font: add bitmap font tests for BDF, PCF, and OTB formats (#10193)

Adds test coverage for bitmap font rendering in the FreeType backend
using the Spleen 8x16 font in three formats:

- BDF (Bitmap Distribution Format)
- PCF (Portable Compiled Format)
- OTB (OpenType Bitmap)

Tests validate glyph dimensions and pixel-perfect rendering against
expected patterns, following the model established by the existing
TerminusTTF test.

Spleen was chosen because it ships in all three required formats from a
single source, providing consistent test data across formats. Its BSD
2-Clause license is compatible with the existing font licenses in the
repo (OFL, MIT). No existing embedded fonts could be used since they are
all TTF/OTF files that use the TrueType loader rather than the
BDF/PCF/OTB loaders being tested.

Addresses #8524.

---

This PR was written with assistance from Claude Code.

.gitattributes

@@ -10,4 +10,5 @@ pkg/libintl/libintl.h linguist-generated=true
 pkg/simdutf/vendor/** linguist-vendored
 src/font/nerd_font_attributes.zig linguist-generated=true
 src/font/nerd_font_codepoint_tables.py linguist-generated=true
+src/font/res/** linguist-vendored
 src/terminal/res/** linguist-vendored

src/font/embedded.zig

@@ -47,3 +47,9 @@ 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");
+
+/// Spleen is a monospaced bitmap font available in multiple formats.
+/// Used for testing bitmap font support across different file formats.
+pub const spleen_bdf = @embedFile("res/spleen-8x16.bdf");
+pub const spleen_pcf = @embedFile("res/spleen-8x16.pcf");
+pub const spleen_otb = @embedFile("res/spleen-8x16.otb");

