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#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;
}
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