How I can get the width of an CVOpenGLTextureRef object?

Question

I am new to core video and would like to find out the pixel width of CVOpenGLTextureRef object. Is there a way I can do it?

Answer 1

By the time you're dealing with a CVOpenGLESTextureRef you're firmly in OpenGL territory — the only coordinate information you can get from there is in terms of texture coordinates (which run from 0.0 to 1.0 in both axes).

If you want information about the dimensions of the video going into the texture, go back up the CoreVideo pipeline. The CVOpenGLESTextureRef you're working with was presumably created from a sample buffer (which for video you can expect to be an image buffer), so you can use CVImageBuffer functions to get its size in terms of video pixels.

Answer 2

Thank you very much for your help! The following are the codes I use to get the size and clean rect of a CVImageBuffer and clean texture coordinates of CVOpenGLESTexture base on the CVImageBuffer. The CVImageBuffer was grabbed from iPhone5 camera running on IOS7.

`CVImageBufferRef cameraFrame = CMSampleBufferGetImageBuffer(sampleBuffer); 
err = CVOpenGLESTextureCacheCreateTextureFromImage(kCFAllocatorDefault,    coreVideoTextureCache, cameraFrame, NULL, GL_TEXTURE_2D, GL_LUMINANCE, bufferWidth, bufferHeight, GL_LUMINANCE, GL_UNSIGNED_BYTE, 0, &luminanceTextureRef);
NSLog(@"Clean Rect: %@", NSStringFromCGRect(cleanRect));
NSLog(@"Nominal Output Display Size: %@", NSStringFromCGSize(nominalOutputDisplaySize));
NSLog(@"Encoded full Size: %@", NSStringFromCGSize(encodedSize));
NSLog(@"Lower left coordinate: %f, %f", lowerLeft[0], lowerLeft[1]);
NSLog(@"Lower right coordinate: %f, %f", lowerRight[0], lowerRight[1]);
NSLog(@"Upper right coordinate: %f, %f", upperRight[0], upperRight[1]);
NSLog(@"Upper left coordinate: %f, %f", upperLeft[0], upperLeft[1]);`

`The out put is as following:
Clean Rect: {{0, 0}, {640, 480}}
Nominal Output Display Size: {640, 480}
Encoded full Size: {640, 480}
Lower left coordinate: 0.000000, 1.000000
Lower right coordinate: 1.000000, 1.000000
Upper right coordinate: 1.000000, 0.000000
Upper left coordinate: 0.000000, 0.000000`

It is not very clear from the output here as the Encoded full size is the same as nominal output display size. I feel the clean texture coordinates might be used to crop pixels from full encoded image buffer.