remove fonts from graphics state

src/app.zig

@@ -97,7 +97,7 @@ const Entity = struct {
     const Id = SlotMap.Id;
 };
 
-roboto_font: Gfx.Font.Id,
+roboto_font: Gfx.Font,
 tilemap: Tilemap,
 entities: Entity.SlotMap,
 
@@ -161,8 +161,10 @@ const Tilesheet = struct {
 };
 
 pub fn init(self: *App, plt: Platform.Init) !?u8 {
-    const robot_font = Gfx.initFont();
-    Gfx.setFont(robot_font, plt.assets.readFile("roboto-font/Roboto-Regular.ttf"));
+    const roboto_font = try Gfx.Font.init(plt.gpa, .{
+        .spritesheet = Gfx.initSpritesheet(.{ .format = .r8 }),
+        .ttf_data = plt.assets.readFile("roboto-font/Roboto-Regular.ttf")
+    });
 
     const tilesheet_png = try STBImage.load(plt.assets.readFile("sokoban/sokoban_tilesheet.png"));
     const tilesheet = try Tilesheet.init(
@@ -206,7 +208,7 @@ pub fn init(self: *App, plt: Platform.Init) !?u8 {
 
     self.* = App{
         .player_sprites = player_sprites,
-        .roboto_font = robot_font,
+        .roboto_font = roboto_font,
         .animation_timer = 0,
         .tilesheet = tilesheet,
         .footstep_buffer = footstep_sound,
@@ -394,9 +396,17 @@ pub fn frame(self: *App, plt: Platform.Frame) !void {
         }
     }
 
+    // self.roboto_font.drawText(.{
+    //     .text = try std.fmt.allocPrint(plt.frame, "Hello {:.0}!", .{plt.time()}),
+    //     .pos = .init(0, 0),
+    //     .height = 32,
+    // });
 }
 
 pub fn deinit(self: *App, plt: Platform.Deinit) void {
+    self.roboto_font.deinit(plt.gpa);
+    Gfx.deinitSpritesheet(self.roboto_font.spritesheet);
+
     self.tilemap.deinit(plt.gpa);
     self.entities.slots.deinit(plt.gpa);
 }

