Add colored underline support

This commit adds support for colored underline and refines the dynamic
extra storage. The extra storage now is using `Arc` making cloning it way
faster compared to `Box` approach which scales really well when it comes
to cloning in `Term::write_at_cursor`, since cloning `Arc` is constant
time.

Fixes #4142.

CHANGELOG.md

@@ -17,6 +17,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Escape sequence for undercurl, dotted and dashed underlines (`CSI 4 : [3-5] m`)
 - `ToggleMaximized` key binding action to (un-)maximize the active window, not bound by default
 - Support for OpenGL ES 2.0
+- Escape sequence to set underline color (`CSI 58 : 2 : Ps : Ps : Ps m`/`CSI 58 : 5 : Ps m`)
+- Escape sequence to reset underline color (`CSI 59 m`)
 
 ### Changed
 

alacritty/src/display/content.rs

@@ -186,6 +186,7 @@ pub struct RenderableCell {
     pub fg: Rgb,
     pub bg: Rgb,
     pub bg_alpha: f32,
+    pub underline: Rgb,
     pub flags: Flags,
 }
 
@@ -251,14 +252,20 @@ impl RenderableCell {
         let cell_point = cell.point;
         let point = display::point_to_viewport(display_offset, cell_point).unwrap();
 
+        let flags = cell.flags;
+        let underline = cell
+            .underline_color()
+            .map_or(fg, |underline| Self::compute_fg_rgb(content, underline, flags));
+
         RenderableCell {
             zerowidth: cell.zerowidth().map(|zerowidth| zerowidth.to_vec()),
-            flags: cell.flags,
+            flags,
             character,
             bg_alpha,
             point,
             fg,
             bg,
+            underline,
         }
     }
 

alacritty/src/renderer/mod.rs

@@ -135,6 +135,7 @@ impl Renderer {
             bg_alpha: 1.0,
             fg,
             bg,
+            underline: fg,
         });
 
         self.draw_cells(size_info, glyph_cache, cells);

alacritty/src/renderer/rects.rs

@@ -193,6 +193,9 @@ impl RenderLines {
             return;
         }
 
+        // The underline color escape does not apply to strikeout.
+        let color = if flag.contains(Flags::STRIKEOUT) { cell.fg } else { cell.underline };
+
         // Include wide char spacer if the current cell is a wide char.
         let mut end = cell.point;
         if cell.flags.contains(Flags::WIDE_CHAR) {
@@ -201,7 +204,7 @@ impl RenderLines {
 
         // Check if there's an active line.
         if let Some(line) = self.inner.get_mut(&flag).and_then(|lines| lines.last_mut()) {
-            if cell.fg == line.color
+            if color == line.color
                 && cell.point.column == line.end.column + 1
                 && cell.point.line == line.end.line
             {
@@ -212,7 +215,7 @@ impl RenderLines {
         }
 
         // Start new line if there currently is none.
-        let line = RenderLine { start: cell.point, end, color: cell.fg };
+        let line = RenderLine { start: cell.point, end, color };
         match self.inner.get_mut(&flag) {
             Some(lines) => lines.push(line),
             None => {

alacritty_terminal/Cargo.toml

@@ -17,7 +17,7 @@ version = "0.1.0"
 libc = "0.2"
 bitflags = "1"
 parking_lot = "0.11.0"
-serde = { version = "1", features = ["derive"] }
+serde = { version = "1", features = ["derive", "rc"] }
 serde_yaml = "0.8"
 vte = { version = "0.10.0", default-features = false }
 mio = "0.6.20"

alacritty_terminal/src/ansi.rs

@@ -806,6 +806,8 @@ pub enum Attr {
     Foreground(Color),
     /// Set indexed background color.
     Background(Color),
+    /// Underline color.
+    UnderlineColor(Option<Color>),
 }
 
