Metal每日分享，高斯双边模糊滤镜效果

// 双边模糊滤镜
let filter = C7BilateralBlur.init(radius: 10)
// 方案1:
ImageView.image = try? BoxxIO(element: originImage, filters: [filter, filter2, filter3]).output()
// 方案2:
ImageView.image = originImage.filtering(filter, filter2, filter3)
// 方案3:
ImageView.image = originImage ->> filter ->> filter2 ->> filter3

/// 双边模糊
public struct C7BilateralBlur: C7FilterProtocol {
    public var radius: Float = 1
    public var offect: C7Point2D = C7Point2D.center
    public var modifier: Modifier {
        return .compute(kernel: "C7BilateralBlur")
    }
    public var factors: [Float] {
        return [radius, offect.x, offect.y]
    }
    public init(radius: Float = 1) {
        self.radius = radius
    }
}

kernel void C7BilateralBlur(texture2d<half, access::write> outputTexture [[texture(0)]],
                            texture2d<half, access::sample> inputTexture [[texture(1)]],
                            constant float *blurRadius [[buffer(0)]],
                            constant float *stepOffsetX [[buffer(1)]],
                            constant float *stepOffsetY [[buffer(2)]],
                            uint2 grid [[thread_position_in_grid]]) {
    const int GAUSSIAN_SAMPLES = 9;
    const float x = float(grid.x);
    const float y = float(grid.y);
    const float width = float(inputTexture.get_width());
    const float height = float(inputTexture.get_height());
    const float2 inCoordinate(x / width, y / height);
    int multiplier = 0;
    float2 blurStep;
    float2 singleStepOffset(float(*stepOffsetX * 10) / width, float(*stepOffsetY * 10) / height);
    float2 blurCoordinates[GAUSSIAN_SAMPLES];
    for (int i = 0; i < GAUSSIAN_SAMPLES; i++) {
        multiplier = (i - ((GAUSSIAN_SAMPLES - 1) / 2));
        blurStep = float(multiplier) * singleStepOffset;
        blurCoordinates[i] = inCoordinate + blurStep;
    }
    half4 centralColor;
    half gaussianWeightTotal;
    half4 sum;
    half4 sampleColor;
    half distanceFromCentralColor;
    half gaussianWeight;
    constexpr sampler quadSampler(mag_filter::linear, min_filter::linear);
    const float distanceNormalizationFactor = float(abs(1 - *blurRadius));
    centralColor = inputTexture.sample(quadSampler, blurCoordinates[4]);
    gaussianWeightTotal = 0.18;
    sum = centralColor * 0.18;
    sampleColor = inputTexture.sample(quadSampler, blurCoordinates[0]);
    distanceFromCentralColor = min(distance(centralColor, sampleColor) * distanceNormalizationFactor, 1.0);
    gaussianWeight = 0.05 * (1.0 - distanceFromCentralColor);
    gaussianWeightTotal += gaussianWeight;
    sum += sampleColor * gaussianWeight;
    sampleColor = inputTexture.sample(quadSampler, blurCoordinates[1]);
    distanceFromCentralColor = min(distance(centralColor, sampleColor) * distanceNormalizationFactor, 1.0);
    gaussianWeight = 0.09 * (1.0 - distanceFromCentralColor);
    gaussianWeightTotal += gaussianWeight;
    sum += sampleColor * gaussianWeight;
    sampleColor = inputTexture.sample(quadSampler, blurCoordinates[2]);
    distanceFromCentralColor = min(distance(centralColor, sampleColor) * distanceNormalizationFactor, 1.0);
    gaussianWeight = 0.12 * (1.0 - distanceFromCentralColor);
    gaussianWeightTotal += gaussianWeight;
    sum += sampleColor * gaussianWeight;
    sampleColor = inputTexture.sample(quadSampler, blurCoordinates[3]);
    distanceFromCentralColor = min(distance(centralColor, sampleColor) * distanceNormalizationFactor, 1.0);
    gaussianWeight = 0.15 * (1.0 - distanceFromCentralColor);
    gaussianWeightTotal += gaussianWeight;
    sum += sampleColor * gaussianWeight;
    sampleColor = inputTexture.sample(quadSampler, blurCoordinates[5]);
    distanceFromCentralColor = min(distance(centralColor, sampleColor) * distanceNormalizationFactor, 1.0);
    gaussianWeight = 0.15 * (1.0 - distanceFromCentralColor);
    gaussianWeightTotal += gaussianWeight;
    sum += sampleColor * gaussianWeight;
    sampleColor = inputTexture.sample(quadSampler, blurCoordinates[6]);
    distanceFromCentralColor = min(distance(centralColor, sampleColor) * distanceNormalizationFactor, 1.0);
    gaussianWeight = 0.12 * (1.0 - distanceFromCentralColor);
    gaussianWeightTotal += gaussianWeight;
    sum += sampleColor * gaussianWeight;
    sampleColor = inputTexture.sample(quadSampler, blurCoordinates[7]);
    distanceFromCentralColor = min(distance(centralColor, sampleColor) * distanceNormalizationFactor, 1.0);
    gaussianWeight = 0.09 * (1.0 - distanceFromCentralColor);
    gaussianWeightTotal += gaussianWeight;
    sum += sampleColor * gaussianWeight;
    sampleColor = inputTexture.sample(quadSampler, blurCoordinates[8]);
    distanceFromCentralColor = min(distance(centralColor, sampleColor) * distanceNormalizationFactor, 1.0);
    gaussianWeight = 0.05 * (1.0 - distanceFromCentralColor);
    gaussianWeightTotal += gaussianWeight;
    sum += sampleColor * gaussianWeight;
    const half4 outColor = sum / gaussianWeightTotal;
    outputTexture.write(outColor, grid);
}