swift - 具有 r32Float 像素格式的 MTLTexture 到位图

Question

我有一个带有 .r32Float 像素格式的 MTLTexture，其值在 0 - 1 范围内。

将该纹理转换为 8 位或 16 位 NSBitmapImageRep 的最佳方法是什么？

Answer 1

大概您希望您的图像处于灰度色彩空间中。这很简单，如果冗长的话，使用 vImage:

let width = texture.width
let height = texture.height
let sourceRowBytes = width * MemoryLayout<Float>.size
let floatValues = UnsafeMutablePointer<Float>.allocate(capacity: width * height)
defer {
    floatValues.deallocate()
}
texture.getBytes(floatValues,
                 bytesPerRow: sourceRowBytes,
                 from: MTLRegionMake2D(0, 0, width, height),
                 mipmapLevel: 0)
var sourceBuffer = vImage_Buffer(data: floatValues,
                                 height: vImagePixelCount(height),
                                 width: vImagePixelCount(width),
                                 rowBytes: sourceRowBytes)
let destRowBytes = width
let byteValues = malloc(width * height)!
var destBuffer = vImage_Buffer(data: byteValues,
                               height: vImagePixelCount(height),
                               width: vImagePixelCount(width),
                               rowBytes: destRowBytes)
vImageConvert_PlanarFtoPlanar8(&sourceBuffer, &destBuffer, 1.0, 0.0, vImage_Flags(kvImageNoFlags))
let bytesPtr = byteValues.assumingMemoryBound(to: UInt8.self)
let provider = CGDataProvider(data: CFDataCreateWithBytesNoCopy(kCFAllocatorDefault,
                                                                bytesPtr,
                                                                width * height,
                                                                kCFAllocatorDefault))!
let colorSpace = CGColorSpace(name: CGColorSpace.linearGray)!
let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.none.rawValue)
let image = CGImage(width: width,
                    height: height,
                    bitsPerComponent: 8,
                    bitsPerPixel: 8,
                    bytesPerRow: destRowBytes,
                    space: colorSpace,
                    bitmapInfo: bitmapInfo,
                    provider: provider,
                    decode: nil,
                    shouldInterpolate: false,
                    intent: .defaultIntent)!
let imageRep = NSBitmapImageRep(cgImage: image)