[SDL] Why is SDL so much faster than OpenGl

[pstuetz]

René <renesd <at> gmail.com> writes:

> 
Sorry for replying so late. I took me a while to check all the possibilities 
that were proposed.


> 
> It looks like you are using hardware acceleration with SDL.  If X
> supports it, this is a really quick way to blit pixels.

I Think, also OpenGL uses hardware accelaration. It should be commonly set up 
for all applications. "glxinfo" and "Yast" shows it. Anything else that I could 
check ?

> 
> With SDL you are creating a 16 bit window.
> 
> What are you using with opengl?

How can I check this ?

> 
> Have you tried using GL_RGB instead of GL_BGR(it might be doing the
> conversion in a slow software routine)?  

Changing GL_RGB and GL_BGR results in changed colors (as to be expected)

> Have you tried using faster
> filtering methods?

No, not yet. I guess I´m not much of a C-guru, to claim that I would be able to 
implement a "faster" byte-swapping alorithm tha the on that is used internally.

> 
> Some paths in opengl are slow on different cards/drivers.  So you
> might be hitting a slow path somewhere.  Try tweaking a few things and
> see if it improves things.

What do You mean by path. I allready tried both texturing ang bitmap-drawing

> 
> Is vsync disabled for SDL, and not for opengl?

OpenGl surely uses double-buffering. I see no reason to disable it.
> 
> Have you tried using overlays?  See $QTDIR/examples/opengl/overlay for
> the source code.

The stuff I want to draw on top of the video image is like A Hud-symbology. I 
changes with every frame. So I same no reason to bring this to an Overlay 
buffer.