src/platform/font.zig

@@ -0,0 +1,739 @@
+const std = @import("std");
+const log = std.log.scoped(.font);
+const assert = std.debug.assert;
+const Allocator = std.mem.Allocator;
+const Io = std.Io;
+
+const Math = @import("math");
+const Vec2 = Math.Vec2;
+const Rect = Math.Rect;
+
+const Gfx = @import("./graphics.zig");
+const SlotMapType = @import("slot_map.zig").SlotMapType;
+const STBTrueType = @import("stb_truetype");
+
+const Font = @This();
+
+spritesheet: Gfx.Spritesheet.Id,
+stb: STBTrueType.Font,
+
+cache: GlyphCache,
+
+const Options = struct {
+    spritesheet: Gfx.Spritesheet.Id,
+    ttf_data: [:0]const u8,
+    glyph_slots: u32 = 256
+};
+
+pub fn init(gpa: Allocator, opts: Options) !Font {
+    const offset = STBTrueType.Font.getFontOffsetForIndex(opts.ttf_data, 0)
+        orelse return error.MissingFont0;
+
+    const stb_font = try STBTrueType.Font.init(opts.ttf_data, offset);
+
+    var cache = try GlyphCache.init(gpa, opts.glyph_slots);
+    errdefer cache.deinit(gpa);
+
+    return Font{
+        .spritesheet = opts.spritesheet,
+        .stb = stb_font,
+        .cache = cache,
+    };
+}
+
+pub fn deinit(self: *Font, gpa: Allocator) void {
+    self.cache.deinit(gpa);
+}
+
+pub fn getGlyphIndex(font: *Font, codepoint: u21) ?Glyph.Index {
+    if (font.stb.findGlyphIndex(codepoint)) |index| {
+        return index;
+    } else {
+        // Fallback
+        return font.getGlyphIndex('?');
+    }
+}
+
+pub fn getGlyph(font: *Font, index: Glyph.Index, scale_x: f32, scale_y: f32) ?*Font.Glyph {
+    const glyph_key = Font.Glyph.Key{
+        .index = index,
+        .scale_x = .fromF32(scale_x),
+        .scale_y = .fromF32(scale_y)
+    };
+
+    var iog_result = font.cache.insertOrGet(glyph_key);
+    if (iog_result == null and font.cache.lru_tail != GlyphSlot.nil_id) {
+        const id = font.cache.lru_tail;
+        if (font.cache.get(id).last_used_frame != Gfx.getFrameIndex()) {
+            font.cache.remove(id);
+            iog_result = font.cache.insertOrGet(glyph_key);
+            log.debug("Evicted least recently used glyph", .{});
+        }
+    }
+
+    if (iog_result) |result| {
+        const glyph_id = result.id;
+        const glyph = font.cache.get(glyph_id);
+
+        if (!result.found_existing) {
+            glyph.box = font.stb.getGlyphBitmapBox(
+                glyph_key.index,
+                glyph_key.scale_x.toF32(),
+                glyph_key.scale_y.toF32()
+            );
+
+            const box_width: u32 = @intCast(glyph.box.x1 - glyph.box.x0);
+            const box_height: u32 = @intCast(glyph.box.y1 - glyph.box.y0);
+            if (box_width > 0 and box_height > 0) {
+                const sprite = Gfx.initSprite(.{ .spritesheet = font.spritesheet, .padding = 1 });
+
+                assert(box_width < Font.Glyph.max_width);
+                assert(box_height < Font.Glyph.max_height);
+
+                var bitmap_buffer: [Font.Glyph.max_width * Font.Glyph.max_height]u8 = undefined;
+                const bitmap = Gfx.ImageData{
+                    .pixels = .{ .r8 = (&bitmap_buffer).ptr },
+                    .width = box_width,
+                    .height = box_height
+                };
+                font.stb.makeGlyphBitmap(
+                    bitmap.pixels.?.r8,
+                    box_width, box_height,
+                    box_width,
+                    glyph_key.scale_x.toF32(),
+                    glyph_key.scale_y.toF32(),
+                    glyph_key.index
+                );
+                Gfx.setSprite(sprite, .{ .image = bitmap });
+
+                glyph.sprite = sprite;
+            }
+        }
+
+        glyph.last_used_frame = Gfx.getFrameIndex();
+        return glyph;
+    } else {
+        log.warn("Failed to render glyph, because cache is full", .{});
+        return null;
+    }
+}
+
+pub fn getAscent(font: *Font, height: f32) f32 {
+    const vmetrics = font.stb.getFontVMetrics();
+    const scale = font.stb.scaleForPixelHeight(height);
