Re: [paragui-users] alpha channel question

[Ulf Lorenz]

On Tue, Apr 15, 2003 at 12:30:43PM -0300, Keith wrote:
> i have been looking into why a lot of the widgets are not working properly
> when running double buffered. I have narrowed it down to the function
> SDL_SetAlpha(srf, SDL_SRCALPHA, 255-t);
> 
> or anything similar called before a blit. if i comment out this line, the
> widgets appear normal....... just you can't use transparency settings
> obviously. now with this i also note the when i check the video info via
> sdl_videoinfo i do not have blit_hw_A or blit_sw_A, which deal with alpha
> blending. but i thought it only means i don't have accelerated alpha
> blitting...... but then again, i'm not 100% sure what that means. i'm
> assuming that this relates back to the problem i have found.....which by the
> way also causes access violations on exit when deletethemedsurfaces is
> called.... but all is ok when i comment out the line.
AFAIR, SDL_SetAlpha will enable alpha blending if the second parametre is
SDL_SRCALPHA and give the whole surface an alpha value of argument 3. For a more
detailed description, have a look at the SDL header files (namely SDL_video.h).
They are even better documented than the doc.

> --Keith
Ulf

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