45 lines
1.4 KiB
Text
45 lines
1.4 KiB
Text
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#version 330 core
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uniform sampler2D transmittance_tex;
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uniform float fg_EarthRadius;
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uniform vec3 fg_SunDirectionWorld;
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uniform float fg_CameraDistanceToEarthCenter;
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uniform float fg_SunZenithCosTheta;
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const float ATMOSPHERE_RADIUS = 6471e3;
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// atmos_spectral.glsl
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vec4 get_sun_spectral_irradiance();
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vec3 linear_srgb_from_spectral_samples(vec4 L);
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/*
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* Get the Sun radiance at a point 'p' in world space.
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* We cannot use the Sun extraterrestial irradiance directly because it will be
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* attenuated by the transmittance of the atmospheric medium.
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*/
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vec3 get_sun_radiance(vec3 p)
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{
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float distance_to_earth_center = length(p);
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float normalized_altitude = (distance_to_earth_center - fg_EarthRadius)
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/ (ATMOSPHERE_RADIUS - fg_EarthRadius);
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vec3 zenith_dir = p / distance_to_earth_center;
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float sun_cos_theta = dot(zenith_dir, fg_SunDirectionWorld);
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float u = sun_cos_theta * 0.5 + 0.5;
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float v = clamp(normalized_altitude, 0.0, 1.0);
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vec4 transmittance = texture(transmittance_tex, vec2(u, v));
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vec4 L = get_sun_spectral_irradiance() * transmittance;
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return linear_srgb_from_spectral_samples(L);
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}
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vec3 get_sun_radiance_sea_level()
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{
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vec2 uv = vec2(fg_SunZenithCosTheta * 0.5 + 0.5, 0.0);
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vec4 transmittance = texture(transmittance_tex, uv);
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vec4 L = get_sun_spectral_irradiance() * transmittance;
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return linear_srgb_from_spectral_samples(L);
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}
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