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fgdata/Shaders/HDR/atmos_sky_view.frag

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#version 330 core
layout(location = 0) out vec4 fragColor;
in vec2 texcoord;
uniform sampler2D transmittance_lut;
uniform float fg_SunZenithCosTheta;
uniform float fg_CameraDistanceToEarthCenter;
const int SKY_STEPS = 32;
// math.glsl
float M_2PI();
float M_PI_2();
// atmos.glsl
vec4 compute_inscattering(in vec3 ray_origin,
in vec3 ray_dir,
in float t_max,
in vec3 sun_dir,
in int steps,
in sampler2D transmittance_lut,
out vec4 transmittance);
void main()
{
// Always leave the Sun right in the middle of the sky texture.
// The skydome model implemented in SimGear already takes care of rotating
// the Sun for us.
vec3 sun_dir = vec3(
-sqrt(1.0 - fg_SunZenithCosTheta*fg_SunZenithCosTheta),
0.0,
fg_SunZenithCosTheta);
float azimuth = M_2PI() * texcoord.x; // [0, 2pi]
// Apply a non-linear transformation to the elevation to dedicate more
// texels to the horizon, where having more detail matters.
float l = texcoord.y * 2.0 - 1.0;
float elev = l*l * sign(l) * M_PI_2(); // [-pi/2, pi/2]
vec3 ray_dir = vec3(cos(elev) * cos(azimuth),
cos(elev) * sin(azimuth),
sin(elev));
vec3 ray_origin = vec3(0.0, 0.0, fg_CameraDistanceToEarthCenter);
vec4 transmittance;
vec4 L = compute_inscattering(ray_origin,
ray_dir,
1e7,
sun_dir,
SKY_STEPS,
transmittance_lut,
transmittance);
fragColor = L;
}