PixelBuffer function from iOS (UIImage) to MacOS (NSImage)

[Alexandre Lordelo]

The saga for coreML on MacOs continues!

This pixelBuffer function I translated for MacOS (NSImage), but lost on what to use for UIGraphicsPopContext()

If anyone has any input I highly appreciate! : )

iOS/UIImage

   func pixelBuffer(width: Int, height: Int, pixelFormatType: OSType,
                     colorSpace: CGColorSpace, alphaInfo: CGImageAlphaInfo) -> CVPixelBuffer? {
        var maybePixelBuffer: CVPixelBuffer?
        let attrs = [kCVPixelBufferCGImageCompatibilityKey: kCFBooleanTrue,
                     kCVPixelBufferCGBitmapContextCompatibilityKey: kCFBooleanTrue]
        let status = CVPixelBufferCreate(kCFAllocatorDefault,
                                         width,
                                         height,
                                         pixelFormatType,
                                         attrs as CFDictionary,
                                         &maybePixelBuffer)
        
        guard status == kCVReturnSuccess, let pixelBuffer = maybePixelBuffer else {
            return nil
        }
        
        CVPixelBufferLockBaseAddress(pixelBuffer, CVPixelBufferLockFlags(rawValue: 0))
        let pixelData = CVPixelBufferGetBaseAddress(pixelBuffer)
        
        guard let context = CGContext(data: pixelData,
                                      width: width,
                                      height: height,
                                      bitsPerComponent: 8,
                                      bytesPerRow: CVPixelBufferGetBytesPerRow(pixelBuffer),
                                      space: colorSpace,
                                      bitmapInfo: alphaInfo.rawValue)
            else {
                return nil
        }
        
        UIGraphicsPushContext(context)
        context.translateBy(x: 0, y: CGFloat(height))
        context.scaleBy(x: 1, y: -1)
        self.draw(in: CGRect(x: 0, y: 0, width: width, height: height))
        UIGraphicsPopContext()
        
        CVPixelBufferUnlockBaseAddress(pixelBuffer, CVPixelBufferLockFlags(rawValue: 0))
        return pixelBuffer
    }

MacOS/NSImage

    func pixelBuffer(width: Int, height: Int, pixelFormatType: OSType,
                     colorSpace: CGColorSpace, alphaInfo: CGImageAlphaInfo) -> CVPixelBuffer? {
        var maybePixelBuffer: CVPixelBuffer?
        let attrs = [kCVPixelBufferCGImageCompatibilityKey: kCFBooleanTrue,
                     kCVPixelBufferCGBitmapContextCompatibilityKey: kCFBooleanTrue]
        let status = CVPixelBufferCreate(kCFAllocatorDefault,
                                         width,
                                         height,
                                         pixelFormatType,
                                         attrs as CFDictionary,
                                         &maybePixelBuffer)
        
        guard status == kCVReturnSuccess, let pixelBuffer = maybePixelBuffer else {
            return nil
        }
        
        CVPixelBufferLockBaseAddress(pixelBuffer, CVPixelBufferLockFlags(rawValue: 0))
        let pixelData = CVPixelBufferGetBaseAddress(pixelBuffer)
        
        guard let context = CGContext(data: pixelData,
                                      width: width,
                                      height: height,
                                      bitsPerComponent: 8,
                                      bytesPerRow: CVPixelBufferGetBytesPerRow(pixelBuffer),
                                      space: colorSpace,
                                      bitmapInfo: alphaInfo.rawValue)
            else {
                return nil
        }
        
        context.saveGState()
        context.translateBy(x: 0, y: CGFloat(height))
        context.scaleBy(x: 1, y: -1)
        self.draw(in: CGRect(x: 0, y: 0, width: width, height: height))
         NSGraphicsContext()

      // to do: find an equivalent for NSImage
      //  UIGraphicsPopContext()
      

        CVPixelBufferUnlockBaseAddress(pixelBuffer, CVPixelBufferLockFlags(rawValue: 0))
        return pixelBuffer
    }

[Alexandre Lordelo]

@hollance , update from Apple Support...

Apple advised me to use saveGState() and restoreGState(). I updated the function bellow but still getting an empty output.

    func pixelBuffer(width: Int, height: Int, pixelFormatType: OSType,
                     colorSpace: CGColorSpace, alphaInfo: CGImageAlphaInfo) -> CVPixelBuffer? {
        var maybePixelBuffer: CVPixelBuffer?
        let attrs = [kCVPixelBufferCGImageCompatibilityKey: kCFBooleanTrue,
                     kCVPixelBufferCGBitmapContextCompatibilityKey: kCFBooleanTrue]
        let status = CVPixelBufferCreate(kCFAllocatorDefault,
                                         width,
                                         height,
                                         pixelFormatType,
                                         attrs as CFDictionary,
                                         &maybePixelBuffer)
        
        guard status == kCVReturnSuccess, let pixelBuffer = maybePixelBuffer else {
            return nil
        }
        
        CVPixelBufferLockBaseAddress(pixelBuffer, CVPixelBufferLockFlags(rawValue: 0))
        let pixelData = CVPixelBufferGetBaseAddress(pixelBuffer)
        
        guard let context = CGContext(data: pixelData,
                                      width: width,
                                      height: height,
                                      bitsPerComponent: 8,
                                      bytesPerRow: CVPixelBufferGetBytesPerRow(pixelBuffer),
                                      space: colorSpace,
                                      bitmapInfo: alphaInfo.rawValue)
            else {
                return nil
        }
        
        
        context.saveGState()
        context.translateBy(x: 0, y: CGFloat(height))
        context.scaleBy(x: 1, y: -1)
        self.draw(in: CGRect(x: 0, y: 0, width: width, height: height))
        context.restoreGState()
       // NSGraphicsContext()


        CVPixelBufferUnlockBaseAddress(pixelBuffer, CVPixelBufferLockFlags(rawValue: 0))
        return pixelBuffer
    }

[Matthijs Hollemans]

In the past I've used this instead of UIGraphicsPushContext:

  NSGraphicsContext.saveGraphicsState()
  let nscg = NSGraphicsContext(cgContext: context, flipped: true)
  NSGraphicsContext.current = nscg

And this instead of UIGraphicsPopContext:

    NSGraphicsContext.restoreGraphicsState()

[Alexandre Lordelo]

awesome, worked great! thanks mate!