Fix #8731

docs/changelog.rst

@@ -126,6 +126,8 @@ Detailed list of changes
 - Wayland GNOME: Fix incorrect OS Window tracking because GNOME has started
   activating windows on non-current workspaces (:iss:`8716`)
 
+- Fix a regression in 0.40.0 that broke rendering of VS15 variation selectors in some circumstances (:iss:`8731`)
+
 0.42.1 [2025-05-17]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

kitty/screen.c

@@ -861,7 +861,7 @@ halve_multicell_width(Screen *self, index_type x_, index_type y_) {
     unsigned new_width = cp[x_].width / 2;
     while (cp[x_].x && x_ > 0) x_--;
     index_type x_limit = MIN(self->columns, x_ + mcd_x_limit(&cp[x_]));
-    index_type half_x_limit = x_limit / 2;
+    index_type half_x_limit = MIN(self->columns, x_ + mcd_x_limit(&cp[x_]) / 2);
     int y_max_limit = MIN(self->lines, y_ + cp[x_].scale);
     for (int y = y_min_limit + 1; y < y_max_limit; y++) {
         Line *line = range_line_(self, y); cp = line->cpu_cells; gp = line->gpu_cells;

kitty_tests/screen.py

@@ -694,6 +694,11 @@ class TestScreen(BaseTest):
 
     def test_variation_selectors(self):
         s = self.create_screen()
+        def tt(text_to_draw):
+            s.reset()
+            s.draw(text_to_draw)
+            self.ae(str(s.line(0)), text_to_draw)
+        tt('abc\U0001f44d\ufe0ed')
         def t(*a):
             s.reset()
             for i in range(0, len(a), 2):