Merge branch 'blender-v4.2-release'

source/blender/compositor/realtime_compositor/shaders/library/gpu_shader_compositor_difference_matte.glsl

@@ -2,13 +2,16 @@
  *
  * SPDX-License-Identifier: GPL-2.0-or-later */
 
+#pragma BLENDER_REQUIRE(gpu_shader_common_math_utils.glsl)
+
 void node_composite_difference_matte(
     vec4 color, vec4 key, float tolerance, float falloff, out vec4 result, out float matte)
 {
-  vec4 difference = abs(color - key);
-  float average_difference = (difference.r + difference.g + difference.b) / 3.0;
-  bool is_opaque = average_difference > tolerance + falloff;
-  float alpha = is_opaque ? color.a : (max(0.0, average_difference - tolerance) / falloff);
+  float difference = dot(abs(color - key).rgb, vec3(1.0)) / 3.0;
+
+  bool is_opaque = difference > tolerance + falloff;
+  float alpha = is_opaque ? color.a : safe_divide(max(0.0, difference - tolerance), falloff);
+
   matte = min(alpha, color.a);
   result = color * matte;
 }