Metal每日分享，波动滤镜/涂鸦滤镜效果

// 波动效果
let filter = C7Fluctuate.init(extent: 50, amplitude: 0.003, fluctuate: 2.5)
// 方案1:
let dest = BoxxIO.init(element: originImage, filter: filter)
ImageView.image = try? dest.output()
dest.filters.forEach {
    NSLog("%@", "\($0.parameterDescription)")
}
// 方案2:
ImageView.image = try? originImage.make(filter: filter)
// 方案3:
ImageView.image = originImage ->> filter

/// 波动效果，还可类似涂鸦效果
public struct C7Fluctuate: C7FilterProtocol {
    /// 控制振幅的大小，越大图像越夸张
    /// Control the size of the amplitude, the larger the image, the more exaggerated the image.
    public var amplitude: Float = 0.002
    public var extent: Float = 50.0
    public var fluctuate: Float = 0.5
    public var modifier: Modifier {
        return .compute(kernel: "C7Fluctuate")
    }
    public var factors: [Float] {
        return [extent, amplitude, fluctuate]
    }
    public init(extent: Float = 50.0, amplitude: Float = 0.002, fluctuate: Float = 0.5) {
        self.extent = extent
        self.amplitude = amplitude
        self.fluctuate = fluctuate
    }
}

kernel void C7Fluctuate(texture2d<half, access::write> outputTexture [[texture(0)]],
                        texture2d<half, access::sample> inputTexture [[texture(1)]],
                        device float *extent [[buffer(0)]],
                        device float *amplitude [[buffer(1)]],
                        device float *fluctuate [[buffer(2)]],
                        uint2 grid [[thread_position_in_grid]]) {
    constexpr sampler quadSampler(mag_filter::linear, min_filter::linear);
    const float2 textureCoordinate = float2(float(grid.x) / outputTexture.get_width(), float(grid.y) / outputTexture.get_height());
    float2 offset = float2(0, 0);
    offset.x = sin(grid.x * *extent + *fluctuate) * *amplitude;
    offset.y = cos(grid.y * *extent + *fluctuate) * *amplitude;
    const float2 tx = textureCoordinate + offset;//mix(textureCoordinate, textureCoordinate+offset, 0.01);
    const half4 outColor = inputTexture.sample(quadSampler, tx);
    outputTexture.write(outColor, grid);
}