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Technographics

3DTextures

By now, everybody is probably familiar with textures. In short, textures are 2 dimensional patterns that are painted onto the surface of any object. The more textures are applied, the more realistic will any object look but it will also require more rendering passes. The emphasis here is the 2-D nature of any texture, like a layer of paint. There are certain applications, though that require the application of 3 dimensional textures. Imagine a piece of wood or marble that is cut, the conventional 2D texture approach would simply perform anisotropic filtering to deform the given texture and make it fit onto the new surface generated by the cut. In reality, such things never happen, and this is where a 3D texture comes in to represent the structure of the grain inside the entire block of wood. Needless to say that such 3D textures contain a huge amount of data, which is why, hitherto, they have rarely ever been implemented in any application.

A cube with textures applied to its sides can be cut to reveal the same textures present throughout its entire structure. You can try it at home with a piece of Swiss cheese instead of wood or marble.

Implementing 3D textures in a truly usable form is a unique but rewarding challenge. Here are some of the problems in implementing 3D textures along with NVIDIA's unique nfiniteFX engine solutions:

• Problem: 3D Textures are Huge Files.
• A 256x256x256 texture would take 64MB uncompressed, while a 512x512x512 texture would consume 512MB uncompressed! This means that a 256x256x256 texture loaded completely into memory would consume the entire frame buffer of a 64MB board. An effective compression scheme is essential to making large 3D textures usable. They need to be small enough so that can be moved quickly and efficiently between memory and the GPU.
• Solution: NVIDIA's 3D Texture Technology
• NVIDIA's 3D texture technology is the only implementation that supports compression in not just one or two, but three dimensions. In addition, NVIDIA's compression technology supports multiple modes including multiple 4:1 compression modes and even an 8:1 compression mode! A 64MB texture can be reduced to 8MB. NVIDIA's 3D texture compression delivers a texture size that is manageable and usable.

Imposters

An additional new feature of the Ti GPU is the capability of using Imposters. Imposters are 2D primitives that remain orthogonal (directly facing) to the camera. A single 2D texture is then applied to the primitive.

In plain English, this means that Imposters are dummy textures that can be applied to repetitive patterns. nVidia uses the example of chairs that are filling up the background. The trick is that only one chair has been rendered. All other chairs are simple 2D copies of the texture that is the net effect of the first rendered chair and, therefore, called Imposters.

An ensemble of chairs in the background that are just imposters grouped around a single real 3D structure in the center .

This gives the appearance that the application has transformed, lit, and calculated every vertex and pixel of a more complicated model, when in fact it has merely applied a single texture (which is much faster). The problem with this type of approach (only using a 2D texture) occurs if the object or light source is moving. In that instance, the single 2D texture will stand out and not look right.

With any standard 2D texture mapping, this is what is going to happen, with the new 3D textures, Imposters can be used without generating an artificial out of place look.

Function Lookup and Volumetric Fog

There are a few other features that have been improved over the earlier versions of the GeForce3 like Volumetric Fog, meaning that the depth of the fog becomes an actual feature with respect to visibility of objects hidden in it. Volumetric fog, though, is basically just another word for Range Based Fog which is what ATi introduced with the Radeon's Charisma Engine. Likewise the Depth of Field can be stored as a Function Lookup meaning that all 3D textures are subject to e.g. the same f-stop of the camera. The result is a focal plane which is crisp whereas the foreground and background are more or less blurred (out of focus).

So much for the theoretical background about the novel features of the GeForce3 Ti 500. By now, most manufacturers have come up with their new line of GeForce Ti-based cards. ASUS currently is the highest volume manufacturer of nVidia-based graphics cards and of course, they have the entire line of the Ti cards in their repertoire. My personal interest focuses mostly on the high-end solution, that is the V8200 T5 which comes, among other things in the Deluxe flavor.

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