stk-code_catmod/data/shaders/ssao.frag

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// From paper http://graphics.cs.williams.edu/papers/AlchemyHPG11/
// and improvements here http://graphics.cs.williams.edu/papers/SAOHPG12/
uniform sampler2D dtex;
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uniform float radius;
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uniform float k = 1.5;
uniform float sigma = 1.;
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out float AO;
const float tau = 7.;
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const float beta = 0.002;
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const float epsilon = .00001;
#define SAMPLES 16
const float invSamples = 1. / SAMPLES;
vec3 getXcYcZc(int x, int y, float zC)
{
// We use perspective symetric projection matrix hence P(0,2) = P(1, 2) = 0
float xC= (2 * (float(x)) / screen.x - 1.) * zC / ProjectionMatrix[0][0];
float yC= (2 * (float(y)) / screen.y - 1.) * zC / ProjectionMatrix[1][1];
return vec3(xC, yC, zC);
}
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void main(void)
{
vec2 uv = gl_FragCoord.xy / screen;
float lineardepth = textureLod(dtex, uv, 0.).x;
int x = int(gl_FragCoord.x), y = int(gl_FragCoord.y);
vec3 FragPos = getXcYcZc(x, y, lineardepth);
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// get the normal of current fragment
vec3 ddx = dFdx(FragPos);
vec3 ddy = dFdy(FragPos);
vec3 norm = normalize(cross(ddy, ddx));
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float r = radius / FragPos.z;
float phi = 3. * (x ^ y) + x * y;
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float bl = 0.0;
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float m = log2(r) + 6 + log2(invSamples);
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float theta = mod(2. * 3.14 * tau * .5 * invSamples + phi, 6.283185307179586);
vec2 rotations = vec2(cos(theta), sin(theta)) * screen;
vec2 offset = vec2(cos(invSamples), sin(invSamples));
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for(int i = 0; i < SAMPLES; ++i) {
float alpha = (i + .5) * invSamples;
rotations = vec2(rotations.x * offset.x - rotations.y * offset.y, rotations.x * offset.y + rotations.y * offset.x);
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float h = r * alpha;
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vec2 localoffset = h * rotations;
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m = m + .5;
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ivec2 ioccluder_uv = ivec2(x, y) + ivec2(localoffset);
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if (ioccluder_uv.x < 0 || ioccluder_uv.x > screen.x || ioccluder_uv.y < 0 || ioccluder_uv.y > screen.y) continue;
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float LinearoccluderFragmentDepth = textureLod(dtex, vec2(ioccluder_uv) / screen, max(m, 0.)).x;
vec3 OccluderPos = getXcYcZc(ioccluder_uv.x, ioccluder_uv.y, LinearoccluderFragmentDepth);
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vec3 vi = OccluderPos - FragPos;
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bl += max(0, dot(vi, norm) - FragPos.z * beta) / (dot(vi, vi) + epsilon);
}
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AO = max(pow(1.0 - min(2. * sigma * bl * invSamples, 0.99), k), 0.);
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}