Add support for dashed and dotted underlines

This finishes implementation of underline styles provided by
`CSI 4 : [1-5] m` escape sequence.

6 files changed, 185 insertions, 80 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 83aa152e..60bb7301 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,7 +15,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 - Option `font.builtin_box_drawing` to disable the built-in font for drawing box characters
 - Track and report surface damage information to Wayland compositors
-- Escape sequence for undercurl (`CSI 4 : 3 m`)
+- Escape sequence for undercurl, dotted and dashed underlines (`CSI 4 : [3-5] m`)
 
 ### Changed
 
diff --git a/alacritty/res/rect.f.glsl b/alacritty/res/rect.f.glsl
index ab1d9dcd..9af76ae4 100644
--- a/alacritty/res/rect.f.glsl
+++ b/alacritty/res/rect.f.glsl
@@ -9,46 +9,121 @@ flat in vec4 color;
 
 out vec4 FragColor;
 
-uniform int isUndercurl;
+uniform int rectKind;
 
 uniform float cellWidth;
 uniform float cellHeight;
 uniform float paddingY;
 uniform float paddingX;
 
-uniform float undercurlThickness;
+uniform float underlinePosition;
+uniform float underlineThickness;
+
 uniform float undercurlPosition;
 
+#define UNDERCURL 1
+#define DOTTED 2
+#define DASHED 3
+
 #define PI 3.1415926538
 
-void main()
-{
-    if (isUndercurl == 0) {
-        FragColor = color;
-        return;
-    }
+vec4 draw_undercurl(int x, int y) {
+  // We use `undercurlPosition` as an amplitude, since it's half of the descent
+  // value.
+  float undercurl =
+      -1. * undercurlPosition / 2. * cos(float(x) * 2 * PI / cellWidth) +
+      cellHeight - undercurlPosition;
 
-    int x = int(gl_FragCoord.x - paddingX) % int(cellWidth);
-    int y = int(gl_FragCoord.y - paddingY) % int(cellHeight);
+  float undercurlTop = undercurl + max((underlineThickness - 1), 0);
+  float undercurlBottom = undercurl - max((underlineThickness - 1), 0);
 
-    // We use `undercurlPosition` as amplitude, since it's half of the descent
-    // value.
-    float undercurl = -1. * undercurlPosition / 2.
-        * cos(float(x) * 2 * PI / float(cellWidth))
-        + cellHeight - undercurlPosition;
+  // Compute resulted alpha based on distance from `gl_FragCoord.y` to the
+  // cosine curve.
+  float alpha = 1.;
+  if (y > undercurlTop || y < undercurlBottom) {
+    alpha = 1. - min(abs(undercurlTop - y), abs(undercurlBottom - y));
+  }
 
-    // We subtract one, since curve is already 1px thick.
-    float undercurl_top = undercurl + max((undercurlThickness - 1), 0);
-    float undercurl_bottom = undercurl - max((undercurlThickness - 1), 0);
+  // The result is an alpha mask on a rect, which leaves only curve opaque.
+  return vec4(color.rgb, alpha);
+}
 
+// When the dot size increases we can use AA to make spacing look even and the
+// dots rounded.
+vec4 draw_dotted_aliased(float x, float y) {
+  int dotNumber = int(x / underlineThickness);
 
-    // Compute resulted alpha based on distance from `gl_FragCoord.y` to the
-    // cosine curve.
-    float alpha = 1.;
-    if (y > undercurl_top || y < undercurl_bottom) {
-        alpha = 1. - min(abs(undercurl_top - y), abs(undercurl_bottom - y));
-    }
+  float radius = underlineThickness / 2.;
+  float centerY = cellHeight - underlinePosition;
+
+  float leftCenter = (dotNumber - dotNumber % 2) * underlineThickness + radius;
+  float rightCenter = leftCenter + 2 * underlineThickness;
+
+  float distanceLeft = sqrt(pow(x - leftCenter, 2) + pow(y - centerY, 2));
+  float distanceRight = sqrt(pow(x - rightCenter, 2) + pow(y - centerY, 2));
+
+  float alpha = max(1 - (min(distanceLeft, distanceRight) - radius), 0);
+  return vec4(color.rgb, alpha);
+}
+
+/// Draw dotted line when dot is just a single pixel.
+vec4 draw_dotted(int x, int y) {
+  int cellEven = 0;
+
+  // Since the size of the dot and its gap combined is 2px we should ensure that
+  // spacing will be even. If the cellWidth is even it'll work since we start
+  // with dot and end with gap. However if cellWidth is odd, the cell will start
+  // and end with a dot, creating a dash. To resolve this issue, we invert the
+  // pattern every two cells.
+  if (int(cellWidth) % 2 != 0) {
+    cellEven = int((gl_FragCoord.x - paddingX) / cellWidth) % 2;
+  }
 
