font: draw single and double underlines as sprites

src/Window.zig

@@ -289,13 +289,6 @@ pub fn create(alloc: Allocator, app: *App, config: *const Config) !*Window {
     // Pre-calculate our initial cell size ourselves.
     const cell_size = try renderer.CellSize.init(alloc, font_group);
 
-    // Setup our box font
-    font_group.group.sprite = font.sprite.Face{
-        .width = @floatToInt(u32, cell_size.width),
-        .height = @floatToInt(u32, cell_size.height),
-        .thickness = 2,
-    };
-
     // Convert our padding from points to pixels
     const padding_x = (@intToFloat(f32, config.@"window-padding-x") * x_dpi) / 72;
     const padding_y = (@intToFloat(f32, config.@"window-padding-y") * y_dpi) / 72;

src/font/main.zig

@@ -11,6 +11,7 @@ pub const Glyph = @import("Glyph.zig");
 pub const Library = @import("Library.zig");
 pub const Shaper = @import("Shaper.zig");
 pub const sprite = @import("sprite.zig");
+pub const Sprite = sprite.Sprite;
 pub const Descriptor = discovery.Descriptor;
 pub const Discover = discovery.Discover;
 
@@ -60,6 +61,9 @@ pub const Presentation = enum(u1) {
     emoji = 1, // U+FEOF
 };
 
+/// A FontIndex that can be used to use the sprite font directly.
+pub const sprite_index = Group.FontIndex.initSpecial(.sprite);
+
 test {
     @import("std").testing.refAllDecls(@This());
 }

src/font/sprite.zig

@@ -11,10 +11,11 @@ pub const Face = @import("sprite/Face.zig");
 /// Area of Unicode.
 pub const Sprite = enum(u32) {
     // Start 1 above the maximum Unicode codepoint.
-    const start: u32 = std.math.maxInt(u21) + 1;
-    const end: u32 = std.math.maxInt(u32);
+    pub const start: u32 = std.math.maxInt(u21) + 1;
+    pub const end: u32 = std.math.maxInt(u32);
 
     underline = start,
+    underline_double = start + 1,
 
     // Note: we don't currently put the box drawing glyphs in here because
     // there are a LOT and I'm lazy. What I want to do is spend more time

src/font/sprite/Canvas.zig

@@ -117,13 +117,13 @@ pub fn writeAtlas(self: *Canvas, alloc: Allocator, atlas: *Atlas) !Atlas.Region
 
 /// 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: pixman.Color) void {
+pub fn rect(self: *Canvas, v: Rect, color: Color) void {
     const boxes = &[_]pixman.Box32{
         .{
             .x1 = @intCast(i32, v.x),
             .y1 = @intCast(i32, v.y),
-            .x2 = @intCast(i32, v.width),
-            .y2 = @intCast(i32, v.height),
+            .x2 = @intCast(i32, v.x + v.width),
+            .y2 = @intCast(i32, v.y + v.height),
         },
     };
 

src/font/sprite/Face.zig

@@ -17,8 +17,10 @@ const builtin = @import("builtin");
 const assert = std.debug.assert;
 const Allocator = std.mem.Allocator;
 const font = @import("../main.zig");
+const Sprite = font.sprite.Sprite;
 const Atlas = @import("../../Atlas.zig");
 const Box = @import("Box.zig");
+const underline = @import("underline.zig");
 
 /// The cell width and height.
 width: u32,
@@ -28,6 +30,9 @@ height: u32,
 /// want to do any DPI scaling, it is expected to be done earlier.
 thickness: u32,
 
+/// The position fo the underline.
+underline_position: u32 = 0,
+
 /// Returns true if the codepoint exists in our sprite font.
 pub fn hasCodepoint(self: Face, cp: u32, p: ?font.Presentation) bool {
     // We ignore presentation. No matter what presentation is requested
@@ -47,25 +52,42 @@ pub fn renderGlyph(
     if (std.debug.runtime_safety) assert(self.hasCodepoint(cp, null));
 
     // Safe to ".?" because of the above assertion.
-    switch (Kind.init(cp).?) {
-        .box => {
+    return switch (Kind.init(cp).?) {
+        .box => box: {
             const f: Box = .{
                 .width = self.width,
                 .height = self.height,
                 .thickness = self.thickness,
             };
 
