GLSL: polygon soup on nVidia cards.

My engine uses GLSL for all high-level shader effects. I've tested the engine on two ATI GPUs and two onboard Intel GPUs, and the engine runs perfectly. It was tested on various nVidia cards today, and all of them produced "polygon soup" rendering. I disabled the engines GLSL, and this issue went away.

What's causing this on the nVidia cards? What are the differences in the way ATI and nVidia cards handle GLSL?

I didn't test on my computer, so i'm not completly sure of the system specs, but they are somthing like:
2.17 GHz processor
nVidia GeForce 52xx FX (possibly higher)
512 MB RAM

You may want to try this and Emulate the card just to make sure it is not the card model. I would also make sure the drivers are up to date.

Emulator:
http://developer.nvidia.com/object/nvemulate.html

For me, my GLSL shaders work best on nVidia cards. On ATI ones it only updates like every tenth second. Also ATI cards I've tried it on failed to compile the shaders due to a warning which I wasn't aware of since it compiled great on my nVidia card.

Both of those cards had updated drivers.

Quote:

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"polygon soup" rendering

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what's that?

Polygon's that taste delicious with crackers.

The attached image is my polygon soup. (Sorry, secret recipe :p )

I know I sound a little bit like an idiot, but what exactly do pixel and vertex shaders do? I sort of vaguely know that they somehow make graphics look better, but not much more than that. I actually don't really need to know; I'm just curious.

I've seen this happen before on Midtown Madness and Midtown Madness 2 with a GeForce 3 TI. It only happened on my PC because a friend had the same card and same game and no problem.

The solution is something called a W buffer or some type of width adjustment the card does. The fix is in the registry on the computer causing it - you can disable the buffer by adding a key to the registry. Perhaps a search on this issue might be in order.

This is definitely an NVidia issue and I don't know that it's related to the shaders. It seems to be but then, MM1 & 2 never used shaders and it had the same problem. But it looked exactly the same - polygons everywhere.

Vertex shaders are a tool so you can change the color, position etc for all vertices.
Pixel shaders are the same thing but for every pixel that is rendered. Those shaders are written in a specific language, in OpenGL it's GLSL, and compiled at runtime. Check this page for a tutorial: http://www.lighthouse3d.com/opengl/glsl/index.php?intro its really fun to play around with those shaders ;)

Oh, THAT'S polygon soup. I've caused that to happen a few times when building a skinned animation system, and also used to have that problem with EQ2's UI when shadow's were on (they fixed it, and it too only happened for NVidia cards).

If you could, try it on another machine that has the same card as you, it might be a heating problem, or just a beat up card.

May also want to try building a software shader that does the same thing (if you could) to try and find out exactly what the card doesn't like.