Font face handles zero-width glyphs (weird but happens)

src/Atlas.zig

@@ -48,10 +48,18 @@ modified: bool = false,
 /// updated in-place.
 resized: bool = false,
 
-pub const Format = enum(u3) {
-    greyscale = 1,
-    rgb = 3,
-    rgba = 4,
+pub const Format = enum {
+    greyscale,
+    rgb,
+    rgba,
+
+    pub fn depth(self: Format) u8 {
+        return switch (self) {
+            .greyscale => 1,
+            .rgb => 3,
+            .rgba => 4,
+        };
+    }
 };
 
 const Node = struct {
@@ -76,7 +84,7 @@ pub const Region = struct {
 
 pub fn init(alloc: Allocator, size: u32, format: Format) !Atlas {
     var result = Atlas{
-        .data = try alloc.alloc(u8, size * size * @enumToInt(format)),
+        .data = try alloc.alloc(u8, size * size * format.depth()),
         .size = size,
         .nodes = .{},
         .format = format,
@@ -220,7 +228,7 @@ pub fn set(self: *Atlas, reg: Region, data: []const u8) void {
     assert(reg.y < (self.size - 1));
     assert((reg.y + reg.height) <= (self.size - 1));
 
-    const depth = @enumToInt(self.format);
+    const depth = self.format.depth();
     var i: u32 = 0;
     while (i < reg.height) : (i += 1) {
         const tex_offset = (((reg.y + i) * self.size) + reg.x) * depth;
@@ -245,7 +253,7 @@ pub fn grow(self: *Atlas, alloc: Allocator, size_new: u32) Allocator.Error!void
     const size_old = self.size;
 
     // Allocate our new data
-    self.data = try alloc.alloc(u8, size_new * size_new * @enumToInt(self.format));
+    self.data = try alloc.alloc(u8, size_new * size_new * self.format.depth());
     defer alloc.free(data_old);
     errdefer {
         alloc.free(self.data);
@@ -270,7 +278,7 @@ pub fn grow(self: *Atlas, alloc: Allocator, size_new: u32) Allocator.Error!void
         .y = 1, // skip the first border row
         .width = size_old,
         .height = size_old - 2, // skip the last border row
-    }, data_old[size_old * @enumToInt(self.format) ..]);
+    }, data_old[size_old * self.format.depth() ..]);
 
     // We are both modified and resized
     self.modified = true;
@@ -380,7 +388,7 @@ test "writing RGB data" {
     });
 
     // 33 because of the 1px border and so on
-    const depth = @intCast(usize, @enumToInt(atlas.format));
+    const depth = @intCast(usize, atlas.format.depth());
     try testing.expectEqual(@as(u8, 1), atlas.data[33 * depth]);
     try testing.expectEqual(@as(u8, 2), atlas.data[33 * depth + 1]);
     try testing.expectEqual(@as(u8, 3), atlas.data[33 * depth + 2]);
@@ -410,7 +418,7 @@ test "grow RGB" {
 
     // Our top left skips the first row (size * depth) and the first
     // column (depth) for the 1px border.
-    const depth = @intCast(usize, @enumToInt(atlas.format));
+    const depth = @intCast(usize, atlas.format.depth());
     var tl = (atlas.size * depth) + depth;
     try testing.expectEqual(@as(u8, 10), atlas.data[tl]);
     try testing.expectEqual(@as(u8, 11), atlas.data[tl + 1]);

src/font/Face.zig

@@ -15,6 +15,7 @@ const Allocator = std.mem.Allocator;
 const Atlas = @import("../Atlas.zig");
 const Glyph = @import("main.zig").Glyph;
 const Library = @import("main.zig").Library;
+const convert = @import("convert.zig");
 
 const log = std.log.scoped(.font_face);
 
@@ -120,30 +121,60 @@ pub fn renderGlyph(self: Face, alloc: Allocator, atlas: *Atlas, glyph_index: u32
     });
 
     const glyph = self.face.handle.*.glyph;
-    const bitmap = glyph.*.bitmap;
+    const bitmap_ft = glyph.*.bitmap;
+
+    // This bitmap is blank. I've seen it happen in a font, I don't know why.
+    // If it is empty, we just return a valid glyph struct that does nothing.
+    if (bitmap_ft.rows == 0) return Glyph{
+        .width = 0,
+        .height = 0,
+        .offset_x = 0,
+        .offset_y = 0,
+        .atlas_x = 0,
+        .atlas_y = 0,
+        .advance_x = 0,
+    };
 
