macOS: Fix scrolling very slowly with wheel mice not working

Fixes #1238

docs/changelog.rst

@@ -20,6 +20,8 @@ Changelog
 
 - macOS: Add an entry to the dock menu to open a new OS window (:iss:`1242`)
 
+- macOS: Fix scrolling very slowly with wheel mice not working (:iss:`1238`)
+
 - Fix changing :opt:`cursor_text_color` via remote control not working
   (:iss:`1229`)
 

kitty/mouse.c

@@ -585,6 +585,9 @@ scroll_event(double UNUSED xoffset, double yoffset, int flags) {
         global_state.callback_os_window->pending_scroll_pixels = pixels - s * (int) global_state.callback_os_window->fonts_data->cell_height;
     } else {
         s = (int) round(yoffset * OPT(wheel_scroll_multiplier));
+        // apparently on cocoa some mice generate really small yoffset values
+        // when scrolling slowly https://github.com/kovidgoyal/kitty/issues/1238
+        if (s == 0 && yoffset != 0) s = yoffset > 0 ? 1 : -1;
         global_state.callback_os_window->pending_scroll_pixels = 0;
     }
     if (s == 0) return;