Merge pull request #345 from mitchellh/variable-fonts

Variable font support

pkg/freetype/Library.zig

@@ -57,6 +57,11 @@ pub fn initMemoryFace(self: Library, data: []const u8, index: i32) Error!Face {
     return face;
 }
 
+/// Call when you're done with a loaded MM var.
+pub fn doneMMVar(self: Library, mm: *c.FT_MM_Var) void {
+    _ = c.FT_Done_MM_Var(self.handle, mm);
+}
+
 pub const Version = struct {
     major: i32,
     minor: i32,

pkg/freetype/face.zig

@@ -24,6 +24,12 @@ pub const Face = struct {
         return c.FT_HAS_COLOR(self.handle);
     }
 
+    /// A macro that returns true whenever a face object contains some
+    /// multiple masters.
+    pub fn hasMultipleMasters(self: Face) bool {
+        return c.FT_HAS_MULTIPLE_MASTERS(self.handle);
+    }
+
     /// A macro that returns true whenever a face object contains a scalable
     /// font face (true for TrueType, Type 1, Type 42, CID, OpenType/CFF,
     /// and PFR font formats).
@@ -95,6 +101,33 @@ pub const Face = struct {
         const res = c.FT_Get_Sfnt_Name(self.handle, @intCast(i), &name);
         return if (intToError(res)) |_| name else |err| err;
     }
+
+    /// Retrieve the font variation descriptor for a font.
+    pub fn getMMVar(self: Face) Error!*c.FT_MM_Var {
+        var result: *c.FT_MM_Var = undefined;
+        const res = c.FT_Get_MM_Var(self.handle, @ptrCast(&result));
+        return if (intToError(res)) |_| result else |err| err;
+    }
+
+    /// Get the design coordinates of the currently selected interpolated font.
+    pub fn getVarDesignCoordinates(self: Face, coords: []c.FT_Fixed) Error!void {
+        const res = c.FT_Get_Var_Design_Coordinates(
+            self.handle,
+            @intCast(coords.len),
+            coords.ptr,
+        );
+        return intToError(res);
+    }
+
+    /// Choose an interpolated font design through design coordinates.
+    pub fn setVarDesignCoordinates(self: Face, coords: []c.FT_Fixed) Error!void {
+        const res = c.FT_Set_Var_Design_Coordinates(
+            self.handle,
+            @intCast(coords.len),
+            coords.ptr,
+        );
+        return intToError(res);
+    }
 };
 
 /// An enumeration to specify indices of SFNT tables loaded and parsed by

pkg/freetype/freetype-zig.h

@@ -1,5 +1,6 @@
 #include <ft2build.h>
 #include FT_FREETYPE_H
 #include FT_TRUETYPE_TABLES_H
+#include <freetype/ftmm.h>
 #include <freetype/ftsnames.h>
 #include <freetype/ttnameid.h>

pkg/macos/foundation/array.zig

@@ -24,7 +24,7 @@ pub const Array = opaque {
     /// constness so that further API calls work correctly. The Foundation
     /// API doesn't properly mark things const/non-const.
     pub fn getValueAtIndex(self: *Array, comptime T: type, idx: usize) *T {
-        return @ptrCast(CFArrayGetValueAtIndex(self, idx));
+        return @ptrCast(@alignCast(CFArrayGetValueAtIndex(self, idx)));
     }
 
     pub extern "c" fn CFArrayCreate(

pkg/macos/text/font.zig

@@ -39,6 +39,14 @@ pub const Font = opaque {
         c.CFRelease(self);
     }
 
+    pub fn retain(self: *Font) void {
+        _ = c.CFRetain(self);
+    }
+
+    pub fn copyDescriptor(self: *Font) *text.FontDescriptor {
+        return @ptrCast(@constCast(c.CTFontCopyFontDescriptor(@ptrCast(self))));
+    }
+
     pub fn getGlyphsForCharacters(self: *Font, chars: []const u16, glyphs: []graphics.Glyph) bool {
         assert(chars.len == glyphs.len);
         return c.CTFontGetGlyphsForCharacters(

pkg/macos/text/font_descriptor.zig

@@ -31,6 +31,21 @@ pub const FontDescriptor = opaque {
         ) orelse Allocator.Error.OutOfMemory;
     }
 
