Forums > Jitter

fast openGL rendering

February 5, 2009 | 5:35 pm

hi,

i’m trying to do some fast video tracking (>200fps)
so i’ve started to program a GLSL shader for image segmentation
but i realised that i can’t render a very simple OpenGL scene faster than 60 fps ether with jit.window nor jit.pwindow destination
whereas i can do rendering up to 500 fps with a matrix destination
but as i’m using some shader i got the same error as described here :

http://www.cycling74.com/forums/index.php?t=msg&goto=155341&rid=902&S=bab6c5f44f861ffab92ebfb8d6efb474&srch=shader+matrix+render#msg_155341

does anyone know a solution to do openGL readback at high frame rate with shader computing ?

thanks a lot

antoine


February 5, 2009 | 6:04 pm

With screen refresh of 60 hertz = 60 cycles/sec = max of 60 fps
(closely equivalent to what your eyes can perceive)

of course you could compute things faster, but to output to screen it
is limited by your refresh rate of you monitor. By default in Jitter,
the GL renderer (render+window) and the refresh rate are synced.

JS

On 5-Feb-09, at 12:35 PM, Antoine Villeret wrote:

>
> hi,
>
> i’m trying to do some fast video tracking (>200fps)
> so i’ve started to program a GLSL shader for image segmentation
> but i realised that i can’t render a very simple OpenGL scene faster
> than 60 fps ether with jit.window nor jit.pwindow destination
> whereas i can do rendering up to 500 fps with a matrix destination
> but as i’m using some shader i got the same error as described here :
> http://www.cycling74.com/forums/index.php?t=msg&goto=155341&rid=902&S=bab6c5f44f861ffab92ebfb8d6efb474&srch=shader+matrix+render#msg_155341
>
> does anyone know a solution to do openGL readback at high frame rate
> with shader computing ?
>
> thanks a lot
>
> antoine


February 5, 2009 | 6:05 pm

On Feb 5, 2009, at 9:35 AM, Antoine Villeret wrote:

> but i realised that i can’t render a very simple OpenGL scene faster
> than 60 fps ether with jit.window nor jit.pwindow destination
> whereas i can do rendering up to 500 fps with a matrix destination

I would suggest you disable synchronization on your window (@sync 0).
Otherwise, the maximum framerate is tied to the update of the display.
There will be tearing however, but it sounds like you are using this
less for display than for image analysis.

-Joshua


February 5, 2009 | 6:26 pm

thanks for your reply joshua

sync parameter doesn’t affect the frame rate
but i turned off doublebuffer attribute and i achieve 500 fps !!
and you’re right, i’m interested in image analysing not in displaying 500 fps !

thanks

antoine



FP
February 6, 2009 | 3:50 pm

>
>
>> but i realised that i can’t render a very simple OpenGL scene
>> faster than 60 fps ether with jit.window nor jit.pwindow destination
>> whereas i can do rendering up to 500 fps with a matrix destination
>
> I would suggest you disable synchronization on your window (@sync
> 0). Otherwise, the maximum framerate is tied to the update of the
> display. There will be tearing however, but it sounds like you are
> using this less for display than for image analysis.
very interesting.
what’s the difference put "sync 0" on render or/and window ?
thx.


fabrice planquette
elt@altern.org


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