There seems to be an issue with the Image Writer plugin (from the
Developer/Examples/Quartz Composer/Plugins folder) on Intel machines. I've done
some tests, and determined that it's swapping the RGBA channels of the captured
image so that they become GRAB (ie Red becomes Green, Green becomes Red, Blue
becomes Alpha, and the Alpha is swapped with the Blue channel).
I've tried swizzling the color channels of the image before they go into the
Image Writer plugin, but this doesn't seem to make any difference to the
output, which is odd, because if I pipe the output of the swizzle CIFilter to a
billboard, the channels appear reordered as I'd expect.
I'm guessing this is some kind of endian-related issue. Anyone know how this
might be fixed?
I've managed to isolate the part of the code in the XCode project relating to
colorspaces, if this helps at all:
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
/* Figure out pixel format and colorspace to use */
colorSpace = [qcImage imageColorSpace];
if(CGColorSpaceGetModel(colorSpace) == kCGColorSpaceModelMonochrome)
pixelFormat = QCPlugInPixelFormatI8;
else if(CGColorSpaceGetModel(colorSpace) == kCGColorSpaceModelRGB)
pixelFormat = QCPlugInPixelFormatARGB8;
else
return NO;
/* Get a buffer representation from the image in its native colorspace
*/
if(![qcImage lockBufferRepresentationWithPixelFormat:pixelFormat
colorSpace:colorSpace forBounds:[qcImage imageBounds]])
return NO;
/* Create CGImage from buffer */
dataProvider = CGDataProviderCreateWithData(NULL, [qcImage
bufferBaseAddress], [qcImage bufferPixelsHigh] * [qcImage bufferBytesPerRow],
NULL);
cgImage = CGImageCreate([qcImage bufferPixelsWide], [qcImage
bufferPixelsHigh], 8, (pixelFormat == QCPlugInPixelFormatI8 ? 8 : 32), [qcImage
bufferBytesPerRow], colorSpace, (pixelFormat == QCPlugInPixelFormatI8 ? 0 :
kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Host), dataProvider,
NULL, false, kCGRenderingIntentDefault);
CGDataProviderRelease(dataProvider);
if(cgImage == NULL) {
[qcImage unlockBufferRepresentation];
return NO;
}
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
Cheers,
alx
http://machinesdontcare.wordpress.com
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