Merge pull request #179 from mitchellh/autoitalic

Auto-italicize regular font if no italic font is found (CoreText only)

pkg/macos/text/font.zig

@@ -18,13 +18,18 @@ pub const Font = opaque {
         ) orelse Allocator.Error.OutOfMemory;
     }
 
-    pub fn copyWithAttributes(self: *Font, size: f32, attrs: ?*text.FontDescriptor) Allocator.Error!*Font {
+    pub fn copyWithAttributes(
+        self: *Font,
+        size: f32,
+        matrix: ?*const graphics.AffineTransform,
+        attrs: ?*text.FontDescriptor,
+    ) Allocator.Error!*Font {
         return @as(
             ?*Font,
             @ptrFromInt(@intFromPtr(c.CTFontCreateCopyWithAttributes(
                 @ptrCast(self),
                 size,
-                null,
+                @ptrCast(matrix),
                 @ptrCast(attrs),
             ))),
         ) orelse Allocator.Error.OutOfMemory;
@@ -217,6 +222,6 @@ test "copy" {
     const font = try Font.createWithFontDescriptor(desc, 12);
     defer font.release();
 
-    const f2 = try font.copyWithAttributes(14, null);
+    const f2 = try font.copyWithAttributes(14, null, null);
     defer f2.release();
 }

src/Surface.zig

@@ -231,7 +231,7 @@ pub fn init(
                 if (try disco_it.next()) |face| {
                     log.info("font regular: {s}", .{try face.name()});
                     try group.addFace(alloc, .regular, face);
-                } else std.log.warn("font-family not found: {s}", .{family});
+                } else log.warn("font-family not found: {s}", .{family});
             }
             if (config.@"font-family-bold") |family| {
                 var disco_it = try disco.discover(.{
@@ -243,7 +243,7 @@ pub fn init(
                 if (try disco_it.next()) |face| {
                     log.info("font bold: {s}", .{try face.name()});
                     try group.addFace(alloc, .bold, face);
-                } else std.log.warn("font-family-bold not found: {s}", .{family});
+                } else log.warn("font-family-bold not found: {s}", .{family});
             }
             if (config.@"font-family-italic") |family| {
                 var disco_it = try disco.discover(.{
@@ -255,7 +255,7 @@ pub fn init(
                 if (try disco_it.next()) |face| {
                     log.info("font italic: {s}", .{try face.name()});
                     try group.addFace(alloc, .italic, face);
-                } else std.log.warn("font-family-italic not found: {s}", .{family});
+                } else log.warn("font-family-italic not found: {s}", .{family});
             }
             if (config.@"font-family-bold-italic") |family| {
                 var disco_it = try disco.discover(.{
@@ -268,7 +268,7 @@ pub fn init(
                 if (try disco_it.next()) |face| {
                     log.info("font bold+italic: {s}", .{try face.name()});
                     try group.addFace(alloc, .bold_italic, face);
-                } else std.log.warn("font-family-bold-italic not found: {s}", .{family});
+                } else log.warn("font-family-bold-italic not found: {s}", .{family});
             }
         }
 
@@ -284,6 +284,26 @@ pub fn init(
             font.DeferredFace.initLoaded(try font.Face.init(font_lib, face_bold_ttf, font_size)),
         );
 
+        // If we support auto-italicization and we don't have an italic face,
+        // then we can try to auto-italicize our regular face.
+        if (comptime font.DeferredFace.canItalicize()) {
+            if (group.getFace(.italic) == null) {
+                if (group.getFace(.regular)) |regular| {
+                    if (try regular.italicize()) |face| {
+                        log.info("font auto-italicized: {s}", .{try face.name()});
+                        try group.addFace(alloc, .italic, face);
+                    }
+                }
+            }
+        } else {
+            // We don't support auto-italics. If we don't have an italic font
+            // face let the user know so they aren't surprised (if they look
+            // at logs).
+            if (group.getFace(.italic) == null) {
+                log.warn("no italic font face available, italics will not render", .{});
+            }
+        }
+
         // Emoji fallback. We don't include this on Mac since Mac is expected
         // to always have the Apple Emoji available.
         if (builtin.os.tag != .macos or font.Discover == void) {

src/font/DeferredFace.zig

@@ -19,6 +19,17 @@ const Presentation = @import("main.zig").Presentation;
 
 const log = std.log.scoped(.deferred_face);
 
+/// The struct used for deferred face state.
+///
+/// TODO: Change the "fc", "ct", "wc" fields in @This to just use one field
+/// with the state since there should be no world in which multiple are used.
+const FaceState = switch (options.backend) {
+    .freetype => void,
+    .fontconfig_freetype => Fontconfig,
+    .coretext_freetype, .coretext => CoreText,
+    .web_canvas => WebCanvas,
+};
+
 /// The loaded face (once loaded).
 face: ?Face = null,
 
