",
+            "│Row21 Row22 Row23           │",
+            "│                            │",
+            "│Row31 Row32 Row33           │",
+            "└────────────────────────────┘",
+        ]),
+    );
+
+    // select first
+    state.select(Some(0));
+    test_case(
+        &mut state,
+        Buffer::with_lines(vec![
+            "┌────────────────────────────┐",
+            "│   Head1 Head2 Head3        │",
+            "│                            │",
+            "│>> Row11 Row12 Row13        │",
+            "│   Row21 Row22 Row23        │",
+            "│                            │",
+            "│   Row31 Row32 Row33        │",
+            "└────────────────────────────┘",
+        ]),
+    );
+
+    // select second (we don't show partially the 4th row)
+    state.select(Some(1));
+    test_case(
+        &mut state,
+        Buffer::with_lines(vec![
+            "┌────────────────────────────┐",
+            "│   Head1 Head2 Head3        │",
+            "│                            │",
+            "│   Row11 Row12 Row13        │",
+            "│>> Row21 Row22 Row23        │",
+            "│                            │",
+            "│   Row31 Row32 Row33        │",
+            "└────────────────────────────┘",
+        ]),
+    );
+
+    // select 4th (we don't show partially the 1st row)
+    state.select(Some(3));
+    test_case(
+        &mut state,
+        Buffer::with_lines(vec![
+            "┌────────────────────────────┐",
+            "│   Head1 Head2 Head3        │",
+            "│                            │",
+            "│   Row31 Row32 Row33        │",
+            "│>> Row41 Row42 Row43        │",
+            "│                            │",
+            "│                            │",
+            "└────────────────────────────┘",
+        ]),
+    );
+}
+
+#[test]
+fn widgets_table_can_have_elements_styled_individually() {
+    let backend = TestBackend::new(30, 4);
+    let mut terminal = Terminal::new(backend).unwrap();
+    let mut state = TableState::default();
+    state.select(Some(0));
+    terminal
+        .draw(|f| {
+            let size = f.size();
+            let table = Table::new(vec![
+                Row::new(vec!["Row11", "Row12", "Row13"]).style(Style::default().fg(Color::Green)),
+                Row::new(vec![
+                    Cell::from("Row21"),
+                    Cell::from("Row22").style(Style::default().fg(Color::Yellow)),
+                    Cell::from(Spans::from(vec![
+                        Span::raw("Row"),
+                        Span::styled("23", Style::default().fg(Color::Blue)),
+                    ]))
+                    .style(Style::default().fg(Color::Red)),
+                ])
+                .style(Style::default().fg(Color::LightGreen)),
+            ])
+            .header(Row::new(vec!["Head1", "Head2", "Head3"]).bottom_margin(1))
+            .block(Block::default().borders(Borders::LEFT | Borders::RIGHT))
+            .highlight_symbol(">> ")
+            .highlight_style(Style::default().add_modifier(Modifier::BOLD))
+            .widths(&[
+                Constraint::Length(6),
+                Constraint::Length(6),
+                Constraint::Length(6),
+            ])
+            .column_spacing(1);
+            f.render_stateful_widget(table, size, &mut state);
+        })
+        .unwrap();
+
+    let mut expected = Buffer::with_lines(vec![
+        "│   Head1  Head2  Head3      │",
+        "│                            │",
+        "│>> Row11  Row12  Row13      │",
+        "│   Row21  Row22  Row23      │",
+    ]);
+    // First row = row color + highlight style
+    for col in 1..=28 {
+        expected.get_mut(col, 2).set_style(
+            Style::default()
+                .fg(Color::Green)
+                .add_modifier(Modifier::BOLD),
+        );
+    }
+    // Second row:
+    // 1. row color
+    for col in 1..=28 {
+        expected
+            .get_mut(col, 3)
+            .set_style(Style::default().fg(Color::LightGreen));
+    }
+    // 2. cell color
+    for col in 11..=16 {
+        expected
+            .get_mut(col, 3)
+            .set_style(Style::default().fg(Color::Yellow));
+    }
+    for col in 18..=23 {
+        expected
+            .get_mut(col, 3)
+            .set_style(Style::default().fg(Color::Red));
+    }
+    // 3. text color
+    for col in 21..=22 {
+        expected
+            .get_mut(col, 3)
+            .set_style(Style::default().fg(Color::Blue));
+    }
+    terminal.backend().assert_buffer(&expected);
+}
+
+#[test]
+fn widgets_table_should_render_even_if_empty() {
+    let backend = TestBackend::new(30, 4);
+    let mut terminal = Terminal::new(backend).unwrap();
+    terminal
+        .draw(|f| {
+            let size = f.size();
+            let table = Table::new(vec![])
+                .header(Row::new(vec!["Head1", "Head2", "Head3"]))
+                .block(Block::default().borders(Borders::LEFT | Borders::RIGHT))
+                .widths(&[
+                    Constraint::Length(6),
+                    Constraint::Length(6),
+                    Constraint::Length(6),
+                ])
+                .column_spacing(1);
+            f.render_widget(table, size);
+        })
+        .unwrap();
+
+    let expected = Buffer::with_lines(vec![
+        "│Head1  Head2  Head3         │",
+        "│                            │",
+        "│                            │",
+        "│                            │",
+    ]);
+
+    terminal.backend().assert_buffer(&expected);
+}

helix-view/Cargo.toml

@@ -16,7 +16,7 @@ helix-core = { path = "../helix-core" }
 helix-lsp = { path = "../helix-lsp"}
 
 # Conversion traits
-tui = { version = "0.15", default-features = false, features = ["crossterm"], optional = true}
+tui = { path = "../helix-tui", package = "helix-tui", default-features = false, features = ["crossterm"], optional = true }
 crossterm = { version = "0.19", features = ["event-stream"], optional = true }
 once_cell = "1.4"
 url = "2"