Alpha channel in the video surface

SDL Development
1
  1. 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?–
Marco Iannaccone
marciann at tin.it
ICQ UIN: 18748121 MetalCoder

"I bei film drammatici fanno sentire intelligenti anche gli stupidi, i bei
film comici fanno tornare bambini anche le persone intelligenti.
Peccato che sia pi? facile trovare stupidi che vogliono sembrare
intelligenti che persone intelligenti col coraggio di saper tornare bambini"
Stan Laurel

2
  1. 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