swift - 从 MTKView 创建的 UIImage 导致颜色/不透明度差异

Question

当我将 MTKView 的内容捕获到 UIImage 中时，生成的图像看起来有质的不同，如下所示:

我用来生成UIImage的代码如下:

let kciOptions = [kCIContextWorkingColorSpace: CGColorSpace(name: CGColorSpace.sRGB)!,
                         kCIContextOutputPremultiplied: true,
                         kCIContextUseSoftwareRenderer: false] as [String : Any]
let lastDrawableDisplayed = self.currentDrawable! // needed to hold the last drawable presented to screen
drawingUIView.image = UIImage(ciImage: CIImage(mtlTexture: lastDrawableDisplayed.texture, options: kciOptions)!)

由于我没有修改 ciImage 方向 (.oriented(CGImagePropertyOrientation.downMirrored))，因此生成的图像是上下颠倒的，如上图所示。我保留镜像方向不变，这样我就可以指出两个图像捕获之间的颜色差异。

无论我如何更改 kciOptions 参数(例如，甚至将色彩空间更改为灰度)，我都没有看到生成的 UIImage 有任何变化，它看起来比原始图像更加暗淡/不饱和。有人对我如何准确地将我在 MTKView 上绘制的内容捕获到 UIImage 有任何建议吗？任何建议将不胜感激。

以下是我的 MTKView 设置，可能证明相关:

let renderPipelineDescriptor = MTLRenderPipelineDescriptor()
renderPipelineDescriptor.vertexFunction = vertexProgram
renderPipelineDescriptor.sampleCount = self.sampleCount
renderPipelineDescriptor.colorAttachments[0].pixelFormat = MTLPixelFormat.bgra8Unorm
renderPipelineDescriptor.colorAttachments[0].isBlendingEnabled = true
renderPipelineDescriptor.colorAttachments[0].rgbBlendOperation = .add
renderPipelineDescriptor.colorAttachments[0].alphaBlendOperation = .add
renderPipelineDescriptor.colorAttachments[0].sourceRGBBlendFactor = .sourceAlpha         renderPipelineDescriptor.colorAttachments[0].destinationRGBBlendFactor = .oneMinusSourceAlpha            renderPipelineDescriptor.colorAttachments[0].sourceAlphaBlendFactor = .sourceAlpha              renderPipelineDescriptor.colorAttachments[0].destinationAlphaBlendFactor = .oneMinusSourceAlpha
self.isOpaque = false // makes MTKView bg transparent

Answer 1

let context = CIContext()
let texture = metalView.currentDrawable!.texture
let cImg = CIImage(mtlTexture: texture, options: nil)!
let cgImg = context.createCGImage(cImg, from: cImg.extent)!
let uiImg = UIImage(cgImage: cgImg)