@@ -61,6 +72,13 @@ pub const CoreText = struct {
         self.font.release();
         self.* = undefined;
     }
+
+    /// Auto-italicize the font by applying a skew.
+    pub fn italicize(self: *const CoreText) !CoreText {
+        const ct_font = try self.font.copyWithAttributes(0.0, &Face.italic_skew, null);
+        errdefer ct_font.release();
+        return .{ .font = ct_font };
+    }
 };
 
 /// WebCanvas specific data. This is only present when building with canvas.
@@ -333,6 +351,40 @@ pub fn hasCodepoint(self: DeferredFace, cp: u32, p: ?Presentation) bool {
     unreachable;
 }
 
+/// Returns true if our deferred font implementation supports auto-itacilization.
+pub fn canItalicize() bool {
+    return @hasDecl(FaceState, "italicize") and @hasDecl(Face, "italicize");
+}
+
+/// Returns a new deferred face with the italicized version of this face
+/// by applying a skew. This is NOT TRUE italics. You should use the discovery
+/// mechanism to try to find an italic font. This is a fallback for when
+/// that fails.
+pub fn italicize(self: *const DeferredFace) !?DeferredFace {
+    if (comptime !canItalicize()) return null;
+
+    var result: DeferredFace = .{};
+
+    if (self.face) |face| {
+        result.face = try face.italicize();
+    }
+
+    switch (options.backend) {
+        .freetype => {},
+        .fontconfig_freetype => if (self.fc) |*fc| {
+            result.fc = try fc.italicize();
+        },
+        .coretext, .coretext_freetype => if (self.ct) |*ct| {
+            result.ct = try ct.italicize();
+        },
+        .web_canvas => if (self.wc) |*wc| {
+            result.wc = try wc.italicize();
+        },
+    }
+
+    return result;
+}
+
 /// The wasm-compatible API.
 pub const Wasm = struct {
     const wasm = @import("../os/wasm.zig");

src/font/Group.zig

@@ -99,6 +99,15 @@ pub fn addFace(self: *Group, alloc: Allocator, style: Style, face: DeferredFace)
     try list.append(alloc, face);
 }
 
+/// Get the face for the given style. This will always return the first
+/// face (if it exists). The returned pointer is only valid as long as
+/// the faces do not change.
+pub fn getFace(self: *Group, style: Style) ?*DeferredFace {
+    const list = self.faces.getPtr(style);
+    if (list.items.len == 0) return null;
+    return &list.items[0];
+}
+
 /// Resize the fonts to the desired size.
 pub fn setSize(self: *Group, size: font.face.DesiredSize) !void {
     // Note: there are some issues here with partial failure. We don't
@@ -189,8 +198,15 @@ pub fn indexForCodepoint(
     // If we can find the exact value, then return that.
     if (self.indexForCodepointExact(cp, style, p)) |value| return value;
 
-    // Try looking for another font that will satisfy this request.
-    if (font.Discover != void) {
+    // If we're not a regular font style, try looking for a regular font
+    // that will satisfy this request. Blindly looking for unmatched styled
+    // fonts to satisfy one codepoint results in some ugly rendering.
+    if (style != .regular) {
+        if (self.indexForCodepoint(cp, .regular, p)) |value| return value;
+    }
+
+    // If we are regular, try looking for a fallback using discovery.
+    if (style == .regular and font.Discover != void) {
         if (self.discover) |*disco| discover: {
             var disco_it = disco.discover(.{
                 .codepoint = cp,

src/font/face/coretext.zig

@@ -20,6 +20,16 @@ pub const Face = struct {
     /// Metrics for this font face. These are useful for renderers.
     metrics: font.face.Metrics,
 
+    /// The matrix applied to a regular font to auto-italicize it.
+    pub const italic_skew = macos.graphics.AffineTransform{
+        .a = 1,
+        .b = 0,
+        .c = 0.267949, // approx. tan(15)
+        .d = 1,
+        .tx = 0,
+        .ty = 0,
+    };
+
     /// Initialize a CoreText-based font from a TTF/TTC in memory.
     pub fn init(lib: font.Library, source: [:0]const u8, size: font.face.DesiredSize) !Face {
         _ = lib;
@@ -47,7 +57,7 @@ pub const Face = struct {
         // Create a copy. The copyWithAttributes docs say the size is in points,
         // but we need to scale the points by the DPI and to do that we use our
         // function called "pixels".
-        const ct_font = try base.copyWithAttributes(@floatFromInt(size.pixels()), null);
+        const ct_font = try base.copyWithAttributes(@floatFromInt(size.pixels()), null, null);
         errdefer ct_font.release();
 
         var hb_font = try harfbuzz.coretext.createFont(ct_font);
@@ -69,6 +79,14 @@ pub const Face = struct {
         self.* = undefined;
     }
 
+    /// Return a new face that is the same as this but has a transformation
+    /// 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 });
+    }
+
     /// Resize the font in-place. If this succeeds, the caller is responsible
     /// for clearing any glyph caches, font atlas data, etc.
     pub fn setSize(self: *Face, size: font.face.DesiredSize) !void {