font/coretext: Use positions to fix x/y offsets

pkg/macos/text/run.zig

@@ -106,6 +106,19 @@ pub const Run = opaque {
     pub fn getStatus(self: *Run) Status {
         return @bitCast(c.CTRunGetStatus(@ptrCast(self)));
     }
+
+    pub fn getAttributes(self: *Run) *foundation.Dictionary {
+        return @ptrCast(@constCast(c.CTRunGetAttributes(@ptrCast(self))));
+    }
+
+    pub fn getFont(self: *Run) ?*text.Font {
+        const attrs = self.getAttributes();
+        const font_ptr = attrs.getValue(*const anyopaque, c.kCTFontAttributeName);
+        if (font_ptr) |ptr| {
+            return @ptrCast(@constCast(ptr));
+        }
+        return null;
+    }
 };
 
 /// https://developer.apple.com/documentation/coretext/ctrunstatus?language=objc

src/font/shaper/coretext.zig

@@ -377,11 +377,21 @@ pub const Shaper = struct {
         const line = typesetter.createLine(.{ .location = 0, .length = 0 });
         self.cf_release_pool.appendAssumeCapacity(line);
 
-        // This keeps track of the current offsets within a single cell.
+        // This keeps track of the current offsets within a run.
+        var run_offset: struct {
+            x: f64 = 0,
+            y: f64 = 0,
+        } = .{};
+
+        // This keeps track of the current offsets within a cell.
         var cell_offset: struct {
             cluster: u32 = 0,
             x: f64 = 0,
             y: f64 = 0,
+
+            // For debugging positions, turn this on:
+            start_index: usize = 0,
+            end_index: usize = 0,
         } = .{};
 
         // Clear our cell buf and make sure we have enough room for the whole
@@ -411,15 +421,18 @@ pub const Shaper = struct {
             // Get our glyphs and positions
             const glyphs = ctrun.getGlyphsPtr() orelse try ctrun.getGlyphs(alloc);
             const advances = ctrun.getAdvancesPtr() orelse try ctrun.getAdvances(alloc);
+            const positions = ctrun.getPositionsPtr() orelse try ctrun.getPositions(alloc);
             const indices = ctrun.getStringIndicesPtr() orelse try ctrun.getStringIndices(alloc);
             assert(glyphs.len == advances.len);
+            assert(glyphs.len == positions.len);
             assert(glyphs.len == indices.len);
 
             for (
                 glyphs,
                 advances,
+                positions,
                 indices,
-            ) |glyph, advance, index| {
+            ) |glyph, advance, position, index| {
                 // Our cluster is also our cell X position. If the cluster changes
                 // then we need to reset our current cell offsets.
                 const cluster = state.codepoints.items[index].cluster;
@@ -431,20 +444,71 @@ pub const Shaper = struct {
                     // wait for that.
                     if (cell_offset.cluster > cluster) break :pad;
 
-                    cell_offset = .{ .cluster = cluster };
+                    cell_offset = .{
+                        .cluster = cluster,
+                        .x = run_offset.x,
+                        .y = run_offset.y,
+
+                        // For debugging positions, turn this on:
+                        .start_index = index,
+                        .end_index = index,
+                    };
+                } else {
+                    if (index < cell_offset.start_index) {
+                        cell_offset.start_index = index;
+                    }
+                    if (index > cell_offset.end_index) {
+                        cell_offset.end_index = index;
+                    }
+                }
+
+                const x_offset = position.x - cell_offset.x;
+                const y_offset = position.y - cell_offset.y;
+
+                const advance_x_offset = run_offset.x - cell_offset.x;
+                const advance_y_offset = run_offset.y - cell_offset.y;
+                const x_offset_diff = x_offset - advance_x_offset;
+                const y_offset_diff = y_offset - advance_y_offset;
+
+                if (@abs(x_offset_diff) > 0.0001 or @abs(y_offset_diff) > 0.0001) {
+                    var allocating = std.Io.Writer.Allocating.init(alloc);
+                    const writer = &allocating.writer;
+                    const codepoints = state.codepoints.items[cell_offset.start_index .. cell_offset.end_index + 1];
+                    for (codepoints) |cp| {
+                        if (cp.codepoint == 0) continue; // Skip surrogate pair padding
+                        try writer.print("\\u{{{x}}}", .{cp.codepoint});
+                    }
+                    try writer.writeAll(" → ");
+                    for (codepoints) |cp| {
+                        if (cp.codepoint == 0) continue; // Skip surrogate pair padding
+                        try writer.print("{u}", .{@as(u21, @intCast(cp.codepoint))});
+                    }
+                    const formatted_cps = try allocating.toOwnedSlice();
+
+                    log.warn("position differs from advance: cluster={d} pos=({d:.2},{d:.2}) adv=({d:.2},{d:.2}) diff=({d:.2},{d:.2}) current cp={x}, cps={s}", .{
+                        cluster,
+                        x_offset,
+                        y_offset,
+                        advance_x_offset,
+                        advance_y_offset,
+                        x_offset_diff,
+                        y_offset_diff,
+                        state.codepoints.items[index].codepoint,
+                        formatted_cps,
+                    });
                 }
 
                 self.cell_buf.appendAssumeCapacity(.{
                     .x = @intCast(cluster),
-                    .x_offset = @intFromFloat(@round(cell_offset.x)),
-                    .y_offset = @intFromFloat(@round(cell_offset.y)),
+                    .x_offset = @intFromFloat(@round(x_offset)),
+                    .y_offset = @intFromFloat(@round(y_offset)),
                     .glyph_index = glyph,
                 });
 
-                // Add our advances to keep track of our current cell offsets.
+                // Add our advances to keep track of our run offsets.
                 // Advances apply to the NEXT cell.
-                cell_offset.x += advance.width;
-                cell_offset.y += advance.height;
+                run_offset.x += advance.width;
+                run_offset.y += advance.height;
             }
         }