Ios 更改KCGIMAGEALPHONLY渲染CGImage的颜色
我正在尝试使用一些巨大的32位PNG,这些PNG实际上只是带有alpha通道的黑色,并以内存友好的方式在iOS应用程序中呈现 为此,我尝试在“仅alpha”CGContext中重新渲染图像:Ios 更改KCGIMAGEALPHONLY渲染CGImage的颜色,ios,uikit,core-graphics,Ios,Uikit,Core Graphics,我正在尝试使用一些巨大的32位PNG,这些PNG实际上只是带有alpha通道的黑色,并以内存友好的方式在iOS应用程序中呈现 为此,我尝试在“仅alpha”CGContext中重新渲染图像: extension UIImage { func toLayer() -> CALayer? { let cgImage = self.cgImage! let height = Int(self.size.height) let width =
extension UIImage {
func toLayer() -> CALayer? {
let cgImage = self.cgImage!
let height = Int(self.size.height)
let width = Int(self.size.width)
let colorSpace = CGColorSpaceCreateDeviceGray()
let context = CGContext(data: nil, width: width, height: height, bitsPerComponent: 8, bytesPerRow: width, space: colorSpace, bitmapInfo: CGImageAlphaInfo.alphaOnly.rawValue)!
context.draw(cgImage, in: CGRect(origin: .zero, size: self.size))
let image = context.makeImage()!
let layer = CALayer()
layer.contents = image
layer.contentsScale = self.scale
return layer
}
}
这太棒了!它将内存使用从180MB降低到18MB左右,这实际上比我预期的要好
问题是,图像的黑色(或现在的不透明)部分不再是黑色,而是白色
看起来改变不透明部分的颜色应该是一个简单的方法,但是我在网上找不到任何关于它的信息。你有什么想法吗?我已经设法回答了我自己的问题。通过将alpha-only图像设置为输出层的
掩码的内容
,我们可以将层的背景颜色设置为我们想要的任何颜色(包括非灰度值),并且仍然保持内存优势
我包含了最终的代码,因为我肯定不是唯一对这种方法感兴趣的人:
extension UIImage {
func to8BitLayer(color: UIColor = .black) -> CALayer? {
guard let cgImage = self.cgImage else { return nil }
let height = Int(self.size.height * scale)
let width = Int(self.size.width * scale)
let colorSpace = CGColorSpaceCreateDeviceGray()
guard let context = CGContext(data: nil, width: width, height: height, bitsPerComponent: 8, bytesPerRow: width, space: colorSpace, bitmapInfo: CGImageAlphaInfo.alphaOnly.rawValue) else {
print("Couldn't create CGContext")
return nil
}
context.draw(cgImage, in: CGRect(x: 0, y: 0, width: width, height: height))
guard let image = context.makeImage() else {
print("Couldn't create image from context")
return nil
}
// Note that self.size corresponds to the non-scaled (retina) dimensions, so is not the same size as the context
let frame = CGRect(origin: .zero, size: self.size)
let mask = CALayer()
mask.contents = image
mask.contentsScale = scale
mask.frame = frame
let layer = CALayer()
layer.backgroundColor = color.cgColor
layer.mask = mask
layer.contentsScale = scale
layer.frame = frame
return layer
}
}