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#pragma BLENDER_REQUIRE(gpu_shader_common_math_utils.glsl)
#pragma BLENDER_REQUIRE(gpu_shader_compositor_texture_utilities.glsl)
/* Given the texel in the range [-radius, radius] in both axis, load the appropriate weight from
* the weights texture, where the given texel (0, 0) corresponds the center of weights texture.
* Note that we load the weights texture inverted along both directions to maintain the shape of
* the weights if it was not symmetrical. To understand why inversion makes sense, consider a 1D
* weights texture whose right half is all ones and whose left half is all zeros. Further, consider
* that we are blurring a single white pixel on a black background. When computing the value of a
* pixel that is to the right of the white pixel, the white pixel will be in the left region of the
* search window, and consequently, without inversion, a zero will be sampled from the left side of
* the weights texture and result will be zero. However, what we expect is that pixels to the right
* of the white pixel will be white, that is, they should sample a weight of 1 from the right side
* of the weights texture, hence the need for inversion. */
vec4 load_weight(ivec2 texel, float radius)
{
/* The center zero texel is always assigned a unit weight regardless of the corresponding weight
* in the weights texture. That's to guarantee that at last the center pixel will be accumulated
* even if the weights texture is zero at its center. */
if (texel == ivec2(0)) {
return vec4(1.0);
}
/* Add the radius to transform the texel into the range [0, radius * 2], with an additional 0.5
* to sample at the center of the pixels, then divide by the upper bound plus one to transform
* the texel into the normalized range [0, 1] needed to sample the weights sampler. Finally,
* invert the textures coordinates by subtracting from 1 to maintain the shape of the weights as
* mentioned in the function description. */
return texture(weights_tx, 1.0 - ((texel + vec2(radius + 0.5)) / (radius * 2 + 1)));
}
void main()
{
ivec2 texel = ivec2(gl_GlobalInvocationID.xy);
/* The mask input is treated as a boolean. If it is zero, then no blurring happens for this
* pixel. Otherwise, the pixel is blurred normally and the mask value is irrelevant. */
float mask = texture_load(mask_tx, texel).x;
if (mask == 0.0) {
imageStore(output_img, texel, texture_load(input_tx, texel));
return;
}
float center_size = texture_load(size_tx, texel).x * base_size;
/* Go over the window of the given search radius and accumulate the colors multiplied by their
* respective weights as well as the weights themselves, but only if both the size of the center
* pixel and the size of the candidate pixel are less than both the x and y distances of the
* candidate pixel. */
vec4 accumulated_color = vec4(0.0);
vec4 accumulated_weight = vec4(0.0);
for (int y = -search_radius; y <= search_radius; y++) {
for (int x = -search_radius; x <= search_radius; x++) {
float candidate_size = texture_load(size_tx, texel + ivec2(x, y)).x * base_size;
/* Skip accumulation if either the x or y distances of the candidate pixel are larger than
* either the center or candidate pixel size. Note that the max and min functions here denote
* "either" in the aforementioned description. */
float size = min(center_size, candidate_size);
if (max(abs(x), abs(y)) > size) {
continue;
}
vec4 weight = load_weight(ivec2(x, y), size);
accumulated_color += texture_load(input_tx, texel + ivec2(x, y)) * weight;
accumulated_weight += weight;
}
}
imageStore(output_img, texel, safe_divide(accumulated_color, accumulated_weight));
}
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