Merge pull request #753 from mitchellh/update-undercurl

feat: update undercurl with antialiasing

src/font/sprite/canvas.zig

@@ -140,6 +140,12 @@ const WebCanvasImpl = struct {
         self.* = undefined;
     }
 
+    pub fn pixel(self: *WebCanvasImpl, x: u32, y: u32, color: Color) void {
+        const ctx = self.context(color) catch return;
+        defer ctx.deinit();
+        ctx.call(void, "fillRect", .{ x, y, 1, 1 }) catch return;
+    }
+
     pub fn rect(self: *WebCanvasImpl, v: Rect, color: Color) void {
         const ctx = self.context(color) catch return;
         defer ctx.deinit();
@@ -401,6 +407,20 @@ const PixmanImpl = struct {
         return region;
     }
 
+    /// Draw and fill a single pixel
+    pub fn pixel(self: *Canvas, x: u32, y: u32, color: Color) void {
+        const boxes = &[_]pixman.Box32{
+            .{
+                .x1 = @intCast(x),
+                .y1 = @intCast(y),
+                .x2 = @intCast(x + 1),
+                .y2 = @intCast(y + 1),
+            },
+        };
+
+        self.image.fillBoxes(.src, color.pixmanColor(), boxes) catch {};
+    }
+
     /// Draw and fill a rectangle. This is the main primitive for drawing
     /// lines as well (which are just generally skinny rectangles...)
     pub fn rect(self: *Canvas, v: Rect, color: Color) void {

src/font/sprite/underline.zig

@@ -166,40 +166,43 @@ const Draw = struct {
         // This is the lowest that the curl can go.
         const y_max = self.height - 1;
 
+        // Determines the density of the waves.
+        //   `2 * pi...` = 1 peak per character
+        //   `4 * pi...` = 2 peaks per character
+        const x_factor = 2 * std.math.pi / @as(f64, @floatFromInt(self.width - 1));
+
         // Some fonts put the underline too close to the bottom of the
         // cell height and this doesn't allow us to make a high enough
         // wave. This constant is arbitrary, change it for aesthetics.
-        const pos = pos: {
+        const pos: u32 = pos: {
-            const MIN_HEIGHT = 7;
+            const MIN_HEIGHT = 5;
             const clamped_pos = @min(y_max, self.pos);
             const height = y_max - clamped_pos;
             break :pos if (height < MIN_HEIGHT) clamped_pos -| MIN_HEIGHT else clamped_pos;
         };
 
-        // The full heightof the wave can be from the bottom to the
+        // The full height of the wave can be from the bottom to the
-        // underline position. We also calculate our starting y which is
+        // underline position. We also calculate our mid y point of the wave
-        // slightly below our descender since our wave will move about that.
+        const wave_height: f64 = @floatFromInt(y_max - pos);
-        const wave_height = @as(f64, @floatFromInt(y_max - pos));
+        const half_height: f64 = @max(1, wave_height / 4);
-        const half_height = wave_height / 4;
+        const y_mid: u32 = pos + @as(u32, @intFromFloat(2 * half_height));
-        const y = pos + @as(u32, @intFromFloat(half_height));
 
-        const x_factor = (2 * std.math.pi) / @as(f64, @floatFromInt(self.width));
+        // follow Xiaolin Wu's antialias algorithm to draw the curve
         var x: u32 = 0;
         while (x < self.width) : (x += 1) {
-            const vertical = @as(
+            const y: f64 = @as(f64, @floatFromInt(y_mid)) + (half_height * @cos(@as(f64, @floatFromInt(x)) * x_factor));
-                u32,
+            const y_upper: u32 = @intFromFloat(@floor(y));
-                @intFromFloat((-1 * half_height) * @sin(@as(f64, @floatFromInt(x)) * x_factor) + half_height),
+            const y_lower: u32 = y_upper - 1 + self.thickness;
-            );
+            const alpha: u8 = @intFromFloat(255 * @abs(y - @floor(y)));
 
-            var row: u32 = 0;
+            // upper and lower bounds
-            while (row < self.thickness) : (row += 1) {
+            canvas.pixel(x, @min(y_upper, y_max), @enumFromInt(255 - alpha));
-                const y1 = @min(row + y + vertical, y_max);
+            canvas.pixel(x, @min(y_lower, y_max), @enumFromInt(alpha));
-                canvas.rect(.{
+
-                    .x = @intCast(x),
+            // fill between upper and lower bound
-                    .y = @intCast(y1),
+            var y_fill: u32 = y_upper + 1;
-                    .width = 1,
+            while (y_fill < y_lower) : (y_fill += 1) {
-                    .height = 1,
+                canvas.pixel(x, @min(y_fill, y_max), .on);
-                }, .on);
             }
         }
     }