53 lines
1.7 KiB
GLSL
53 lines
1.7 KiB
GLSL
// An implementation of Sébastien Hillaire's "A Scalable and Production Ready
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// Sky and Atmosphere Rendering Technique".
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//
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// This shader generates the transmittance LUT. It stores the transmittance to
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// the Sun through the atmosphere for a given Sun zenith angle and a height
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// inside the atmosphere (0 being the ground).
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#version 330 core
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out vec3 fragColor;
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in vec2 texCoord;
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uniform float fg_EarthRadius;
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const float ATMOSPHERE_RADIUS = 6471e3;
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const int TRANSMITTANCE_STEPS = 40;
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float raySphereIntersection(vec3 ro, vec3 rd, float radius);
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vec3 sampleMedium(in float height,
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out float mieScattering, out float mieAbsorption,
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out vec3 rayleighScattering, out vec3 ozoneAbsorption);
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void main()
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{
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float sunCosTheta = texCoord.x * 2.0 - 1.0;
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vec3 sunDir = vec3(-sqrt(1.0 - sunCosTheta*sunCosTheta), 0.0, sunCosTheta);
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float altitude = mix(fg_EarthRadius, ATMOSPHERE_RADIUS, texCoord.y);
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vec3 rayOrigin = vec3(0.0, 0.0, altitude);
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float dist = raySphereIntersection(rayOrigin, sunDir, ATMOSPHERE_RADIUS);
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float t = 0.0;
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vec3 transmittance = vec3(1.0);
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for (int i = 0; i < TRANSMITTANCE_STEPS; ++i) {
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float newT = ((float(i) + 0.3) / TRANSMITTANCE_STEPS) * dist;
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float dt = newT - t;
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t = newT;
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vec3 samplePos = rayOrigin + sunDir * t;
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float height = length(samplePos) - fg_EarthRadius;
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float mieScattering, mieAbsorption;
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vec3 rayleighScattering, ozoneAbsorption;
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vec3 extinction = sampleMedium(height, mieScattering, mieAbsorption,
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rayleighScattering, ozoneAbsorption);
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transmittance *= exp(-dt * extinction);
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}
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fragColor = transmittance;
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}
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