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Switch-Toolbox/Toolbox/Shader/PBR/irradianceShader.frag

43 lines
1.4 KiB
GLSL

#version 330 core
out vec4 FragColor;
in vec3 WorldPos;
uniform samplerCube environmentMap;
const float PI = 3.14159265359;
void main()
{
// The world vector acts as the normal of a tangent surface
// from the origin, aligned to WorldPos. Given this normal, calculate all
// incoming radiance of the environment. The result of this radiance
// is the radiance of light coming from -Normal direction, which is what
// we use in the PBR shader to sample irradiance.
vec3 N = normalize(WorldPos);
vec3 irradiance = vec3(0.0);
// tangent space calculation from origin point
vec3 up = vec3(0.0, 1.0, 0.0);
vec3 right = cross(up, N);
up = cross(N, right);
float sampleDelta = 0.025;
float nrSamples = 0.0;
for(float phi = 0.0; phi < 2.0 * PI; phi += sampleDelta)
{
for(float theta = 0.0; theta < 0.5 * PI; theta += sampleDelta)
{
// spherical to cartesian (in tangent space)
vec3 tangentSample = vec3(sin(theta) * cos(phi), sin(theta) * sin(phi), cos(theta));
// tangent space to world
vec3 sampleVec = tangentSample.x * right + tangentSample.y * up + tangentSample.z * N;
irradiance += texture(environmentMap, sampleVec).rgb * cos(theta) * sin(theta);
nrSamples++;
}
}
irradiance = PI * irradiance * (1.0 / float(nrSamples));
FragColor = vec4(irradiance, 1.0);
}