threema-ios/Threema/ThreemaQRCodeGenerator.swift

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// |_   _| |_  _ _ ___ ___ _ __  __ _
//   | | | ' \| '_/ -_) -_) '  \/ _` |_
//   |_| |_||_|_| \___\___|_|_|_\__,_(_)
//
// Threema iOS Client
// Copyright (c) 2019-2020 Threema GmbH
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License, version 3,
// as published by the Free Software Foundation.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.

import Foundation

@objc class ThreemaQRCodeGenerator: NSObject {
    @objc class func generate(qrString: String, dimension: Int) -> UIImage? {
        guard let qrFilter = CIFilter(name: "CIQRCodeGenerator") else { return nil }
        let qrData = qrString.data(using: String.Encoding.ascii)
        qrFilter.setValue(qrData, forKey: "inputMessage")
        let scale = dimension/39
        let qrTransform = CGAffineTransform.init(scaleX: CGFloat(scale), y: CGFloat(scale))
        guard let qrImage = qrFilter.outputImage?.transformed(by: qrTransform) else { return nil }
        
        guard let logo = BundleUtil.imageNamed("QRLogo").cgImage else {
            return convert(cmage: qrImage)
        }
        guard let threemaQr: CIImage = qrImage.combined(with: CIImage(cgImage: logo)) else {
            return convert(cmage: qrImage)
        }
        return convert(cmage: threemaQr)
    }
    
    class func convert(cmage:CIImage) -> UIImage {
        let context:CIContext = CIContext.init(options: nil)
        let cgImage:CGImage = context.createCGImage(cmage, from: cmage.extent)!
        let image:UIImage = UIImage.init(cgImage: cgImage)
        return image
    }
}

extension CIImage {
    /// Inverts the colors and creates a transparent image by converting the mask to alpha.
    /// Input image should be black and white.
    var transparent: CIImage? {
        return inverted?.blackTransparent
    }
    
    /// Inverts the colors.
    var inverted: CIImage? {
        guard let invertedColorFilter = CIFilter(name: "CIColorInvert") else { return nil }
        
        invertedColorFilter.setValue(self, forKey: "inputImage")
        return invertedColorFilter.outputImage
    }
    
    /// Converts all black to transparent.
    var blackTransparent: CIImage? {
        guard let blackTransparentFilter = CIFilter(name: "CIMaskToAlpha") else { return nil }
        blackTransparentFilter.setValue(self, forKey: "inputImage")
        return blackTransparentFilter.outputImage
    }
    
    /// Applies the given color as a tint color.
    func tinted(using color: UIColor) -> CIImage?
    {
        guard
            let transparentQRImage = transparent,
            let filter = CIFilter(name: "CIMultiplyCompositing"),
            let colorFilter = CIFilter(name: "CIConstantColorGenerator") else { return nil }
        
        let ciColor = CIColor(color: color)
        colorFilter.setValue(ciColor, forKey: kCIInputColorKey)
        let colorImage = colorFilter.outputImage
        
        filter.setValue(colorImage, forKey: kCIInputImageKey)
        filter.setValue(transparentQRImage, forKey: kCIInputBackgroundImageKey)
        
        return filter.outputImage!
    }
    
    /// Combines the current image with the given image centered.
    func combined(with image: CIImage) -> CIImage? {
        guard let combinedFilter = CIFilter(name: "CISourceOverCompositing") else { return nil }
        let centerTransform = CGAffineTransform(translationX: extent.midX - (image.extent.size.width / 2), y: extent.midY - (image.extent.size.height / 2))
        combinedFilter.setValue(image.transformed(by: centerTransform), forKey: "inputImage")
        combinedFilter.setValue(self, forKey: "inputBackgroundImage")
        return combinedFilter.outputImage!
    }

}