NSBitmapImageRep scaling/copying issue

[Riccardo Mottola]

Hi,

while trying to debug the issue betweeen GUI and GWorkspace icons with 
multi-page tiffs and high-res versions of our GUI controls, I noticed 
something strange.

I did a test-case on Mac where due to different backgrounds it is easier 
to detect.

The "scale" (but actually any) code I use IN PRICE and thus in also in 
GWorkspace appears to be broken, it produces artefacts with images with 
Alpha channel.

Even verys imple code, where I copy from the source to destination all 
"samples per pixels" copies all colors correctly, copies but produces 
effect around the borders and, apparently, on certain images it totally 
ruins alpha, on others not, just around the borders.

e.g in simplified pseudocode.

for (height)
  for (width)
    for (i in samples per pixel)
     destData[xy +  i] = srcData[xy +i];

fails. The actual code is actually smarter and tries to use bytesPerRow.

Does a bell ring for anybody? I know that e.g. when scaling, 
pre-multiplied alpha should be considered, but this produces minor 
issues and should not affect just simple copying or flipping or such. 
The nested loops should essentially do a byte-copy.. and they do for 
images without alpha.

Riccardo