+    return @as(f32, @floatFromInt(vmetrics.ascent)) * scale;
+}
+
+pub fn measureText(font: *Font, height: f32, text: []const u8) Rect {
+    var bounds: Rect = .init(0, 0, 0, 0);
+    var first_glyph = false;
+
+    var layout = TextRunLayout.init(font, height);
+    var iter = std.unicode.Utf8Iterator{
+        .bytes = text,
+        .i = 0
+    };
+    while (iter.nextCodepoint()) |codepoint| {
+        const glyph_index = font.getGlyphIndex(codepoint) orelse continue;
+        const glyph_layout = layout.next(glyph_index) orelse continue;
+
+        if (first_glyph) {
+            bounds = glyph_layout.rect;
+            first_glyph = false;
+        } else {
+            bounds = bounds.expand(glyph_layout.rect);
+        }
+    }
+
+    return bounds;
+}
+
+pub const DrawTextOptions = struct {
+    text: []const u8,
+    pos: Vec2,
+    height: f32,
+    color: Gfx.Color = .white,
+    alignment: Vec2 = .init(0, 0)
+};
+
+pub fn drawText(font: *Font, opts: DrawTextOptions) void {
+    var layout = Font.TextRunLayout.init(font, opts.height);
+
+    var pos = opts.pos; 
+    pos.y += font.getAscent(opts.height);
+
+    if (!opts.alignment.eql(.zero)) {
+        const bounds = font.measureText(opts.height, opts.text);
+        pos = pos.sub(bounds.size.multiply(opts.alignment));
+    }
+
+    var iter = std.unicode.Utf8Iterator{
+        .bytes = opts.text,
+        .i = 0
+    };
+    while (iter.nextCodepoint()) |codepoint| {
+        const glyph_index = font.getGlyphIndex(codepoint) orelse continue;
+        const glyph_layout = layout.next(glyph_index) orelse continue;
+        if (glyph_layout.sprite == Gfx.Sprite.Id.nil) {
+            continue;
+        }
+
+        var glyph_pos = glyph_layout.rect.pos.add(pos);
+
+        // Round to nearest pixel to avoid artifacts
+        glyph_pos.x = @round(glyph_pos.x);
+        glyph_pos.y = @round(glyph_pos.y);
+
+        Gfx.drawSprite(
+            glyph_layout.sprite,
+            glyph_pos,
+            glyph_layout.rect.size,
+            opts.color
+        );
+    }
+}
+
+const GlyphCache = struct {
+    glyphs: []GlyphSlot,
+    glyphs_hashmap: []GlyphSlot.Id,
+    glyphs_used: std.bit_set.DynamicBitSetUnmanaged,
+    lru_head: GlyphSlot.Id,
+    lru_tail: GlyphSlot.Id,
+    free_head: GlyphSlot.Id,
+
+    fn init(gpa: Allocator, capacity: u32) !GlyphCache {
+        assert(capacity > 0);
+
+        const glyphs = try gpa.alloc(GlyphSlot, capacity);
+        errdefer gpa.free(glyphs);
+
+        const glyphs_hashmap = try gpa.alloc(GlyphSlot.Id, 2*capacity);
+        errdefer gpa.free(glyphs);
+
+        var glyphs_used = try std.bit_set.DynamicBitSetUnmanaged.initEmpty(gpa, capacity);
+        errdefer glyphs_used.deinit(gpa);
+
+        var self: GlyphCache = .{
+            .glyphs = glyphs,
+            .glyphs_hashmap = glyphs_hashmap,
+            .glyphs_used = glyphs_used,
+            .lru_head = GlyphSlot.nil_id,
+            .lru_tail = GlyphSlot.nil_id,
+            .free_head = undefined
+        };
+        @memset(self.glyphs_hashmap, GlyphSlot.nil_id);
+        @memset(self.glyphs, .{
+            .glyph = undefined,
+            .lru_prev = GlyphSlot.nil_id,
+            .lru_next = GlyphSlot.nil_id,
+            .next_free = GlyphSlot.nil_id,
+        });
+
+        assert(self.glyphs_hashmap.len > self.glyphs.len);
+
+        self.free_head = 1;
+        for (1.., self.glyphs[1..(self.glyphs.len-1)]) |i, *glyph| {
+            glyph.next_free = @intCast(i + 1);
+        }
+
+        return self;
+    }
+
+    fn deinit(self: *GlyphCache, gpa: Allocator) void {
+        for (self.glyphs_hashmap) |glyph_id| {
+            if (glyph_id == GlyphSlot.nil_id) {
+                continue;
+            }
+            const slot = self.glyphs[glyph_id];
+            slot.glyph.deinit();
+        }
+
+        gpa.free(self.glyphs);
+        gpa.free(self.glyphs_hashmap);
+        self.glyphs_used.deinit(gpa);
+
+        self.* = undefined;
