1// The lens distortion postprocessing effect.
2
3#define_import_path bevy_post_process::effect_stack::lens_distortion
4
5// See `bevy_post_process::effect_stack::LensDistortion` for more
6// information on these fields.
7struct LensDistortionSettings {
8    intensity: f32,
9    scale: f32,
10    multiplier: vec2<f32>,
11    center: vec2<f32>,
12    edge_curvature: f32,
13    unused: u32,
14}
15
16const VISUAL_THRESHOLD: f32 = 1e-4;
17const MATH_EPSILON: f32 = 1e-6;
18
19// The settings supplied by the developer.
20@group(0) @binding(5) var<uniform> lens_distortion_settings: LensDistortionSettings;
21
22fn lens_distortion(uv: vec2<f32>) -> vec2<f32> {
23    let intensity = lens_distortion_settings.intensity;
24    if (abs(intensity) < VISUAL_THRESHOLD) {
25        return uv;
26    }
27    let multiplier = lens_distortion_settings.multiplier;
28    let center = lens_distortion_settings.center;
29
30    let uv_centered = uv - center;
31    // Prevent division by zero.
32    let radius = max(length(uv_centered), MATH_EPSILON);
33
34    let direction = uv_centered / radius;
35    let adjust = dot(abs(direction), multiplier);
36
37    // Maintains the correlation between k2 and k1, while ensuring the sign of k2
38    // is determined solely by `edge_curvature` rather than being influenced by intensity.
39    let k1 = intensity * adjust;
40    let k2 = k1 * intensity * lens_distortion_settings.edge_curvature;
41
42    let r2 = radius * radius;
43    let r_distorted = radius * (1.0 + (k1 + k2 * r2) * r2);
44
45    let uv_distorted = direction * r_distorted + center;
46
47    // Compensates for the distortion pushing pixels outside the [0,1] UV bounds.
48    let uv_scaled = (uv_distorted - center) / lens_distortion_settings.scale + center;
49
50    // Discard out-of-bounds pixels to prevent edge bleeding artifacts.
51    let uv_safe = clamp(uv_scaled, vec2<f32>(0.0), vec2<f32>(1.0));
52
53    return uv_safe;
54}