iDither/Sources/iDither/Resources/Shaders.metal

#include <metal_stdlib>
using namespace metal;

struct RenderParameters {
    float brightness;
    float contrast;
    float pixelScale;
    float colorDepth; // New parameter: 1.0 to 32.0 (Levels)
    int algorithm; // 0: None, 1: Bayer 2x2, 2: Bayer 4x4, 3: Bayer 8x8, 4: Cluster 4x4, 5: Cluster 8x8, 6: Blue Noise
    int isGrayscale;
};

// Bayer 2x2 Matrix
constant float bayer2x2[2][2] = {
    {0.0/4.0, 2.0/4.0},
    {3.0/4.0, 1.0/4.0}
};

// Bayer 4x4 Matrix
constant float bayer4x4[4][4] = {
    { 0.0/16.0,  8.0/16.0,  2.0/16.0, 10.0/16.0 },
    {12.0/16.0,  4.0/16.0, 14.0/16.0,  6.0/16.0 },
    { 3.0/16.0, 11.0/16.0,  1.0/16.0,  9.0/16.0 },
    {15.0/16.0,  7.0/16.0, 13.0/16.0,  5.0/16.0 }
};

// Bayer 8x8 Matrix
constant float bayer8x8[8][8] = {
    { 0.0/64.0, 32.0/64.0,  8.0/64.0, 40.0/64.0,  2.0/64.0, 34.0/64.0, 10.0/64.0, 42.0/64.0 },
    {48.0/64.0, 16.0/64.0, 56.0/64.0, 24.0/64.0, 50.0/64.0, 18.0/64.0, 58.0/64.0, 26.0/64.0 },
    {12.0/64.0, 44.0/64.0,  4.0/64.0, 36.0/64.0, 14.0/64.0, 46.0/64.0,  6.0/64.0, 38.0/64.0 },
    {60.0/64.0, 28.0/64.0, 52.0/64.0, 20.0/64.0, 62.0/64.0, 30.0/64.0, 54.0/64.0, 22.0/64.0 },
    { 3.0/64.0, 35.0/64.0, 11.0/64.0, 43.0/64.0,  1.0/64.0, 33.0/64.0,  9.0/64.0, 41.0/64.0 },
    {51.0/64.0, 19.0/64.0, 59.0/64.0, 27.0/64.0, 49.0/64.0, 17.0/64.0, 57.0/64.0, 25.0/64.0 },
    {15.0/64.0, 47.0/64.0,  7.0/64.0, 39.0/64.0, 13.0/64.0, 45.0/64.0,  5.0/64.0, 37.0/64.0 },
    {63.0/64.0, 31.0/64.0, 55.0/64.0, 23.0/64.0, 61.0/64.0, 29.0/64.0, 53.0/64.0, 21.0/64.0 }
};

// Cluster 4x4 Matrix
constant float cluster4x4[4][4] = {
    {12.0/16.0, 5.0/16.0,  6.0/16.0, 13.0/16.0},
    { 4.0/16.0, 0.0/16.0,  1.0/16.0,  7.0/16.0},
    {11.0/16.0, 3.0/16.0,  2.0/16.0,  8.0/16.0},
    {15.0/16.0, 10.0/16.0, 9.0/16.0, 14.0/16.0}
};

// Cluster 8x8 Matrix
constant float cluster8x8[8][8] = {
    {24.0/64.0, 10.0/64.0, 12.0/64.0, 26.0/64.0, 35.0/64.0, 47.0/64.0, 49.0/64.0, 37.0/64.0},
    { 8.0/64.0,  0.0/64.0,  2.0/64.0, 14.0/64.0, 45.0/64.0, 59.0/64.0, 61.0/64.0, 51.0/64.0},
    {22.0/64.0,  6.0/64.0,  4.0/64.0, 20.0/64.0, 43.0/64.0, 57.0/64.0, 63.0/64.0, 53.0/64.0},
    {30.0/64.0, 18.0/64.0, 16.0/64.0, 28.0/64.0, 33.0/64.0, 41.0/64.0, 55.0/64.0, 39.0/64.0},
    {34.0/64.0, 46.0/64.0, 48.0/64.0, 36.0/64.0, 25.0/64.0, 11.0/64.0, 13.0/64.0, 27.0/64.0},
    {44.0/64.0, 58.0/64.0, 60.0/64.0, 50.0/64.0,  9.0/64.0,  1.0/64.0,  3.0/64.0, 15.0/64.0},
    {42.0/64.0, 56.0/64.0, 62.0/64.0, 52.0/64.0, 23.0/64.0,  7.0/64.0,  5.0/64.0, 21.0/64.0},
    {32.0/64.0, 40.0/64.0, 54.0/64.0, 38.0/64.0, 31.0/64.0, 19.0/64.0, 17.0/64.0, 29.0/64.0}
};

