Answered my own question ... apologize for the noise!
On Jan 7, 2010, at 4:05 PM, David Blanton wrote:
Thanks to all.
I have my bitmap being drawn but it is upside down.
Do isFlipped play any role in this / how do I get it to draw right
side up without inverting my raw data?
For those interested this is the correct definition of
NSBitMapImageRep:
m_ptrs[0] = (unsigned char*)m_bitmap.m_array;
m_NSBitmapImageRep = [[NSBitmapImageRep alloc]
initWithBitmapDataPlanes:m_ptrs
pixelsWide:m_bitmap.m_pixelsx
pixelsHigh:m_bitmap.m_pixelsy
bitsPerSample:8
samplesPerPixel:3
hasAlpha:NO
isPlanar:NO
colorSpaceName:NSCalibratedRGBColorSpace
bitmapFormat:NSAlphaNonpremultipliedBitmapFormat
bytesPerRow:(4*m_bitmap.m_pixelsx)
bitsPerPixel:32];
On Jan 6, 2010, at 11:32 AM, David Duncan wrote:
On Jan 6, 2010, at 10:19 AM, David Blanton wrote:
Now, from David Duncan's comment.
My bitmap data does have alpha, i.e 4 samples per pixel ARGB. I
thought kCGImageAlphaNoneSkipFirst says don't make an alpha plane,
skip byte 1 and go to RED.
I am not sure how to specify this in the 'bitmapFormat' parameter.
AlphaNoneSkipFirst means you have no alpha, and skip any leading
bytes per necessary to fill the pixel size. In your particular case
since you have 8 bits per component and 3 components, that means
skip the first 8 bits of each word then decode 8 bits for each of 3
components.
When you create your NSBitmapImageRep however, you specify that
there is alpha, which means that you are specifying the equivalent
of kCGImageAlphaPremultipliedFirst (since you don't specify the
NSAlphaNonpremultipliedBitmapFormat flag). What you really want is
to specify no alpha and 3 samples per pixel (if I'm not mistaken, I
usually work in Quartz rather than NS for graphics). Specifying 32
bits per pixel as you do should get the same interpretation that
you are currently getting via Quartz.
Also keep in mind that your Quartz code is more work than you would
actually need. Since you aren't drawing to your image data, you
should create the CGImage directly via CGImageCreate rather than
using CGBitmapContextCreate to then extract a CGImage – the
performance difference is in the syscalls necessary to mark the
memory for the bitmap context as copy-on-write.
--
David Duncan
Apple DTS Animation and Printing
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