+    pub fn createCopyWithVariation(
+        original: *FontDescriptor,
+        id: *foundation.Number,
+        value: f64,
+    ) Allocator.Error!*FontDescriptor {
+        return @as(
+            ?*FontDescriptor,
+            @ptrCast(@constCast(c.CTFontDescriptorCreateCopyWithVariation(
+                @ptrCast(original),
+                @ptrCast(id),
+                value,
+            ))),
+        ) orelse Allocator.Error.OutOfMemory;
+    }
+
     pub fn release(self: *FontDescriptor) void {
         c.CFRelease(self);
     }
@@ -75,6 +90,9 @@ pub const FontAttribute = enum {
     downloadable,
     downloaded,
 
+    // https://developer.apple.com/documentation/coretext/core_text_constants?language=objc
+    variation_axes,
+
     pub fn key(self: FontAttribute) *foundation.String {
         return @as(*foundation.String, @ptrFromInt(@intFromPtr(switch (self) {
             .url => c.kCTFontURLAttribute,
@@ -101,6 +119,7 @@ pub const FontAttribute = enum {
             .enabled => c.kCTFontEnabledAttribute,
             .downloadable => c.kCTFontDownloadableAttribute,
             .downloaded => c.kCTFontDownloadedAttribute,
+            .variation_axes => c.kCTFontVariationAxesAttribute,
         })));
     }
 
@@ -130,6 +149,7 @@ pub const FontAttribute = enum {
             .enabled => *foundation.Number,
             .downloadable => *anyopaque, // CFBoolean
             .downloaded => *anyopaque, // CFBoolean
+            .variation_axes => ?*foundation.Array,
         };
     }
 };
@@ -159,6 +179,38 @@ pub const FontTraitKey = enum {
     }
 };
 
+// https://developer.apple.com/documentation/coretext/ctfont/font_variation_axis_dictionary_keys?language=objc
+pub const FontVariationAxisKey = enum {
+    identifier,
+    minimum_value,
+    maximum_value,
+    default_value,
+    name,
+    hidden,
+
+    pub fn key(self: FontVariationAxisKey) *foundation.String {
+        return @as(*foundation.String, @ptrFromInt(@intFromPtr(switch (self) {
+            .identifier => c.kCTFontVariationAxisIdentifierKey,
+            .minimum_value => c.kCTFontVariationAxisMinimumValueKey,
+            .maximum_value => c.kCTFontVariationAxisMaximumValueKey,
+            .default_value => c.kCTFontVariationAxisDefaultValueKey,
+            .name => c.kCTFontVariationAxisNameKey,
+            .hidden => c.kCTFontVariationAxisHiddenKey,
+        })));
+    }
+
+    pub fn Value(comptime self: FontVariationAxisKey) type {
+        return switch (self) {
+            .identifier => foundation.Number,
+            .minimum_value => foundation.Number,
+            .maximum_value => foundation.Number,
+            .default_value => foundation.Number,
+            .name => foundation.String,
+            .hidden => foundation.Number,
+        };
+    }
+};
+
 pub const FontSymbolicTraits = packed struct(u32) {
     italic: bool = false,
     bold: bool = false,

