74 lines
2.4 KiB
GLSL
74 lines
2.4 KiB
GLSL
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#version 330 core
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uniform sampler2D aerial_perspective_lut;
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uniform sampler2D transmittance_lut;
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uniform float fg_SunZenithCosTheta;
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uniform float fg_CameraDistanceToEarthCenter;
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uniform float fg_EarthRadius;
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const float AERIAL_SLICES = 32.0;
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const float AERIAL_LUT_TILE_SIZE = 1.0 / AERIAL_SLICES;
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const float AERIAL_LUT_TEXEL_SIZE = 1.0 / 1024.0;
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const float AERIAL_MAX_DEPTH = 128000.0;
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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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vec4 sampleAerialPerspectiveSlice(vec2 coord, int slice)
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{
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// Sample at the pixel center
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float offset = slice * AERIAL_LUT_TILE_SIZE + AERIAL_LUT_TEXEL_SIZE * 0.5;
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float x = coord.x * (AERIAL_LUT_TILE_SIZE - AERIAL_LUT_TEXEL_SIZE) + offset;
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return texture(aerial_perspective_lut, vec2(x, coord.y));
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}
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vec4 sampleAerialPerspective(vec2 coord, float depth)
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{
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vec4 color;
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// Map to [0,1]
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float w = depth / AERIAL_MAX_DEPTH;
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// Squared distribution
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w = sqrt(clamp(w, 0.0, 1.0));
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w *= AERIAL_SLICES;
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if (w <= 1.0) {
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// Handle special case of fragments behind the first slice
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color = mix(vec4(0.0, 0.0, 0.0, 1.0),
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sampleAerialPerspectiveSlice(coord, 0),
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w);
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} else {
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w -= 1.0;
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// Manually interpolate between slices
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color = mix(sampleAerialPerspectiveSlice(coord, int(floor(w))),
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sampleAerialPerspectiveSlice(coord, int(ceil(w))),
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sqrt(fract(w)));
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}
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return color;
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}
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vec3 addAerialPerspective(vec3 color, vec2 coord, float depth)
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{
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vec4 aerialPerspective = sampleAerialPerspective(coord, depth);
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return color * aerialPerspective.a + aerialPerspective.rgb
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* EXTRATERRESTRIAL_SOLAR_ILLUMINANCE;
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}
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/**
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* Get the illuminance of the Sun for a surface perpendicular to the Sun
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* direction. The illuminance is calculated at the altitude of the viewer,
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* which might or might not be correct in certain circumstances. If the object
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* being illuminated is not too far from the viewer it's a good enough
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* approximation.
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*/
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vec3 getSunIntensity()
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{
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float normalizedHeight = (fg_CameraDistanceToEarthCenter - fg_EarthRadius)
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/ (ATMOSPHERE_RADIUS - fg_EarthRadius);
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vec2 coord = vec2(fg_SunZenithCosTheta * 0.5 + 0.5,
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clamp(normalizedHeight, 0.0, 1.0));
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vec3 transmittance = texture(transmittance_lut, coord).rgb;
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return EXTRATERRESTRIAL_SOLAR_ILLUMINANCE * transmittance;
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}
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