+    }
+
+    fn get(self: *GlyphCache, id: GlyphSlot.Id) *Glyph {
+        return &self.glyphs[id].glyph;
+    }
+
+    fn appendToLRUHead(self: *GlyphCache, id: GlyphSlot.Id) void {
+        if (self.lru_head != GlyphSlot.nil_id) {
+            self.glyphs[self.lru_head].lru_prev = id;
+            self.glyphs[id].lru_next = self.lru_head;
+        } else {
+            assert(self.lru_tail == GlyphSlot.nil_id);
+            self.lru_tail = id;
+        }
+
+        self.glyphs[id].lru_prev = GlyphSlot.nil_id;
+        self.lru_head = id;
+    }
+
+    fn removeFromLRU(self: *GlyphCache, id: GlyphSlot.Id) void {
+        assert(id != GlyphSlot.nil_id);
+
+        const lru_prev = self.glyphs[id].lru_prev;
+        const lru_next = self.glyphs[id].lru_next;
+
+        if (lru_prev != GlyphSlot.nil_id) {
+            self.glyphs[lru_prev].lru_next = lru_next;
+        }
+
+        if (lru_next != GlyphSlot.nil_id) {
+            self.glyphs[lru_next].lru_prev = lru_prev;
+        }
+
+        if (id == self.lru_head) {
+            self.lru_head = lru_next;
+        }
+        if (id == self.lru_tail) {
+            self.lru_tail = lru_prev;
+        }
+    }
+
+    fn popFreeId(self: *GlyphCache) ?GlyphSlot.Id {
+        if (self.free_head != GlyphSlot.nil_id) {
+            const result = self.free_head;
+            self.free_head = self.glyphs[result].next_free;
+            return result;
+        }
+
+        return null;
+    }
+
+    fn pushFreeId(self: *GlyphCache, id: GlyphSlot.Id) void {
+        assert(id != GlyphSlot.nil_id);
+        self.glyphs[id].next_free = self.free_head;
+        self.free_head = id;
+    }
+
+    pub const InsertOrGetResult = struct {
+        id: GlyphSlot.Id,
+        found_existing: bool,
+    };
+
+    fn insertOrGet(self: *GlyphCache, key: Glyph.Key) ?InsertOrGetResult {
+        for (0..self.glyphs_hashmap.len) |offset| {
+            const i = (key.toInt() + offset) % self.glyphs_hashmap.len;
+            const hashmap_id = self.glyphs_hashmap[i];
+            if (hashmap_id == GlyphSlot.nil_id) {
+                const id = self.popFreeId() orelse return null;
+                self.glyphs_hashmap[i] = id;
+
+                self.glyphs[id].glyph = .init(key);
+                self.glyphs[id].lru_next = GlyphSlot.nil_id;
+                self.glyphs[id].lru_prev = GlyphSlot.nil_id;
+                self.appendToLRUHead(id);
+                return InsertOrGetResult{
+                    .id = id,
+                    .found_existing = false
+                };
+            } else {
+                const glyph = &self.glyphs[hashmap_id].glyph;
+                if (glyph.key == key) {
+                    // An entry for this key already exists
+                    self.removeFromLRU(hashmap_id);
+                    self.appendToLRUHead(hashmap_id);
+                    return InsertOrGetResult{
+                        .id = hashmap_id,
+                        .found_existing = true
+                    };
+                }
+            }
+        }
+
+        return null;
+    }
+
+    fn removeFromHashmap(self: *GlyphCache, id: GlyphSlot.Id) void {
+        var bucket = self.glyphs[id].glyph.key.toInt() % self.glyphs_hashmap.len;
+        for (0..self.glyphs_hashmap.len) |_| {
+            assert(self.glyphs_hashmap[bucket] != GlyphSlot.nil_id);
+            if (self.glyphs_hashmap[bucket] == id) {
+                break;
+            }
+
+            bucket = (bucket + 1) % self.glyphs_hashmap.len;
+        }
+
+        assert(self.glyphs_hashmap[bucket] == id);
+
+        var empty = bucket;
+        var current = (bucket + 1) % self.glyphs_hashmap.len;
+
+        while (self.glyphs_hashmap[current] != GlyphSlot.nil_id) {
+            const current_glyph_id = self.glyphs_hashmap[current];
+            const home = self.glyphs[current_glyph_id].glyph.key.toInt() % self.glyphs_hashmap.len;
+
+            if (self.hashmapDistance(home, current) > self.hashmapDistance(home, empty)) {