src/Surface.zig

@@ -229,6 +229,7 @@ pub fn init(
                 var disco_it = try disco.discover(.{
                     .family = family,
                     .size = font_size.points,
+                    .variations = config.@"font-variation".list.items,
                 });
                 defer disco_it.deinit();
                 if (try disco_it.next()) |face| {
@@ -241,6 +242,7 @@ pub fn init(
                     .family = family,
                     .size = font_size.points,
                     .bold = true,
+                    .variations = config.@"font-variation-bold".list.items,
                 });
                 defer disco_it.deinit();
                 if (try disco_it.next()) |face| {
@@ -253,6 +255,7 @@ pub fn init(
                     .family = family,
                     .size = font_size.points,
                     .italic = true,
+                    .variations = config.@"font-variation-italic".list.items,
                 });
                 defer disco_it.deinit();
                 if (try disco_it.next()) |face| {
@@ -266,6 +269,7 @@ pub fn init(
                     .size = font_size.points,
                     .bold = true,
                     .italic = true,
+                    .variations = config.@"font-variation-bold-italic".list.items,
                 });
                 defer disco_it.deinit();
                 if (try disco_it.next()) |face| {

src/config.zig

@@ -3,6 +3,7 @@ const std = @import("std");
 const builtin = @import("builtin");
 const Allocator = std.mem.Allocator;
 const ArenaAllocator = std.heap.ArenaAllocator;
+const fontpkg = @import("font/main.zig");
 const inputpkg = @import("input.zig");
 const terminal = @import("terminal/main.zig");
 const internal_os = @import("os/main.zig");
@@ -43,6 +44,30 @@ pub const Config = struct {
         else => 12,
     },
 
+    /// A repeatable configuration to set one or more font variations values
+    /// for a variable font. A variable font is a single font, usually
+    /// with a filename ending in "-VF.ttf" or "-VF.otf" that contains
+    /// one or more configurable axes for things such as weight, slant,
+    /// etc. Not all fonts support variations; only fonts that explicitly
+    /// state they are variable fonts will work.
+    ///
+    /// The format of this is "id=value" where "id" is the axis identifier.
+    /// An axis identifier is always a 4 character string, such as "wght".
+    /// To get the list of supported axes, look at your font documentation
+    /// or use a font inspection tool.
+    ///
+    /// Invalid ids and values are usually ignored. For example, if a font
+    /// only supports weights from 100 to 700, setting "wght=800" will
+    /// do nothing (it will not be clamped to 700). You must consult your
+    /// font's documentation to see what values are supported.
+    ///
+    /// Common axes are: "wght" (weight), "slnt" (slant), "ital" (italic),
+    /// "opsz" (optical size), "wdth" (width), "GRAD" (gradient), etc.
+    @"font-variation": RepeatableFontVariation = .{},
+    @"font-variation-bold": RepeatableFontVariation = .{},
+    @"font-variation-italic": RepeatableFontVariation = .{},
+    @"font-variation-bold-italic": RepeatableFontVariation = .{},
+
     /// Draw fonts with a thicker stroke, if supported. This is only supported
     /// currently on macOS.
     @"font-thicken": bool = false,
@@ -1217,6 +1242,97 @@ pub const RepeatableString = struct {
     }
 };
 