-    // The result is an alpha mask on a rect, which leaves only curve opaque.
-    FragColor = vec4(color.xyz, alpha);
+  // Since we use the entire descent area for dotted underlines, we limit its
+  // height to a single pixel so we don't draw bars instead of dots.
+  float alpha = 1. - abs(round(cellHeight - underlinePosition) - y);
+  if (x % 2 != cellEven) {
+    alpha = 0;
+  }
+
+  return vec4(color.rgb, alpha);
+}
+
+vec4 draw_dashed(int x) {
+  // Since dashes of adjacent cells connect with each other our dash length is
+  // half of the desired total length.
+  int halfDashLen = int(cellWidth) / 4;
+
+  float alpha = 1.;
+
+  // Check if `x` coordinate is where we should draw gap.
+  if (x > halfDashLen && x < cellWidth - halfDashLen - 1) {
+    alpha = 0.;
+  }
+
+  return vec4(color.rgb, alpha);
+}
+
+void main() {
+  int x = int(gl_FragCoord.x - paddingX) % int(cellWidth);
+  int y = int(gl_FragCoord.y - paddingY) % int(cellHeight);
+
+  switch (rectKind) {
+  case UNDERCURL:
+    FragColor = draw_undercurl(x, y);
+    break;
+  case DOTTED:
+    if (underlineThickness < 2) {
+      FragColor = draw_dotted(x, y);
+    } else {
+      FragColor = draw_dotted_aliased(x, y);
+    }
+    break;
+  case DASHED:
+    FragColor = draw_dashed(x);
+    break;
+  default:
+    FragColor = color;
+    break;
+  }
 }
diff --git a/alacritty/src/renderer/rects.rs b/alacritty/src/renderer/rects.rs
index e9eb107f..5f9d13e3 100644
--- a/alacritty/src/renderer/rects.rs
+++ b/alacritty/src/renderer/rects.rs
@@ -23,12 +23,12 @@ pub struct RenderRect {
     pub height: f32,
     pub color: Rgb,
     pub alpha: f32,
-    pub is_undercurl: bool,
+    pub kind: RectKind,
 }
 
 impl RenderRect {
     pub fn new(x: f32, y: f32, width: f32, height: f32, color: Rgb, alpha: f32) -> Self {
-        RenderRect { x, y, width, height, color, alpha, is_undercurl: false }
+        RenderRect { kind: RectKind::Normal, x, y, width, height, color, alpha }
     }
 }
 
@@ -39,6 +39,17 @@ pub struct RenderLine {
     pub color: Rgb,
 }
 
+// NOTE: These flags must be in sync with their usage in the rect.*.glsl shaders.
+#[repr(u8)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum RectKind {
+    Normal = 0,
+    Undercurl = 1,
+    DottedUnderline = 2,
+    DashedUnderline = 3,
+    NumKinds = 4,
+}
+
 impl RenderLine {
     pub fn rects(&self, flag: Flags, metrics: &Metrics, size: &SizeInfo) -> Vec<RenderRect> {
         let mut rects = Vec::new();
@@ -64,7 +75,7 @@ impl RenderLine {
         end: Point<usize>,
         color: Rgb,
     ) {
-        let (position, thickness) = match flag {
+        let (position, thickness, ty) = match flag {
             Flags::DOUBLE_UNDERLINE => {
                 // Position underlines so each one has 50% of descent available.
                 let top_pos = 0.25 * metrics.descent;
@@ -80,18 +91,29 @@ impl RenderLine {
                     color,
                 ));
 
