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View Full Version : stencil buffers, S3TC compression? How do these affect performance in 3D games?



Magneto
12-08-2001, 03:15 AM
Hi,
This is my first post to this forum. I've been trying to find information about stencil buffers, what they do, and how they affect performance and texture quality in 3D games, and whether they are used in 16 bit mode, or mainly 32 bit color.
One sim in particular has another option to select texture compression. The options are:
none, 16 bit, S3TC. I realize that nVidia does make use of S3TC in openGL, but are there performance advantages in using any of these texture compression methods?
I'm running a GeForce2 GTS 64 on my system.
Any help or useful links would be greatly appreciated..
Mag...

Rob The Bloke
12-08-2001, 07:55 AM
Originally posted by Magneto:
Hi,
This is my first post to this forum. I've been trying to find information about stencil buffers, what they do, and how they affect performance and texture quality in 3D games, and whether they are used in 16 bit mode, or mainly 32 bit color.

they allow the programmer the ability to limit the drawing to certain areas of the sceen, almost like a mask. They have a number of uses, but one of the most useful is for shadows. Texture quality should not be affected by their usage, the color mode is dependant on what the programmer decides to use and the capabilites of the hardware.


Originally posted by Magneto:

One sim in particular has another option to select texture compression. The options are:
none, 16 bit, S3TC. I realize that nVidia does make use of S3TC in openGL, but are there performance advantages in using any of these texture compression methods?

The idea with texture compression is to reduce the amount of memory required to hold a texture. With compression the number of textures you can hold therefore goes up. The down side is that the quality of the textures can be affected in certain situations. To counter this there are a number of different levels of compression that determine the quality of the final image.

there is a small example app here that will demostrate it at work :
http://www.nutty.org/OpenGL/Extensions/index.html



[This message has been edited by Rob The Bloke (edited 12-08-2001).]

Magneto
12-08-2001, 03:00 PM
Rob,

Thanks for replying, and thanks for the info. It was helpful, as was the link that you provided.
Mag...

Julien Cayzac
12-12-2001, 02:58 AM
Originally posted by Magneto:
I've been trying to find information about stencil buffers, what they do, and how they affect performance and texture quality in 3D games, and whether they are used in 16 bit mode, or mainly 32 bit color.


The stencil buffer is not a color buffer, thus its related performances are independant of your color buffers format.

Furthermore, on most hardware such as NVidia or ATI cards, the stencil buffer is 8-bit, neither 16 nor 32...

Julien.

ET3D
12-13-2001, 02:49 PM
Here's some more info and clarification for you:

The stencil buffer on NVIDIA hardware is only available in 32 bit Z mode. Since it it used for additional effects, it's not really a matter of speed.

In terms of colour range, S3TC is equivalent to 16 bit colour.

Magneto
12-13-2001, 03:36 PM
Thanks a bunch for the information. The game in question mainly implements the stencil buffer in 32 bit mode, and has another setting that makes shadows and effects look translucent, called "polygon stipple". Without the use of the stencil buffer or poly stipple, the shadows are hard and very opaque.
I'm not really sure how well my Hercules GF2 GTS 64 makes use of the stencil buffer, as I've heard it's a feature that's best known with the GF3 video cards.
Anyway.. thanks a bunch..
Mag...

ET3D
12-15-2001, 03:10 AM
Stencil buffer has been the same since the TNT days, AFAIK.