+/// FontVariation is a repeatable configuration value that sets a single
+/// font variation value. Font variations are configurations for what
+/// are often called "variable fonts." The font files usually end in
+/// "-VF.ttf."
+///
+/// The value for this is in the format of `id=value` where `id` is the
+/// 4-character font variation axis identifier and `value` is the
+/// floating point value for that axis. For more details on font variations
+/// see the MDN font-variation-settings documentation since this copies that
+/// behavior almost exactly:
+///
+/// https://developer.mozilla.org/en-US/docs/Web/CSS/font-variation-settings
+pub const RepeatableFontVariation = struct {
+    const Self = @This();
+
+    // Allocator for the list is the arena for the parent config.
+    list: std.ArrayListUnmanaged(fontpkg.face.Variation) = .{},
+
+    pub fn parseCLI(self: *Self, alloc: Allocator, input_: ?[]const u8) !void {
+        const input = input_ orelse return error.ValueRequired;
+        const eql_idx = std.mem.indexOf(u8, input, "=") orelse return error.InvalidFormat;
+        const whitespace = " \t";
+        const key = std.mem.trim(u8, input[0..eql_idx], whitespace);
+        const value = std.mem.trim(u8, input[eql_idx + 1 ..], whitespace);
+        if (key.len != 4) return error.InvalidFormat;
+        try self.list.append(alloc, .{
+            .id = fontpkg.face.Variation.Id.init(@ptrCast(key.ptr)),
+            .value = std.fmt.parseFloat(f64, value) catch return error.InvalidFormat,
+        });
+    }
+
+    /// Deep copy of the struct. Required by Config.
+    pub fn clone(self: *const Self, alloc: Allocator) !Self {
+        return .{
+            .list = try self.list.clone(alloc),
+        };
+    }
+
+    /// Compare if two of our value are requal. Required by Config.
+    pub fn equal(self: Self, other: Self) bool {
+        const itemsA = self.list.items;
+        const itemsB = other.list.items;
+        if (itemsA.len != itemsB.len) return false;
+        for (itemsA, itemsB) |a, b| {
+            if (!std.meta.eql(a, b)) return false;
+        } else return true;
+    }
+
+    test "parseCLI" {
+        const testing = std.testing;
+        var arena = ArenaAllocator.init(testing.allocator);
+        defer arena.deinit();
+        const alloc = arena.allocator();
+
+        var list: Self = .{};
+        try list.parseCLI(alloc, "wght=200");
+        try list.parseCLI(alloc, "slnt=-15");
+
+        try testing.expectEqual(@as(usize, 2), list.list.items.len);
+        try testing.expectEqual(fontpkg.face.Variation{
+            .id = fontpkg.face.Variation.Id.init("wght"),
+            .value = 200,
+        }, list.list.items[0]);
+        try testing.expectEqual(fontpkg.face.Variation{
+            .id = fontpkg.face.Variation.Id.init("slnt"),
+            .value = -15,
+        }, list.list.items[1]);
+    }
+
+    test "parseCLI with whitespace" {
+        const testing = std.testing;
+        var arena = ArenaAllocator.init(testing.allocator);
+        defer arena.deinit();
+        const alloc = arena.allocator();
+
+        var list: Self = .{};
+        try list.parseCLI(alloc, "wght =200");
+        try list.parseCLI(alloc, "slnt= -15");
+
+        try testing.expectEqual(@as(usize, 2), list.list.items.len);
+        try testing.expectEqual(fontpkg.face.Variation{
+            .id = fontpkg.face.Variation.Id.init("wght"),
+            .value = 200,
+        }, list.list.items[0]);
+        try testing.expectEqual(fontpkg.face.Variation{
+            .id = fontpkg.face.Variation.Id.init("slnt"),
+            .value = -15,
+        }, list.list.items[1]);
+    }
+};
+
 /// Stores a set of keybinds.
 pub const Keybinds = struct {
     set: inputpkg.Binding.Set = .{},

src/font/DeferredFace.zig

@@ -54,6 +54,9 @@ pub const Fontconfig = struct {
     charset: *const fontconfig.CharSet,
     langset: *const fontconfig.LangSet,
 
+    /// Variations to apply to this font.
+    variations: []const font.face.Variation,
+
     pub fn deinit(self: *Fontconfig) void {
         self.pattern.destroy();
         self.* = undefined;
@@ -154,7 +157,10 @@ fn loadFontconfig(
     const filename = (try fc.pattern.get(.file, 0)).string;
     const face_index = (try fc.pattern.get(.index, 0)).integer;
 
-    return try Face.initFile(lib, filename, face_index, size);
+    var face = try Face.initFile(lib, filename, face_index, size);
+    errdefer face.deinit();
+    try face.setVariations(fc.variations);
+    return face;
 }
 
 fn loadCoreText(

src/font/discovery.zig

@@ -5,6 +5,7 @@ const fontconfig = @import("fontconfig");
 const macos = @import("macos");
 const options = @import("main.zig").options;
 const DeferredFace = @import("main.zig").DeferredFace;
+const Variation = @import("main.zig").face.Variation;
 
 const log = std.log.scoped(.discovery);
 
@@ -43,6 +44,11 @@ pub const Descriptor = struct {
     bold: bool = false,
     italic: bool = false,
 
