High-Tech And Vertex Juggling - NVIDIA's New GeForce3 GPU

The Programmable Pixel Shader Of GeForce3

The next part of GeForce3's 'nfiniteFX Engine' is the 'Pixel Shader'. Just as its brother the 'Vertex Shader', it is programmable as well. It is a development of GeForce2's NSR = NVIDIA Shader Rasterizer. The surprising thing however is that NVIDIA doesn't supply by far as much information about it as about the Vertex Shader. It almost seems a bit as if NVIDIA is not quite as proud of the Pixel Shader. John Carmack's recent comments about GeForce3's pixel rendering unit seems to point in the same direction. They weren't all that flattery.

What Happens In The 3D-Pipeline Before The Pixel Shader?

First of all I guess I need to explain what the Pixel Shader stands for. It's basically the part of GeForce2 that does the rendering of the actual pixels that make up the image on your screen. Let's have a look what happened in the 3D-pipeline so far.

The vertices of the 3D-scene left the vertex shader as transformed and lit vertices. The next stage was the clipping, which removes all vertices of the scene that are not within the area of the screen. Back Face Culling removes all vertices that are facing 'back', away from the viewer, and thus don't show up on the screen. The viewport mapping is finally transforming the x and y coordinates of the vertices to viewport coordinates.

Now there comes the triangle setup. This is where the life of the vertices ends and the life of the pixels begins. It also marks the change of the 3D-scene from 'real' 3D to 'virtual' 3D or 2D. The computer screen is only 2D after all, so the final frame has got to be 2D as well.