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

You should think of it the other way around, create a metal texture object that uses a CoreVideo buffer as the backing buffer and then render into the texture in the normal way.

- (id<MTLTexture>) makeBGRACoreVideoTexture:(CGSize)size
                        cvPixelBufferRefPtr:(CVPixelBufferRef*)cvPixelBufferRefPtr
{
  int width = (int) size.width;
  int height = (int) size.height;

  // CoreVideo pixel buffer backing the indexes texture

  NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                           [NSNumber numberWithBool:YES], kCVPixelBufferMetalCompatibilityKey,
                           [NSNumber numberWithBool:YES], kCVPixelBufferCGImageCompatibilityKey,
                           [NSNumber numberWithBool:YES], kCVPixelBufferCGBitmapContextCompatibilityKey,
                           nil];

  CVPixelBufferRef pxbuffer = NULL;

  CVReturn status = CVPixelBufferCreate(kCFAllocatorDefault,
                                        width,
                                        height,
                                        kCVPixelFormatType_32BGRA,
                                        (__bridge CFDictionaryRef) options,
                                        &pxbuffer);

  NSParameterAssert(status == kCVReturnSuccess && pxbuffer != NULL);

  *cvPixelBufferRefPtr = pxbuffer;

  CVMetalTextureRef cvTexture = NULL;

  CVReturn ret = CVMetalTextureCacheCreateTextureFromImage(kCFAllocatorDefault,
                                                           _textureCache,
                                                           pxbuffer,
                                                           nil,
                                                           MTLPixelFormatBGRA8Unorm,
                                                           CVPixelBufferGetWidth(pxbuffer),
                                                           CVPixelBufferGetHeight(pxbuffer),
                                                           0,
                                                           &cvTexture);

  NSParameterAssert(ret == kCVReturnSuccess && cvTexture != NULL);

  id<MTLTexture> metalTexture = CVMetalTextureGetTexture(cvTexture);

  CFRelease(cvTexture);

  return metalTexture;
}