+    /// Variation axes to apply to the font. This also impacts searching
+    /// for fonts since fonts with the ability to set these variations
+    /// will be preferred, but not guaranteed.
+    variations: []const Variation = &.{},
+
     /// Convert to Fontconfig pattern to use for lookup. The pattern does
     /// not have defaults filled/substituted (Fontconfig thing) so callers
     /// must still do this.
@@ -149,7 +155,21 @@ pub const Descriptor = struct {
             );
         }
 
-        return try macos.text.FontDescriptor.createWithAttributes(@ptrCast(attrs));
+        // Build our descriptor from attrs
+        var desc = try macos.text.FontDescriptor.createWithAttributes(@ptrCast(attrs));
+        errdefer desc.release();
+
+        // Variations are built by copying the descriptor. I don't know a way
+        // to set it on attrs directly.
+        for (self.variations) |v| {
+            const id = try macos.foundation.Number.create(.int, @ptrCast(&v.id));
+            defer id.release();
+            const next = try desc.createCopyWithVariation(id, v.value);
+            desc.release();
+            desc = next;
+        }
+
+        return desc;
     }
 };
 
@@ -185,6 +205,7 @@ pub const Fontconfig = struct {
             .pattern = pat,
             .set = res.fs,
             .fonts = res.fs.fonts(),
+            .variations = desc.variations,
             .i = 0,
         };
     }
@@ -194,6 +215,7 @@ pub const Fontconfig = struct {
         pattern: *fontconfig.Pattern,
         set: *fontconfig.FontSet,
         fonts: []*fontconfig.Pattern,
+        variations: []const Variation,
         i: usize,
 
         pub fn deinit(self: *DiscoverIterator) void {
@@ -221,6 +243,7 @@ pub const Fontconfig = struct {
                     .pattern = font_pattern,
                     .charset = (try font_pattern.get(.charset, 0)).char_set,
                     .langset = (try font_pattern.get(.lang, 0)).lang_set,
+                    .variations = self.variations,
                 },
             };
         }

src/font/face.zig

@@ -1,3 +1,4 @@
+const std = @import("std");
 const builtin = @import("builtin");
 const options = @import("main.zig").options;
 const freetype = @import("face/freetype.zig");
@@ -36,6 +37,31 @@ pub const DesiredSize = struct {
     }
 };
 
+/// A font variation setting. The best documentation for this I know of
+/// is actually the CSS font-variation-settings property on MDN:
+/// https://developer.mozilla.org/en-US/docs/Web/CSS/font-variation-settings
+pub const Variation = struct {
+    id: Id,
+    value: f64,
+
+    pub const Id = packed struct(u32) {
+        d: u8,
+        c: u8,
+        b: u8,
+        a: u8,
+
+        pub fn init(v: *const [4]u8) Id {
+            return .{ .a = v[0], .b = v[1], .c = v[2], .d = v[3] };
+        }
+
+        /// Converts the ID to a string. The return value is only valid
+        /// for the lifetime of the self pointer.
+        pub fn str(self: Id) [4]u8 {
+            return .{ self.a, self.b, self.c, self.d };
+        }
+    };
+};
+
 /// Metrics associated with the font that are useful for renderers to know.
 pub const Metrics = struct {
     /// Recommended cell width and height for a monospace grid using this font.
@@ -77,3 +103,17 @@ pub const Foo = if (options.backend == .coretext) coretext.Face else void;
 test {
     @import("std").testing.refAllDecls(@This());
 }
+
+test "Variation.Id: wght should be 2003265652" {
+    const testing = std.testing;
+    const id = Variation.Id.init("wght");
+    try testing.expectEqual(@as(u32, 2003265652), @as(u32, @bitCast(id)));
+    try testing.expectEqualStrings("wght", &(id.str()));
+}
+
+test "Variation.Id: slnt should be 1936486004" {
+    const testing = std.testing;
+    const id: Variation.Id = .{ .a = 's', .b = 'l', .c = 'n', .d = 't' };
+    try testing.expectEqual(@as(u32, 1936486004), @as(u32, @bitCast(id)));
+    try testing.expectEqualStrings("slnt", &(id.str()));
+}

