getBytes from MtlTexture to create CVPixelBufferRef

Question

Trying to create CVPixelBufferRef from MTLTexture on each call render of SCNRender object:

  CVPixelBufferLockBaseAddress(pixelBuffer!, CVPixelBufferLockFlags(rawValue: 0))
        let bytesPerRow = 4 * Int(textureSizeX)
        let region = MTLRegionMake2D(0, 0, Int(textureSizeX), Int(textureSizeY))

    var tmpBuffer = CVPixelBufferGetBaseAddress(pixelBuffer!);

    offscreenTexture.getBytes(tmpBuffer!, bytesPerRow: bytesPerRow, from: region, mipmapLevel: 0)

    CVPixelBufferUnlockBaseAddress(pixelBuffer!, CVPixelBufferLockFlags(rawValue: 0))

And then convert to UIImage to display on screen

    let ciImage = CIImage.init(cvPixelBuffer: pixelBuffer!)
    let temporaryContext = CIContext(options: nil)
    let tempImage = temporaryContext.createCGImage(ciImage, from: CGRect(x: 0, y: 0, width: textureSizeX, height: textureSizeY))
    let uiImage = UIImage.init(cgImage: tempImage!)

But image is not displayed

Answer 1

I was having the same issue and found the following solution. It works like a charm :)

func image(from texture: MTLTexture) -> UIImage? {
    let bytesPerPixel = 4

    // The total number of bytes of the texture
    let imageByteCount = texture.width * texture.height * bytesPerPixel

    // The number of bytes for each image row
    let bytesPerRow = texture.width * bytesPerPixel

    // An empty buffer that will contain the image
    var src = [UInt8](repeating: 0, count: Int(imageByteCount))

    // Gets the bytes from the texture
    let region = MTLRegionMake2D(0, 0, texture.width, texture.height)
    texture.getBytes(&src, bytesPerRow: bytesPerRow, from: region, mipmapLevel: 0)

    // Creates an image context
    let bitmapInfo = CGBitmapInfo(rawValue: (CGBitmapInfo.byteOrder32Big.rawValue | CGImageAlphaInfo.premultipliedLast.rawValue))
    let bitsPerComponent = 8
    let colorSpace = CGColorSpaceCreateDeviceRGB()
    let context = CGContext(data: &src, width: texture.width, height: texture.height, bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: colorSpace, bitmapInfo: bitmapInfo.rawValue)

    // Creates the image from the graphics context
    guard let dstImage = context?.makeImage() else { return nil }

    // Creates the final UIImage
    return UIImage(cgImage: dstImage, scale: 0.0, orientation: .up)
}

Source: https://www.invasivecode.com/weblog/metal-image-processing You may also be interested in: https://github.com/hollance/CoreMLHelpers/tree/master/CoreMLHelpers