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#[compute]
#version 450
VERSION_DEFINES
layout(local_size_x = 8, local_size_y = 8, local_size_z = 1) in;
layout(set = 0, binding = 0) uniform sampler2D source_normal;
layout(r8, set = 1, binding = 0) uniform restrict writeonly image2D dest_roughness;
layout(push_constant, binding = 1, std430) uniform Params {
ivec2 screen_size;
float curve;
uint pad;
}
params;
#define HALF_PI 1.5707963267948966
void main() {
// Pixel being shaded
ivec2 pos = ivec2(gl_GlobalInvocationID.xy);
if (any(greaterThan(pos, params.screen_size))) { //too large, do nothing
return;
}
vec3 normal_accum = vec3(0.0);
float accum = 0.0;
for (int i = 0; i <= 1; i++) {
for (int j = 0; j <= 1; j++) {
normal_accum += normalize(texelFetch(source_normal, pos + ivec2(i, j), 0).xyz * 2.0 - 1.0);
accum += 1.0;
}
}
normal_accum /= accum;
float r = length(normal_accum);
float limit;
if (r < 1.0) {
float threshold = 0.4;
/*
//Formula from Filament, does not make sense to me.
float r2 = r * r;
float kappa = (3.0f * r - r * r2) / (1.0f - r2);
float variance = 0.25f / kappa;
limit = sqrt(min(2.0f * variance, threshold * threshold));
*/
/*
//Formula based on probability distribution graph
float width = acos(max(0.0,r)); // convert to angle (width)
float roughness = pow(width,1.7)*0.854492; //approximate (crappy) formula to convert to roughness
limit = min(sqrt(roughness), threshold); //convert to perceptual roughness and apply threshold
*/
limit = min(sqrt(pow(acos(max(0.0, r)) / HALF_PI, params.curve)), threshold); //convert to perceptual roughness and apply threshold
//limit = 0.5;
} else {
limit = 0.0;
}
imageStore(dest_roughness, pos, vec4(limit));
}
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