GeForce switches to software OpenGL

[VECI]

We resell a high-end CAD package that uses OpenGL. We have been using the ASUS V6600 & V6800 cards and have noticed that after opening a third window in this application, the system seems to switch to software based OpenGL. This initial sign of the problem is that the screen is repainted diagonally from the upper left to the lower right in several bands. I have seen other articles posted that suggest this is happening in other applications. This application does not have this problem using GLint based cards such as the GVX1 by 3D Labs. I too have sent e-mails to NVIDIA and ASUS tech support. I have not received any responses. It's too bad. We have found that the performance of the board is faster than cards twice its price! I did notice that dropping the # or colors to 65K will allow us to open more windows before we run into the problem. I tried the WIN.INI (VDA=0) but we are running NT. Is there a registry hack equivalent? Also does anyone know what the available registry entries are for these cards? Is anyone else using the GeForce with CAD apps?

[Humus]

Since dropping the # of colors makes it possible to open more windows i would guess the problem is that the card runs out of memory with many window which all have to have thier own buffers. However, i don't know any solutions to your problem other than buying something like a 64 MB card ...

[VECI]

Thanks for responding. Question: I thought AGP was supposed to use existing system memory if it was needed? I am running these systems with a minimum of 256MB. Also, other 32MB cards do not seem to have this problem. I tried an experiment where I moved the "nvoglnt.dll" file to a temp directory, then launched the CAD app. It used Microsofts software OPenGL driver "Opengl32.dll". The initial performance was not as good as hardware based OpenGL, but... I did not see the degradation in performance with over 10 windows open. Any ideas?

Originally posted by Humus:
Since dropping the # of colors makes it possible to open more windows i would guess the problem is that the card runs out of memory with many window which all have to have thier own buffers. However, i don't know any solutions to your problem other than buying something like a 64 MB card ...

[Serge K]

> I thought AGP was supposed to use existing system memory if it was needed?

Usually 3D cards uses AGP memory for textures, but not for back/Z buffers.

In full-screen mode everything quite simple:
one front buffer, one back & Z.
But what if you have several windows, especially overlapped?

Most 3D cards uses one of 2 ways to implement windowed rendering:
1) with shared back & Z buffers.
If you works in 1280x1024, 3D card uses single 1280x1024 back & Z buffer, shared between all windows. This method required window clipping (some cards uses per/pixel WindowID for it)
2) separate back & Z buffers (per window).
This method much simpler, but...

32MB GeForce, 1280x1024, 32bpp.
Front buffer: 5MB
How huch windows can you have?

1280 x 1024 : 10MB (32b back buffer + 32b Z)
(32-5) / 10 = 2.7

So, if you open >2 1280x1024 windows, the system will switch to software rendering.

Look like this feature helps NVIDIA to separate GeForce from hi-end market (they need to sell Quadro after all
Quadro/GeForce comparison

[VECI]

I have been enlightened! Thanks for your time!

Originally posted by Serge K:
> I thought AGP was supposed to use existing system memory if it was needed?

Usually 3D cards uses AGP memory for textures, but not for back/Z buffers.

In full-screen mode everything quite simple:
one front buffer, one back & Z.
But what if you have several windows, especially overlapped?

Most 3D cards uses one of 2 ways to implement windowed rendering:
1) with shared back & Z buffers.
If you works in 1280x1024, 3D card uses single 1280x1024 back & Z buffer, shared between all windows. This method required window clipping (some cards uses per/pixel WindowID for it)
2) separate back & Z buffers (per window).
This method much simpler, but...

32MB GeForce, 1280x1024, 32bpp.
Front buffer: 5MB
How huch windows can you have?

1280 x 1024 : 10MB (32b back buffer + 32b Z)
(32-5) / 10 = 2.7

So, if you open >2 1280x1024 windows, the system will switch to software rendering.

Look like this feature helps NVIDIA to separate GeForce from hi-end market (they need to sell Quadro after all
Quadro/GeForce comparison