1#import bevy_pbr::{
2    mesh_view_bindings,
3    forward_io::VertexOutput,
4}
5
6#import bevy_render::maths::PI
7
8#ifdef TONEMAP_IN_SHADER
9#import bevy_core_pipeline::tonemapping::tone_mapping
10#endif
11
12// Sweep across hues on y axis with value from 0.0 to +15EV across x axis 
13// quantized into 24 steps for both axis.
14fn color_sweep(uv_input: vec2<f32>) -> vec3<f32> {
15    var uv = uv_input;
16    let steps = 24.0;
17    uv.y = uv.y * (1.0 + 1.0 / steps);
18    let ratio = 2.0;
19    
20    let h = PI * 2.0 * floor(1.0 + steps * uv.y) / steps;
21    let L = floor(uv.x * steps * ratio) / (steps * ratio) - 0.5;
22    
23    var color = vec3(0.0);
24    if uv.y < 1.0 { 
25        color = cos(h + vec3(0.0, 1.0, 2.0) * PI * 2.0 / 3.0);
26        let maxRGB = max(color.r, max(color.g, color.b));
27        let minRGB = min(color.r, min(color.g, color.b));
28        color = exp(15.0 * L) * (color - minRGB) / (maxRGB - minRGB);
29    } else {
30        color = vec3(exp(15.0 * L));
31    }
32    return color;
33}
34
35fn hsv_to_srgb(c: vec3<f32>) -> vec3<f32> {
36    let K = vec4(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0);
37    let p = abs(fract(c.xxx + K.xyz) * 6.0 - K.www);
38    return c.z * mix(K.xxx, clamp(p - K.xxx, vec3(0.0), vec3(1.0)), c.y);
39}
40
41// Generates a continuous sRGB sweep.
42fn continuous_hue(uv: vec2<f32>) -> vec3<f32> {
43    return hsv_to_srgb(vec3(uv.x, 1.0, 1.0)) * max(0.0, exp2(uv.y * 9.0) - 1.0);
44}
45
46@fragment
47fn fragment(
48    in: VertexOutput,
49) -> @location(0) vec4<f32> {
50    var uv = in.uv;
51    var out = vec3(0.0);
52    if uv.y > 0.5 {
53        uv.y = 1.0 - uv.y;
54        out = color_sweep(vec2(uv.x, uv.y * 2.0));
55    } else {
56        out = continuous_hue(vec2(uv.y * 2.0, uv.x));
57    }
58    var color = vec4(out, 1.0);
59#ifdef TONEMAP_IN_SHADER
60    color = tone_mapping(color, mesh_view_bindings::view.color_grading);
61#endif
62    return color;
63}