《函数式 Swift》封装 Core Image

image.png

typealias Filter = (CIImage) -> CIImage

/// 模糊
func blur(radius: Double) -> Filter {
    return { image in
        let parameters: [String: Any] = [
            kCIInputRadiusKey: radius,
            kCIInputImageKey: image
        ]
        guard let filter = CIFilter(name: "CIGaussianBlur",
                                    parameters: parameters)
        else { fatalError() }
        guard let outputImage = filter.outputImage
        else { fatalError() }
        return outputImage
    }
}

/// 颜色叠层
func overlay(color: UIColor) -> Filter {
    return { image in
        let overlay = generate(color: color)(image).cropped(to: image.extent)
        return compositeSourceOver(overlay: overlay)(image)
    }
}

/// 生成固定颜色的滤镜
func generate(color: UIColor) -> Filter {
    return { _ in
        let parameters = [kCIInputColorKey: CIColor(cgColor: color.cgColor)]
        // CIConstantColorGenerator: 颜色生成滤镜
        guard let filter = CIFilter(name: "CIConstantColorGenerator",
                                    parameters: parameters)
        else { fatalError() }
        guard let outputImage = filter.outputImage
        else { fatalError() }
        return outputImage
    }
}

/// 合成滤镜
func compositeSourceOver(overlay: CIImage) -> Filter {
    return { image in
        let parameters = [
            kCIInputBackgroundImageKey: image,
            kCIInputImageKey: overlay
        ]
        // CISourceOverCompositing: 图像覆盖合成滤镜
        guard let filter = CIFilter(name: "CISourceOverCompositing",
                                    parameters: parameters)
        else { fatalError() }
        guard let outputImage = filter.outputImage
        else { fatalError() }
        return outputImage.cropped(to: image.extent)
    }
}

let url = URL(string: "https://picsum.photos/300/300")!
let image = CIImage(contentsOf: url)!
let radius = 5.0
let color = UIColor.red.withAlphaComponent(0.2)
let blurredImage = blur(radius: radius)(image)
let overlaidImage = overlay(color: color)(blurredImage)

自定义运算符

/// 自定义运算符
infix operator >>>
func >>>(filter1: @escaping Filter, filter2: @escaping Filter) -> Filter {
    return { image in filter2(filter1(image)) }
}

let url = URL(string: "https://picsum.photos/300/300")!
let image = CIImage(contentsOf: url)!
let radius = 5.0
let color = UIColor.red.withAlphaComponent(0.2)
        
let blurAndOverlay = blur(radius: radius) >>> overlay(color: color)
let result = blurAndOverlay(image)

image.png

摘录来自《函数式 Swift》