src/font/face/freetype.zig

@@ -1284,3 +1284,153 @@ test "bitmap glyph" {
         }
     }
 }
+
+// Expected pixel pattern for Spleen 8x16 'A' (glyph index from char 'A')
+// Derived from BDF BITMAP data: 00,00,7C,C6,C6,C6,FE,C6,C6,C6,C6,C6,00,00,00,00
+const spleen_A =
+    \\........
+    \\........
+    \\.#####..
+    \\##...##.
+    \\##...##.
+    \\##...##.
+    \\#######.
+    \\##...##.
+    \\##...##.
+    \\##...##.
+    \\##...##.
+    \\##...##.
+    \\........
+    \\........
+    \\........
+    \\........
+;
+// Including the newline
+const spleen_A_pitch = 9;
+// Test parameters for bitmap font tests
+const spleen_test_point_size = 12;
+const spleen_test_dpi = 96;
+
+test "bitmap glyph BDF" {
+    const alloc = testing.allocator;
+    const testFont = font.embedded.spleen_bdf;
+
+    var lib = try Library.init(alloc);
+    defer lib.deinit();
+
+    var atlas = try font.Atlas.init(alloc, 512, .grayscale);
+    defer atlas.deinit(alloc);
+
+    // Spleen 8x16 is a pure bitmap font at 16px height
+    var ft_font = try Face.init(lib, testFont, .{ .size = .{
+        .points = spleen_test_point_size,
+        .xdpi = spleen_test_dpi,
+        .ydpi = spleen_test_dpi,
+    } });
+    defer ft_font.deinit();
+
+    // Get glyph index for 'A'
+    const glyph_index = ft_font.glyphIndex('A') orelse return error.GlyphNotFound;
+
+    const glyph = try ft_font.renderGlyph(
+        alloc,
+        &atlas,
+        glyph_index,
+        .{ .grid_metrics = font.Metrics.calc(ft_font.getMetrics()) },
+    );
+
+    // Verify dimensions match Spleen 8x16
+    try testing.expectEqual(8, glyph.width);
+    try testing.expectEqual(16, glyph.height);
+
+    // Verify pixel-perfect rendering
+    for (0..glyph.height) |y| {
+        for (0..glyph.width) |x| {
+            const pixel = spleen_A[y * spleen_A_pitch + x];
+            try testing.expectEqual(
+                @as(u8, if (pixel == '#') 255 else 0),
+                atlas.data[(glyph.atlas_y + y) * atlas.size + (glyph.atlas_x + x)],
+            );
+        }
+    }
+}
+
+test "bitmap glyph PCF" {
+    const alloc = testing.allocator;
+    const testFont = font.embedded.spleen_pcf;
+
+    var lib = try Library.init(alloc);
+    defer lib.deinit();
+
+    var atlas = try font.Atlas.init(alloc, 512, .grayscale);
+    defer atlas.deinit(alloc);
+
+    var ft_font = try Face.init(lib, testFont, .{ .size = .{
+        .points = spleen_test_point_size,
+        .xdpi = spleen_test_dpi,
+        .ydpi = spleen_test_dpi,
+    } });
+    defer ft_font.deinit();
+
+    const glyph_index = ft_font.glyphIndex('A') orelse return error.GlyphNotFound;
+
+    const glyph = try ft_font.renderGlyph(
+        alloc,
+        &atlas,
+        glyph_index,
+        .{ .grid_metrics = font.Metrics.calc(ft_font.getMetrics()) },
+    );
+
+    try testing.expectEqual(8, glyph.width);
+    try testing.expectEqual(16, glyph.height);
+
+    for (0..glyph.height) |y| {
+        for (0..glyph.width) |x| {
+            const pixel = spleen_A[y * spleen_A_pitch + x];
+            try testing.expectEqual(
+                @as(u8, if (pixel == '#') 255 else 0),
+                atlas.data[(glyph.atlas_y + y) * atlas.size + (glyph.atlas_x + x)],
+            );
+        }
+    }
+}
+
+test "bitmap glyph OTB" {
+    const alloc = testing.allocator;
+    const testFont = font.embedded.spleen_otb;
+
+    var lib = try Library.init(alloc);
+    defer lib.deinit();
+
+    var atlas = try font.Atlas.init(alloc, 512, .grayscale);
+    defer atlas.deinit(alloc);
+
+    var ft_font = try Face.init(lib, testFont, .{ .size = .{
+        .points = spleen_test_point_size,
+        .xdpi = spleen_test_dpi,
+        .ydpi = spleen_test_dpi,
+    } });
+    defer ft_font.deinit();
+
+    const glyph_index = ft_font.glyphIndex('A') orelse return error.GlyphNotFound;
+
+    const glyph = try ft_font.renderGlyph(
+        alloc,
+        &atlas,
+        glyph_index,
+        .{ .grid_metrics = font.Metrics.calc(ft_font.getMetrics()) },
+    );
+
+    try testing.expectEqual(8, glyph.width);
+    try testing.expectEqual(16, glyph.height);
+
+    for (0..glyph.height) |y| {
+        for (0..glyph.width) |x| {
+            const pixel = spleen_A[y * spleen_A_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/BSD-2-Clause.txt

@@ -0,0 +1,24 @@
+Copyright (c) 2018-2024, Frederic Cambus
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+  * Redistributions of source code must retain the above copyright
+    notice, this list of conditions and the following disclaimer.
+
+  * Redistributions in binary form must reproduce the above copyright
+    notice, this list of conditions and the following disclaimer in the
+    documentation and/or other materials provided with the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS
+BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGE.

src/font/res/README.md

@@ -1,6 +1,6 @@
 # Fonts and Licenses
 
-This project uses several fonts which fall under the SIL Open Font License (OFL-1.1) and MIT License:
+This project uses several fonts which fall under the SIL Open Font License (OFL-1.1), MIT License, and BSD 2-Clause License:
 
 - Code New Roman (OFL-1.1)
   - [© 2014 Sam Radian. All Rights Reserved.](https://github.com/chrissimpkins/codeface/blob/master/fonts/code-new-roman/license.txt)
@@ -28,8 +28,12 @@ This project uses several fonts which fall under the SIL Open Font License (OFL-
 - 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/)
+- Spleen (BSD 2-Clause)
+  - [Copyright (c) 2018-2024, Frederic Cambus](https://github.com/fcambus/spleen)
 
 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/>.
 
 A full copy of the MIT license can be found at [MIT.txt](./MIT.txt).
+
+A full copy of the BSD 2-Clause license can be found at [BSD-2-Clause.txt](./BSD-2-Clause.txt).

typos.toml

@@ -19,6 +19,7 @@ extend-exclude = [
   # Fonts
   "*.ttf",
   "*.otf",
+  "*.bdf",
   # Images
   "*.png",
   "*.ico",