从 MTKView 创建的 UIImage 导致颜色/不透明度差异

问题描述

当我将 MTKView 的内容捕获到 UIImage 中时，生成的图像看起来质量不同，如下所示:

When I capture the contents of an MTKView into a UIImage, the resulting image looks qualitatively different, as shown below:

我用来生成 UIImage 的代码如下:

The code I use to generate the UIImage is as follows:

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)!)

由于我不修改 ciImage 方向 (.orient(CGImagePropertyOrientation.downMirrored))，因此生成的图像是颠倒的，如上图所示.我保留镜像方向，以便指出两个图像捕获之间的颜色差异.

Since I don't modify the ciImage orientation (.oriented(CGImagePropertyOrientation.downMirrored)) the resulting image is upside down, as shown in the image above. I leave the mirrored orientation as is so I can point out the color differences between the two image captures.

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.

No matter how I change the kciOptions parameters, (say, even changing the colorspace to grayscale) I'm not seeing any changes in the resulting UIImage, which appears much more dim/desaturated than the original. Does anybody have any suggestions for how I can accurately capture what I'm drawing on MTKView to an UIImage? Any suggestions would be much appreciated.

以下是我的 MTKView 设置，可能证明是相关的:

Below are my MTKView settings which may prove relevant:

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

推荐答案

你的 CGColorSpace 是 .sRGB 但你的 renderPipelineDescriptor 的 pixelFormat 是 .bgra8Unorm.尝试将该行更改为:

Your CGColorSpace is .sRGB but your renderPipelineDescriptor's pixelFormat is .bgra8Unorm. Try changing that line to:

renderPipelineDescriptor.colorAttachments[0].pixelFormat = MTLPixelFormat.bgra8Unorm_srgb

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