55 lines
1.8 KiB
GLSL
55 lines
1.8 KiB
GLSL
#version 330 core
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layout(location = 0) out vec4 fragColor;
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in vec2 texcoord;
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const int TRANSMITTANCE_STEPS = 40;
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// atmos.glsl
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float get_earth_radius();
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float get_atmosphere_radius();
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float ray_sphere_intersection(vec3 ro, vec3 rd, float radius);
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void get_atmosphere_collision_coefficients(in float h,
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out vec4 aerosol_absorption,
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out vec4 aerosol_scattering,
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out vec4 molecular_absorption,
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out vec4 molecular_scattering,
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out vec4 extinction);
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void main()
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{
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float sun_cos_theta = texcoord.x * 2.0 - 1.0;
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vec3 sun_dir = vec3(-sqrt(1.0 - sun_cos_theta*sun_cos_theta), 0.0, sun_cos_theta);
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float distance_to_earth_center = mix(get_earth_radius(),
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get_atmosphere_radius(),
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texcoord.y);
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vec3 ray_origin = vec3(0.0, 0.0, distance_to_earth_center);
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float t_d = ray_sphere_intersection(ray_origin, sun_dir, get_atmosphere_radius());
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float dt = t_d / float(TRANSMITTANCE_STEPS);
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vec4 result = vec4(0.0);
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for (int i = 0; i < TRANSMITTANCE_STEPS; ++i) {
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float t = (float(i) + 0.5) * dt;
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vec3 x_t = ray_origin + sun_dir * t;
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float altitude = length(x_t) - get_earth_radius();
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vec4 aerosol_absorption, aerosol_scattering;
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vec4 molecular_absorption, molecular_scattering;
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vec4 extinction;
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get_atmosphere_collision_coefficients(
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altitude,
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aerosol_absorption, aerosol_scattering,
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molecular_absorption, molecular_scattering,
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extinction);
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result += extinction * dt;
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}
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vec4 transmittance = exp(-result);
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fragColor = transmittance;
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}
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