我正在使用iOS 11,XCode 9和Metal2。我MTLTexture
使用像素格式bgra8Unorm
。我无法更改此像素格式,因为根据pixelFormat文档:
金属层的像素格式必须为bgra8Unorm,bgra8Unorm_srgb,rgba16Float,BGRA10_XR或bgra10_XR_sRGB。
其他像素格式不适合我的应用程序。
现在,我想UIImage
从纹理创建一个。我可以通过从纹理(doc)中提取像素字节来做到这一点:
getBytes(_:bytesPerRow:bytesPerImage:from:mipmapLevel:slice:)
我正在处理这些字节以获取UIImage
:
func getUIImageForRGBAData(data: Data) -> UIImage? {
let d = (data as NSData)
let width = GlobalConfiguration.textureWidth
let height = GlobalConfiguration.textureHeight
let rowBytes = width * 4
let size = rowBytes * height
let pointer = malloc(size)
memcpy(pointer, d.bytes, d.length)
let colorSpace = CGColorSpaceCreateDeviceRGB()
let context = CGContext(data: pointer, width: width, height: height, bitsPerComponent: 8, bytesPerRow: rowBytes, space: colorSpace, bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue)!
let imgRef = context.makeImage()
let image = UIImage(cgImage: imgRef!)
return image
}
但是,CGContext假定像素为rgba8格式。例如,在最终的UIImage中,红色纹理像素为蓝色。有没有办法在此过程中更改pixelFormat以获得正确的颜色?
该函数会将.bgra8Unorm
纹理的字节转换为RGBA顺序,并UIImage
根据数据创建一个:
func makeImage(from texture: MTLTexture) -> UIImage? {
let width = texture.width
let height = texture.height
let bytesPerRow = width * 4
let data = UnsafeMutableRawPointer.allocate(bytes: bytesPerRow * height, alignedTo: 4)
defer {
data.deallocate(bytes: bytesPerRow * height, alignedTo: 4)
}
let region = MTLRegionMake2D(0, 0, width, height)
texture.getBytes(data, bytesPerRow: bytesPerRow, from: region, mipmapLevel: 0)
var buffer = vImage_Buffer(data: data, height: UInt(height), width: UInt(width), rowBytes: bytesPerRow)
let map: [UInt8] = [2, 1, 0, 3]
vImagePermuteChannels_ARGB8888(&buffer, &buffer, map, 0)
guard let colorSpace = CGColorSpace(name: CGColorSpace.genericRGBLinear) else { return nil }
guard let context = CGContext(data: data, width: width, height: height, bitsPerComponent: 8, bytesPerRow: bytesPerRow,
space: colorSpace, bitmapInfo: CGImageAlphaInfo.noneSkipLast.rawValue) else { return nil }
guard let cgImage = context.makeImage() else { return nil }
return UIImage(cgImage: cgImage)
}
警告:此功能非常昂贵。从金属纹理创建图像几乎从来都不是您想要做的。
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