SOLVED: QR Code Generator (CIFilter) colours for light/dark mode ?

@rHockWorks

Feb '22

Using the CIFilter.qrCodeGenerator() to create a QR code I wanted to change the colours dynamically to suit Light/Dark mode, but was unable to figure out how to achieve this, is it possible please ?

struct QrCodeImage {

    let context = CIContext()

    func generateQRCode(from text: String) -> UIImage {

        var qrImage = UIImage(systemName: "xmark.circle") ?? UIImage()

        let data = Data(text.utf8)

        let filter = CIFilter.qrCodeGenerator()

        filter.setValue(data, forKey: "inputMessage")

        let transform = CGAffineTransform(scaleX: 2, y: 2)

        if let outputImage = filter.outputImage?.transformed(by: transform) {

            if let image = context.createCGImage(

                outputImage,

                from: outputImage.extent) {

                qrImage = UIImage(cgImage: image)

            }

        }

        return qrImage

    }
}

Further, I cannot see an option for the different modes and assume that any colour could be used, which would be a lot better for me.

ref: https://developer.apple.com/documentation/coreimage/ciqrcodegenerator

@rHockWorks

Mar '22

The answer was to use the QRcode as a mask and to switch them with the Core Image filter "CIColorInvert" when the mode changes:

struct QrCodeImage {

    let context = CIContext()

    func generateQRCode(from text: String) -> UIImage {
        var qrImage = UIImage(systemName: "xmark.circle") ?? UIImage()
        let data    = Data(text.utf8)
        let filter  = CIFilter.qrCodeGenerator()

        // ref : https://stackoverflow.com/questions/57704885/how-can-i-check-ios-devices-current-userinterfacestyle-programmatically
        var osTheme: UIUserInterfaceStyle { return UIScreen.main.traitCollection.userInterfaceStyle }
        filter.setValue(data, forKey: "inputMessage")

        let transform = CGAffineTransform(scaleX: 2, y: 2)
        if let outputImage = filter.outputImage?.transformed(by: transform) {
            if let image = context.createCGImage(
                outputImage,
                from: outputImage.extent) {

                let maskFilter = CIFilter.blendWithMask()
                maskFilter.maskImage = outputImage.applyingFilter("CIColorInvert")

                maskFilter.inputImage = CIImage(color: .white)

                let darkCIImage = maskFilter.outputImage!
                maskFilter.inputImage = CIImage(color: .black)

                let lightCIImage = maskFilter.outputImage!

                let darkImage   = context.createCGImage(darkCIImage, from: darkCIImage.extent).map(UIImage.init)!
                let lightImage  = context.createCGImage(lightCIImage, from: lightCIImage.extent).map(UIImage.init)!

                qrImage = osTheme == .light ? lightImage : darkImage
            }
        }
        return qrImage
    }
}

h/t : https://developer.apple.com/forums/thread/701448?login=true&page=1#706613022

@Obelix

Mar '22

Excellent find! Please mark your own answer as "Correct" !

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