font/freetype: Add test for crisp bitmap font rendering

Now we can be certain that bitmap fonts stay crisp. :^)

src/font/embedded.zig

@@ -34,3 +34,6 @@ pub const cozette = @embedFile("res/CozetteVector.ttf");
 /// Monaspace has weird ligature behaviors we want to test in our shapers
 /// so we embed it here.
 pub const monaspace_neon = @embedFile("res/MonaspaceNeon-Regular.otf");
+
+/// Terminus TTF is a scalable font with bitmap glyphs at various sizes.
+pub const terminus_ttf = @embedFile("res/TerminusTTF-Regular.ttf");

src/font/face/freetype.zig

@@ -996,3 +996,55 @@ test "svg font table" {
 
     try testing.expectEqual(430, table.len);
 }
+
+const terminus_i =
+    \\........
+    \\........
+    \\...#....
+    \\...#....
+    \\........
+    \\..##....
+    \\...#....
+    \\...#....
+    \\...#....
+    \\...#....
+    \\...#....
+    \\..###...
+    \\........
+    \\........
+    \\........
+    \\........
+;
+// Including the newline
+const terminus_i_pitch = 9;
+
+test "bitmap glyph" {
+    const alloc = testing.allocator;
+    const testFont = font.embedded.terminus_ttf;
+
+    var lib = try Library.init();
+    defer lib.deinit();
+
+    var atlas = try font.Atlas.init(alloc, 512, .grayscale);
+    defer atlas.deinit(alloc);
+
+    // Any glyph at 12pt @ 96 DPI is a bitmap
+    var ft_font = try Face.init(lib, testFont, .{ .size = .{ .points = 12 } });
+    defer ft_font.deinit();
+
+    // glyph 77 = 'i'
+    const glyph = try ft_font.renderGlyph(alloc, &atlas, 77, .{});
+
+    // should render crisp
+    try testing.expectEqual(8, glyph.width);
+    try testing.expectEqual(16, glyph.height);
+    for (0..glyph.height) |y| {
+        for (0..glyph.width) |x| {
+            const pixel = terminus_i[y * terminus_i_pitch + x];
+            try testing.expectEqual(
+                @as(u8, if (pixel == '#') 255 else 0),
+                atlas.data[(glyph.atlas_y + y) * atlas.size + (glyph.atlas_x + x)],
+            );
+        }
+    }
+}

src/font/res/README.md

@@ -25,6 +25,9 @@ This project uses several fonts which fall under the SIL Open Font License (OFL-
   - [Copyright 2013 Google LLC](https://github.com/googlefonts/noto-emoji/blob/main/LICENSE)
 - Cozette (MIT)
   - [Copyright (c) 2020, Slavfox](https://github.com/slavfox/Cozette/blob/main/LICENSE)
+- Terminus TTF (OFL-1.1)
+  - [Copyright (c) 2010-2020 Dimitar Toshkov Zhekov with Reserved Font Name "Terminus Font"](https://sourceforge.net/projects/terminus-font/)
+  - [Copyright (c) 2011-2023 Tilman Blumenbach with Reserved Font Name "Terminus (TTF)"](https://files.ax86.net/terminus-ttf/)
 
 A full copy of the OFL license can be found at [OFL.txt](./OFL.txt).
 An accompanying FAQ is also available at <https://openfontlicense.org/>.