ios - 如何使用Metal API或Accelerate Framework绘制裁剪后的位图？

Question

我正在实现裁剪视频帧的自定义视频合成器。目前，我使用Core Graphics来做到这一点:

-(void)renderImage:(CGImageRef)image inBuffer:(CVPixelBufferRef)destination {
    CGRect cropRect = // some rect ...
    CGImageRef currentRectImage = CGImageCreateWithImageInRect(photoFullImage, cropRect);

    size_t width = CVPixelBufferGetWidth(destination);
    size_t height = CVPixelBufferGetHeight(destination);

    CGContextRef context = CGBitmapContextCreate(CVPixelBufferGetBaseAddress(destination),       // data
                                             width,
                                             height,
                                             8,                                              // bpp
                                             CVPixelBufferGetBytesPerRow(destination),
                                             CGImageGetColorSpace(backImage),
                                             CGImageGetBitmapInfo(backImage));

    CGRect frame = CGRectMake(0, 0, width, height);
    CGContextDrawImage(context, frame, currentRectImage);
    CGContextRelease(context);
}

我如何使用Metal API来做到这一点？它应该快得多，对吗？
使用Accelerate Framework(特别是vImage)怎么样？会更简单吗？

Answer 1

好的，我不知道这对您是否有用，但仍然如此。
查看以下代码:

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{
  CVPixelBufferRef pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);

  id<MTLTexture> textureY = nil;

  {
    size_t width = CVPixelBufferGetWidth(pixelBuffer);
    size_t height = CVPixelBufferGetHeight(pixelBuffer);

    MTLPixelFormat pixelFormat = MTLPixelFormatBGRA8Unorm;

    CVMetalTextureRef texture = NULL;
    CVReturn status = CVMetalTextureCacheCreateTextureFromImage(NULL, _textureCache, pixelBuffer, NULL, pixelFormat, width, height, 0, &texture);
    if(status == kCVReturnSuccess)
    {
      textureY = CVMetalTextureGetTexture(texture);
      if (self.delegate){
        [self.delegate textureUpdated:textureY];
      }
      CFRelease(texture);
    }
  }
}

我使用此代码将CVPixelBufferRef转换为MTLTexture。之后，您可能应该创建blitCommandEncoder并使用它

func copyFromTexture(sourceTexture: MTLTexture, sourceSlice: Int, sourceLevel: Int, sourceOrigin: MTLOrigin, sourceSize: MTLSize, toTexture destinationTexture: MTLTexture, destinationSlice: Int, destinationLevel: Int, destinationOrigin: MTLOrigin)

在其中，您可以选择裁剪的矩形并将其复制到其他纹理。

下一步是将生成的MTLTextures转换回CVPixelBufferRefs，然后从中制作视频，很遗憾，我不知道该怎么做。

真的很想听听您的想法。干杯。