1// The chromatic aberration postprocessing effect.
2//
3// This makes edges of objects turn into multicolored streaks.
4
5#define_import_path bevy_post_process::effect_stack::chromatic_aberration
6
7// See `bevy_post_process::effect_stack::ChromaticAberration` for more
8// information on these fields.
9struct ChromaticAberrationSettings {
10    intensity: f32,
11    max_samples: u32,
12    unused_a: u32,
13    unused_b: u32,
14}
15
16// The source framebuffer texture.
17@group(0) @binding(0) var source_texture: texture_2d<f32>;
18// The sampler used to sample the source framebuffer texture.
19@group(0) @binding(1) var common_sampler: sampler;
20// The 1D lookup table for chromatic aberration.
21@group(0) @binding(2) var chromatic_aberration_lut_texture: texture_2d<f32>;
22// The settings supplied by the developer.
23@group(0) @binding(3) var<uniform> chromatic_aberration_settings: ChromaticAberrationSettings;
24
25fn chromatic_aberration(start_pos: vec2<f32>) -> vec3<f32> {
26    // Radial chromatic aberration implemented using the *Inside* technique:
27    //
28    // <https://github.com/playdeadgames/publications/blob/master/INSIDE/rendering_inside_gdc2016.pdf>
29
30    let end_pos = mix(start_pos, vec2(0.5), chromatic_aberration_settings.intensity);
31
32    // Determine the number of samples. We aim for one sample per texel, unless
33    // that's higher than the developer-specified maximum number of samples, in
34    // which case we choose the maximum number of samples.
35    let texel_length = length((end_pos - start_pos) *
36        vec2<f32>(textureDimensions(source_texture)));
37    let sample_count = min(u32(ceil(texel_length)), chromatic_aberration_settings.max_samples);
38
39    var color: vec3<f32>;
40    if (sample_count > 1u) {
41        // The LUT texture is in clamp-to-edge mode, so we start at 0.5 texels
42        // from the sides so that we have a nice gradient over the entire LUT
43        // range.
44        let lut_u_offset = 0.5 / f32(textureDimensions(chromatic_aberration_lut_texture).x);
45
46        var sample_sum = vec3(0.0);
47        var modulate_sum = vec3(0.0);
48
49        // Start accumulating samples.
50        for (var sample_index = 0u; sample_index < sample_count; sample_index += 1u) {
51            let t = (f32(sample_index) + 0.5) / f32(sample_count);
52
53            // Sample the framebuffer.
54            let sample_uv = mix(start_pos, end_pos, t);
55            let sample = textureSampleLevel(
56                source_texture,
57                common_sampler,
58                sample_uv,
59                0.0,
60            ).rgb;
61
62            // Sample the LUT.
63            let lut_u = mix(lut_u_offset, 1.0 - lut_u_offset, t);
64            let modulate = textureSampleLevel(
65                chromatic_aberration_lut_texture,
66                common_sampler,
67                vec2(lut_u, 0.5),
68                0.0,
69            ).rgb;
70
71            // Modulate the sample by the LUT value.
72            sample_sum += sample * modulate;
73            modulate_sum += modulate;
74        }
75
76        color = sample_sum / modulate_sum;
77    } else {
78        // If there's only one sample, don't do anything. If we don't do this,
79        // then this shader will apply whatever tint is in the center of the LUT
80        // texture to such pixels, which is wrong.
81        color = textureSampleLevel(
82            source_texture,
83            common_sampler,
84            start_pos,
85            0.0,
86        ).rgb;
87    }
88
89    return color;
90}