Metal每日分享，调整曝光滤镜效果

// 调整曝光效果
let filter = C7Exposure.init(exposure: 0.25)
// 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

/// 曝光效果
public struct C7Exposure: C7FilterProtocol {
    public static let range: ParameterRange<Float, Self> = .init(min: -10.0, max: 10.0, value: 0.0)
    /// The adjusted exposure, from -10.0 to 10.0, with a default of 0.0
    public var exposure: Float = range.value
    public var modifier: Modifier {
        return .compute(kernel: "C7Exposure")
    }
    public var factors: [Float] {
        return [exposure]
    }
    public init(exposure: Float = range.value) {
        self.exposure = exposure
    }
}

kernel void C7Exposure(texture2d<half, access::write> outputTexture [[texture(0)]],
                       texture2d<half, access::read> inputTexture [[texture(1)]],
                       device float *exposure [[buffer(0)]],
                       uint2 grid [[thread_position_in_grid]]) {
    const half4 inColor = inputTexture.read(grid);
    const half4 outColor = half4((inColor.rgb * pow(2.0, *exposure)), inColor.a);
    outputTexture.write(outColor, grid);
}