According to the documentation of SDL, you can set the size of the red/green/blue framebuffer component in bits with SDL_GL_SetAttribute and passing SDL_GL_RED_SIZE or such. My question is, how exactly does this differ than screen bpp? I see code that passes 5 for all rgb components: SDL_GL_SetAttribute( SDL_GL_RED_SIZE, 5 ); SDL_GL_SetAttribute( SDL_GL_GREEN_SIZE, 5 ); SDL_GL_SetAttribute( SDL_GL_BLUE_SIZE, 5 ); First of all, shouldn't the green size be 6 if its 16 bpp? And if you set these values, but then set the screen to 24 or 32 bpp, isn't it still clamped by the 16-bit framebuffer? Because I also see code that passes 8 for all the components. I haven't seen any code that really checks for the bpp, such as: Also, can someone clarify the difference between 24 and 32 bpp? I know that 32 would include an alpha component, but a screen doesn't exactly display alpha itself.

Don't use SDL enough to answer the rest of your question, but

Quote:Original post by okonomiyaki
Also, can someone clarify the difference between 24 and 32 bpp? I know that 32 would include an alpha component, but a screen doesn't exactly display alpha itself.

Alpha in the framebuffer is needed if you want to use destination blending.

Right, but for the actual screen bpp, what does 32 bits matter?

You pass in a bpp value when calling SDL_SetVideoMode as well, and I'm assuming that's the screen bpp. I usually see 16 or 32 passed in.

But I can understand the need for the alpha component in the framebuffer for blending. Am I getting this confused? To clarify what I'm thinking: there is a bpp for the framebuffer, and a bpp for the screen?

Edit: thanks codemunkie (replied while I was). Ok that explains that bit.

Thinking about it over, I'm confused and tired. I get it now. You set the individual bits for rgb values, and also pass in the total bpp to SetVideoMode. got it.

Quote:Original post by okonomiyaki
To clarify what I'm thinking: there is a bpp for the framebuffer, and a bpp for the screen?

No, they are the same thing, at least in this context.

The way I see it, it's more of a request for the minimal bpp for that color.

Quote:
/*
* Now, we want to setup our requested
* window attributes for our OpenGL window.
* We want *at least* 5 bits of red, green
* and blue.

To be sure though, try this: after you set the video mode, make a call to SDL_GL_GetAttribute to see really what happened. Try that for both when you set 16/32 bpps.

Quote:Original post by Drew_Benton
The way I see it, it's more of a request for the minimal bpp for that color.

Quote:
/*
* Now, we want to setup our requested
* window attributes for our OpenGL window.
* We want *at least* 5 bits of red, green
* and blue.

To be sure though, try this: after you set the video mode, make a call to SDL_GL_GetAttribute to see really what happened. Try that for both when you set 16/32 bpps.

Yep, you're right. I request 16 bit mode but it gave me 32 bit (each component was 8 bits).

Cool. Thanks guys.