[SDL] Flickering DX.

[David Olofson]

On Monday 05 November 2007, Miguel Pragier wrote:
> When I use DirectX, my screen is flickering.

How? Directly or via SDL? If the latter, are you using SDL 1.2 
(stable) or 1.3 (development)? (These have rather different video 
subsystems.)


> Is it common?

Yes, it's perfectly normal if you're trying (and failing) to 
perform "smart updates" (ie redraw only what's changed) over a double 
buffered hardware surface.

The reason is that a double buffered hardware surface normally uses 
two actual VRAM surfaces that are *flipped* by SDL_FlipSurface(). No 
copying is done, so the new "drawing page" you get after a flip is 
two frames old, rather than identical to the last drawing page.

Simple solution: Always redraw the whole screen. Basically, assume 
that the drawing page is filled with random garbage after a flip.

If you want to do it the hard (but in some cases, very fast) way, you 
can have a look at my Fixed Rate Pig example (pig-1.0), which (among 
other things) demonstrates one way of performing smart updates, even 
on true page flipped displays:
	http://olofson.net/mixed.html

For starters, just verify that "Pig" actually works in with a double 
buffered hardware surface. (Retrace sync'ed frame rate probably; no 
flickering, no tearing.)


> I know my videoBoard support the DX I'm using.

I don't think you would be able to set up a display at all if it 
wasn't.


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

.-------  http://olofson.net - Games, SDL examples  -------.
|        http://zeespace.net - 2.5D rendering engine       |
|       http://audiality.org - Music/audio engine          |
|     http://eel.olofson.net - Real time scripting         |
'--  http://www.reologica.se - Rheology instrumentation  --'