NSBitmapImageRep - draws in 32bit, but not in 16bit depth

FROM : Jens Bauer
DATE : Fri Nov 01 22:00:10 2002

Hi all,

Got some code, which allocates a NSBitmapImageRep and draws into this
newly allocated image.

I subclass NSImage and add a few methods for drawing the picture.
I've included 2 methods, the init and an example drawing method:

---8<-----8<-----8<-----
- (id)initWithWidth:(int)width andHeight:(int)height
{
   NSSize        imageSize;
   enum
   {
       kBitsPerSample        = 8,
       kSamplesPerPixel        = 4,
       kBytesPerPixel        = 4,
       kBitsPerPixel            = kBytesPerPixel * 8,
       kHasAlpha                = YES,
       kIsPlanar                = NO
   };

   self = [super init];
   if(self)
   {
       imageSize.width = (float) width;
       imageSize.height = (float) height;
       bitmapImageRep = [NSBitmapImageRep alloc];
       [bitmapImageRep
           initWithBitmapDataPlanes:NULL
           pixelsWide:width
           pixelsHigh:height
           bitsPerSample:kBitsPerSample
           samplesPerPixel:kSamplesPerPixel
           hasAlpha:kHasAlpha
           isPlanar:kIsPlanar
           colorSpaceName:NSCalibratedRGBColorSpace
           bytesPerRow:0
           bitsPerPixel:kBitsPerPixel];

       [self addRepresentation:bitmapImageRep];
       [self setSize:imageSize];
       [self setFlipped:YES];
   }
   return(self);
}

- (void)orPlotX:(long)xPos y:(long)yPos with:(long)pixel
{
   register long    x;
   register long    y;
   register long    width;

   x = xPos;
   y = yPos;
   if(x >= 0 && y >= 0)
   {
       width = (int) [self size].width;
       if(x < width)
       {
           if(y < (int) [self size].height)
           {
               ((long *) [bitmapImageRep bitmapData])[y * width + x] |= pixel;
           }
       }
   }
}
--->8----->8----->8-----

Now, I use this line...
   [offscreen compositeToPoint:NSZeroPoint fromRect:[self subImageRect]
operation:NSCompositeCopy];
...to place it in the window.

This all works very well if I set my screen depth to 32bit.
If I switch to 16bit *after* the allocation or 8bit for that matter, it
*still* works.
Now... If I start the application in 16bit mode and switch to 32bit
mode, nothing shows up.
I've tried turning alpha on/off, and it seems there's no difference
there.

If I dump the NSBitmapImageRep info after the allocation, I get...
bitsPerPixel:32
bytesPerRow:404
samplesPerPixel:4
bytesPerPlane:32724
isPlanar:0
pixelsWide:101.000000
pixelsHigh:81.000000

which looks right in my eyes.

Can anyone see what I'm doing wrong ?
-Why does the image show up as black in 16bit color depth, when it's
correct in 32bit color depth ?


Love,
Jens
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