+                self.glyphs_hashmap[empty] = self.glyphs_hashmap[current];
+                empty = current;
+            }
+
+            current = (current + 1) % self.glyphs_hashmap.len;
+        }
+
+        assert(self.glyphs_hashmap[empty] != GlyphSlot.nil_id);
+        self.glyphs_hashmap[empty] = GlyphSlot.nil_id;
+    }
+
+    fn hashmapDistance(self: GlyphCache, from: usize, to: usize) usize {
+        if (to >= from) {
+            return to - from;
+        } else {
+            return self.glyphs_hashmap.len - from + to;
+        }
+    }
+
+    fn remove(self: *GlyphCache, id: GlyphSlot.Id) void {
+        assert(id != GlyphSlot.nil_id);
+        self.pushFreeId(id);
+        self.removeFromHashmap(id);
+        self.removeFromLRU(id);
+
+        const glyph = self.glyphs[id].glyph;
+        glyph.deinit();
+    }
+
+    fn getLRUItems(self: *GlyphCache, gpa: Allocator) ![]GlyphSlot.Id {
+        var lru: std.ArrayList(GlyphSlot.Id) = .empty;
+        defer lru.deinit(gpa);
+
+        var lru_iter = self.lru_head;
+        while (lru_iter != GlyphSlot.nil_id) {
+            try lru.append(gpa, lru_iter);
+            lru_iter = self.glyphs[lru_iter].lru_next;
+        }
+
+        return try lru.toOwnedSlice(gpa);
+    }
+
+    test {
+        const gpa = std.testing.allocator;
+        var cache = try GlyphCache.init(gpa, 256);
+        defer cache.deinit(gpa);
+
+        const key = Glyph.Key{ .index = 10, .scale_x = .fromF32(1), .scale_y = .fromF32(1) };
+        const id1 = cache.insert(key).?;
+        const id2 = cache.insert(key).?;
+        try std.testing.expectEqual(id1, id2);
+    }
+
+    test {
+        const gpa = std.testing.allocator;
+        var cache = try GlyphCache.init(gpa, 256);
+        defer cache.deinit(gpa);
+
+        const key = Glyph.Key{ .index = 10, .scale_x = .fromF32(1), .scale_y = .fromF32(1) };
+        const id1 = cache.insert(key).?;
+        cache.remove(id1);
+        const id2 = cache.insert(key).?;
+        try std.testing.expectEqual(id1, id2);
+    }
+
+    test {
+        const gpa = std.testing.allocator;
+        var cache = try GlyphCache.init(gpa, 256);
+        defer cache.deinit(gpa);
+
+        const id1 = cache.insert(Glyph.Key{ .index = 10, .scale_x = .fromF32(1), .scale_y = .fromF32(1) }).?;
+        const id2 = cache.insert(Glyph.Key{ .index = 11, .scale_x = .fromF32(1), .scale_y = .fromF32(1) }).?;
+        try std.testing.expect(id1 != id2);
+    }
+
+    test {
+        const gpa = std.testing.allocator;
+        const limit = 256;
+        var cache = try GlyphCache.init(gpa, limit);
+        defer cache.deinit(gpa);
+
+        for (0..limit-1) |i| {
+            const id = cache.insert(Glyph.Key{ .index = @intCast(i), .scale_x = .fromF32(1), .scale_y = .fromF32(1) });
+            try std.testing.expect(id != null);
+        }
+        const id = cache.insert(Glyph.Key{ .index = limit, .scale_x = .fromF32(1), .scale_y = .fromF32(1) });
+        try std.testing.expect(id == null);
+    }
+
+    test {
+        const gpa = std.testing.allocator;
+        const limit = 256;
+        var cache = try GlyphCache.init(gpa, limit);
+        defer cache.deinit(gpa);
+
+        for (0..10) |_| {
+            var ids: std.ArrayList(GlyphSlot.Id) = .empty;
+            defer ids.deinit(gpa);
+
+            for (0..(limit-1)) |i| {
+                const id = cache.insert(Glyph.Key{ .index = @intCast(i), .scale_x = .fromF32(1), .scale_y = .fromF32(1) });
+                try std.testing.expect(id != null);
+                try ids.append(gpa, id.?);
+            }
+            assert(cache.free_head == GlyphSlot.nil_id);
+
+            const lru = try cache.getLRUItems(gpa);
+            defer gpa.free(lru);
+
+            const expected_lru = try gpa.dupe(GlyphSlot.Id, ids.items);
+            defer gpa.free(expected_lru);
+            std.mem.reverse(GlyphSlot.Id, expected_lru);
+
+            try std.testing.expectEqualSlices(GlyphSlot.Id, expected_lru, lru);
