1#import bevy_pbr::{
2    mesh_view_types::Lights,
3    atmosphere::{
4        types::{Atmosphere, AtmosphereSettings},
5        bindings::{atmosphere, view, settings},
6        functions::{
7            sample_atmosphere, get_local_up, AtmosphereSample,
8            sample_local_inscattering, get_local_r, view_radius,
9            max_atmosphere_distance, direction_atmosphere_to_world,
10            sky_view_lut_uv_to_zenith_azimuth, zenith_azimuth_to_ray_dir,
11            MIDPOINT_RATIO
12        },
13    }
14}
15
16#import bevy_render::{
17    view::View,
18    maths::HALF_PI,
19}
20#import bevy_core_pipeline::fullscreen_vertex_shader::FullscreenVertexOutput
21
22@group(0) @binding(13) var sky_view_lut_out: texture_storage_2d<rgba16float, write>;
23
24@compute
25@workgroup_size(16, 16, 1)
26fn main(@builtin(global_invocation_id) idx: vec3<u32>) {
27    let uv = vec2<f32>(idx.xy) / vec2<f32>(settings.sky_view_lut_size);
28
29    let r = view_radius();
30    var zenith_azimuth = sky_view_lut_uv_to_zenith_azimuth(r, uv);
31
32    let ray_dir_as = zenith_azimuth_to_ray_dir(zenith_azimuth.x, zenith_azimuth.y);
33    let ray_dir_ws = direction_atmosphere_to_world(ray_dir_as);
34
35    let mu = ray_dir_ws.y;
36    let t_max = max_atmosphere_distance(r, mu);
37
38    let sample_count = mix(1.0, f32(settings.sky_view_lut_samples), clamp(t_max * 0.01, 0.0, 1.0));
39    var total_inscattering = vec3(0.0);
40    var throughput = vec3(1.0);
41    var prev_t = 0.0;
42    for (var s = 0.0; s < sample_count; s += 1.0) {
43        let t_i = t_max * (s + MIDPOINT_RATIO) / sample_count;
44        let dt_i = (t_i - prev_t);
45        prev_t = t_i;
46
47        let local_r = get_local_r(r, mu, t_i);
48        let local_up = get_local_up(r, t_i, ray_dir_ws);
49        let local_atmosphere = sample_atmosphere(local_r);
50
51        let sample_optical_depth = local_atmosphere.extinction * dt_i;
52        let sample_transmittance = exp(-sample_optical_depth);
53
54        let inscattering = sample_local_inscattering(
55            local_atmosphere,
56            ray_dir_ws,
57            local_r,
58            local_up
59        );
60
61        // Analytical integration of the single scattering term in the radiance transfer equation
62        let s_int = (inscattering - inscattering * sample_transmittance) / local_atmosphere.extinction;
63        total_inscattering += throughput * s_int;
64
65        throughput *= sample_transmittance;
66        if all(throughput < vec3(0.001)) {
67            break;
68        }
69    }
70
71    textureStore(sky_view_lut_out, idx.xy, vec4(total_inscattering, 1.0));
72}