src/font/face/coretext.zig

@@ -1,4 +1,5 @@
 const std = @import("std");
+const builtin = @import("builtin");
 const assert = std.debug.assert;
 const Allocator = std.mem.Allocator;
 const macos = @import("macos");
@@ -64,6 +65,12 @@ pub const Face = struct {
         const ct_font = try base.copyWithAttributes(@floatFromInt(size.pixels()), null, null);
         errdefer ct_font.release();
 
+        return try initFont(ct_font);
+    }
+
+    /// Initialize a face with a CTFont. This will take ownership over
+    /// the CTFont. This does NOT copy or retain the CTFont.
+    pub fn initFont(ct_font: *macos.text.Font) !Face {
         var hb_font = try harfbuzz.coretext.createFont(ct_font);
         errdefer hb_font.destroy();
 
@@ -76,6 +83,52 @@ pub const Face = struct {
             .metrics = try calcMetrics(ct_font),
         };
         result.quirks_disable_default_font_features = quirks.disableDefaultFontFeatures(&result);
+
+        // In debug mode, we output information about available variation axes,
+        // if they exist.
+        if (comptime builtin.mode == .Debug) {
+            if (ct_font.copyAttribute(.variation_axes)) |axes| {
+                defer axes.release();
+
+                var buf: [1024]u8 = undefined;
+                log.debug("variation axes font={s}", .{try result.name(&buf)});
+
+                const len = axes.getCount();
+                for (0..len) |i| {
+                    const dict = axes.getValueAtIndex(macos.foundation.Dictionary, i);
+                    const Key = macos.text.FontVariationAxisKey;
+                    const cf_name = dict.getValue(Key.name.Value(), Key.name.key()).?;
+                    const cf_id = dict.getValue(Key.identifier.Value(), Key.identifier.key()).?;
+                    const cf_min = dict.getValue(Key.minimum_value.Value(), Key.minimum_value.key()).?;
+                    const cf_max = dict.getValue(Key.maximum_value.Value(), Key.maximum_value.key()).?;
+                    const cf_def = dict.getValue(Key.default_value.Value(), Key.default_value.key()).?;
+
+                    const namestr = cf_name.cstring(&buf, .utf8) orelse "";
+
+                    var id_raw: c_int = 0;
+                    _ = cf_id.getValue(.int, &id_raw);
+                    const id: font.face.Variation.Id = @bitCast(id_raw);
+
+                    var min: f64 = 0;
+                    _ = cf_min.getValue(.double, &min);
+
+                    var max: f64 = 0;
+                    _ = cf_max.getValue(.double, &max);
+
+                    var def: f64 = 0;
+                    _ = cf_def.getValue(.double, &def);
+
+                    log.debug("variation axis: name={s} id={s} min={} max={} def={}", .{
+                        namestr,
+                        id.str(),
+                        min,
+                        max,
+                        def,
+                    });
+                }
+            }
+        }
+
         return result;
     }
 
@@ -89,8 +142,8 @@ pub const Face = struct {
     /// matrix applied to italicize it.
     pub fn italicize(self: *const Face) !Face {
         const ct_font = try self.font.copyWithAttributes(0.0, &italic_skew, null);
-        defer ct_font.release();
-        return try initFontCopy(ct_font, .{ .points = 0 });
+        errdefer ct_font.release();
+        return try initFont(ct_font);
     }
 
     /// Returns the font name. If allocation is required, buf will be used,
@@ -115,6 +168,31 @@ pub const Face = struct {
         self.* = face;
     }
 