+
+            for (ids.items) |id| {
+                cache.remove(id);
+            }
+            assert(cache.lru_head == GlyphSlot.nil_id);
+            assert(cache.lru_tail == GlyphSlot.nil_id);
+        }
+    }
+
+    test {
+        const gpa = std.testing.allocator;
+        var cache = try GlyphCache.init(gpa, 256);
+        defer cache.deinit(gpa);
+
+        const id1 = cache.insert(.{ .index = 0, .scale_x = .fromF32(1), .scale_y = .fromF32(1) }).?;
+        const id2 = cache.insert(.{ .index = 1, .scale_x = .fromF32(1), .scale_y = .fromF32(1) }).?;
+        const id3 = cache.insert(.{ .index = 2, .scale_x = .fromF32(1), .scale_y = .fromF32(1) }).?;
+
+        const lru = try cache.getLRUItems(gpa);
+        defer gpa.free(lru);
+
+        try std.testing.expectEqualSlices(GlyphSlot.Id, &.{ id3, id2, id1 }, lru);
+    }
+
+    test {
+        const gpa = std.testing.allocator;
+        var cache = try GlyphCache.init(gpa, 256);
+        defer cache.deinit(gpa);
+
+        const id1 = cache.insert(.{ .index = 0, .scale_x = .fromF32(1), .scale_y = .fromF32(1) }).?;
+        const id2 = cache.insert(.{ .index = 1, .scale_x = .fromF32(1), .scale_y = .fromF32(1) }).?;
+        const id3 = cache.insert(.{ .index = 2, .scale_x = .fromF32(1), .scale_y = .fromF32(1) }).?;
+
+        const lru = try cache.getLRUItems(gpa);
+        defer gpa.free(lru);
+
+        try std.testing.expectEqualSlices(GlyphSlot.Id, &.{ id3, id2, id1 }, lru);
+    }
+
+    test {
+        const gpa = std.testing.allocator;
+        var cache = try GlyphCache.init(gpa, 256);
+        defer cache.deinit(gpa);
+
+        const id = cache.insert(.{ .index = 0, .scale_x = .fromF32(1), .scale_y = .fromF32(1) }).?;
+        try std.testing.expect(cache.lru_head != GlyphSlot.nil_id);
+        try std.testing.expect(cache.lru_tail != GlyphSlot.nil_id);
+        cache.remove(id);
+        try std.testing.expect(cache.lru_head == GlyphSlot.nil_id);
+        try std.testing.expect(cache.lru_tail == GlyphSlot.nil_id);
+    }
+
+    test {
+        const gpa = std.testing.allocator;
+        var cache = try GlyphCache.init(gpa, 256);
+        defer cache.deinit(gpa);
+
+        const key1 = Glyph.Key{ .index = 0, .scale_x = .fromF32(1), .scale_y = .fromF32(1) };
+        const id1 = cache.insert(key1).?;
+        const key2 = Glyph.Key{ .index = 1, .scale_x = .fromF32(1), .scale_y = .fromF32(1) };
+        const id2 = cache.insert(key2).?;
+        const key3 = Glyph.Key{ .index = 2, .scale_x = .fromF32(1), .scale_y = .fromF32(1) };
+        const id3 = cache.insert(key3).?;
+
+        _ = cache.lookup(key2);
+
+        {
+            const lru = try cache.getLRUItems(gpa);
+            defer gpa.free(lru);
+            try std.testing.expectEqualSlices(GlyphSlot.Id, &.{ id2, id3, id1 }, lru);
+        }
+
+        _ = cache.lookup(key1);
+
+        {
+            const lru = try cache.getLRUItems(gpa);
+            defer gpa.free(lru);
+            try std.testing.expectEqualSlices(GlyphSlot.Id, &.{ id1, id2, id3 }, lru);
+        }
+    }
+
+    test {
+        const gpa = std.testing.allocator;
+        var cache = try GlyphCache.init(gpa, 256);
+        defer cache.deinit(gpa);
+
+        const id1 = cache.insert(.{ .index = 0, .scale_x = .fromF32(1), .scale_y = .fromF32(1) }).?;
+        const id2 = cache.insert(.{ .index = 1, .scale_x = .fromF32(1), .scale_y = .fromF32(1) }).?;
+        const id3 = cache.insert(.{ .index = 2, .scale_x = .fromF32(1), .scale_y = .fromF32(1) }).?;
+
+        {
+            const lru = try cache.getLRUItems(gpa);
+            defer gpa.free(lru);
+            try std.testing.expectEqualSlices(GlyphSlot.Id, &.{ id3, id2, id1 }, lru);
+        }
+
+        _ = cache.remove(id2);
+
+        {
+            const lru = try cache.getLRUItems(gpa);
+            defer gpa.free(lru);
+            try std.testing.expectEqualSlices(GlyphSlot.Id, &.{ id3, id1 }, lru);
+        }
+
