Kingfisher/Sources/Image/Filter.swift

//
//  Filter.swift
//  Kingfisher
//
//  Created by Wei Wang on 2016/08/31.
//
//  Copyright (c) 2019 Wei Wang <onevcat@gmail.com>
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in
//  all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
//  THE SOFTWARE.

import CoreImage

// Reuse the same CI Context for all CI drawing.
private let ciContext = CIContext(options: nil)

/// Represents the type of transformer method, which will be used in to provide a `Filter`.
public typealias Transformer = (CIImage) -> CIImage?

/// Represents a processor based on a `CIImage` `Filter`.
/// It requires a filter to create an `ImageProcessor`.
public protocol CIImageProcessor: ImageProcessor {
    var filter: Filter { get }
}

extension CIImageProcessor {
    
    /// Processes the input `ImageProcessItem` with this processor.
    ///
    /// - Parameters:
    ///   - item: Input item which will be processed by `self`.
    ///   - options: Options when processing the item.
    /// - Returns: The processed image.
    ///
    /// - Note: See documentation of `ImageProcessor` protocol for more.
    public func process(item: ImageProcessItem, options: KingfisherParsedOptionsInfo) -> Image? {
        switch item {
        case .image(let image):
            return image.kf.apply(filter)
        case .data:
            return (DefaultImageProcessor.default >> self).process(item: item, options: options)
        }
    }
}

/// A wrapper struct for a `Transformer` of CIImage filters. A `Filter`
/// value could be used to create a `CIImage` processor.
public struct Filter {
    
    let transform: Transformer

    public init(transform: @escaping Transformer) {
        self.transform = transform
    }
    
    /// Tint filter which will apply a tint color to images.
    public static var tint: (Color) -> Filter = {
        color in
        Filter {
            input in
            
            let colorFilter = CIFilter(name: "CIConstantColorGenerator")!
            colorFilter.setValue(CIColor(color: color), forKey: kCIInputColorKey)
            
            let filter = CIFilter(name: "CISourceOverCompositing")!
            
            let colorImage = colorFilter.outputImage
            filter.setValue(colorImage, forKey: kCIInputImageKey)
            filter.setValue(input, forKey: kCIInputBackgroundImageKey)
            
            return filter.outputImage?.cropped(to: input.extent)
        }
    }
    
    /// Represents color control elements. It is a tuple of
    /// `(brightness, contrast, saturation, inputEV)`
    public typealias ColorElement = (CGFloat, CGFloat, CGFloat, CGFloat)
    
    /// Color control filter which will apply color control change to images.
    public static var colorControl: (ColorElement) -> Filter = { arg -> Filter in
        let (brightness, contrast, saturation, inputEV) = arg
        return Filter { input in
            let paramsColor = [kCIInputBrightnessKey: brightness,
                               kCIInputContrastKey: contrast,
                               kCIInputSaturationKey: saturation]
            let blackAndWhite = input.applyingFilter("CIColorControls", parameters: paramsColor)
            let paramsExposure = [kCIInputEVKey: inputEV]
            return blackAndWhite.applyingFilter("CIExposureAdjust", parameters: paramsExposure)
        }
    }
}

extension KingfisherWrapper where Base: Image {

    /// Applies a `Filter` containing `CIImage` transformer to `self`.
    ///
    /// - Parameter filter: The filter used to transform `self`.
    /// - Returns: A transformed image by input `Filter`.
    ///
    /// - Note:
    ///    Only CG-based images are supported. If any error happens
    ///    during transforming, `self` will be returned.
    public func apply(_ filter: Filter) -> Image {
        
        guard let cgImage = cgImage else {
            assertionFailure("[Kingfisher] Tint image only works for CG-based image.")
            return base
        }
        
        let inputImage = CIImage(cgImage: cgImage)
        guard let outputImage = filter.transform(inputImage) else {
            return base
        }

        guard let result = ciContext.createCGImage(outputImage, from: outputImage.extent) else {
            assertionFailure("[Kingfisher] Can not make an tint image within context.")
            return base
        }
        
        #if os(macOS)
            return fixedForRetinaPixel(cgImage: result, to: size)
        #else
            return Image(cgImage: result, scale: base.scale, orientation: base.imageOrientation)
        #endif
    }

}