Re: Gorm source reorganization

[Jeff Teunissen]

Fred Kiefer wrote:

> Richard Frith-Macdonald wrote:
> > Now, if only we had transparency working (and better focus handling)
> > on windows, I think it would be almost as good as on gnu/linux.  As it
> > is, I think Gorm is now quite usable on windows!
> 
> This transparency stuff is going to haunt me for ever. I really don't
> have a glue why it isn't working, but then the Windows documentation is
> not very clear here.

Actually, it's pretty clear; you just used the wrong pixel format.

Windows GDI has one pixel format for translucent/transparent bitmaps, 32-bit
BGRA. From MSDN:

"Alpha values per pixel are only supported for 32-bpp BI_RGB. This formula
is defined as:

typedef struct {
  BYTE   Blue;
  BYTE   Green;
  BYTE   Red;
  BYTE   Alpha;
};
"

You can't just pass in a GNUstep image, you have to massage the pixels into
the expected format by swapping the red and blue channels. The
BITMAPV4HEADER doesn't change the requirements; the data MUST be 32-bit
BGRA, period. 16-bit images need to be upconverted and then used as 32-bit
bitmaps.

[snip]

> The only note from the documentation I am still thinking about from time
> to time is that colour values should have their alpha value
> pre-multiplied. Not sure, what this will actually mean in code, as we
> leave it to windows to actually create the bitmaps, so I expect Windows
> should be doing whatever it needs. But perhaps this hint means more to
> you...

GNUstep bitmaps generally are premultiplied.

-- 
| Jeff Teunissen  -=-  Pres., Dusk To Dawn Computing  -=-  deek @ d2dc.net
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