Re: [PyOpenGL-Users] Rolling spectrogram with pyopengl

[Ian M. <geo...@gm...>]

2009/12/6 Timothée Lecomte <tim...@lp...>

> Hi Ian,
>
> I precisely need it to run as fast as the refresh rate, and it already is
> running fast enough, either with opengl or with pure 2D. However, it burns
> too much CPU to my taste, since the drawing part takes more time than the
> processing part, although the latter is quite heavy (FFT...), so I think
> there is room for large improvements.
>
I'm confused.  The CPU doesn't work too hard to coordinate the actions of
the GPU--it just takes time to do it, because it must wait, as Gijs
explained.   If the CPU is working hard, that means something else is going
on.  You can reduce processing time by optimizing, if applicable, and/or
using a JIT compiler (e.g. psyco).

It sounds like you're computing the FFT (which I assume is for signal
processing) on the CPU.  If you're doing that for a thousand some times
every frame, that is likely to be your speed problem.  Using a shader would
take all that load of the CPU.

> As you rightly say, I am drawing the texture off by one. As far as
> alternatives to pure glTexSubImage2D, I have considered and tried to use
> PBO, but it does not decrease the time needed by the two glTexSubImage2D
> calls. I don't really see how I could use glCopyTexSubImage2D instead of
> glTexSubImage2D.
>
My mistake: try glCopyTexImage2D:
#Draw the scene, then . . .
glBindTexture(GL_TEXTURE_2D,texture)
glCopyTexImage2D(GL_TEXTURE_2D,0,format,x,y,width,height,0)

I can't help you with PBOs, as I don't have a working implementation
myself.  FBOs should work comparably, though.  There's a Python FBO class
and tutorial in my latest OpenGL Library, on pygame.org, which may be of use
to you.

Ian