-                (bottom_pos, metrics.underline_thickness)
+                (bottom_pos, metrics.underline_thickness, RectKind::Normal)
             },
             // Make undercurl occupy the entire descent area.
-            Flags::UNDERCURL => (metrics.descent, metrics.descent.abs()),
-            Flags::UNDERLINE => (metrics.underline_position, metrics.underline_thickness),
-            Flags::STRIKEOUT => (metrics.strikeout_position, metrics.strikeout_thickness),
+            Flags::UNDERCURL => (metrics.descent, metrics.descent.abs(), RectKind::Undercurl),
+            Flags::UNDERLINE => {
+                (metrics.underline_position, metrics.underline_thickness, RectKind::Normal)
+            },
+            // Make dotted occupy the entire descent area.
+            Flags::DOTTED_UNDERLINE => {
+                (metrics.descent, metrics.descent.abs(), RectKind::DottedUnderline)
+            },
+            Flags::DASHED_UNDERLINE => {
+                (metrics.underline_position, metrics.underline_thickness, RectKind::DashedUnderline)
+            },
+            Flags::STRIKEOUT => {
+                (metrics.strikeout_position, metrics.strikeout_thickness, RectKind::Normal)
+            },
             _ => unimplemented!("Invalid flag for cell line drawing specified"),
         };
 
         let mut rect =
             Self::create_rect(size, metrics.descent, start, end, position, thickness, color);
-        rect.is_undercurl = flag == Flags::UNDERCURL;
+        rect.kind = ty;
         rects.push(rect);
     }
 
@@ -161,6 +183,8 @@ impl RenderLines {
         self.update_flag(cell, Flags::DOUBLE_UNDERLINE);
         self.update_flag(cell, Flags::STRIKEOUT);
         self.update_flag(cell, Flags::UNDERCURL);
+        self.update_flag(cell, Flags::DOTTED_UNDERLINE);
+        self.update_flag(cell, Flags::DASHED_UNDERLINE);
     }
 
     /// Update the lines for a specific flag.
@@ -224,8 +248,7 @@ pub struct RectRenderer {
 
     program: RectShaderProgram,
 
-    rect_vertices: Vec<Vertex>,
-    curl_vertices: Vec<Vertex>,
+    vertices: [Vec<Vertex>; 4],
 }
 
 impl RectRenderer {
@@ -274,7 +297,7 @@ impl RectRenderer {
             gl::BindBuffer(gl::ARRAY_BUFFER, 0);
         }
 
-        Ok(Self { vao, vbo, program, rect_vertices: Vec::new(), curl_vertices: Vec::new() })
+        Ok(Self { vao, vbo, program, vertices: Default::default() })
     }
 
     pub fn draw(&mut self, size_info: &SizeInfo, metrics: &Metrics, rects: Vec<RenderRect>) {
@@ -293,43 +316,32 @@ impl RectRenderer {
         let half_height = size_info.height() / 2.;
 
         // Build rect vertices vector.
-        self.rect_vertices.clear();
-        self.curl_vertices.clear();
+        self.vertices.iter_mut().for_each(|vertices| vertices.clear());
         for rect in &rects {
-            if rect.is_undercurl {
-                Self::add_rect(&mut self.curl_vertices, half_width, half_height, rect);
-            } else {
-                Self::add_rect(&mut self.rect_vertices, half_width, half_height, rect);
-            }
+            Self::add_rect(&mut self.vertices[rect.kind as usize], half_width, half_height, rect);
         }
 
         unsafe {
-            if !self.curl_vertices.is_empty() {
-                self.program.set_undercurl(true);
-                // Upload accumulated undercurl vertices.
-                gl::BufferData(
-                    gl::ARRAY_BUFFER,
-                    (self.curl_vertices.len() * mem::size_of::<Vertex>()) as isize,
-                    self.curl_vertices.as_ptr() as *const _,
-                    gl::STREAM_DRAW,
-                );
+            // We iterate in reverse order to draw plain rects at the end, since we want visual
+            // bell or damage rects be above the lines.
+            for rect_kind in (RectKind::Normal as u8..RectKind::NumKinds as u8).rev() {
+                let vertices = &mut self.vertices[rect_kind as usize];
+                if vertices.is_empty() {
+                    continue;
+                }
 
-                // Draw all vertices as list of triangles.
-                gl::DrawArrays(gl::TRIANGLES, 0, self.curl_vertices.len() as i32);
-            }
+                self.program.set_rect_kind(rect_kind as u8);
 
