[SDL] R: Alpha channel in the video surface

Sam Lantinga slouken at devolution.com
Mon Apr 23 15:02:22 PDT 2001

> > >2) if I set 32 bit video mode, is it considered to have an alpha channel?
> >
> > No, the screen does not have an alpha channel. The exception is when
> > you use SDL_OPENGLBLIT.
> And with SDL_OPENGL? Shouldn't there be an alpha channel too?

No, with SDL_OPENGL, you don't get access to the framebuffer at all.
Actually you don't with SDL_OPENGLBLIT either, but SDL fakes it for you,
and renders your "screen" surface into the scene, which is why the
alpha blending is important.

BTW, we still need a tutorial on using SDL_OPENGLBLIT, if anyone is
interested.  In particular, how to use alpha blending effects with
it and when to call UpdateRects() in the scene rendering would be
very helpful.

See ya,
	-Sam Lantinga, Lead Programmer, Loki Entertainment Software

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