1 files changed, 43 insertions, 0 deletions
diff --git a/source/blender/gpu/shaders/compositor/library/gpu_shader_compositor_chroma_matte.glsl b/source/blender/gpu/shaders/compositor/library/gpu_shader_compositor_chroma_matte.glsl
new file mode 100644
index 00000000000..5d6bea0c9db
--- /dev/null
+++ b/source/blender/gpu/shaders/compositor/library/gpu_shader_compositor_chroma_matte.glsl
@@ -0,0 +1,43 @@
+#pragma BLENDER_REQUIRE(gpu_shader_common_math_utils.glsl)
+#pragma BLENDER_REQUIRE(gpu_shader_common_color_utils.glsl)
+
+/* Algorithm from the book Video Demystified. Chapter 7. Chroma Keying. */
+void node_composite_chroma_matte(vec4 color,
+                                 vec4 key,
+                                 float acceptance,
+                                 float cutoff,
+                                 float falloff,
+                                 out vec4 result,
+                                 out float matte)
+{
+  vec4 color_ycca;
+  rgba_to_ycca_itu_709(color, color_ycca);
+  vec4 key_ycca;
+  rgba_to_ycca_itu_709(key, key_ycca);
+
+  /* Normalize the CrCb components into the [-1, 1] range. */
+  vec2 color_cc = color_ycca.yz * 2.0 - 1.0;
+  vec2 key_cc = key_ycca.yz * 2.0 - 1.0;
+
+  /* Rotate the color onto the space of the key such that x axis of the color space passes through
+   * the key color. */
+  color_cc = vector_to_rotation_matrix(key_cc * vec2(1.0, -1.0)) * color_cc;
+
+  /* Compute foreground key. If positive, the value is in the [0, 1] range. */
+  float foreground_key = color_cc.x - (abs(color_cc.y) / acceptance);
+
+  /* Negative foreground key values retain the original alpha. Positive values are scaled by the
+   * falloff, while colors that make an angle less than the cutoff angle get a zero alpha. */
+  float alpha = color.a;
+  if (foreground_key > 0.0) {
+    alpha = 1.0 - (foreground_key / falloff);
+
+    if (abs(atan(color_cc.y, color_cc.x)) < (cutoff / 2.0)) {
+      alpha = 0.0;
+    }
+  }
+
+  /* Compute output. */
+  matte = min(alpha, color.a);
+  result = color * matte;
+}