-            if !self.rect_vertices.is_empty() {
-                self.program.set_undercurl(false);
-                // Upload accumulated rect vertices.
+                // Upload accumulated undercurl vertices.
                 gl::BufferData(
                     gl::ARRAY_BUFFER,
-                    (self.rect_vertices.len() * mem::size_of::<Vertex>()) as isize,
-                    self.rect_vertices.as_ptr() as *const _,
+                    (vertices.len() * mem::size_of::<Vertex>()) as isize,
+                    vertices.as_ptr() as *const _,
                     gl::STREAM_DRAW,
                 );
 
                 // Draw all vertices as list of triangles.
-                gl::DrawArrays(gl::TRIANGLES, 0, self.rect_vertices.len() as i32);
+                gl::DrawArrays(gl::TRIANGLES, 0, vertices.len() as i32);
             }
 
             // Disable program.
@@ -384,10 +396,8 @@ pub struct RectShaderProgram {
     /// Shader program.
     program: ShaderProgram,
 
-    /// Undercurl flag.
-    ///
-    /// Rect rendering has two modes; one for normal filled rects, and other for undercurls.
-    u_is_undercurl: GLint,
+    /// Kind of rect we're drawing.
+    u_rect_kind: GLint,
 
     /// Cell width.
     u_cell_width: GLint,
@@ -399,8 +409,11 @@ pub struct RectShaderProgram {
     u_padding_x: GLint,
     u_padding_y: GLint,
 
-    /// Undercurl thickness.
-    u_undercurl_thickness: GLint,
+    /// Underline position.
+    u_underline_position: GLint,
+
+    /// Underline thickness.
+    u_underline_thickness: GLint,
 
     /// Undercurl position.
     u_undercurl_position: GLint,
@@ -411,13 +424,14 @@ impl RectShaderProgram {
         let program = ShaderProgram::new(RECT_SHADER_V, RECT_SHADER_F)?;
 
         Ok(Self {
-            u_is_undercurl: program.get_uniform_location(cstr!("isUndercurl"))?,
+            u_rect_kind: program.get_uniform_location(cstr!("rectKind"))?,
             u_cell_width: program.get_uniform_location(cstr!("cellWidth"))?,
             u_cell_height: program.get_uniform_location(cstr!("cellHeight"))?,
             u_padding_x: program.get_uniform_location(cstr!("paddingX"))?,
             u_padding_y: program.get_uniform_location(cstr!("paddingY"))?,
+            u_underline_position: program.get_uniform_location(cstr!("underlinePosition"))?,
+            u_underline_thickness: program.get_uniform_location(cstr!("underlineThickness"))?,
             u_undercurl_position: program.get_uniform_location(cstr!("undercurlPosition"))?,
-            u_undercurl_thickness: program.get_uniform_location(cstr!("undercurlThickness"))?,
             program,
         })
     }
@@ -426,22 +440,22 @@ impl RectShaderProgram {
         self.program.id()
     }
 
-    fn set_undercurl(&self, is_undercurl: bool) {
-        let value = if is_undercurl { 1 } else { 0 };
-
+    fn set_rect_kind(&self, ty: u8) {
         unsafe {
-            gl::Uniform1i(self.u_is_undercurl, value);
+            gl::Uniform1i(self.u_rect_kind, ty as i32);
         }
     }
 
