1#define_import_path bevy_pbr::fog
2
3#import bevy_pbr::{
4    mesh_view_bindings::fog,
5    mesh_view_types::Fog,
6}
7
8// Fog formulas adapted from:
9// https://learn.microsoft.com/en-us/windows/win32/direct3d9/fog-formulas
10// https://catlikecoding.com/unity/tutorials/rendering/part-14/
11// https://iquilezles.org/articles/fog/ (Atmospheric Fog and Scattering)
12
13fn scattering_adjusted_fog_color(
14    fog_params: Fog,
15    scattering: vec3<f32>,
16) -> vec4<f32> {
17    if (fog_params.directional_light_color.a > 0.0) {
18        return vec4<f32>(
19            fog_params.base_color.rgb
20                + scattering * fog_params.directional_light_color.rgb * fog_params.directional_light_color.a,
21            fog_params.base_color.a,
22        );
23    } else {
24        return fog_params.base_color;
25    }
26}
27
28fn linear_fog(
29    fog_params: Fog,
30    input_color: vec4<f32>,
31    distance: f32,
32    scattering: vec3<f32>,
33) -> vec4<f32> {
34    var fog_color = scattering_adjusted_fog_color(fog_params, scattering);
35    let start = fog_params.be.x;
36    let end = fog_params.be.y;
37    fog_color.a *= 1.0 - clamp((end - distance) / (end - start), 0.0, 1.0);
38    return vec4<f32>(mix(input_color.rgb, fog_color.rgb, fog_color.a), input_color.a);
39}
40
41fn exponential_fog(
42    fog_params: Fog,
43    input_color: vec4<f32>,
44    distance: f32,
45    scattering: vec3<f32>,
46) -> vec4<f32> {
47    var fog_color = scattering_adjusted_fog_color(fog_params, scattering);
48    let density = fog_params.be.x;
49    fog_color.a *= 1.0 - 1.0 / exp(distance * density);
50    return vec4<f32>(mix(input_color.rgb, fog_color.rgb, fog_color.a), input_color.a);
51}
52
53fn exponential_squared_fog(
54    fog_params: Fog,
55    input_color: vec4<f32>,
56    distance: f32,
57    scattering: vec3<f32>,
58) -> vec4<f32> {
59    var fog_color = scattering_adjusted_fog_color(fog_params, scattering);
60    let distance_times_density = distance * fog_params.be.x;
61    fog_color.a *= 1.0 - 1.0 / exp(distance_times_density * distance_times_density);
62    return vec4<f32>(mix(input_color.rgb, fog_color.rgb, fog_color.a), input_color.a);
63}
64
65fn atmospheric_fog(
66    fog_params: Fog,
67    input_color: vec4<f32>,
68    distance: f32,
69    scattering: vec3<f32>,
70) -> vec4<f32> {
71    var fog_color = scattering_adjusted_fog_color(fog_params, scattering);
72    let extinction_factor = 1.0 - 1.0 / exp(distance * fog_params.be);
73    let inscattering_factor = 1.0 - 1.0 / exp(distance * fog_params.bi);
74    return vec4<f32>(
75        input_color.rgb * (1.0 - extinction_factor * fog_color.a)
76            + fog_color.rgb * inscattering_factor * fog_color.a,
77        input_color.a
78    );
79}