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Old 12-03-07, 06:11 AM   #1
hamishm
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Join Date: Nov 2007
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Unhappy Performance problems with FSAA & window size

Hi.

I have a small program that takes 32 textures of size 512x256 pixels, loads them and displays them on a window, rotating in 8 cubes (Sides only).

The program runs fine on a PNY 8600GT with nv drivers 100.14.19 (Using gentoo amd64 and installing with the nvidia-drivers package from gentoos emerge) at a window size of 1200x950. When running like this it's using almost 0% CPU, and at ~20FPS (It updates via a timed callback at 50ms using gluTimerFunc()).

However... If I max the window to 1280x1024 the program suddenly starts to use 100% CPU (And FPS drops to around 5)... Like the rendering had suddenly started to use software fallback instead of the 8600's hardware rendering.

if I set FSAA to 0 (Via environment vars) the slowdown doesn't occur. Set it to 7 and it does (But I need the FSAA because othersie the images shimmer too badly).

is there a known limitation on wondow size and FSAA? A limitation on number of textures? Size of textures?

Oh... I have two monitors connected and running twinview (In case that makes a difference). With the 1280x1024 monitor to the left and the primary monitor at 16080x1050).


TIA
Hamsh.
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Old 12-03-07, 07:32 AM   #2
Thunderbird
 
Join Date: Jul 2002
Location: Netherlands, Europe
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Default Re: Performance problems with FSAA & window size

You say you are using FSAA to reduce shimmering, so you use it to reduce the framerate. Why don't you enable vsync? You can also do this programmatically using the right GLX extensions. (e.g. GLX_SGI_swap_control or GLX_SGI_video_sync). Also the use of timed callback doesn't sound that nice. Due to higher cpu usage it might be that this callback gets issues.
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Old 12-03-07, 09:20 AM   #3
hamishm
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Join Date: Nov 2007
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Default Re: Performance problems with FSAA & window size

Quote:
Originally Posted by Thunderbird
You say you are using FSAA to reduce shimmering, so you use it to reduce the framerate. Why don't you enable vsync? You can also do this programmatically using the right GLX extensions. (e.g. GLX_SGI_swap_control or GLX_SGI_video_sync). Also the use of timed callback doesn't sound that nice. Due to higher cpu usage it might be that this callback gets issues.
I don't use FSAA to reduce the framerate... And normally using FSAA with the 8600GT doesn't affect performance (And framerate)... Unless the window grows too large... I don't require vsync, so don't use it. There's no tearing involved.

Why don't you like a timed callback? You have a better way of doing regular updates? I don't like polling, so gluTimerFunc works quite well (The other option is using a separate thread & usleeping I suppose, but gluTimerFunc is there, so why not use it). (Yes you could do gluIdleFunc(), but that's as bad as polling... All those wasted CPU cycles to hit an update rate when TimerFunc does it at 50ms intervals no problems).

Besides that... The only issue I have is this feature of a sudden jump of 0%CPU up to 100%CPU just because the window size exceeds a certain value... (It's not X chewing the CPU, it's the application itself. I suspect inside libGL somewhere).

(I also don't use vendor specific extensions because (a) it's a simple program, and (b) I'd like it to work on other cards without problems (I have various machines, none of them with the same card).
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