     pub fn update_uniforms(&self, size_info: &SizeInfo, metrics: &Metrics) {
         let position = (0.5 * metrics.descent).abs();
+        let underline_position = metrics.descent.abs() - metrics.underline_position.abs();
         unsafe {
             gl::Uniform1f(self.u_cell_width, size_info.cell_width());
             gl::Uniform1f(self.u_cell_height, size_info.cell_height());
             gl::Uniform1f(self.u_padding_y, size_info.padding_y());
             gl::Uniform1f(self.u_padding_x, size_info.padding_x());
-            gl::Uniform1f(self.u_undercurl_thickness, metrics.underline_thickness);
+            gl::Uniform1f(self.u_underline_position, underline_position);
+            gl::Uniform1f(self.u_underline_thickness, metrics.underline_thickness);
             gl::Uniform1f(self.u_undercurl_position, position);
         }
     }
diff --git a/alacritty_terminal/src/ansi.rs b/alacritty_terminal/src/ansi.rs
index 91dd3540..8475685d 100644
--- a/alacritty_terminal/src/ansi.rs
+++ b/alacritty_terminal/src/ansi.rs
@@ -772,6 +772,10 @@ pub enum Attr {
     DoubleUnderline,
     /// Undercurled text.
     Undercurl,
+    /// Dotted underlined text.
+    DottedUnderline,
+    /// Dashed underlined text.
+    DashedUnderline,
     /// Blink cursor slowly.
     BlinkSlow,
     /// Blink cursor fast.
@@ -1332,6 +1336,8 @@ fn attrs_from_sgr_parameters(params: &mut ParamsIter<'_>) -> Vec<Option<Attr>> {
             [4, 0] => Some(Attr::CancelUnderline),
             [4, 2] => Some(Attr::DoubleUnderline),
             [4, 3] => Some(Attr::Undercurl),
+            [4, 4] => Some(Attr::DottedUnderline),
+            [4, 5] => Some(Attr::DashedUnderline),
             [4, ..] => Some(Attr::Underline),
             [5] => Some(Attr::BlinkSlow),
             [6] => Some(Attr::BlinkFast),
diff --git a/alacritty_terminal/src/term/cell.rs b/alacritty_terminal/src/term/cell.rs
index 49d25eb3..2af1fbac 100644
--- a/alacritty_terminal/src/term/cell.rs
+++ b/alacritty_terminal/src/term/cell.rs
@@ -25,7 +25,11 @@ bitflags! {
         const LEADING_WIDE_CHAR_SPACER  = 0b0000_0100_0000_0000;
         const DOUBLE_UNDERLINE          = 0b0000_1000_0000_0000;
         const UNDERCURL                 = 0b0001_0000_0000_0000;
-        const ALL_UNDERLINES            = Self::UNDERLINE.bits | Self::DOUBLE_UNDERLINE.bits | Self::UNDERCURL.bits;
+        const DOTTED_UNDERLINE          = 0b0010_0000_0000_0000;
+        const DASHED_UNDERLINE          = 0b0100_0000_0000_0000;
+        const ALL_UNDERLINES            = Self::UNDERLINE.bits | Self::DOUBLE_UNDERLINE.bits
+                                        | Self::UNDERCURL.bits | Self::DOTTED_UNDERLINE.bits
+                                        | Self::DASHED_UNDERLINE.bits;
     }
 }
 
@@ -119,9 +123,7 @@ impl GridCell for Cell {
             && self.fg == Color::Named(NamedColor::Foreground)
             && !self.flags.intersects(
                 Flags::INVERSE
-                    | Flags::UNDERLINE
-                    | Flags::DOUBLE_UNDERLINE
-                    | Flags::UNDERCURL
+                    | Flags::ALL_UNDERLINES
                     | Flags::STRIKEOUT
                     | Flags::WRAPLINE
                     | Flags::WIDE_CHAR_SPACER
diff --git a/alacritty_terminal/src/term/mod.rs b/alacritty_terminal/src/term/mod.rs
index 4d30602b..5ad1b4ad 100644
--- a/alacritty_terminal/src/term/mod.rs
+++ b/alacritty_terminal/src/term/mod.rs
@@ -1850,6 +1850,14 @@ impl<T: EventListener> Handler for Term<T> {
                 cursor.template.flags.remove(Flags::ALL_UNDERLINES);
                 cursor.template.flags.insert(Flags::UNDERCURL);
             },
+            Attr::DottedUnderline => {
+                cursor.template.flags.remove(Flags::ALL_UNDERLINES);
+                cursor.template.flags.insert(Flags::DOTTED_UNDERLINE);
+            },
+            Attr::DashedUnderline => {
+                cursor.template.flags.remove(Flags::ALL_UNDERLINES);
+                cursor.template.flags.insert(Flags::DASHED_UNDERLINE);
+            },
             Attr::CancelUnderline => cursor.template.flags.remove(Flags::ALL_UNDERLINES),
             Attr::Hidden => cursor.template.flags.insert(Flags::HIDDEN),
             Attr::CancelHidden => cursor.template.flags.remove(Flags::HIDDEN),