I have two images, which both have alpha channel. I want to comine them together. It do works for UIImageView, but I want to do it by using cgimage, which without creat a UIImageView. I tried cgimage like this is not working:
func combine3(_ bg: UIImage, cover: UIImage) -> UIImage?{
let size = CGSize(width: self.view.frame.width, height: self.view.frame.height)
UIGraphicsBeginImageContext(size)
let maskRef = cover.cgImage!
let mask = CGImage.init(maskWidth: maskRef.width, height: maskRef.height, bitsPerComponent: maskRef.bitsPerComponent, bitsPerPixel: maskRef.bitsPerPixel, bytesPerRow: maskRef.bytesPerRow, provider: maskRef.dataProvider!, decode: nil, shouldInterpolate: false)
let masked = bg.cgImage?.masking(mask!)
let outPutImage = UIImage(cgImage: masked!)
UIGraphicsEndImageContext()
return outPutImage
}
but for UIImageView, it works pretty good:
let bg = creatBGImageFinal()!
bgIV.image = bg
let cover = createCoverImageFinal(progress: 0)!
let layer = CALayer()
layer.contents = cover.cgImage
layer.frame = CGRect(x: 0, y: 0, width: size.width, height: size.height)
maskIV.layer.mask = layer
bg: cover,which is a picture with an white circle in the middle, the others is Transparent: result:
The rule for cgImage masking is Dst = 1 - Src
.
Then draw the masked image onto image context with opacity:
func combine3(_ bg: UIImage, cover: UIImage, size: CGSize) -> UIImage? {
UIGraphicsBeginImageContextWithOptions(size, true, 1)
defer {
UIGraphicsEndImageContext()
}
let context = UIGraphicsGetCurrentContext()!
let maskRef = cover.cgImage!
let mask = CGImage.init(maskWidth: maskRef.width, height: maskRef.height, bitsPerComponent: maskRef.bitsPerComponent, bitsPerPixel: maskRef.bitsPerPixel, bytesPerRow: maskRef.bytesPerRow, provider: maskRef.dataProvider!, decode: nil, shouldInterpolate: false)!
let masked = bg.cgImage!.masking(mask)!
// adjust for lower-left-origin CG coordinates
context.translateBy(x: 0, y: size.height)
context.scaleBy(x: 1, y: -1)
context.draw(masked, in: CGRect(origin: .zero, size: size))
return UIGraphicsGetImageFromCurrentImageContext()
}
Result: