64 lines
1.9 KiB
GLSL
64 lines
1.9 KiB
GLSL
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/* Based on Frosbite Unified Volumetric.
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* https://www.ea.com/frostbite/news/physically-based-unified-volumetric-rendering-in-frostbite */
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/* Step 3 : Integrate for each froxel the final amount of light
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* scattered back to the viewer and the amount of transmittance. */
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uniform sampler3D volumeScattering; /* Result of the scatter step */
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uniform sampler3D volumeExtinction;
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flat in int slice;
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layout(location = 0) out vec4 finalScattering;
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layout(location = 1) out vec4 finalTransmittance;
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void main()
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{
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/* Start with full transmittance and no scattered light. */
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finalScattering = vec4(0.0);
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finalTransmittance = vec4(1.0);
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vec3 tex_size = vec3(textureSize(volumeScattering, 0).xyz);
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/* Compute view ray. */
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vec2 uvs = gl_FragCoord.xy / tex_size.xy;
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vec3 ndc_cell = volume_to_ndc(vec3(uvs, 1e-5));
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vec3 view_cell = get_view_space_from_depth(ndc_cell.xy, ndc_cell.z);
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/* Ortho */
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float prev_ray_len = view_cell.z;
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float orig_ray_len = 1.0;
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/* Persp */
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if (ProjectionMatrix[3][3] == 0.0) {
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prev_ray_len = length(view_cell);
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orig_ray_len = prev_ray_len / view_cell.z;
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}
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/* Without compute shader and arbitrary write we need to
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* accumulate from the beginning of the ray for each cell. */
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float integration_end = float(slice);
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for (int i = 0; i < slice; ++i) {
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ivec3 volume_cell = ivec3(gl_FragCoord.xy, i);
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vec4 Lscat = texelFetch(volumeScattering, volume_cell, 0);
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vec4 s_extinction = texelFetch(volumeExtinction, volume_cell, 0);
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float cell_depth = volume_z_to_view_z((float(i) + 1.0) / tex_size.z);
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float ray_len = orig_ray_len * cell_depth;
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/* Evaluate Scattering */
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float s_len = abs(ray_len - prev_ray_len);
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prev_ray_len = ray_len;
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vec4 Tr = exp(-s_extinction * s_len);
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/* integrate along the current step segment */
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Lscat = (Lscat - Lscat * Tr) / s_extinction;
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/* accumulate and also take into account the transmittance from previous steps */
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finalScattering += finalTransmittance * Lscat;
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finalTransmittance *= Tr;
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}
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}
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