RIVA TNT2 and the number 32

Letīs take a look on the 3D features of the card. NVIDIA always speaks about the number 32

32Bit rendering:

You get a much better image quality using 32Bit color depth in games that use many effects at the same time. These effects, for example transparent explosions, smoke and fog, are made by using textures (bitmaps). You can get in a situation where multiple textures are used in layered order. You then donīt have enough colors at 16Bit color depth to display the scene. So the card needs to dither the colors. You can see it in the left image below. The larger the display resolution the better dithering works. But it wonīt ever be as good as 32Bit rendering. There are many games out there that allready support 32Bit Rendering. The game Incoming was one of the first games that looked way better in 32Bit.

16Bit rendering	32Bit rendering
200% 640x480

These two shots show an area of a Expendable screnshot resized to 200%. Once in 16 Bit and once in 32Bit. You should switch your Desktop to 32Bit to see the whole difference. Some people say that itīs not fair to resize screenshots to show the difference. I donīt agree because these shots were made at a resolution of 640x480. If you watch these images in your webbrowser at a desktop resolution of for example 1024x768 you have much smaller pixels and the effect is smaller. Thatīs why I resize these shots.

But for those who donīt agree: I made two shots at a resolution of 1024x768. I donīt need to resize the shots here:

16Bit Rendering	32Bit Rendering
100% 1024x768

I think everybody can see the difference. Many games allready support 32Bit rendering but only a few games are optimized for that colordepth. Developers had to follow the rules not to use too much textures upon another because the cards were not able to show the scene correct. You have good 32Bit performance since TNT and ATi Rage 128 so weīll see 32Bit optimized games in soon. There will be games like Quake3 Arena that look way better in 32Bit.

32MB Memory

32MB Memory is needed for larger textures in games. The size of the textures is increasing rapidly at higher resolution and in 32Bit. So you need more memory on the card. Another point is tripple buffering. TNT and TNT2 support tripple buffering. Normaly you have double buffering. This means that one frame is shown (front buffer) while the other is build in the background (back buffer). The card always switches between front and back buffer. So you need twice the memory on the card. Tripple buffering means that you have one more buffer. This can increase the framerate if the chip on the card is fast enough. The disadvantage is that you need more memory on the card.
The TNT2 does also support textures swapping into the system memory using the AGP-Bus. TNT was able to make AGP2x transfers (transfer at high and low signal - 66MHz clockspeed). The tranferrate at AGP2x is about 500MB/sec. TNT2 now can do AGP4x transfers (double clockrate: 133MHz). This means about 1GB/sec. But this is way under the performance the card can achieve internal. The TNT2 can transfer 3,9GB/sec. on its 128Bit internal graphics-bus. There are also no AGP4x mainboards available yet. Thatīs why you need 32MB memory onboard. Other AGP features that TNT2 does support is AGP sideband adressing.

More detailed information about AGP is available here.

32Bit Z-Buffer (24Bit + 8Bit Stencil)

This image shows the use of the 24Bit z-buffer of the TNT2. You need a color depth of 32MB to use it. The left image shows a large complex scene at 16Bit color depth using 16Bit z-buffer. The right one with 24Bit z-buffer at 32Bit color depth. A z-buffer is used for the depth information in a scene. More distinctions can be made through better exactness at 24Bit. With 16Bit z-buffer the card canīt show the scene correct because it does not have enough steps to differ. The results is that some objects are cut. At 24Bit there are enough steps to show the scene correctly. In games scenes get more and more complex so this is an important feature.

The stencil buffer allows new effects in games. Itīs a bit complicate to explain how a stencil buffer works and how you can use it as a programmer. You can find this information in this techical stuff page on the NVIDIA website. In games stencil buffer is used to create real shadows (Expendable, Q3 test) or volumetric fog (Quake3).

Normal	Shadows using stencil

Misc Stuff

Additional features the TNT can do is Multitexturing (MT). This allows the chip to render 2 pixel that lay upon another in one step (This is where the name TNT comes from: TwiN Texel). Games use MT for mirror effects, for example refelections on a car (Environmental Mapping). The performance of the TNT/TNT2 does not drop much if this is used.

Mirror effects made by Environmental-Mapping

Other features are Mipmapping, Antialiasing, Bumpmapping etc. I donīt want to explain all of them here. The article would be too long.

Letīs take a look on the performance issues of the NVIDIA RIVA TNT2

RIVA Station 1999 - Lars Weinand