+        _ = cache.remove(id3);
+
+        {
+            const lru = try cache.getLRUItems(gpa);
+            defer gpa.free(lru);
+            try std.testing.expectEqualSlices(GlyphSlot.Id, &.{ id1 }, lru);
+        }
+
+        _ = cache.remove(id1);
+
+        {
+            const lru = try cache.getLRUItems(gpa);
+            defer gpa.free(lru);
+            try std.testing.expectEqualSlices(GlyphSlot.Id, &.{ }, lru);
+        }
+    }
+};
+
+const GlyphSlot = struct {
+    glyph: Glyph,
+
+    lru_next: GlyphSlot.Id,
+    lru_prev: GlyphSlot.Id,
+
+    next_free: GlyphSlot.Id,
+
+    const Id = u16;
+    const nil_id: GlyphSlot.Id = 0;
+
+    comptime {
+        assert(@bitSizeOf(Id) % 8 == 0);
+    }
+};
+
+const Glyph = struct {
+    key: Key,
+
+    box: STBTrueType.Box,
+    sprite: Gfx.Sprite.Id,
+    last_used_frame: u32,
+
+    const max_width: u32 = 512;
+    const max_height: u32 = 512;
+
+    const Index = u32;
+
+    const Key = packed struct(u64) {
+        index: Index,
+        scale_x: q4d12,
+        scale_y: q4d12,
+
+        pub fn toInt(self: Key) u64 {
+            return @bitCast(self);
+        }
+
+        // 4 integer bits, 12 fractional bits
+        const q4d12 = enum(u16) {
+            _,
+
+            pub fn toF32(integer: q4d12) f32 {
+                return @as(f32, @floatFromInt(@intFromEnum(integer))) / (1 << 12);
+            }
+
+            pub fn fromF32(float: f32) q4d12 {
+                return @enumFromInt(@as(u16, @intFromFloat(float * (1 << 12))));
+            }
+
+            pub fn format(self: q4d12, writer: *Io.Writer) Io.Writer.Error!void {
+                try writer.print("q12d4{{ {} }}", .{self.toF32()});
+            }
+        };
+
+        test {
+            try std.testing.expectEqual(q4d12.fromF32(10.0625).toF32(), 10.0625);
+        }
+    };
+
+    fn init(key: Key) Glyph {
+        return Glyph{
+            .key = key,
+            .box = .{
+                .x0 = 0,
+                .y0 = 0,
+                .x1 = 0,
+                .y1 = 0,
+            },
+            .sprite = .nil,
+            .last_used_frame = 0
+        };
+    }
+
+    fn deinit(self: Glyph) void {
+        Gfx.deinitSprite(self.sprite);
+    }
+};
+
+pub const TextRunLayout = struct {
+    font: *Font,
+    scale_x: f32,
+    scale_y: f32,
+
+    prev_glyph: ?Font.Glyph.Index,
+    pen_pos: Vec2,
+
+    const GlyphRect = struct {
+        rect: Rect,
+        sprite: Gfx.Sprite.Id,
+    };
+
+    pub fn init(font: *Font, height: f32) TextRunLayout {
+        const scale = font.stb.scaleForPixelHeight(height);
+
+        return TextRunLayout{
+            .font = font,
+            .scale_x = scale,
+            .scale_y = scale,
+            .prev_glyph = null,
+            .pen_pos = .init(0, 0)
+        };
+    }
+
+    pub fn next(self: *TextRunLayout, glyph_index: Font.Glyph.Index) ?GlyphRect {
+        const glyph = self.font.getGlyph(glyph_index, self.scale_x, self.scale_y) orelse return null;
+
+        if (self.prev_glyph) |prev_glyph| {
+            const kerning = self.font.stb.getGlyphKernAdvance(prev_glyph, glyph_index);
+            self.pen_pos.x += @as(f32, @floatFromInt(kerning)) * self.scale_x;
+        }
+
+        const hmetrics = self.font.stb.getGlyphHMetrics(glyph_index);
+        const glyph_size = Vec2.initFromInt(i32, glyph.box.x1 - glyph.box.x0, glyph.box.y1 - glyph.box.y0);
+
+        var draw_pos = self.pen_pos;
+        draw_pos.x -= @floatFromInt(glyph.box.x0);
+        draw_pos.x += @as(f32, @floatFromInt(hmetrics.left_side_bearing)) * self.scale_x;
+        draw_pos.y += @floatFromInt(glyph.box.y0);
+        const draw_rect = Rect{
+            .pos = draw_pos,
+            .size = glyph_size
+        };
+
+        self.pen_pos.x += @as(f32, @floatFromInt(hmetrics.advance_width)) * self.scale_x;
+        self.prev_glyph = glyph_index;
+
+        return GlyphRect{
+            .rect = draw_rect,
+            .sprite = glyph.sprite
+        };
+    }
+};