+    /// Set the variation axes for this font. This will modify this font
+    /// in-place.
+    pub fn setVariations(
+        self: *Face,
+        vs: []const font.face.Variation,
+    ) !void {
+        // Create a new font descriptor with all the variations set.
+        var desc = self.font.copyDescriptor();
+        defer desc.release();
+        for (vs) |v| {
+            const id = try macos.foundation.Number.create(.int, @ptrCast(&v.id));
+            defer id.release();
+            const next = try desc.createCopyWithVariation(id, v.value);
+            desc.release();
+            desc = next;
+        }
+
+        // Initialize a font based on these attributes.
+        const ct_font = try self.font.copyWithAttributes(0, null, desc);
+        errdefer ct_font.release();
+        const face = try initFont(ct_font);
+        self.deinit();
+        self.* = face;
+    }
+
     /// Returns the glyph index for the given Unicode code point. If this
     /// face doesn't support this glyph, null is returned.
     pub fn glyphIndex(self: Face, cp: u32) ?u32 {
@@ -492,3 +570,55 @@ test "in-memory" {
         _ = try face.renderGlyph(alloc, &atlas, face.glyphIndex(i).?, .{});
     }
 }
+
+test "variable" {
+    const testing = std.testing;
+    const alloc = testing.allocator;
+    const testFont = @import("../test.zig").fontVariable;
+
+    var atlas = try font.Atlas.init(alloc, 512, .greyscale);
+    defer atlas.deinit(alloc);
+
+    var lib = try font.Library.init();
+    defer lib.deinit();
+
+    var face = try Face.init(lib, testFont, .{ .points = 12 });
+    defer face.deinit();
+
+    try testing.expectEqual(font.Presentation.text, face.presentation);
+
+    // Generate all visible ASCII
+    var i: u8 = 32;
+    while (i < 127) : (i += 1) {
+        try testing.expect(face.glyphIndex(i) != null);
+        _ = try face.renderGlyph(alloc, &atlas, face.glyphIndex(i).?, .{});
+    }
+}
+
+test "variable set variation" {
+    const testing = std.testing;
+    const alloc = testing.allocator;
+    const testFont = @import("../test.zig").fontVariable;
+
+    var atlas = try font.Atlas.init(alloc, 512, .greyscale);
+    defer atlas.deinit(alloc);
+
+    var lib = try font.Library.init();
+    defer lib.deinit();
+
+    var face = try Face.init(lib, testFont, .{ .points = 12 });
+    defer face.deinit();
+
+    try testing.expectEqual(font.Presentation.text, face.presentation);
+
+    try face.setVariations(&.{
+        .{ .id = font.face.Variation.Id.init("wght"), .value = 400 },
+    });
+
+    // Generate all visible ASCII
+    var i: u8 = 32;
+    while (i < 127) : (i += 1) {
+        try testing.expect(face.glyphIndex(i) != null);
+        _ = try face.renderGlyph(alloc, &atlas, face.glyphIndex(i).?, .{});
+    }
+}

src/font/face/freetype.zig

@@ -23,6 +23,9 @@ const quirks = @import("../../quirks.zig");
 const log = std.log.scoped(.font_face);
 
 pub const Face = struct {
+    /// Our freetype library
+    lib: freetype.Library,
+
     /// Our font face.
     face: freetype.Face,
 
@@ -43,30 +46,55 @@ pub const Face = struct {
     pub fn initFile(lib: Library, path: [:0]const u8, index: i32, size: font.face.DesiredSize) !Face {
         const face = try lib.lib.initFace(path, index);
         errdefer face.deinit();
-        return try initFace(face, size);
+        return try initFace(lib, face, size);
     }
 
     /// Initialize a new font face with the given source in-memory.
     pub fn init(lib: Library, source: [:0]const u8, size: font.face.DesiredSize) !Face {
         const face = try lib.lib.initMemoryFace(source, 0);
         errdefer face.deinit();
-        return try initFace(face, size);
+        return try initFace(lib, face, size);
     }
 
-    fn initFace(face: freetype.Face, size: font.face.DesiredSize) !Face {
+    fn initFace(lib: Library, face: freetype.Face, size: font.face.DesiredSize) !Face {
         try face.selectCharmap(.unicode);
         try setSize_(face, size);
 
