moria/assets/shaders/post-processing.wgsl

// https://github.com/Rudranil-Sarkar/Ordered-Dithering-Shader-GLSL/blob/master/Dither8x8.frag
// http://alex-charlton.com/posts/Dithering_on_the_GPU/

#import bevy_pbr::mesh_view_bindings

@group(1) @binding(0)
var texture: texture_2d<f32>;
@group(1) @binding(1)
var our_sampler: sampler;

@group(1) @binding(2)
var noise: texture_2d<f32>;
@group(1) @binding(3)
var noise_sampler: sampler;

@group(1) @binding(4)
var<uniform> palette: array<vec3<f32>, 16>;

let dither_table = array<i32, 64>(
    0, 48, 12, 60, 3, 51, 15, 63,
    32, 16, 44, 28, 35, 19, 47, 31,
    8,  56, 4,  52, 11, 59, 7,  55,
    40, 24, 36, 20, 43, 27, 39, 23,
    2,  50, 14, 62, 1,  49, 13, 61,
    34, 18, 46, 30, 33, 17, 45, 29,
    10, 58, 6,  54, 9,  57, 5,  53,
    42, 26, 38, 22, 41, 25, 37, 21
);


fn hsl2rgb(c: vec3<f32>) -> vec3<f32> {
    let rgb = clamp(
      abs(
        ((c.x * 6.0 + vec3<f32>(0.0,4.0,2.0)) % 6.0)
        - 3.0
      ) - 1.0,
      vec3<f32>(0.0),
      vec3<f32>(1.0)
      );

    return c.z + c.y * (rgb - .5) * (1. - abs(2. * c.z - 1.));
}

fn rgb2hsl(c: vec3<f32>) -> vec3<f32> {
    var h = 0.;
    var s = 0.;
    var l = 0.;
    var r = c.r;
    var g = c.g;
    var b = c.b;
    var cMin = min(r, min(g, b));
    var cMax = max(r, max(g, b));

    l = (cMax + cMin) / 2.;
    if (cMax > cMin) {
        var cDelta = cMax - cMin;

        if (l < 0.0) {
            s = cDelta / (cMax+cMin);
        } else {
            s = cDelta / (2. - (cMax + cMin));
        }

        if(r == cMax) {
            h = (g - b) / cDelta;
        } else if (g == cMax) {
            h = 2. + (b - r) / cDelta;
        } else {
            h = 4. + (r - g) / cDelta;
        }

        if(h < 0.) {
            h += 6.;
        }
        h = h / 6.;
    }
    return vec3<f32>(h, s, l);
}

fn hueDistance(h1: f32, h2: f32) -> f32 {
    let diff = abs(h1 - h2);

    return min(abs(1. - diff), diff);
}

let lightnessSteps: f32 = 4.;

// SOURCE: http://alex-charlton.com/posts/Dithering_on_the_GPU/
fn lightnessStep(l: f32) -> f32 {
    return floor((.5 + l * lightnessSteps)) / lightnessSteps;
}

let SaturationSteps: f32 = 4.;

fn SaturationStep(s: f32) -> f32 {
    /* Quantize the saturation to one of SaturationSteps values */
    return floor((.5 + s * SaturationSteps)) / SaturationSteps;
}

fn Closest_color(hue: f32) -> array<vec3<f32>, 2> {
    var closest = vec3<f32>(-2., 0., 0.);
    var secondClosest = vec3<f32>(-2., 0., 0.);

    var temp: vec3<f32>;

    var p: array<vec3<f32>, 16> = palette;
    for(var i: i32 = 0; i < 16; i++) {
      temp = p[i];

      let tempDistance = hueDistance(temp.x, hue);

      if(tempDistance < hueDistance(closest.x, hue)) {
          secondClosest = closest;
          closest = temp;
      } else if(tempDistance < hueDistance(secondClosest.x, hue)){
          secondClosest = temp;
      }
    }

    var result: array<vec3<f32>, 2>;
    result[0] = closest;
    result[1] = secondClosest;
    return result;
}

fn dither(pos: vec2<f32>, color: vec3<f32>) -> vec3<f32> {
    let x = floor(pos.x % 8.);
    let y = floor(pos.y % 8.);

    let index = i32(x + y * 8.);

    // This variable can be adjusted in range of -1 to 1 for more desirable result
    let bias = 0.0;

    var p: array<i32, 64> = dither_table;
    let limit = (f32(p[index]) + 1.) / 64. + bias;

    let Colors: array<vec3<f32>, 2> = Closest_color(color.x);

    let hueDiff = hueDistance(color.x, Colors[0].x) / hueDistance(Colors[1].x, Colors[0].x);

    let l1 = lightnessStep(max((color.z - .125), 0.));
    let l2 = lightnessStep(min((color.z + .124), 1.));
    let lightnessDiff = (color.z - l1) / (l2 - l1);

    var resultColor: vec3<f32>;
    if (hueDiff < limit) {
        resultColor = Colors[0];
    } else {
        resultColor = Colors[1];
    }
    if (lightnessDiff < limit) {
        resultColor.z = l1;
    } else {
        resultColor.z = l2;
    }

    let s1 = SaturationStep(max((color.y - .125), 0.));
    let s2 = SaturationStep(min((color.y + .124), 1.));
    let SaturationDiff = (color.y - s1) / (s2 - s1);

    if (SaturationDiff < limit) {
        resultColor.y = s1;
    } else {
        resultColor.y = s2;
    }

    return hsl2rgb(resultColor);
}

@fragment
fn fragment(
    @builtin(position) position: vec4<f32>,
    #import bevy_sprite::mesh2d_vertex_output
) -> @location(0) vec4<f32> {
    let uv = position.xy / vec2<f32>(view.width, view.height);
    // let uv = floor(uv * 400.0) / 400.0;

    let col = textureSample(texture, our_sampler, uv);

    return vec4<f32>(dither(position.xy / 2.0, rgb2hsl(col.rgb)), col.a);

    // return round(col * 50.0) / 50.0;
    // return col;
}