[Qt-interest] Quicktime C -> QImage

[Stephen Chu]

In article <20100419211825.217320 at gmx.net>,
 "Alexander Carôt" <alexander_carot at gmx.net> wrote:

> Hi Stephen,
> 
> yes, it worked out bypassing the CGImage. Furthermore, it was indeed an 
> endinaness problem, however, I couldn't fix it as you proposed (changing the 
> mode) such as 
> 
> ************** 
> createDecompressionSession(imageDesc,videoData->width,videoData->height,k32BGR
> APixelFormat,displayAndCompressFrame,videoData,&videoData->decompressionSessio
> n);
> *************
> 
> Not sure why this didn't work out but recoding the byteswap loop fixed it:
> 
> ***************
> size_t width, height, rowBytes, bitsPerComponent;
> void *baseAddr = NULL;
> CVPixelBufferLockBaseAddress( pixelBuffer, 0 );
> baseAddr = CVPixelBufferGetBaseAddress( pixelBuffer );
> width = CVPixelBufferGetWidth( pixelBuffer );
> height = CVPixelBufferGetHeight( pixelBuffer );
> unsigned char *rawData = new unsigned char[1000000];
> rawData = (unsigned char*) baseAddr;
> 
> unsigned char theRed,theGreen,theBlue,theAlpha;
> 
> int i = 0;
> do{
>   theAlpha = rawData[i];
>   theRed = rawData[i+1];
>   theGreen = rawData[i+2];
>   theBlue = rawData[i+3];
>   rawData[i] = theBlue;   
>   rawData[i+1] = theGreen;
>   rawData[i+2] = theRed;
>   rawData[i+3] = theAlpha;
>   i =  i + 4;
> }
> while(i < 400000);
> 
> currentObject->displayImage = new 
> QImage(rawData,320,240,QImage::Format_ARGB32);
> 
> currentObject->update();
> *******************
> 
> So all fine for now,
> thanks again,
> best
> 

I am not familiar with either QuickTime or CoreVideo so I can't say how 
to get it to flip the bytes for you.

Now for the endian swapping, this should work better:

#if Q_BYTE_ORDER == Q_LITTLE_ENDIAN

quint32 *   p = (quint32*) baseAddr;
for(int i=0;i<numPixels;++i) {
   p[i] = qToBigEndian(p[i]);
}

#endif

You don't need to do this on a big endian machine since the byte order 
is already what Qt wants.

Happy coding.

-- 
Stephen Chu