64 lines
2.1 KiB
GLSL
64 lines
2.1 KiB
GLSL
#version 330 core
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out vec4 fragColor;
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in vec3 vRayDir;
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in vec3 vRayDirView;
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uniform bool sun_disk;
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uniform sampler2D sky_view_lut;
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uniform sampler2D transmittance_lut;
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uniform vec3 fg_SunDirection;
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uniform float fg_CameraDistanceToEarthCenter;
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uniform float fg_EarthRadius;
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uniform vec3 fg_CameraViewUp;
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const float PI = 3.141592653;
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const vec3 EXTRATERRESTRIAL_SOLAR_ILLUMINANCE = vec3(128.0);
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const float ATMOSPHERE_RADIUS = 6471e3;
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const float sun_solid_angle = 0.545*PI/180.0; // ~half a degree
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const float sun_cos_solid_angle = cos(sun_solid_angle);
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void main()
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{
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vec3 rayDir = normalize(vRayDir);
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float azimuth = atan(rayDir.y, rayDir.x) / PI * 0.5 + 0.5;
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// Undo the non-linear transformation from the sky-view LUT
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float l = asin(rayDir.z);
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float elev = sqrt(abs(l) / (PI * 0.5)) * sign(l) * 0.5 + 0.5;
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vec3 color = texture(sky_view_lut, vec2(azimuth, elev)).rgb;
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color *= EXTRATERRESTRIAL_SOLAR_ILLUMINANCE;
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if (sun_disk) {
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// Render the Sun disk
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vec3 rayDirView = normalize(vRayDirView);
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float cosTheta = dot(rayDirView, fg_SunDirection);
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if (cosTheta >= sun_cos_solid_angle) {
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float normalizedHeight = (fg_CameraDistanceToEarthCenter - fg_EarthRadius)
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/ (ATMOSPHERE_RADIUS - fg_EarthRadius);
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float sunZenithCosTheta = dot(-rayDirView, fg_CameraViewUp);
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vec2 coords = vec2(sunZenithCosTheta * 0.5 + 0.5,
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clamp(normalizedHeight, 0.0, 1.0));
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vec3 transmittance = texture(transmittance_lut, coords).rgb;
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// Limb darkening
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// http://www.physics.hmc.edu/faculty/esin/a101/limbdarkening.pdf
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vec3 u = vec3(1.0);
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vec3 a = vec3(0.397, 0.503, 0.652);
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float centerToEdge = 1.0 - (cosTheta - sun_cos_solid_angle)
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/ (1.0 - sun_cos_solid_angle);
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float mu = sqrt(max(1.0 - centerToEdge * centerToEdge, 0.0));
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vec3 factor = vec3(1.0) - u * (vec3(1.0) - pow(vec3(mu), a));
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color += EXTRATERRESTRIAL_SOLAR_ILLUMINANCE * transmittance * factor;
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}
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}
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fragColor = vec4(color, 1.0);
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}
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