Support YUV CVPixelBuffer output

[notedit]

When use none BGRA color format(for example nv12 or i420), it is boring to to color format convert. Hope MetalPetal can support this

[omarojo]

Output to CVPixelBuffer at the end of the chain, would be great. So we can use that output for other stuff like making videos or publishing to a live stream or something else.

[YuAo]

MTIContext object supports rendering a MTIImage to a CVPixelBuffer. However it can only render to a BGRA pixel buffer for now.

[YuAo]

Will consider the "render to YUV" feature.

[notedit]

i see CoreImage support render to yuv CVPixelBuffer. but it cost too much cpu. more than 100% cpu will be used.

  [ciContext render:outimage toCVPixelBuffer:outPixelBuffer];

is there any way to reduce the cpu use?

[notedit]

it seems it is because of https://github.com/YuAo/YUCIHighPassSkinSmoothing, move the discussion to YuAo/YUCIHighPassSkinSmoothing#11

[YuAo]

@omarojo @notedit Render to YUV pixel buffer is implemented on supported hardware (MTLFeatureSet_iOS_GPUFamily3_v1). ref: 2226c0f

Not fully tested, use with caution.

Here's an example:

NSError *error;
CVPixelBufferRef pixelBuffer;
CVPixelBufferCreate(kCFAllocatorDefault, outputImage.size.width, outputImage.size.height, kCVPixelFormatType_420YpCbCr8BiPlanarFullRange, (__bridge CFDictionaryRef)(@{(id)kCVPixelBufferIOSurfacePropertiesKey: @{}}), &pixelBuffer);
[context renderImage:outputImage toCVPixelBuffer:pixelBuffer error:&error];
//use the pixelBuffer
//....
//release the pixelBuffer
CVPixelBufferRelease(pixelBuffer);