[SDL] Screen syncronizing

[David Olofson]

On Friday 14 May 2004 01.57, Bo Jangeborg wrote:
> David Olofson wrote:
> >If you use (SDL_DOUBLEBUF | SDL_FULLSCREEN), SDL_Flip() *may* sync
> >with the retrace. Depends on the backend, OS and drivers. There is
> >usually no reliable way of achieving explicit "direct" retrace
> > sync (as in "SDL_WaitRetrace()"), and you can't really use it for
> > anything in a normal OS anyway (need an RTOS), so there isn't
> > much point in trying to implement it.
> >
> >
> >As to combining the "smart update" approach (SDL_UpdateRects())
> > with a double buffered display surface, you can have a look at my
> > Pig example:
> >
> >	http://olofson.net/examples.html
> >
> >It's not trivial, but I think it's about as simple as a useful
> > "smart updating" solution gets if it has to support both "fake"
> > double buffering and hardware page flipping.
>
> How does the "fake" dubble buffering work ? Im not very good at
> reading C code

By "fake" double buffering, I mean a setup where making a new frame 
visible is done by copying a shadow buffer into the display buffer, 
as opposed to just swapping two display buffers.

What Pig does when hardware page flipping is not available is stay 
away from SDL_Flip() and use SDL_UpdateRects() instead. That way, it 
can get away with copying only the areas that have actually changed, 
which is how you get those insane frame rates (hundreds or thousands 
of fps) even without h/w accelerated blits.

Note that SDL gives you *either* double buffering with h/w page 
flipping, *or* a single display buffer + s/w shadow buffer! That is, 
if you want a s/w back buffer for fast rendering, you'll have to 
create that yourself, and implement your own alternative to 
SDL_UpdateRects(). Pig does that to avoid doing alpha blending (which 
there is a lot of) directly into VRAM.


> Btw, the Pig game looks very smooth.

Yeah, that's the idea. ;-)


//David Olofson - Programmer, Composer, Open Source Advocate

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