-            return try f.renderGlyph(alloc, atlas, cp);
+            break :box try f.renderGlyph(alloc, atlas, cp);
         },
-    }
+
+        .underline => try underline.renderGlyph(
+            alloc,
+            atlas,
+            @intToEnum(Sprite, cp),
+            self.width,
+            self.height,
+            self.underline_position,
+            self.thickness,
+        ),
+    };
 }
 
 /// Kind of sprites we have. Drawing is implemented separately for each kind.
 const Kind = enum {
     box,
+    underline,
 
     pub fn init(cp: u32) ?Kind {
         return switch (cp) {
+            Sprite.start...Sprite.end => switch (@intToEnum(Sprite, cp)) {
+                .underline,
+                .underline_double,
+                => .underline,
+            },
+
             // Box fonts
             0x2500...0x257F, // "Box Drawing" block
             0x2580...0x259F, // "Block Elements" block

src/font/sprite/underline.zig

@@ -0,0 +1,119 @@
+//! This file renders underline sprites. To draw underlines, we render the
+//! full cell-width as a sprite and then draw it as a separate pass to the
+//! text.
+//!
+//! We used to render the underlines directly in the GPU shaders but its
+//! annoying to support multiple types of underlines and its also annoying
+//! to maintain and debug another set of shaders for each renderer instead of
+//! just relying on the glyph system we already need to support for text
+//! anyways.
+const std = @import("std");
+const builtin = @import("builtin");
+const assert = std.debug.assert;
+const Allocator = std.mem.Allocator;
+const font = @import("../main.zig");
+const Sprite = font.sprite.Sprite;
+const Atlas = @import("../../Atlas.zig");
+
+/// Draw an underline.
+pub fn renderGlyph(
+    alloc: Allocator,
+    atlas: *Atlas,
+    sprite: Sprite,
+    width: u32,
+    height: u32,
+    line_pos: u32,
+    line_thickness: u32,
+) !font.Glyph {
+    // Create the canvas we'll use to draw. We draw the underline in
+    // a full cell size and position it according to "pos".
+    var canvas = try font.sprite.Canvas.init(alloc, width, height);
+    defer canvas.deinit(alloc);
+
+    // Perform the actual drawing
+    (Draw{
+        .width = width,
+        .height = height,
+        .pos = line_pos,
+        .thickness = line_thickness,
+    }).draw(&canvas, sprite);
+
+    // Write the drawing to the atlas
+    const region = try canvas.writeAtlas(alloc, atlas);
+
+    // Our coordinates start at the BOTTOM for our renderers so we have to
+    // specify an offset of the full height because we rendered a full size
+    // cell.
+    const offset_y = @intCast(i32, height);
+
+    return font.Glyph{
+        .width = width,
+        .height = height,
+        .offset_x = 0,
+        .offset_y = offset_y,
+        .atlas_x = region.x,
+        .atlas_y = region.y,
+        .advance_x = @intToFloat(f32, width),
+    };
+}
+
+/// Stores drawing state.
+const Draw = struct {
+    width: u32,
+    height: u32,
+    pos: u32,
+    thickness: u32,
+
+    /// Draw a specific underline sprite to the canvas.
+    fn draw(self: Draw, canvas: *font.sprite.Canvas, sprite: Sprite) void {
+        switch (sprite) {
+            .underline => self.drawSingle(canvas),
+            .underline_double => self.drawDouble(canvas),
+        }
+    }
+
+    /// Draw a single underline.
+    fn drawSingle(self: Draw, canvas: *font.sprite.Canvas) void {
+        canvas.rect(.{
+            .x = 0,
+            .y = self.pos,
+            .width = self.width,
+            .height = self.thickness,
+        }, .on);
+    }
+
+    /// Draw a double underline.
+    fn drawDouble(self: Draw, canvas: *font.sprite.Canvas) void {
+        canvas.rect(.{
+            .x = 0,
+            .y = self.pos,
+            .width = self.width,
+            .height = self.thickness,
+        }, .on);
+
+        canvas.rect(.{
+            .x = 0,
+            .y = self.pos + (self.thickness * 2),
+            .width = self.width,
+            .height = self.thickness,
+        }, .on);
+    }
+};
+
+test "single" {
+    const testing = std.testing;
+    const alloc = testing.allocator;
+
+    var atlas_greyscale = try Atlas.init(alloc, 512, .greyscale);
+    defer atlas_greyscale.deinit(alloc);
+
+    _ = try renderGlyph(
+        alloc,
+        &atlas_greyscale,
+        .underline,
+        36,
+        18,
+        9,
+        2,
+    );
+}