-        const hb_font = try harfbuzz.freetype.createFont(face.handle);
+        var hb_font = try harfbuzz.freetype.createFont(face.handle);
         errdefer hb_font.destroy();
 
         var result: Face = .{
+            .lib = lib.lib,
             .face = face,
             .hb_font = hb_font,
             .presentation = if (face.hasColor()) .emoji else .text,
             .metrics = calcMetrics(face),
         };
         result.quirks_disable_default_font_features = quirks.disableDefaultFontFeatures(&result);
+
+        // In debug mode, we output information about available variation axes,
+        // if they exist.
+        if (comptime builtin.mode == .Debug) mm: {
+            if (!face.hasMultipleMasters()) break :mm;
+            var buf: [1024]u8 = undefined;
+            log.debug("variation axes font={s}", .{try result.name(&buf)});
+
+            const mm = try face.getMMVar();
+            defer lib.lib.doneMMVar(mm);
+            for (0..mm.num_axis) |i| {
+                const axis = mm.axis[i];
+                const id_raw = std.math.cast(c_int, axis.tag) orelse continue;
+                const id: font.face.Variation.Id = @bitCast(id_raw);
+                log.debug("variation axis: name={s} id={s} min={} max={} def={}", .{
+                    std.mem.sliceTo(axis.name, 0),
+                    id.str(),
+                    axis.minimum >> 16,
+                    axis.maximum >> 16,
+                    axis.def >> 16,
+                });
+            }
+        }
+
         return result;
     }
 
@@ -132,6 +160,50 @@ pub const Face = struct {
         try face.selectSize(best_i);
     }
 
+    /// Set the variation axes for this font. This will modify this font
+    /// in-place.
+    pub fn setVariations(
+        self: *Face,
+        vs: []const font.face.Variation,
+    ) !void {
+        // If this font doesn't support variations, we can't do anything.
+        if (!self.face.hasMultipleMasters() or vs.len == 0) return;
+
+        // Freetype requires that we send ALL coordinates in at once so the
+        // first thing we have to do is get all the vars and put them into
+        // an array.
+        const mm = try self.face.getMMVar();
+        defer self.lib.doneMMVar(mm);
+
+        // To avoid allocations, we cap the number of variation axes we can
+        // support. This is arbitrary but Firefox caps this at 16 so I
+        // feel like that's probably safe... and we do double cause its
+        // cheap.
+        var coords_buf: [32]freetype.c.FT_Fixed = undefined;
+        var coords = coords_buf[0..@min(coords_buf.len, mm.num_axis)];
+        try self.face.getVarDesignCoordinates(coords);
+
+        // Now we go through each axis and see if its set. This is slow
+        // but there usually aren't many axes and usually not many set
+        // variations, either.
+        for (0..mm.num_axis) |i| {
+            const axis = mm.axis[i];
+            const id = std.math.cast(u32, axis.tag) orelse continue;
+            for (vs) |v| {
+                if (id == @as(u32, @bitCast(v.id))) {
+                    coords[i] = @intFromFloat(v.value * 65536);
+                    break;
+                }
+            }
+        }
+
+        // Set them!
+        try self.face.setVarDesignCoordinates(coords);
+
+        // We need to recalculate font metrics which may have changed.
+        self.metrics = calcMetrics(self.face);
+    }
+
     /// Returns the glyph index for the given Unicode code point. If this
     /// face doesn't support this glyph, null is returned.
     pub fn glyphIndex(self: Face, cp: u32) ?u32 {

src/font/test.zig

@@ -2,3 +2,4 @@ pub const fontRegular = @embedFile("res/Inconsolata-Regular.ttf");
 pub const fontBold = @embedFile("res/Inconsolata-Bold.ttf");
 pub const fontEmoji = @embedFile("res/NotoColorEmoji.ttf");
 pub const fontEmojiText = @embedFile("res/NotoEmoji-Regular.ttf");
+pub const fontVariable = @embedFile("res/Lilex-VF.ttf");