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