chain-reaction/assets/shaders/background.wgsl

#import bevy_sprite::mesh2d_view_bindings::globals

struct BackgroundMaterial {
    resolution: vec2<f32>,
    time_offset: f32,
}

@group(2) @binding(0) var<uniform> material: BackgroundMaterial;

// --- CONFIGURATION ---
const RAYS_COUNT: i32 = 32;       // Increase to 64 if on PC for smoother quality
const RENDER_DISTANCE: f32 = 5.0; // How far rays travel
const NEAR_PLANE: f32 = 1.5;      // Higher = Zoomed in (Less "Fisheye/Disco")
const ROTATION_SPEED: f32 = 0.1;
const JITTERING: f32 = 0.05;

// Colors
const COLOR1: vec3<f32> = vec3<f32>(0.1, 0.0, 0.3); // Deep Nebula Purple
const COLOR2: vec3<f32> = vec3<f32>(0.8, 0.2, 0.5); // Hot Pink Highlights

// --- NOISE FUNCTIONS ---
fn hash(v: vec3<f32>) -> f32 {
    return fract(sin(dot(v, vec3<f32>(11.51721, 67.12511, 9.7561))) * 1551.4172);
}

fn getNoiseFromVec3(v: vec3<f32>) -> f32 {
    let rootV = floor(v);
    let f = smoothstep(vec3<f32>(0.0), vec3<f32>(1.0), fract(v));

    let n000 = hash(rootV);
    let n001 = hash(rootV + vec3<f32>(0.0, 0.0, 1.0));
    let n010 = hash(rootV + vec3<f32>(0.0, 1.0, 0.0));
    let n011 = hash(rootV + vec3<f32>(0.0, 1.0, 1.0));
    let n100 = hash(rootV + vec3<f32>(1.0, 0.0, 0.0));
    let n101 = hash(rootV + vec3<f32>(1.0, 0.0, 1.0));
    let n110 = hash(rootV + vec3<f32>(1.0, 1.0, 0.0));
    let n111 = hash(rootV + vec3<f32>(1.0, 1.0, 1.0));

    let n = mix(vec4<f32>(n000, n010, n100, n110), vec4<f32>(n001, n011, n101, n111), f.z);
    let n_xy = mix(vec2<f32>(n.x, n.z), vec2<f32>(n.y, n.w), f.y);
    return mix(n_xy.x, n_xy.y, f.x);
}

fn volumetricFog(v: vec3<f32>, noiseMod: f32) -> f32 {
    var noise: f32 = 0.0;
    var alpha: f32 = 1.0;
    var point: vec3<f32> = v;
    
    // 5 Octaves of noise
    for(var i: i32 = 0; i < 5; i++) {
        noise += getNoiseFromVec3(point) * alpha;
        point *= 2.0;
        alpha *= 0.5;
    }
    
    noise *= 0.575;
    
    // Add time-based movement to edges
    let edge = 0.1 + getNoiseFromVec3(v * 0.5 + vec3<f32>(globals.time * 0.03)) * 0.8;
    
    // Apply "Beat" modulation (noiseMod)
    let modNoise = (0.5 - abs(edge * (1.0 + noiseMod * 0.05) - noise)) * 2.0;
    
    // Contrast Curve
    return (smoothstep(0.0, 0.9, modNoise * modNoise) + (1.0 - smoothstep(1.3, 0.6, modNoise))) * 0.2;
}

fn fogMarch(rayStart: vec3<f32>, rayDirection: vec3<f32>, disMod: f32) -> vec3<f32> {
    var stepLength = RENDER_DISTANCE / f32(RAYS_COUNT);
    var fog = vec3<f32>(0.0);
    var point = rayStart;

    for(var i: i32 = 0; i < RAYS_COUNT; i++) {
        point += rayDirection * stepLength;
        fog += volumetricFog(point, disMod) 
             * mix(COLOR1, COLOR2 * (1.0 + disMod * 0.5), getNoiseFromVec3((point + vec3<f32>(12.51, 52.167, 1.146)) * 0.5))
             * getNoiseFromVec3(point * 0.2 + 20.0) * 2.0; // "Holes" in fog
        stepLength *= 1.05; // Exponential step (fewer samples close up)
    }