 /// Identifiers which can be assigned to a graphic character set.
@@ -1364,13 +1366,7 @@ fn attrs_from_sgr_parameters(params: &mut ParamsIter<'_>) -> Vec<Option<Attr>> {
                 let mut iter = params.map(|param| param[0]);
                 parse_sgr_color(&mut iter).map(Attr::Foreground)
             },
-            [38, params @ ..] => {
-                let rgb_start = if params.len() > 4 { 2 } else { 1 };
-                let rgb_iter = params[rgb_start..].iter().copied();
-                let mut iter = iter::once(params[0]).chain(rgb_iter);
-
-                parse_sgr_color(&mut iter).map(Attr::Foreground)
-            },
+            [38, params @ ..] => handle_colon_rgb(params).map(Attr::Foreground),
             [39] => Some(Attr::Foreground(Color::Named(NamedColor::Foreground))),
             [40] => Some(Attr::Background(Color::Named(NamedColor::Black))),
             [41] => Some(Attr::Background(Color::Named(NamedColor::Red))),
@@ -1384,14 +1380,16 @@ fn attrs_from_sgr_parameters(params: &mut ParamsIter<'_>) -> Vec<Option<Attr>> {
                 let mut iter = params.map(|param| param[0]);
                 parse_sgr_color(&mut iter).map(Attr::Background)
             },
-            [48, params @ ..] => {
-                let rgb_start = if params.len() > 4 { 2 } else { 1 };
-                let rgb_iter = params[rgb_start..].iter().copied();
-                let mut iter = iter::once(params[0]).chain(rgb_iter);
-
-                parse_sgr_color(&mut iter).map(Attr::Background)
-            },
+            [48, params @ ..] => handle_colon_rgb(params).map(Attr::Background),
             [49] => Some(Attr::Background(Color::Named(NamedColor::Background))),
+            [58] => {
+                let mut iter = params.map(|param| param[0]);
+                parse_sgr_color(&mut iter).map(|color| Attr::UnderlineColor(Some(color)))
+            },
+            [58, params @ ..] => {
+                handle_colon_rgb(params).map(|color| Attr::UnderlineColor(Some(color)))
+            },
+            [59] => Some(Attr::UnderlineColor(None)),
             [90] => Some(Attr::Foreground(Color::Named(NamedColor::BrightBlack))),
             [91] => Some(Attr::Foreground(Color::Named(NamedColor::BrightRed))),
             [92] => Some(Attr::Foreground(Color::Named(NamedColor::BrightGreen))),
@@ -1416,6 +1414,16 @@ fn attrs_from_sgr_parameters(params: &mut ParamsIter<'_>) -> Vec<Option<Attr>> {
     attrs
 }
 
+/// Handle colon separated rgb color escape sequence.
+#[inline]
+fn handle_colon_rgb(params: &[u16]) -> Option<Color> {
+    let rgb_start = if params.len() > 4 { 2 } else { 1 };
+    let rgb_iter = params[rgb_start..].iter().copied();
+    let mut iter = iter::once(params[0]).chain(rgb_iter);
+
+    parse_sgr_color(&mut iter)
+}
+
 /// Parse a color specifier from list of attributes.
 fn parse_sgr_color(params: &mut dyn Iterator<Item = u16>) -> Option<Color> {
     match params.next() {

alacritty_terminal/src/term/cell.rs

@@ -1,4 +1,4 @@
-use std::boxed::Box;
+use std::sync::Arc;
 
 use bitflags::bitflags;
 use serde::{Deserialize, Serialize};
@@ -57,19 +57,20 @@ impl ResetDiscriminant<Color> for Cell {
 /// allocation required ahead of time for every cell, with some additional overhead when the extra
 /// storage is actually required.
 #[derive(Serialize, Deserialize, Default, Debug, Clone, Eq, PartialEq)]
-struct CellExtra {
+pub struct CellExtra {
     zerowidth: Vec<char>,
+
+    underline_color: Option<Color>,
 }
 
 /// Content and attributes of a single cell in the terminal grid.
-#[derive(Serialize, Deserialize, Debug, Clone, Eq, PartialEq)]
+#[derive(Serialize, Deserialize, Clone, Debug, Eq, PartialEq)]
 pub struct Cell {
     pub c: char,
     pub fg: Color,
     pub bg: Color,
     pub flags: Flags,
-    #[serde(default)]
-    extra: Option<Box<CellExtra>>,
+    pub extra: Option<Arc<CellExtra>>,
 }
 
 impl Default for Cell {
@@ -94,25 +95,39 @@ impl Cell {
 
     /// Write a new zerowidth character to this cell.
     #[inline]
-    pub fn push_zerowidth(&mut self, c: char) {
-        self.extra.get_or_insert_with(Default::default).zerowidth.push(c);
-    }
-
-    /// Free all dynamically allocated cell storage.
-    #[inline]
-    pub fn drop_extra(&mut self) {
-        if self.extra.is_some() {
-            self.extra = None;
-        }
+    pub fn push_zerowidth(&mut self, character: char) {
+        let extra = self.extra.get_or_insert(Default::default());
+        Arc::make_mut(extra).zerowidth.push(character);
     }
 
     /// Remove all wide char data from a cell.
     #[inline(never)]
     pub fn clear_wide(&mut self) {
         self.flags.remove(Flags::WIDE_CHAR);
-        self.drop_extra();
+        if let Some(extra) = self.extra.as_mut() {
+            Arc::make_mut(extra).zerowidth = Vec::new();
+        }
         self.c = ' ';
     }
+
+    /// Set underline color on the cell.
+    pub fn set_underline_color(&mut self, color: Option<Color>) {
+        // If we reset color and we don't have zerowidth we should drop extra storage.
+        if color.is_none() && self.extra.as_ref().map_or(true, |extra| !extra.zerowidth.is_empty())
+        {
+            self.extra = None;
+            return;
+        }
+
+        let extra = self.extra.get_or_insert(Default::default());
+        Arc::make_mut(extra).underline_color = color;
+    }
+
+    /// Underline color stored in this cell.
+    #[inline]
+    pub fn underline_color(&self) -> Option<Color> {
+        self.extra.as_ref()?.underline_color
+    }
 }
 
 impl GridCell for Cell {
@@ -184,11 +199,22 @@ impl LineLength for grid::Row<Cell> {
 
