Re: [Q] Trasparent Tiff drawing on Windows.

[Fred Kiefer]

MA Garcias wrote:
> After some try, I didn't get transparent tiff drawing work right in the
> win32 backend. Actually, making alpha blending work (for the
> NSCompositeSourceOver operation, which is 90% of the image drawing) was
> quite simply, just using AlphaBlend instead of BitBlt. Found two
> problems though:
> 1 - the standard tiff images in the gnustep distribution work fine with
> alpha blending, with their alpha channel correctly interpreted, but
> somehow the red and blue channels are swapped. When trying to set proper
> masks in the GSCreateBitmap function, the results are much worse.
> 2 - other tiff images (like the ones generated with Paint or other win32
> image tools) are drawn with oversaturated values, so that the image
> appears almost (or completely) white. Again, the color masks in the
> BITMAPV4HEADER struct seem to be completely useless to fix it. Anyway,
> it seems that the tiff library doesn't load correctly all tiff formats
> (or maybe the win32 tools don't stick to standard?).
> Anyway, you can find a patch in the attached file so that you people can
> play around (I'm not releasing it officially because of the poor
> results). Please report if you get any results.

I did apply this patch, to prevent other people to try the same. About 
half a year ago I wrote exaclty the same code with the same results, but 
only documented this with a mail not in the code. Thats why you and 
S.J.Chun had to go through the same experiance. At that time I came to 
the conclusion that only the switch to GDI++ would help.
Perhaps somebody will find a different solution, now that they don't 
have to start from scratch.

Fred