    // "Dither" the end result by the far-plane noise to hide banding
    let farNoise = pow(getNoiseFromVec3((rayStart + rayDirection * RENDER_DISTANCE)), 2.0);
    fog = (fog / f32(RAYS_COUNT)) * (farNoise * 3.0 + disMod * 0.5);
    
    return fog;
}

@fragment
fn fragment(
    @builtin(position) position: vec4<f32>,
    @location(0) uv: vec2<f32>,
) -> @location(0) vec4<f32> {
    let time = globals.time + material.time_offset;
    
    // 1. Aspect Ratio Correction
    // Map UVs from 0..1 to -1..1
    let centered = (uv - 0.5) * 2.0;
    // Fix aspect ratio by scaling Y (Width is dominant)
    let aspect_y = material.resolution.y / material.resolution.x;
    let final_uv = vec2<f32>(centered.x, centered.y * aspect_y);

    // 2. Camera Rotation Angles
    let angleY = sin(time * ROTATION_SPEED * 2.0);
    let angleX = cos(time * 0.712 * ROTATION_SPEED);
    let angleZ = sin(time * 1.779 * ROTATION_SPEED);

    // 3. Rotation Matrices - COPIED EXACTLY FROM ORIGINAL GLSL
    // The original author used a non-standard axis alignment (sin on diagonal).
    // We construct these column-by-column to match GLSL memory layout.

    // GLSL: mat3(1, 0, 0,  0, sin, cos,  0, -cos, sin)
    let rotX = mat3x3<f32>(
        vec3<f32>(1.0, 0.0, 0.0),            // Col 0
        vec3<f32>(0.0, sin(angleX), cos(angleX)), // Col 1
        vec3<f32>(0.0, -cos(angleX), sin(angleX)) // Col 2
    );

    // GLSL: mat3(sin, cos, 0,  -cos, sin, 0,  0, 0, 1)
    let rotZ = mat3x3<f32>(
        vec3<f32>(sin(angleZ), cos(angleZ), 0.0), // Col 0
        vec3<f32>(-cos(angleZ), sin(angleZ), 0.0), // Col 1
        vec3<f32>(0.0, 0.0, 1.0)             // Col 2
    );

    // GLSL: mat3(sin, 0, cos,  0, 1, 0,  -cos, 0, sin)
    let rotY = mat3x3<f32>(
        vec3<f32>(sin(angleY), 0.0, -cos(angleY)), // Col 0
        vec3<f32>(0.0, 1.0, 0.0),            // Col 1
        vec3<f32>(cos(angleY), 0.0, sin(angleY))  // Col 2
    );

    // 4. Ray Construction
    // Combine rotations
    let rotation = rotY * rotZ * rotX; 
    
    // Forward movement (breathing effect)
    let near_plane_mod = NEAR_PLANE * (1.0 + sin(time * 0.2) * 0.4);
    
    // Original Vector: X=Right, Y=Forward (Depth), Z=Vertical
    let ray_dir_local = normalize(vec3<f32>(final_uv.x, near_plane_mod, final_uv.y));
    
    // Apply Rotation
    let rayDirection = rotation * ray_dir_local;

    // 5. Camera Position
    let cameraCenter = vec3<f32>(
        sin(time * 0.2) * 10.0, 
        time * 0.2 * 10.0, 
        cos(time * 0.78 * 0.2 + 2.14) * 10.0
    );
    
    // 6. Ray Start with Jitter
    let jitter = (hash(vec3<f32>(final_uv + 4.0, fract(time) + 2.0)) - 0.5) * JITTERING;
    let rayStart = cameraCenter + rayDirection * jitter;

    // 7. Render
    // Fake "Audio Reactivity" using sine wave
    let beat = smoothstep(0.6, 0.9, pow(sin(time * 4.0) * 0.5 + 0.5, 2.0) * 0.06);
    var fog = fogMarch(rayStart, rayDirection, beat);

    // Post-Process
    fog *= 2.5 * 1.2; // Brightness
    fog += 0.07 * mix(COLOR1, COLOR2, 0.5); // Base Color
    
    // Tone mapping to prevent burnout
    fog = sqrt(smoothstep(vec3<f32>(0.0), vec3<f32>(1.5), fog));

    return vec4<f32>(fog, 1.0);
}