有效地将 MTKView 纹理捕获到 UIImageView

Question

我想捕获最近更新到 UIImageView 的 MTKView 部分的内容。我下面的一段代码来完成这个任务：

let cicontext = CIContext(mtlDevice: self.device!) // set up once along with rest of renderPipeline

...

let lastSubStrokeCIImage = CIImage(mtlTexture: lastDrawableDisplayed.texture, options: nil)!.oriented(CGImagePropertyOrientation.downMirrored)
let bboxChunkSubCurvesScaledAndYFlipped = CGRect(...) // get bounding box of region just drawn
let imageCropCG = cicontext.createCGImage(lastSubStrokeCIImage, from: bboxStrokeAccumulatingScaledAndYFlipped)

// Now that we have a CGImage of just the right size, we have to do the following expensive operations before assigning to a UIIView

UIGraphicsBeginImageContextWithOptions(bboxStrokeAccumulating.size, false, 0)  // open a bboxKeyframe-sized context
UIGraphicsGetCurrentContext()?.translateBy(x: 0, y: bboxStrokeAccumulating.height)
UIGraphicsGetCurrentContext()?.scaleBy(x: 1.0, y: -1.0)
UIGraphicsGetCurrentContext()?.draw(imageCropCG!, in: CGRect(x: 0, y: 0 , width: bboxStrokeAccumulating.width, height: bboxStrokeAccumulating.height))

// Okay, finally we create a CALayer to be a container for what we've just drawn

let layerStroke = CALayer()
layerStroke.frame = bboxStrokeAccumulating
layerStroke.contents = UIGraphicsGetImageFromCurrentImageContext()?.cgImage
UIGraphicsEndImageContext()

strokeView.layer.sublayers = nil  // empty out strokeView
strokeView.layer.addSublayer(layerStroke) // add our hard-earned drawing in its latest state

因此，此代码有效，但效率不高，并且当 bboxStrokeAccumulating 变得非常大时会使应用程序滞后。谁能提出更有效的替代方案？

Answer 1

对于 swift 4.0，

let lastDrawableDisplayed = metalView?.currentDrawable?.texture

if let imageRef = lastDrawableDisplayed?.toImage() {
    let uiImage:UIImage = UIImage.init(cgImage: imageRef)
}

extension MTLTexture {

    func bytes() -> UnsafeMutableRawPointer {
        let width = self.width
        let height   = self.height
        let rowBytes = self.width * 4
        let p = malloc(width * height * 4)

        self.getBytes(p!, bytesPerRow: rowBytes, from: MTLRegionMake2D(0, 0, width, height), mipmapLevel: 0)

        return p!
    }

    func toImage() -> CGImage? {
        let p = bytes()

        let pColorSpace = CGColorSpaceCreateDeviceRGB()

        let rawBitmapInfo = CGImageAlphaInfo.noneSkipFirst.rawValue | CGBitmapInfo.byteOrder32Little.rawValue
        let bitmapInfo:CGBitmapInfo = CGBitmapInfo(rawValue: rawBitmapInfo)

        let selftureSize = self.width * self.height * 4
        let rowBytes = self.width * 4
        let releaseMaskImagePixelData: CGDataProviderReleaseDataCallback = { (info: UnsafeMutableRawPointer?, data: UnsafeRawPointer, size: Int) -> () in
            return
        }
        let provider = CGDataProvider(dataInfo: nil, data: p, size: selftureSize, releaseData: releaseMaskImagePixelData)
        let cgImageRef = CGImage(width: self.width, height: self.height, bitsPerComponent: 8, bitsPerPixel: 32, bytesPerRow: rowBytes, space: pColorSpace, bitmapInfo: bitmapInfo, provider: provider!, decode: nil, shouldInterpolate: true, intent: CGColorRenderingIntent.defaultIntent)!

        return cgImageRef
    }
}

您可以将 uiImage 设置为您的 uiImageView