44 lines
1.5 KiB
GLSL
44 lines
1.5 KiB
GLSL
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#version 450 core
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out vec4 FragColor;
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in vec3 WorldPos;
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uniform samplerCube environmentMap;
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const float PI = 3.14159265359;
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void main()
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{
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// The world vector acts as the normal of a tangent surface
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// from the origin, aligned to WorldPos. Given this normal, calculate all
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// incoming radiance of the environment. The result of this radiance
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// is the radiance of light coming from -Normal direction, which is what
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// we use in the PBR shader to sample irradiance.
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vec3 N = normalize(WorldPos);
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vec3 irradiance = vec3(0.0);
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// tangent space calculation from origin point
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vec3 up = vec3(0.0, 1.0, 0.0);
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vec3 right = normalize(cross(up, N));
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up = normalize(cross(N, right));
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float sampleDelta = 0.025;
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float nrSamples = 0.0;
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for(float phi = 0.0; phi < 2.0 * PI; phi += sampleDelta)
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{
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for(float theta = 0.0; theta < 0.5 * PI; theta += sampleDelta)
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{
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// spherical to cartesian (in tangent space)
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vec3 tangentSample = vec3(sin(theta) * cos(phi), sin(theta) * sin(phi), cos(theta));
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// tangent space to world
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vec3 sampleVec = tangentSample.x * right + tangentSample.y * up + tangentSample.z * N;
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irradiance += texture(environmentMap, sampleVec).rgb * cos(theta) * sin(theta);
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nrSamples++;
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}
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}
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irradiance = PI * irradiance * (1.0 / float(nrSamples));
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FragColor = vec4(irradiance, 1.0);
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}
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