Metal每日分享，颜色转换滤镜效果

// 转成灰度图滤镜
let filter = C7ColorConvert(with: .gray)
// 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

/// 颜色通道`RGB`位置转换
public struct C7ColorConvert: C7FilterProtocol {
    public enum ColorType: String, CaseIterable {
        case invert = "C7ColorInvert"
        case gray = "C7Color2Gray"
        case bgra = "C7Color2BGRA"
        case brga = "C7Color2BRGA"
        case gbra = "C7Color2GBRA"
        case grba = "C7Color2GRBA"
        case rbga = "C7Color2RBGA"
    }
    private let type: ColorType
    public var modifier: Modifier {
        return .compute(kernel: type.rawValue)
    }
    public init(with type: ColorType) {
        self.type = type
    }
}

// 颜色反转，1 - rgb
kernel void C7ColorInvert(texture2d<half, access::write> outputTexture [[texture(0)]],
                          texture2d<half, access::read> inputTexture [[texture(1)]],
                          uint2 grid [[thread_position_in_grid]]) {
    const half4 inColor = inputTexture.read(grid);
    const half4 outColor(1.0h - inColor.rgb, inColor.a);
    outputTexture.write(outColor, grid);
}
// 转灰度图
kernel void C7Color2Gray(texture2d<half, access::write> outputTexture [[texture(0)]],
                         texture2d<half, access::read> inputTexture [[texture(1)]],
                         uint2 grid [[thread_position_in_grid]]) {
    const half4 inColor = inputTexture.read(grid);
    const half3 kRec709Luma = half3(0.2126, 0.7152, 0.0722);
    const half gray = dot(inColor.rgb, kRec709Luma);
    const half4 outColor = half4(half3(gray), 1.0h);
    outputTexture.write(outColor, grid);
}
kernel void C7Color2BGRA(texture2d<half, access::write> outputTexture [[texture(0)]],
                         texture2d<half, access::read> inputTexture [[texture(1)]],
                         uint2 grid [[thread_position_in_grid]]) {
    const half4 inColor = inputTexture.read(grid);
    const half4 outColor(inColor.bgr, inColor.a);
    outputTexture.write(outColor, grid);
}
kernel void C7Color2BRGA(texture2d<half, access::write> outputTexture [[texture(0)]],
                         texture2d<half, access::read> inputTexture [[texture(1)]],
                         uint2 grid [[thread_position_in_grid]]) {
    const half4 inColor = inputTexture.read(grid);
    const half4 outColor(inColor.brg, inColor.a);
    outputTexture.write(outColor, grid);
}
kernel void C7Color2GBRA(texture2d<half, access::write> outputTexture [[texture(0)]],
                         texture2d<half, access::read> inputTexture [[texture(1)]],
                         uint2 grid [[thread_position_in_grid]]) {
    const half4 inColor = inputTexture.read(grid);
    const half4 outColor(inColor.gbr, inColor.a);
    outputTexture.write(outColor, grid);
}
kernel void C7Color2GRBA(texture2d<half, access::write> outputTexture [[texture(0)]],
                         texture2d<half, access::read> inputTexture [[texture(1)]],
                         uint2 grid [[thread_position_in_grid]]) {
    const half4 inColor = inputTexture.read(grid);
    const half4 outColor(inColor.grb, inColor.a);
    outputTexture.write(outColor, grid);
}
kernel void C7Color2RBGA(texture2d<half, access::write> outputTexture [[texture(0)]],
                         texture2d<half, access::read> inputTexture [[texture(1)]],
                         uint2 grid [[thread_position_in_grid]]) {
    const half4 inColor = inputTexture.read(grid);
    const half4 outColor(inColor.rbg, inColor.a);
    outputTexture.write(outColor, grid);
}

const half3 kRec709Luma = half3(0.2126, 0.7152, 0.0722);
const half gray = dot(inColor.rgb, kRec709Luma);
const half4 outColor = half4(half3(gray), 1.0h);

const float color = (inColor.r + inColor.g + inColor.b) / 3.0;
const half4 outColor = half4(color, color, color, 1.0h);