From 712cc9e55c4dfc006c8e9767c07aee3af96dcbb3 Mon Sep 17 00:00:00 2001
From: Qwerasd <qwerasd205@users.noreply.github.com>
Date: Fri, 14 Nov 2025 16:50:18 -0700
Subject: [PATCH] fix(shaper/coretext): handle non-monotonic runs by sorting

---
 src/font/shaper/coretext.zig | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/src/font/shaper/coretext.zig b/src/font/shaper/coretext.zig
index d73b191b8..45844d3e2 100644
--- a/src/font/shaper/coretext.zig
+++ b/src/font/shaper/coretext.zig
@@ -392,6 +392,12 @@ pub const Shaper = struct {
         self.cell_buf.clearRetainingCapacity();
         try self.cell_buf.ensureTotalCapacity(self.alloc, line.getGlyphCount());
 
+        // CoreText, despite our insistence with an enforced embedding level,
+        // may sometimes output runs that are non-monotonic. In order to fix
+        // this, we check the run status for each run and if any aren't ltr
+        // we set this to true, which indicates that we must sort our buffer.
+        var non_ltr: bool = false;
+
         // CoreText may generate multiple runs even though our input to
         // CoreText is already split into runs by our own run iterator.
         // The runs as far as I can tell are always sequential to each
@@ -401,6 +407,9 @@ pub const Shaper = struct {
         for (0..runs.getCount()) |i| {
             const ctrun = runs.getValueAtIndex(macos.text.Run, i);
 
+            const status = ctrun.getStatus();
+            if (status.non_monotonic or status.right_to_left) non_ltr = true;
+
             // Get our glyphs and positions
             const glyphs = ctrun.getGlyphsPtr() orelse try ctrun.getGlyphs(alloc);
             const advances = ctrun.getAdvancesPtr() orelse try ctrun.getAdvances(alloc);
@@ -441,6 +450,25 @@ pub const Shaper = struct {
             }
         }
 
+        // If our buffer contains some non-ltr sections we need to sort it :/
+        if (non_ltr) {
+            // This is EXCEPTIONALLY rare. Only happens for languages with
+            // complex shaping which we don't even really support properly
+            // right now, so are very unlikely to be used heavily by users
+            // of Ghostty.
+            @branchHint(.cold);
+            std.mem.sort(
+                font.shape.Cell,
+                self.cell_buf.items,
+                {},
+                struct {
+                    fn lt(_: void, a: font.shape.Cell, b: font.shape.Cell) bool {
+                        return a.x < b.x;
+                    }
+                }.lt,
+            );
+        }
+
         return self.cell_buf.items;
     }