font-feature config to enable/disable OpenType Font Features

src/config.zig

@@ -26,6 +26,17 @@ pub const Config = struct {
     @"font-family-italic": ?[:0]const u8 = null,
     @"font-family-bold-italic": ?[:0]const u8 = null,
 
+    /// Apply a font feature. This can be repeated multiple times to enable
+    /// multiple font features. You can NOT set multiple font features with
+    /// a single value (yet).
+    ///
+    /// The font feature will apply to all fonts rendered by Ghostty. A
+    /// future enhancement will allow targetting specific faces.
+    ///
+    /// A valid value is the name of a feature. Prefix the feature with a
+    /// "-" to explicitly disable it. Example: "ss20" or "-ss20".
+    @"font-feature": RepeatableString = .{},
+
     /// Font size in points
     @"font-size": u8 = switch (builtin.os.tag) {
         // On Mac we default a little bigger since this tends to look better.

src/font/shape.zig

@@ -30,3 +30,20 @@ pub const Cell = struct {
     /// the runs.
     glyph_index: u32,
 };
+
+/// Options for shapers.
+pub const Options = struct {
+    /// The cell_buf argument is the buffer to use for storing shaped results.
+    /// This should be at least the number of columns in the terminal.
+    cell_buf: []Cell,
+
+    /// Font features to use when shaping. These can be in the following
+    /// formats: "-feat" "+feat" "feat". A "-"-prefix is used to disable
+    /// a feature and the others are used to enable a feature. If a feature
+    /// isn't supported or is invalid, it will be ignored.
+    ///
+    /// Note: eventually, this will move to font.Face probably as we may
+    /// want to support per-face feature configuration. For now, we only
+    /// support applying features globally.
+    features: []const []const u8 = &.{},
+};

src/font/shaper/harfbuzz.zig

@@ -24,20 +24,49 @@ pub const Shaper = struct {
     /// The shared memory used for shaping results.
     cell_buf: []font.shape.Cell,
 
+    /// The features to use for shaping.
+    hb_feats: FeatureList,
+
+    const FeatureList = std.ArrayList(harfbuzz.Feature);
+
     /// The cell_buf argument is the buffer to use for storing shaped results.
     /// This should be at least the number of columns in the terminal.
-    pub fn init(alloc: Allocator, cell_buf: []font.shape.Cell) !Shaper {
-        // Allocator is not used because harfbuzz uses libc
-        _ = alloc;
+    pub fn init(alloc: Allocator, opts: font.shape.Options) !Shaper {
+        // Parse all the features we want to use. We use
+        var hb_feats = hb_feats: {
+            // These features are hardcoded to always be on by default. Users
+            // can turn them off by setting the features to "-liga" for example.
+            const hardcoded_features = [_][]const u8{ "dlig", "liga" };
+
+            var list = try FeatureList.initCapacity(alloc, opts.features.len + hardcoded_features.len);
+            errdefer list.deinit();
+
+            for (hardcoded_features) |name| {
+                if (harfbuzz.Feature.fromString(name)) |feat| {
+                    try list.append(feat);
+                } else log.warn("failed to parse font feature: {s}", .{name});
+            }
+
+            for (opts.features) |name| {
+                if (harfbuzz.Feature.fromString(name)) |feat| {
+                    try list.append(feat);
+                } else log.warn("failed to parse font feature: {s}", .{name});
+            }
+
+            break :hb_feats list;
+        };
+        errdefer hb_feats.deinit();
 
         return Shaper{
             .hb_buf = try harfbuzz.Buffer.create(),
-            .cell_buf = cell_buf,
+            .cell_buf = opts.cell_buf,
+            .hb_feats = hb_feats,
         };
     }
 
     pub fn deinit(self: *Shaper) void {
         self.hb_buf.destroy();
+        self.hb_feats.deinit();
     }
 
     /// Returns an iterator that returns one text run at a time for the
@@ -75,14 +104,8 @@ pub const Shaper = struct {
         // We only do shaping if the font is not a special-case. For special-case
         // fonts, the codepoint == glyph_index so we don't need to run any shaping.
         if (run.font_index.special() == null) {
-            // TODO: we do not want to hardcode these
-            const hb_feats = &[_]harfbuzz.Feature{
-                harfbuzz.Feature.fromString("dlig").?,
-                harfbuzz.Feature.fromString("liga").?,
-            };
-
             const face = try run.group.group.faceFromIndex(run.font_index);
-            harfbuzz.shape(face.hb_font, self.hb_buf, hb_feats);
+            harfbuzz.shape(face.hb_font, self.hb_buf, self.hb_feats.items);
         }
 
         // If our buffer is empty, we short-circuit the rest of the work
@@ -657,7 +680,7 @@ fn testShaper(alloc: Allocator) !TestShaper {
     var cell_buf = try alloc.alloc(font.shape.Cell, 80);
     errdefer alloc.free(cell_buf);
 
-    var shaper = try Shaper.init(alloc, cell_buf);
+    var shaper = try Shaper.init(alloc, .{ .cell_buf = cell_buf });
     errdefer shaper.deinit();
 
     return TestShaper{

src/font/shaper/web_canvas.zig

@@ -37,10 +37,12 @@ pub const Shaper = struct {
 
     /// The cell_buf argument is the buffer to use for storing shaped results.
     /// This should be at least the number of columns in the terminal.
-    pub fn init(alloc: Allocator, cell_buf: []font.shape.Cell) !Shaper {
+    pub fn init(alloc: Allocator, opts: font.shape.Options) !Shaper {
+        // Note: we do not support opts.font_features
+
         return Shaper{
             .alloc = alloc,
-            .cell_buf = cell_buf,
+            .cell_buf = opts.cell_buf,
             .run_buf = .{},
         };
     }
@@ -238,7 +240,7 @@ pub const Wasm = struct {
         var cell_buf = try alloc.alloc(font.shape.Cell, cap);
         errdefer alloc.free(cell_buf);
 