src/platform/slot_map.zig

@@ -87,7 +87,11 @@ pub fn SlotMapType(Index: type, Generation: type, Value: type) type {
         };
 
         pub fn clearRetainingCapacity(self: *Self) void {
-            self.* = .initBuffer(self.slots.items);
+            var slots = self.slots;
+            slots.clearRetainingCapacity();
+
+            self.* = .empty;
+            self.slots = slots;
         }
 
         fn insertHole(self: *Self, index: Index) void {
@@ -245,16 +249,16 @@ test "insert & remove" {
     const expect = std.testing.expect;
     const gpa = std.testing.allocator;
 
-    var map: TestMap = .empty;
+    var map: TestMap = try .initCapacity(gpa, 32);
     defer map.deinit(gpa);
 
-    const id1 = try map.insertUndefined(gpa);
+    const id1 = try map.insertUndefined();
     try expect(map.exists(id1));
     try expect(map.remove(id1));
     try expect(!map.exists(id1));
     try expect(!map.remove(id1));
 
-    const id2 = try map.insertUndefined(gpa);
+    const id2 = try map.insertUndefined();
     try expect(map.exists(id2));
     try expect(!map.exists(id1));
 }
@@ -263,18 +267,18 @@ test "generation wrap around" {
     const expectEqual = std.testing.expectEqual;
     const gpa = std.testing.allocator;
 
-    var map: TestMap = .empty;
+    var map: TestMap = try .initCapacity(gpa, 32);
     defer map.deinit(gpa);
 
     // Grow array list so that at least 1 slot exists 
-    const id1 = try map.insertUndefined(gpa);
+    const id1 = try map.insertUndefined();
     map.removeAssumeExists(id1);
 
     // Artificially increase generation count
     map.slots.items[id1.index].generation = std.math.maxInt(@FieldType(TestMap.Id, "generation"));
 
     // Check if generation wraps around
-    const id2 = try map.insertUndefined(gpa);
+    const id2 = try map.insertUndefined();
     map.removeAssumeExists(id2);
     try expectEqual(id1.index, id2.index);
     try expectEqual(0, map.slots.items[id1.index].generation);
@@ -284,13 +288,13 @@ test "iterator" {
     const expectEqual = std.testing.expectEqual;
     const gpa = std.testing.allocator;
 
-    var map: TestMap = .empty;
+    var map: TestMap = try .initCapacity(gpa, 32);
     defer map.deinit(gpa);
 
     // Create array which has a hole
-    const id1 = try map.insertUndefined(gpa);
-    const id2 = try map.insertUndefined(gpa);
-    const id3 = try map.insertUndefined(gpa);
+    const id1 = try map.insertUndefined();
+    const id2 = try map.insertUndefined();
+    const id3 = try map.insertUndefined();
 
     map.removeAssumeExists(id2);
 
@@ -305,14 +309,14 @@ test "clear retaining capacity" {
     const expectEqual = std.testing.expectEqual;
     const gpa = std.testing.allocator;
 
-    var map: TestMap = .empty;
+    var map: TestMap = try .initCapacity(gpa, 32);
     defer map.deinit(gpa);
 
-    const id1 = try map.insertUndefined(gpa);
+    const id1 = try map.insertUndefined();
     try expect(map.exists(id1));
     map.clearRetainingCapacity();
 
-    const id2 = try map.insertUndefined(gpa);
+    const id2 = try map.insertUndefined();
     try expect(map.exists(id2));
 
     try expectEqual(id1, id2);