nanogui: Alpha blending using Nano-X APIs
Subject:
Re: [nanogui] Alpha blending using Nano-X APIs
From:
"Greg Haerr" ####@####.####
Date:
7 Jun 2005 06:34:01 +0100
Message-Id: <21c601c56b19$3c8068d0$6401a8c0@winXP>
> I am trying to test alpha-blending using Nano-X APIs. The malpha
demo program is based upon win32 API. The sprite.c file has reference
to GrNewAlpha function, but I can't find it anywhere.
The GrNewAlpha function has been removed, it was originally
used to set the ARGB "A" value before we allowed the values to
be specified directly as ARGB.
In any case, neither nano-X nor win32 APIs actually support
software alpha blending at this time. There is support for
hardware alpha blending using ARGB specifications.
The win32 malpha.c program uses a very tricky subset case where
a window can be alpha blended with another. The basic idea,
from the WM_PAINT section of malpha.c follows, and would
have to be duplicated using the nano-X API (but won't work in
every case since we can't force window repaint based on z-order
in nano-X):
1. repaint (refresh) all lower windows. This doesn't need to
occur on the first alpha blend, but would need to if updating
a blended window afterwords...
2. queue repaint for higher windows (delayed until after our drawing)
3. paint current window contents to offscreen pixmap
4. blend offscreen pixmap with root window using Blit function,
MWROP_BLENDCONSTANT.
Regards,
Greg