-        var shaper = try Shaper.init(alloc, cell_buf);
+        var shaper = try Shaper.init(alloc, .{ .cell_buf = cell_buf });
         errdefer shaper.deinit();
 
         var result = try alloc.create(Shaper);

src/renderer/Metal.zig

@@ -130,6 +130,7 @@ const GPUCellMode = enum(u8) {
 /// pass around Config pointers which makes memory management a pain.
 pub const DerivedConfig = struct {
     font_thicken: bool,
+    font_features: std.ArrayList([]const u8),
     cursor_color: ?terminal.color.RGB,
     background: terminal.color.RGB,
     background_opacity: f64,
@@ -141,11 +142,17 @@ pub const DerivedConfig = struct {
         alloc_gpa: Allocator,
         config: *const configpkg.Config,
     ) !DerivedConfig {
-        _ = alloc_gpa;
+        // Copy our font features
+        var font_features = features: {
+            var clone = try config.@"font-feature".list.clone(alloc_gpa);
+            break :features clone.toManaged(alloc_gpa);
+        };
+        errdefer font_features.deinit();
 
         return .{
             .background_opacity = @max(0, @min(1, config.@"background-opacity")),
             .font_thicken = config.@"font-thicken",
+            .font_features = font_features,
 
             .cursor_color = if (config.@"cursor-color") |col|
                 col.toTerminalRGB()
@@ -168,7 +175,7 @@ pub const DerivedConfig = struct {
     }
 
     pub fn deinit(self: *DerivedConfig) void {
-        _ = self;
+        self.font_features.deinit();
     }
 };
 
@@ -228,7 +235,10 @@ pub fn init(alloc: Allocator, options: renderer.Options) !Metal {
     // avoid allocations later.
     var shape_buf = try alloc.alloc(font.shape.Cell, 160);
     errdefer alloc.free(shape_buf);
-    var font_shaper = try font.Shaper.init(alloc, shape_buf);
+    var font_shaper = try font.Shaper.init(alloc, .{
+        .cell_buf = shape_buf,
+        .features = options.config.font_features.items,
+    });
     errdefer font_shaper.deinit();
 
     // Initialize our Metal buffers
@@ -753,6 +763,20 @@ pub fn changeConfig(self: *Metal, config: *DerivedConfig) !void {
         self.font_group.atlas_color.clear();
     }
 
+    // We always redo the font shaper in case font features changed. We
+    // could check to see if there was an actual config change but this is
+    // easier and rare enough to not cause performance issues.
+    {
+        var font_shaper = try font.Shaper.init(self.alloc, .{
+            .cell_buf = self.font_shaper.cell_buf,
+            .features = config.font_features.items,
+        });
+        errdefer font_shaper.deinit();
+        self.font_shaper.deinit();
+        self.font_shaper = font_shaper;
+    }
+
+    self.config.deinit();
     self.config = config.*;
 }
 

src/renderer/OpenGL.zig

@@ -236,6 +236,7 @@ const GPUCellMode = enum(u8) {
 /// pass around Config pointers which makes memory management a pain.
 pub const DerivedConfig = struct {
     font_thicken: bool,
+    font_features: std.ArrayList([]const u8),
     cursor_color: ?terminal.color.RGB,
     background: terminal.color.RGB,
     background_opacity: f64,
@@ -247,11 +248,17 @@ pub const DerivedConfig = struct {
         alloc_gpa: Allocator,
         config: *const configpkg.Config,
     ) !DerivedConfig {
-        _ = alloc_gpa;
+        // Copy our font features
+        var font_features = features: {
+            var clone = try config.@"font-feature".list.clone(alloc_gpa);
+            break :features clone.toManaged(alloc_gpa);
+        };
+        errdefer font_features.deinit();
 
         return .{
             .background_opacity = @max(0, @min(1, config.@"background-opacity")),
             .font_thicken = config.@"font-thicken",
+            .font_features = font_features,
 
             .cursor_color = if (config.@"cursor-color") |col|
                 col.toTerminalRGB()
@@ -274,7 +281,7 @@ pub const DerivedConfig = struct {
     }
 
     pub fn deinit(self: *DerivedConfig) void {
-        _ = self;
+        self.font_features.deinit();
     }
 };
 
@@ -282,7 +289,10 @@ pub fn init(alloc: Allocator, options: renderer.Options) !OpenGL {
     // Create the initial font shaper
     var shape_buf = try alloc.alloc(font.shape.Cell, 1);
     errdefer alloc.free(shape_buf);
-    var shaper = try font.Shaper.init(alloc, shape_buf);
+    var shaper = try font.Shaper.init(alloc, .{
+        .cell_buf = shape_buf,
+        .features = options.config.font_features.items,
+    });
     errdefer shaper.deinit();
 
     // Create our shader
@@ -1299,6 +1309,20 @@ pub fn changeConfig(self: *OpenGL, config: *DerivedConfig) !void {
         self.font_group.atlas_color.clear();
     }
 
+    // We always redo the font shaper in case font features changed. We
+    // could check to see if there was an actual config change but this is
+    // easier and rare enough to not cause performance issues.
+    {
+        var font_shaper = try font.Shaper.init(self.alloc, .{
+            .cell_buf = self.font_shaper.cell_buf,
+            .features = config.font_features.items,
+        });
+        errdefer font_shaper.deinit();
+        self.font_shaper.deinit();
+        self.font_shaper = font_shaper;
+    }
+
+    self.config.deinit();
     self.config = config.*;
 }