CoreGraphics resizing function from iOS (UIImage) to MacOS (NSImage)

Question

Created Apr ’21

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Goal:
Rewrite CoreGraphics resizing function from iOS (UIImage) to MacOS (NSImage)

Problem:
Getting error on this line of code: let bytesPerPixel = cgImage.bitsPerPixel / bitsPerComponent

Error: Value of type '(UnsafeMutablePointer?, NSGraphicsContext?, [NSImageRep.HintKey : Any]?) -> CGImage?' (aka '(Optional<UnsafeMutablePointer>, Optional, Optional<Dictionary<NSImageRep.HintKey, Any>>) -> Optional') has no member 'bitsPerPixel'

Question: how can I replace "cgImage.bitsPerPixel" for something that works with NSImage?

iOS: UIImage

Code Block extension UIImage {
    
    // Resizeing using CoreGraphics
    func resize(to size:CGSize) -> UIImage? {
        
        let cgImage = self.cgImage!
        let destWidth = Int(size.width)
        let destHeight = Int(size.height)
        let bitsPerComponent = 8
        let bytesPerPixel = cgImage.bitsPerPixel / bitsPerComponent
        let destBytesPerRow = destWidth * bytesPerPixel
        
        let context = CGContext(data: nil,
                                width: destWidth,
                                height: destHeight,
                                bitsPerComponent: bitsPerComponent,
                                bytesPerRow: destBytesPerRow,
                                space: cgImage.colorSpace!,
                                bitmapInfo: cgImage.bitmapInfo.rawValue)!
        context.interpolationQuality = .high
        context.draw(cgImage, in: CGRect(origin: CGPoint.zero, size: size))
        return context.makeImage().flatMap { UIImage(cgImage: $0) }
    }
}

MacOS: NSImage

Code Block extension NSImage {
    
    // Resizeing using CoreGraphics
    func resize(to size:CGSize) -> NSImage? {
        
        let cgImage = self.cgImage
        let destWidth = Int(size.width)
        let destHeight = Int(size.height)
        let bitsPerComponent = 8
        let bytesPerPixel = cgImage.bitsPerPixel / bitsPerComponent
        let destBytesPerRow = destWidth * bytesPerPixel
        
        let context = CGContext(data: nil,
                                width: destWidth,
                                height: destHeight,
                                bitsPerComponent: bitsPerComponent,
                                bytesPerRow: destBytesPerRow,
                                space: cgImage.colorSpace!,
                                bitmapInfo: cgImage.bitmapInfo.rawValue)!
        context.interpolationQuality = .high
        context.draw(cgImage, in: CGRect(origin: CGPoint.zero, size: size))
        return context.makeImage().flatMap { NSImage(cgImage: $0) }
    }
}

Boost

Answer 1

FrankSchlegel OP

Apr ’21

The problem is that NSImage doesn't have the .cgImage accessor that UIImage has. It is a function with optional parameters, so to get the CGImage from an NSImage you need to do this instead:

Code Block swiftlet cgImage = self.cgImage()

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