52 lines
1.8 KiB
GLSL
52 lines
1.8 KiB
GLSL
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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 vec3 fg_CameraPositionCart;
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uniform vec3 fg_CameraPositionGeod;
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uniform vec3 fg_SunDirectionWorld;
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const float PI = 3.141592653;
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void calculateScattering(in vec3 rayOrigin,
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in vec3 rayDir,
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in float tmax,
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in vec3 lightDir,
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in float earthRadius,
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out vec3 inscatter,
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out vec3 transmittance);
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void main()
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{
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// Always leave the sun right in the middle of the texture as the skydome
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// model is already being rotated.
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float sunCosTheta = dot(fg_SunDirectionWorld, normalize(fg_CameraPositionCart));
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vec3 lightDir = vec3(-sqrt(1.0 - sunCosTheta*sunCosTheta), 0.0, sunCosTheta);
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float azimuth = 2.0 * PI * texCoord.x; // [0, 2pi]
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// Apply a non-linear transformation to the elevation to dedicate more
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// texels to the horizon, which is where having more detail matters.
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float l = texCoord.y * 2.0 - 1.0;
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float elev = l*l * sign(l) * PI * 0.5; // [-pi/2, pi/2]
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vec3 rayDir = vec3(cos(elev) * cos(azimuth), cos(elev) * sin(azimuth), sin(elev));
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float cameraPosLength = length(fg_CameraPositionCart);
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// Since FG internally uses WG84 coordinates, we use the current Earth
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// radius under the camera, which varies with the latitude. For practical
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// purposes we model the Earth as a perfect sphere with this radius.
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float earthRadius = cameraPosLength - fg_CameraPositionGeod.z;
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vec3 rayOrigin = vec3(0.0, 0.0, cameraPosLength);
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vec3 inscatter, transmittance;
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calculateScattering(rayOrigin,
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rayDir,
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9.0e8,
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lightDir,
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earthRadius,
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inscatter, transmittance);
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fragColor = inscatter;
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}
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