     // Ensure we know how to work with the font format. And assure that
-    // or color depth is as expected on the texture atlas.
-    const format: Atlas.Format = switch (bitmap.pixel_mode) {
+    // or color depth is as expected on the texture atlas. If format is null
+    // it means there is no native color format for our Atlas and we must try
+    // conversion.
+    const format: ?Atlas.Format = switch (bitmap_ft.pixel_mode) {
         freetype.c.FT_PIXEL_MODE_GRAY => .greyscale,
         freetype.c.FT_PIXEL_MODE_BGRA => .rgba,
         else => {
-            log.warn("pixel mode={}", .{bitmap.pixel_mode});
+            log.warn("glyph={} pixel mode={}", .{ glyph_index, bitmap_ft.pixel_mode });
             @panic("unsupported pixel mode");
         },
     };
-    assert(atlas.format == format);
 
-    const src_w = bitmap.width;
-    const src_h = bitmap.rows;
-    const tgt_w = src_w;
-    const tgt_h = src_h;
+    // If our atlas format doesn't match, look for conversions if possible.
+    const bitmap_converted = if (format == null or atlas.format != format.?) blk: {
+        const func = convert.map[bitmap_ft.pixel_mode].get(atlas.format) orelse {
+            log.warn("glyph={} pixel mode={}", .{ glyph_index, bitmap_ft.pixel_mode });
+            return error.UnsupportedPixelMode;
+        };
+
+        log.warn("converting from pixel_mode={} to atlas_format={}", .{
+            bitmap_ft.pixel_mode,
+            atlas.format,
+        });
+        break :blk try func(alloc, bitmap_ft);
+    } else null;
+    defer if (bitmap_converted) |bm| {
+        const len = bm.width * bm.rows * atlas.format.depth();
+        alloc.free(bm.buffer[0..len]);
+    };
+
+    const bitmap = bitmap_converted orelse bitmap_ft;
+    const tgt_w = bitmap.width;
+    const tgt_h = bitmap.rows;
 
     const region = try atlas.reserve(alloc, tgt_w, tgt_h);
 
     // If we have data, copy it into the atlas
     if (region.width > 0 and region.height > 0) {
-        const depth = @enumToInt(format);
+        const depth = atlas.format.depth();
 
         // We can avoid a buffer copy if our atlas width and bitmap
         // width match and the bitmap pitch is just the width (meaning
@@ -156,7 +187,7 @@ pub fn renderGlyph(self: Face, alloc: Allocator, atlas: *Atlas, glyph_index: u32
             var dst_ptr = temp;
             var src_ptr = bitmap.buffer;
             var i: usize = 0;
-            while (i < src_h) : (i += 1) {
+            while (i < bitmap.rows) : (i += 1) {
                 std.mem.copy(u8, dst_ptr, src_ptr[0 .. bitmap.width * depth]);
                 dst_ptr = dst_ptr[tgt_w * depth ..];
                 src_ptr += @intCast(usize, bitmap.pitch);
@@ -232,3 +263,20 @@ test "color emoji" {
 
     _ = try font.renderGlyph(alloc, &atlas, font.glyphIndex('🥸').?);
 }
+
+test "mono to rgba" {
+    const alloc = testing.allocator;
+    const testFont = @import("test.zig").fontEmoji;
+
+    var lib = try Library.init();
+    defer lib.deinit();
+
+    var atlas = try Atlas.init(alloc, 512, .rgba);
+    defer atlas.deinit(alloc);
+
+    var font = try init(lib, testFont, .{ .points = 12 });
+    defer font.deinit();
+
+    // glyph 3 is mono in Noto
+    _ = try font.renderGlyph(alloc, &atlas, 3);
+}

src/font/main.zig

@@ -27,4 +27,5 @@ pub const Metrics = struct {
 
 test {
     @import("std").testing.refAllDecls(@This());
+    _ = @import("convert.zig");
 }