1// The chromatic aberration postprocessing effect.
2//
3// This makes edges of objects turn into multicolored streaks.
4
5#define_import_path bevy_core_pipeline::post_processing::chromatic_aberration
6
7// See `bevy_core_pipeline::post_process::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 chromatic_aberration_source_texture: texture_2d<f32>;
18// The sampler used to sample the source framebuffer texture.
19@group(0) @binding(1) var chromatic_aberration_source_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 sampler used to sample that lookup table.
23@group(0) @binding(3) var chromatic_aberration_lut_sampler: sampler;
24// The settings supplied by the developer.
25@group(0) @binding(4) var<uniform> chromatic_aberration_settings: ChromaticAberrationSettings;
26
27fn chromatic_aberration(start_pos: vec2<f32>) -> vec3<f32> {
28    // Radial chromatic aberration implemented using the *Inside* technique:
29    //
30    // <https://github.com/playdeadgames/publications/blob/master/INSIDE/rendering_inside_gdc2016.pdf>
31
32    let end_pos = mix(start_pos, vec2(0.5), chromatic_aberration_settings.intensity);
33
34    // Determine the number of samples. We aim for one sample per texel, unless
35    // that's higher than the developer-specified maximum number of samples, in
36    // which case we choose the maximum number of samples.
37    let texel_length = length((end_pos - start_pos) *
38        vec2<f32>(textureDimensions(chromatic_aberration_source_texture)));
39    let sample_count = min(u32(ceil(texel_length)), chromatic_aberration_settings.max_samples);
40
41    var color: vec3<f32>;
42    if (sample_count > 1u) {
43        // The LUT texture is in clamp-to-edge mode, so we start at 0.5 texels
44        // from the sides so that we have a nice gradient over the entire LUT
45        // range.
46        let lut_u_offset = 0.5 / f32(textureDimensions(chromatic_aberration_lut_texture).x);
47
48        var sample_sum = vec3(0.0);
49        var modulate_sum = vec3(0.0);
50
51        // Start accumulating samples.
52        for (var sample_index = 0u; sample_index < sample_count; sample_index += 1u) {
53            let t = (f32(sample_index) + 0.5) / f32(sample_count);
54
55            // Sample the framebuffer.
56            let sample_uv = mix(start_pos, end_pos, t);
57            let sample = textureSampleLevel(
58                chromatic_aberration_source_texture,
59                chromatic_aberration_source_sampler,
60                sample_uv,
61                0.0,
62            ).rgb;
63
64            // Sample the LUT.
65            let lut_u = mix(lut_u_offset, 1.0 - lut_u_offset, t);
66            let modulate = textureSampleLevel(
67                chromatic_aberration_lut_texture,
68                chromatic_aberration_lut_sampler,
69                vec2(lut_u, 0.5),
70                0.0,
71            ).rgb;
72
73            // Modulate the sample by the LUT value.
74            sample_sum += sample * modulate;
75            modulate_sum += modulate;
76        }
77
78        color = sample_sum / modulate_sum;
79    } else {
80        // If there's only one sample, don't do anything. If we don't do this,
81        // then this shader will apply whatever tint is in the center of the LUT
82        // texture to such pixels, which is wrong.
83        color = textureSampleLevel(
84            chromatic_aberration_source_texture,
85            chromatic_aberration_source_sampler,
86            start_pos,
87            0.0,
88        ).rgb;
89    }
90
91    return color;
92}