87 lines
2.9 KiB
GLSL
87 lines
2.9 KiB
GLSL
/*
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* Render the aerial perspective LUT, similar to
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* "A Scalable and Production Ready Sky and Atmosphere Rendering Technique"
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* by Sébastien Hillaire (2020).
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*
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* Unlike the paper, we are using a tiled 2D texture instead of a true 3D
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* texture. For some reason the overhead of rendering to a texture many times
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* (the depth of the 3D texture) seems to be too high, probably because OSG is
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* not sharing state between those passes.
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*/
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#version 330 core
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layout(location = 0) out vec4 fragColor;
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in vec2 texcoord;
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uniform sampler2D transmittance_lut;
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uniform mat4 fg_ViewMatrixInverse;
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uniform vec3 fg_CameraPositionCart;
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uniform vec3 fg_SunDirectionWorld;
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const float AP_SLICE_COUNT = 32.0;
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const float AP_MAX_DEPTH = 128000.0;
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const int AERIAL_PERSPECTIVE_STEPS = 10;
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const float RADIUS_OFFSET = 10.0;
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// pos_from_depth.glsl
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vec3 get_view_space_from_depth(vec2 uv, float depth);
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// atmos.glsl
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float get_earth_radius();
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float get_ray_end(vec3 ray_origin, vec3 ray_dir, float t_max);
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vec4 compute_inscattering(in vec3 ray_origin,
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in vec3 ray_dir,
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in float t_max,
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in vec3 sun_dir,
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in int steps,
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in sampler2D transmittance_lut,
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out vec4 transmittance);
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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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void main()
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{
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// Account for the depth slice we are currently in. Depth goes from 0 to
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// DEPTH_RANGE in a squared distribution. The first slice is not 0 since
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// that would waste a slice.
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float x = texcoord.x * AP_SLICE_COUNT;
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float slice = ceil(x);
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float w = slice / AP_SLICE_COUNT; // [0,1]
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float depth = w*w * AP_MAX_DEPTH;
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vec2 coord = vec2(fract(x), texcoord.y);
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vec3 frag_pos = get_view_space_from_depth(coord, 1.0);
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vec3 ray_dir = vec4(fg_ViewMatrixInverse * vec4(normalize(frag_pos), 0.0)).xyz;
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vec3 ray_origin = fg_CameraPositionCart;
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vec3 ray_end = ray_origin + ray_dir * depth;
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float t_max = depth;
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if (length(ray_end) <= (get_earth_radius() + RADIUS_OFFSET)) {
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ray_end = normalize(ray_end) * (get_earth_radius() + RADIUS_OFFSET + 1.0);
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ray_dir = ray_end - ray_origin;
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t_max = length(ray_dir);
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ray_dir /= max(t_max, 1e-5);
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}
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vec4 transmittance;
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vec4 L = compute_inscattering(ray_origin,
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ray_dir,
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t_max,
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fg_SunDirectionWorld,
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AERIAL_PERSPECTIVE_STEPS,
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transmittance_lut,
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transmittance);
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// In-scattering
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fragColor.rgb = linear_srgb_from_spectral_samples(
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L * get_sun_spectral_irradiance());
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// Transmittance
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fragColor.a = dot(transmittance, vec4(0.25));
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}
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