Metal每日分享，图像单色滤镜效果

// 去雾效果滤镜
let filter = C7Monochrome.init(intensity: 0.83, color: .blue)
// 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

/// 将图像转换为单色版本，根据每个像素的亮度进行着色
public struct C7Monochrome: C7FilterProtocol {
    public static let range: ParameterRange<Float, Self> = .init(min: 0.0, max: 1.0, value: 0.0)
    /// The degree to which the specific color replaces the normal image color, from 0.0 to 1.0, with 0.0 as the default.
    @ZeroOneRange public var intensity: Float = range.value
    /// Keep the color scheme
    public var color: C7Color = .zero
    public var modifier: Modifier {
        return .compute(kernel: "C7Monochrome")
    }
    public var factors: [Float] {
        return [intensity] + RGBAColor(color: color).toRGB()
    }
    public init(intensity: Float = range.value, color: C7Color = .zero) {
        self.intensity = intensity
        self.color = color
    }
}

kernel void C7Monochrome(texture2d<half, access::write> outputTexture [[texture(0)]],
                         texture2d<half, access::read> inputTexture [[texture(1)]],
                         constant float *intensity [[buffer(0)]],
                         constant float *colorR [[buffer(1)]],
                         constant float *colorG [[buffer(2)]],
                         constant float *colorB [[buffer(3)]],
                         uint2 grid [[thread_position_in_grid]]) {
    const half4 inColor = inputTexture.read(grid);
    const half3 luminanceWeighting = half3(0.2125, 0.7154, 0.0721);
    const half luminance = dot(inColor.rgb, luminanceWeighting);
    const half4 desat = half4(half3(luminance), 1.0h);
    const half r = desat.r < 0.5 ? (2.0 * desat.r * half(*colorR)) : (1.0 - 2.0 * (1.0 - desat.r) * (1.0 - half(*colorR)));
    const half g = desat.g < 0.5 ? (2.0 * desat.g * half(*colorG)) : (1.0 - 2.0 * (1.0 - desat.g) * (1.0 - half(*colorG)));
    const half b = desat.b < 0.5 ? (2.0 * desat.b * half(*colorB)) : (1.0 - 2.0 * (1.0 - desat.b) * (1.0 - half(*colorB)));
    const half4 outColor = half4(mix(inColor.rgb, half3(r, g, b), half(*intensity)), inColor.a);
    outputTexture.write(outColor, grid);
}