From 489ed57e2f924e6993158427ad9317f21eede9eb Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Mon, 11 Dec 2023 21:41:13 -0800
Subject: [PATCH] font/harfbuzz: track x/y offsets

---
 pkg/harfbuzz/font.zig        |  8 ++++++++
 src/font/face/coretext.zig   |  1 +
 src/font/shaper/harfbuzz.zig | 34 ++++++++++++++++++++++++++++++----
 src/renderer/Metal.zig       | 14 ++++----------
 4 files changed, 43 insertions(+), 14 deletions(-)

diff --git a/pkg/harfbuzz/font.zig b/pkg/harfbuzz/font.zig
index 259274446..0947ea0b2 100644
--- a/pkg/harfbuzz/font.zig
+++ b/pkg/harfbuzz/font.zig
@@ -17,4 +17,12 @@ pub const Font = struct {
     pub fn destroy(self: *Font) void {
         c.hb_font_destroy(self.handle);
     }
+
+    pub fn setScale(self: *Font, x: u32, y: u32) void {
+        c.hb_font_set_scale(
+            self.handle,
+            @intCast(x),
+            @intCast(y),
+        );
+    }
 };
diff --git a/src/font/face/coretext.zig b/src/font/face/coretext.zig
index 188a3bce8..a57216df4 100644
--- a/src/font/face/coretext.zig
+++ b/src/font/face/coretext.zig
@@ -77,6 +77,7 @@ pub const Face = struct {
     pub fn initFont(ct_font: *macos.text.Font, opts: font.face.Options) !Face {
         var hb_font = try harfbuzz.coretext.createFont(ct_font);
         errdefer hb_font.destroy();
+        hb_font.setScale(opts.size.pixels(), opts.size.pixels());
 
         const traits = ct_font.getSymbolicTraits();
         const metrics = metrics: {
diff --git a/src/font/shaper/harfbuzz.zig b/src/font/shaper/harfbuzz.zig
index 781d5a708..4a3613276 100644
--- a/src/font/shaper/harfbuzz.zig
+++ b/src/font/shaper/harfbuzz.zig
@@ -133,17 +133,43 @@ pub const Shaper = struct {
         // If it isn't true, I'd like to catch it and learn more.
         assert(info.len == pos.len);
 
+        // This keeps track of the current offsets within a single cell.
+        var cell_offset: struct {
+            cluster: u32 = 0,
+            x: i32 = 0,
+            y: i32 = 0,
+        } = .{};
+
         // 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) |v| {
+        for (info, pos) |info_v, pos_v| {
+            if (info_v.cluster != cell_offset.cluster) cell_offset = .{
+                .cluster = info_v.cluster,
+            };
+
             self.cell_buf.appendAssumeCapacity(.{
-                .x = @intCast(v.cluster),
-                .glyph_index = v.codepoint,
+                .x = @intCast(info_v.cluster),
+                .x_offset = @intCast(cell_offset.x),
+                .y_offset = @intCast(cell_offset.y),
+                .glyph_index = info_v.codepoint,
             });
 
-            // log.warn("i={} info={} pos={} cell={}", .{ i, v, pos[i], self.cell_buf[i] });
+            if (font.options.backend.hasFreetype()) {
+                // Freetype returns 26.6 fixed point values, so we need to
+                // divide by 64 to get the actual value. I can't find any
+                // HB API to stop this.
+                cell_offset.x += pos_v.x_advance >> 6;
+                cell_offset.y += pos_v.y_advance >> 6;
+            } else {
+                cell_offset.x += pos_v.x_advance;
+                cell_offset.y += pos_v.y_advance;
+            }
+
+            // const i = self.cell_buf.items.len - 1;
+            // log.warn("i={} info={} pos={} cell={}", .{ i, info_v, pos_v, self.cell_buf.items[i] });
         }
+        //log.warn("----------------", .{});
 
         return self.cell_buf.items;
     }
diff --git a/src/renderer/Metal.zig b/src/renderer/Metal.zig
index 9f7356d4b..ea151819a 100644
--- a/src/renderer/Metal.zig
+++ b/src/renderer/Metal.zig
@@ -1787,15 +1787,6 @@ pub fn updateCell(
             .emoji => .fg_color,
         };
 
-        // If this glyph doesn't have an advance, then we assume it is
-        // connected to the previous glyph (perhaps an unsafe assumption...)
-        // and offset by the cell width.
-        // Related: https://github.com/mitchellh/ghostty/issues/1046
-        const extra_offset: i32 = if (glyph.advance_x == 0)
-            @intCast(self.grid_metrics.cell_width)
-        else
-            0;
-
         self.cells.appendAssumeCapacity(.{
             .mode = mode,
             .grid_pos = .{ @as(f32, @floatFromInt(x)), @as(f32, @floatFromInt(y)) },
@@ -1804,7 +1795,10 @@ pub fn updateCell(
             .bg_color = bg,
             .glyph_pos = .{ glyph.atlas_x, glyph.atlas_y },
             .glyph_size = .{ glyph.width, glyph.height },
-            .glyph_offset = .{ glyph.offset_x + extra_offset, glyph.offset_y },
+            .glyph_offset = .{
+                glyph.offset_x + shaper_cell.x_offset,
+                glyph.offset_y + shaper_cell.y_offset,
+            },
         });
     }