Merge pull request #1241 from mitchellh/monaspace-ligs

font: insert blank cells for multi-cell ligatures for styling

src/font/shape.zig

@@ -37,7 +37,10 @@ pub const Cell = struct {
     /// this cell is available in the text run. This glyph index is only
     /// valid for a given GroupCache and FontIndex that was used to create
     /// the runs.
-    glyph_index: u32,
+    ///
+    /// If this is null then this is an empty cell. If there are styles
+    /// then those should be applied but there is no glyph to render.
+    glyph_index: ?u32,
 };
 
 /// Options for shapers.

src/font/shaper/coretext.zig

@@ -230,6 +230,10 @@ pub const Shaper = struct {
             cell_offset.x += advance.width;
             cell_offset.y += advance.height;
 
+            // TODO: harfbuzz shaper has handling for inserting blank
+            // cells for multi-cell ligatures. Do we need to port that?
+            // Example: try Monaspace "===" with a background color.
+
             _ = pos;
             // const i = self.cell_buf.items.len - 1;
             // log.warn(

src/font/shaper/harfbuzz.zig

@@ -142,13 +142,13 @@ pub const Shaper = struct {
 
         // Convert all our info/pos to cells and set it.
         self.cell_buf.clearRetainingCapacity();
-        try self.cell_buf.ensureTotalCapacity(self.alloc, info.len);
+        for (info, pos, 0..) |info_v, pos_v, i| {
-        for (info, pos) |info_v, pos_v| {
+            // If our cluster changed then we've moved to a new cell.
             if (info_v.cluster != cell_offset.cluster) cell_offset = .{
                 .cluster = info_v.cluster,
             };
 
-            self.cell_buf.appendAssumeCapacity(.{
+            try self.cell_buf.append(self.alloc, .{
                 .x = @intCast(info_v.cluster),
                 .x_offset = @intCast(cell_offset.x),
                 .y_offset = @intCast(cell_offset.y),
@@ -166,6 +166,43 @@ pub const Shaper = struct {
                 cell_offset.y += pos_v.y_advance;
             }
 
+            // Determine the width of the cell. To do this, we have to
+            // find the next cluster that has been shaped. This tells us how
+            // many cells this glyph replaced (i.e. for ligatures). For example
+            // in some fonts "!=" turns into a single glyph from the component
+            // parts "!" and "=" so this cell width would be "2" despite
+            // only having a single glyph.
+            //
+            // Many fonts replace ligature cells with space so that this always
+            // is one (e.g. Fira Code, JetBrains Mono, etc). Some do not
+            // (e.g. Monaspace).
+            const cell_width = width: {
+                if (i + 1 < info.len) {
+                    // We may have to go through multiple glyphs because
+                    // multiple can be replaced. e.g. "==="
+                    for (info[i + 1 ..]) |next_info_v| {
+                        if (next_info_v.cluster != info_v.cluster) {
+                            break :width next_info_v.cluster - info_v.cluster;
+                        }
+                    }
+                }
+
+                // If we reached the end then our width is our max cluster
+                // minus this one.
+                const max = run.offset + run.cells;
+                break :width max - info_v.cluster;
+            };
+            if (cell_width > 1) {
+                // To make the renderer implementations simpler, we convert
+                // the extra spaces for width to blank cells.
+                for (1..cell_width) |j| {
+                    try self.cell_buf.append(self.alloc, .{
+                        .x = @intCast(info_v.cluster + j),
+                        .glyph_index = null,
+                    });
+                }
+            }
+
             // const i = self.cell_buf.items.len - 1;
             // log.warn("i={} info={} pos={} cell={}", .{ i, info_v, pos_v, self.cell_buf.items[i] });
         }
@@ -334,7 +371,9 @@ test "shape inconsolata ligs" {
             count += 1;
 
             const cells = try shaper.shape(run);
-            try testing.expectEqual(@as(usize, 1), cells.len);
+            try testing.expectEqual(@as(usize, 2), cells.len);
+            try testing.expect(cells[0].glyph_index != null);
+            try testing.expect(cells[1].glyph_index == null);
         }
         try testing.expectEqual(@as(usize, 1), count);
     }
@@ -351,7 +390,38 @@ test "shape inconsolata ligs" {
             count += 1;
 
