PC Graphics Beyond XBOX - NVIDIA Introduces GeForce4

Features
By published

NV25's NfiniteFX II Vertex Shaders

If you remember what 'nfiniteFX' stood for in GeForce3, then you will certainly know what 'nfiniteFX II' is all about. NVIDIA chose this name for their programmable vertex and pixel shader engine that was first found in GeForce3.

In case you have no idea what 'vertex shader' stands for, I would like to ask you to please follow this link . You will find a very detailed explanation of a vertex shader and what it is good for.

Now, while GeForce3 had only one vertex shader, GeForce4 Ti comes equipped with two of them. Two vertex shaders in one chip aren't all new, since the NVIDIA chip that powers Microsoft's Xbox is also equipped with two vertex shaders. NV25 comes with an advanced version.

It is easy to imagine that two parallel vertex shaders can process many more vertices at the same time. The two units are multi threaded and the multi threading is done on-chip, to make the performance benefits transparent to the application or the API. Instruction dispatch is handled by NV25, but it has to confirm that each vertex shader is working on a different vertex to make the parallelism sensible. The vertex shaders were tuned from the original version found in GeForce3, thus cutting down instruction latencies.

In summary, you can say that GeForce4 Ti4600 is able to process about 3 times as many vertices as GeForce3 Ti500; this is because it has twice the amount of vertex shaders, they are more advanced and because they are clocked higher.

NV25's NfiniteFX II Pixel Shaders

Please go here to learn more about pixel shaders.

NVIDIA was also able to improve the pixel shader functionality of GeForce4 Ti.

The new chip supports pixel shaders 1.2 and 1.3, but not ATi's 1.4 extension.

Here are the new pixel shader modes:

OFFSET_PROJECTIVE_TEXTURE_2D_NV

OFFSET_PROJECTIVE_TEXTURE_2D_SCALE_NV
OFFSET_PROJECTIVE_TEXTURE_RECTANGLE_NV
OFFSET_PROJECTIVE_TEXTURE_RECTANGLE_SCALE_NV
OFFSET_HILO_TEXTURE_2D_NV
OFFSET_HILO_TEXTURE_RECTANGLE_NV
OFFSET_HILO_PROJECTIVE_TEXTURE_2D_NV
OFFSET_HILO_PROJECTIVE_TEXTURE_RECTANGLE_NV
DEPENDENT_HILO_TEXTURE_2D_NV
DEPENDENT_RGB_TEXTURE_3D_NV
DEPENDENT_RGB_TEXTURE_CUBE_MAP_NV
DOT_PRODUCT_TEXTURE_1D_NV
DOT_PRODUCT_PASS_THROUGH_NV
DOT_PRODUCT_AFFINE_DEPTH_REPLACE_NV

Explaining each new mode would go too far, but I would like to mention GeForce4 Ti's new support of z-correct bump mapping, which fights the artifacts seen where a bump-mapped surface intersects with other geometry, such as the water of a lake or river where it touches land.

Another important improvement was made with the DXT1 compressed texture quality, as you will see in our screen shots.

Finally, NVIDIA tuned a number of pixel shader pipeline paths, which dramatically accelerated the rendering of scenes with 3 or 4 textures per pixel.