 #[cfg(test)]
 mod tests {
-    use super::{Cell, LineLength};
+    use super::*;
+
+    use std::mem;
 
     use crate::grid::Row;
     use crate::index::Column;
 
+    #[test]
+    fn cell_size_is_below_cap() {
+        // Expected cell size on 64-bit architectures.
+        const EXPECTED_CELL_SIZE: usize = 24;
+
+        // Ensure that cell size isn't growning by accident.
+        assert!(mem::size_of::<Cell>() <= EXPECTED_CELL_SIZE);
+    }
+
     #[test]
     fn line_length_works() {
         let mut row = Row::<Cell>::new(10);

alacritty_terminal/src/term/mod.rs

@@ -1047,6 +1047,7 @@ impl<T> Term<T> {
         let fg = self.grid.cursor.template.fg;
         let bg = self.grid.cursor.template.bg;
         let flags = self.grid.cursor.template.flags;
+        let extra = self.grid.cursor.template.extra.clone();
 
         let mut cursor_cell = self.grid.cursor_cell();
 
@@ -1070,12 +1071,11 @@ impl<T> Term<T> {
             cursor_cell = self.grid.cursor_cell();
         }
 
-        cursor_cell.drop_extra();
-
         cursor_cell.c = c;
         cursor_cell.fg = fg;
         cursor_cell.bg = bg;
         cursor_cell.flags = flags;
+        cursor_cell.extra = extra;
     }
 
     #[inline]
@@ -1826,10 +1826,12 @@ impl<T: EventListener> Handler for Term<T> {
         match attr {
             Attr::Foreground(color) => cursor.template.fg = color,
             Attr::Background(color) => cursor.template.bg = color,
+            Attr::UnderlineColor(color) => cursor.template.set_underline_color(color),
             Attr::Reset => {
                 cursor.template.fg = Color::Named(NamedColor::Foreground);
                 cursor.template.bg = Color::Named(NamedColor::Background);
                 cursor.template.flags = Flags::empty();
+                cursor.template.set_underline_color(None);
             },
             Attr::Reverse => cursor.template.flags.insert(Flags::INVERSE),
             Attr::CancelReverse => cursor.template.flags.remove(Flags::INVERSE),

alacritty_terminal/tests/ref.rs

@@ -52,6 +52,7 @@ ref_tests! {
     zerowidth
     selective_erasure
     colored_reset
+    colored_underline
     delete_lines
     delete_chars_reset
     alt_reset

alacritty_terminal/tests/ref/colored_underline/alacritty.recording

@@ -0,0 +1,3 @@
+%                                                                                                                                           
 
]133;A]2;kchibisov@Zodiac:~/src/rust/alacritty-workspace/fork
fork on  colored-underlines-v3 via 🦀 v1.59.0 ➜ [?2004hcargo run -- --ref-test --config-file /dev/null -o scrolling.history=0echo -e '\e[58;2;255;0;255m\e[4:1mUNDERLINE\e[4:2mDOUBLE\e[58:5:196m\e[4:3mUh̷̗ERCURL\e[4:4mDOTTED\e[4:5mDASHED\e[59mNOT_COLORED_DASH\e[0m'[?2004l
+]2;echo -e '\e[58;2;255;0;255m\e[4:1mUNDERLINE\e[4:2mDOUBLE\e[58:5:196m\e[4:3mUh̷̗ERCURL\e[4:4mDOTTED\e[4:5mDASHED\e[59mNOT_COLORED_DASH\e[0m'[4:1mUNDERLINE[4:2mDOUBLE[58:5:196m[4:3mUh̷̗ERCURL[4:4mDOTTED[4:5mDASHEDNOT_COLORED_DASH
+%                                                                                                                                           
 
]133;A]2;kchibisov@Zodiac:~/src/rust/alacritty-workspace/fork
fork on  colored-underlines-v3 via 🦀 v1.59.0 ➜ [?2004h[?2004l

alacritty_terminal/tests/ref/colored_underline/config.json

@@ -0,0 +1 @@
+{"history_size":0}

alacritty_terminal/tests/ref/colored_underline/size.json

@@ -0,0 +1 @@
+{"width":1262.0,"height":690.0,"cell_width":9.0,"cell_height":18.0,"padding_x":0.0,"padding_y":0.0,"screen_lines":38,"columns":140}

docs/escape_support.md

@@ -65,7 +65,7 @@ brevity.
 | `CSI l`    | PARTIAL     | See `CSI h` for supported modes                   |
 | `CSI ? l`  | PARTIAL     | See `CSI ? h` for supported modes                 |
 | `CSI M`    | IMPLEMENTED |                                                   |
-| `CSI m`    | PARTIAL     | Only singular straight underlines are supported   |
+| `CSI m`    | IMPLEMENTED |                                                   |
 | `CSI n`    | IMPLEMENTED |                                                   |
 | `CSI P`    | IMPLEMENTED |                                                   |
 | `CSI SP q` | IMPLEMENTED |                                                   |