// Blue Noise 8x8 (Approx)
constant float blueNoise8x8[8][8] = {
    {52.0/64.0, 21.0/64.0, 58.0/64.0, 10.0/64.0, 45.0/64.0, 33.0/64.0, 56.0/64.0, 17.0/64.0},
    { 4.0/64.0, 38.0/64.0, 28.0/64.0, 51.0/64.0,  5.0/64.0, 22.0/64.0, 40.0/64.0, 62.0/64.0},
    {61.0/64.0, 12.0/64.0, 48.0/64.0, 14.0/64.0, 55.0/64.0, 36.0/64.0,  7.0/64.0, 31.0/64.0},
    {32.0/64.0, 43.0/64.0,  2.0/64.0, 46.0/64.0, 25.0/64.0, 63.0/64.0, 19.0/64.0, 50.0/64.0},
    {16.0/64.0, 53.0/64.0, 23.0/64.0, 60.0/64.0,  9.0/64.0, 47.0/64.0, 29.0/64.0,  6.0/64.0},
    {44.0/64.0, 27.0/64.0, 39.0/64.0, 34.0/64.0, 54.0/64.0, 13.0/64.0, 59.0/64.0, 26.0/64.0},
    { 8.0/64.0, 57.0/64.0, 18.0/64.0,  1.0/64.0, 42.0/64.0, 30.0/64.0,  3.0/64.0, 49.0/64.0},
    {35.0/64.0, 24.0/64.0,  0.0/64.0, 41.0/64.0, 15.0/64.0, 52.0/64.0, 20.0/64.0, 37.0/64.0}
};

float ditherChannel(float value, float threshold, float limit) {
    // Quantization Formula
    // value: 0.0 to 1.0
    // threshold: 0.0 to 1.0 (from matrix)
    // limit: colorDepth (e.g. 4.0)
    
    float ditheredValue = value + (threshold - 0.5) * (1.0 / (limit - 1.0));
    return floor(ditheredValue * (limit - 1.0) + 0.5) / (limit - 1.0);
}

kernel void ditherShader(texture2d<float, access::read> inputTexture [[texture(0)]],
                         texture2d<float, access::write> outputTexture [[texture(1)]],
                         constant RenderParameters &params [[buffer(0)]],
                         uint2 gid [[thread_position_in_grid]]) {
    
    if (gid.x >= outputTexture.get_width() || gid.y >= outputTexture.get_height()) {
        return;
    }
    
    // 1. Pixelation
    float scale = max(1.0, params.pixelScale);
    uint2 sourceCoord = uint2(floor(float(gid.x) / scale) * scale, floor(float(gid.y) / scale) * scale);
    
    sourceCoord.x = min(sourceCoord.x, inputTexture.get_width() - 1);
    sourceCoord.y = min(sourceCoord.y, inputTexture.get_height() - 1);
    
    float4 color = inputTexture.read(sourceCoord);
    
    // 2. Color Adjustment
    float3 rgb = color.rgb;
    rgb = rgb + params.brightness;
    rgb = (rgb - 0.5) * params.contrast + 0.5;
    
    // Grayscale
    float luma = dot(rgb, float3(0.299, 0.587, 0.114));
    
    if (params.isGrayscale > 0) {
        rgb = float3(luma);
    }
    
    // 3. Dithering
    float threshold = 0.5;
    bool shouldDither = (params.algorithm > 0);
    
    if (shouldDither) {
        uint x, y;
        
        // Fetch threshold from matrix
        switch (params.algorithm) {
            case 1: // Bayer 2x2
                x = uint(sourceCoord.x / scale) % 2;
                y = uint(sourceCoord.y / scale) % 2;
                threshold = bayer2x2[y][x];
                break;
            case 2: // Bayer 4x4
                x = uint(sourceCoord.x / scale) % 4;
                y = uint(sourceCoord.y / scale) % 4;
                threshold = bayer4x4[y][x];
                break;
            case 3: // Bayer 8x8
                x = uint(sourceCoord.x / scale) % 8;
                y = uint(sourceCoord.y / scale) % 8;
                threshold = bayer8x8[y][x];
                break;
            case 4: // Cluster 4x4
                x = uint(sourceCoord.x / scale) % 4;
                y = uint(sourceCoord.y / scale) % 4;
                threshold = cluster4x4[y][x];
                break;
            case 5: // Cluster 8x8
                x = uint(sourceCoord.x / scale) % 8;
                y = uint(sourceCoord.y / scale) % 8;
                threshold = cluster8x8[y][x];
                break;
            case 6: // Blue Noise 8x8
                x = uint(sourceCoord.x / scale) % 8;
                y = uint(sourceCoord.y / scale) % 8;
                threshold = blueNoise8x8[y][x];
                break;
            default:
                break;
        }
        
        // Apply Quantized Dithering
        if (params.isGrayscale > 0) {
            // Apply only to luma (which is already in rgb)
            rgb.r = ditherChannel(rgb.r, threshold, params.colorDepth);
            rgb.g = rgb.r;
            rgb.b = rgb.r;
        } else {
            // Apply to each channel
            rgb.r = ditherChannel(rgb.r, threshold, params.colorDepth);
            rgb.g = ditherChannel(rgb.g, threshold, params.colorDepth);
            rgb.b = ditherChannel(rgb.b, threshold, params.colorDepth);
        }
    }
    
    outputTexture.write(float4(rgb, color.a), gid);
}