Added a rudimentary undercurl to Alacritty. Currently does not support setting the color. That is the next task

2 files changed, 86 insertions, 14 deletions

diff --git a/alacritty/src/display/content.rs b/alacritty/src/display/content.rs
index 2deb3d3e..09116508 100644
--- a/alacritty/src/display/content.rs
+++ b/alacritty/src/display/content.rs
@@ -271,7 +271,7 @@ impl RenderableCell {
         self.bg_alpha == 0.
             && self.character == ' '
             && self.zerowidth.is_none()
-            && !self.flags.intersects(Flags::UNDERLINE | Flags::STRIKEOUT | Flags::DOUBLE_UNDERLINE)
+            && !self.flags.intersects(Flags::UNDERLINE | Flags::STRIKEOUT | Flags::DOUBLE_UNDERLINE | Flags::UNDERCURL)
     }
 
     /// Apply [`CellRgb`] colors to the cell's colors.
diff --git a/alacritty/src/renderer/rects.rs b/alacritty/src/renderer/rects.rs
index 77c22011..91a67c22 100644
--- a/alacritty/src/renderer/rects.rs
+++ b/alacritty/src/renderer/rects.rs
@@ -62,7 +62,7 @@ impl RenderLine {
         end: Point<usize>,
         color: Rgb,
     ) {
-        let (position, thickness) = match flag {
+        match flag {
             Flags::DOUBLE_UNDERLINE => {
                 // Position underlines so each one has 50% of descent available.
                 let top_pos = 0.25 * metrics.descent;
@@ -78,22 +78,93 @@ impl RenderLine {
                     color,
                 ));
 
-                (bottom_pos, metrics.underline_thickness)
+                rects.push(Self::create_rect(
+                    size,
+                    metrics.descent,
+                    start,
+                    end,
+                    bottom_pos,
+                    metrics.underline_thickness,
+                    color,
+                ));
+            },
+            Flags::UNDERLINE => {
+                rects.push(Self::create_rect(
+                    size,
+                    metrics.descent,
+                    start,
+                    end,
+                    metrics.underline_position,
+                    metrics.underline_thickness,
+                    color,
+                ));
             },
-            Flags::UNDERLINE => (metrics.underline_position, metrics.underline_thickness),
-            Flags::STRIKEOUT => (metrics.strikeout_position, metrics.strikeout_thickness),
+            Flags::STRIKEOUT => {
+                rects.push(Self::create_rect(
+                    size,
+                    metrics.descent,
+                    start,
+                    end,
+                    metrics.strikeout_position,
+                    metrics.strikeout_thickness,
+                    color,
+                ));
+            },
+            Flags::UNDERCURL => {
+                Self::push_undercurl_rects(
+                    rects,
+                    size,
+                    metrics.descent,
+                    start,
+                    end,
+                    metrics.underline_position,
+                    metrics.underline_thickness,
+                    color)
+            }
             _ => unimplemented!("Invalid flag for cell line drawing specified"),
         };
+    }
 
-        rects.push(Self::create_rect(
-            size,
-            metrics.descent,
-            start,
-            end,
-            position,
-            thickness,
-            color,
-        ));
+    fn push_undercurl_rects(
+        rects: &mut Vec<RenderRect>,
+        size: &SizeInfo,
+        descent: f32,
+        start: Point<usize>,
+        end: Point<usize>,
+        position: f32,
+        mut thickness: f32,
+        color: Rgb,
+    ) {
+        let start_x = start.column.0 as f32 * size.cell_width();
+        let end_x = (end.column.0 + 1) as f32 * size.cell_width();
+
+        // Make sure lines are always visible.
+        thickness = thickness.max(1.);
+
+        let line_bottom = (start.line as f32 + 1.) * size.cell_height();
+        let baseline = line_bottom + descent;
+
+        let mut y = (baseline - position - thickness / 2.).ceil();
+        let max_y = line_bottom - thickness;
+        if y > max_y {
+            y = max_y;
+        }
+
+        let mut x = start_x;
+        let mut idx = 0;
+        while x < end_x {
+            let rect = RenderRect::new(
+                x + size.padding_x(),
+                y + size.padding_y() + ((idx % 2) as f32) - 1.,
+                1.,
+                thickness + 1.,
+                color,
+                1.,
+            );
+            rects.push(rect);
+            x += 1.;
+            idx += 1;
+        }
     }
 
     /// Create a line's rect at a position relative to the baseline.
@@ -161,6 +232,7 @@ impl RenderLines {
         self.update_flag(cell, Flags::UNDERLINE);
         self.update_flag(cell, Flags::DOUBLE_UNDERLINE);
         self.update_flag(cell, Flags::STRIKEOUT);
+        self.update_flag(cell, Flags::UNDERCURL);
     }
 
     /// Update the lines for a specific flag.