             const cells = try shaper.shape(run);
-            try testing.expectEqual(@as(usize, 1), cells.len);
+            try testing.expectEqual(@as(usize, 3), cells.len);
+            try testing.expect(cells[0].glyph_index != null);
+            try testing.expect(cells[1].glyph_index == null);
+            try testing.expect(cells[2].glyph_index == null);
+        }
+        try testing.expectEqual(@as(usize, 1), count);
+    }
+}
+
+test "shape monaspace ligs" {
+    const testing = std.testing;
+    const alloc = testing.allocator;
+
+    var testdata = try testShaperWithFont(alloc, .monaspace_neon);
+    defer testdata.deinit();
+
+    {
+        var screen = try terminal.Screen.init(alloc, 3, 5, 0);
+        defer screen.deinit();
+        try screen.testWriteString("===");
+
+        var shaper = &testdata.shaper;
+        var it = shaper.runIterator(testdata.cache, screen.getRow(.{ .screen = 0 }), null, null);
+        var count: usize = 0;
+        while (try it.next(alloc)) |run| {
+            count += 1;
+
+            const cells = try shaper.shape(run);
+            try testing.expectEqual(@as(usize, 3), cells.len);
+            try testing.expect(cells[0].glyph_index != null);
+            try testing.expect(cells[1].glyph_index == null);
+            try testing.expect(cells[2].glyph_index == null);
         }
         try testing.expectEqual(@as(usize, 1), count);
     }
@@ -376,7 +446,7 @@ test "shape emoji width" {
             count += 1;
 
             const cells = try shaper.shape(run);
-            try testing.expectEqual(@as(usize, 1), cells.len);
+            try testing.expectEqual(@as(usize, 2), cells.len);
         }
         try testing.expectEqual(@as(usize, 1), count);
     }
@@ -411,7 +481,9 @@ test "shape emoji width long" {
         try testing.expectEqual(@as(u32, 4), shaper.hb_buf.getLength());
 
         const cells = try shaper.shape(run);
-        try testing.expectEqual(@as(usize, 1), cells.len);
+
+        // screen.testWriteString isn't grapheme aware, otherwise this is two
+        try testing.expectEqual(@as(usize, 5), cells.len);
     }
     try testing.expectEqual(@as(usize, 1), count);
 }
@@ -574,9 +646,9 @@ test "shape box glyphs" {
         try testing.expectEqual(@as(u32, 2), shaper.hb_buf.getLength());
         const cells = try shaper.shape(run);
         try testing.expectEqual(@as(usize, 2), cells.len);
-        try testing.expectEqual(@as(u32, 0x2500), cells[0].glyph_index);
+        try testing.expectEqual(@as(u32, 0x2500), cells[0].glyph_index.?);
         try testing.expectEqual(@as(u16, 0), cells[0].x);
-        try testing.expectEqual(@as(u32, 0x2501), cells[1].glyph_index);
+        try testing.expectEqual(@as(u32, 0x2501), cells[1].glyph_index.?);
         try testing.expectEqual(@as(u16, 1), cells[1].x);
     }
     try testing.expectEqual(@as(usize, 1), count);
@@ -902,11 +974,23 @@ const TestShaper = struct {
     }
 };
 
+const TestFont = enum {
+    inconsolata,
+    monaspace_neon,
+};
+
 /// Helper to return a fully initialized shaper.
 fn testShaper(alloc: Allocator) !TestShaper {
-    const testFont = @import("../test.zig").fontRegular;
+    return try testShaperWithFont(alloc, .inconsolata);
+}
+
+fn testShaperWithFont(alloc: Allocator, font_req: TestFont) !TestShaper {
     const testEmoji = @import("../test.zig").fontEmoji;
     const testEmojiText = @import("../test.zig").fontEmojiText;
+    const testFont = switch (font_req) {
+        .inconsolata => @import("../test.zig").fontRegular,
+        .monaspace_neon => @import("../test.zig").fontMonaspaceNeon,
+    };
 
     var lib = try Library.init();
     errdefer lib.deinit();

src/font/test.zig

@@ -15,3 +15,7 @@ pub const fontVariable = @embedFile("res/Lilex-VF.ttf");
 /// Cozette is a unique font because it embeds some emoji characters
 /// but has a text presentation.
 pub const fontCozette = @embedFile("res/CozetteVector.ttf");
+
+/// Monaspace has weird ligature behaviors we want to test in our shapers
+/// so we embed it here.
+pub const fontMonaspaceNeon = @embedFile("res/MonaspaceNeon-Regular.otf");

src/renderer/Metal.zig

@@ -1796,12 +1796,12 @@ fn updateCell(
     };
 
     // If the cell has a character, draw it
-    if (cell.char > 0) {
+    if (cell.char > 0) fg: {
         // Render
         const glyph = try self.font_group.renderGlyph(
             self.alloc,
             shaper_run.font_index,
-            shaper_cell.glyph_index,
+            shaper_cell.glyph_index orelse break :fg,
             .{
                 .grid_metrics = self.grid_metrics,
                 .thicken = self.config.font_thicken,

src/renderer/OpenGL.zig

@@ -1504,12 +1504,12 @@ fn updateCell(
     };
 
     // If the cell has a character, draw it
-    if (cell.char > 0) {
+    if (cell.char > 0) fg: {
         // Render
         const glyph = try self.font_group.renderGlyph(
             self.alloc,
             shaper_run.font_index,
-            shaper_cell.glyph_index,
+            shaper_cell.glyph_index orelse break :fg,
             .{
                 .grid_metrics = self.grid_metrics,
                 .thicken = self.config.font_thicken,