XFX GeForce 8800 GTX Video Card Review :: Graphics Architecture 101

11-08-2006 · Category: Hardware - Video Cards

By Doc Overclock

The traditional graphics card architecture starts with the CPU which feeds the graphics chip in the vertex stage. Early video cards (pre-DX7) had the CPU handle the transformation and lighting of the vertices. DX 7 cards had fixed-function T+L hardware that did limited shading operations, with the advent of the GeForce 3 and programmable pixel shaders this part of the graphics pipeline became much more flexible. The RADEON 9700 from ATI brought programmable pixel shaders 2.0 and the GeForce 6800 brought dynamic flow control in SM version 3.0

The next step in the pipeline is the Setup stage, where vertices are made into shapes like triangles, lines, or points called primitives. These primitives are then converted in the rasterization stage into pixel fragments. The next step of the classic graphics pipeline is the ROP stage. In this stage the fragments are subjected to shading, Z-Culling, frame-buffering and anti-aliasing. Here's where the term fragment shading is more accurate than pixel shading, because they are not called pixels until the fragments are written into the frame-buffer but pixel shaders are used most commonly in terminology. The next step of the classic graphics pipeline is the memory stage where the final outputted pixel is sent to be displayed.

Early graphics cards didn't have to worry about shading pixels, as they only did 2D rendering in the pre 3D era. The advent of 3D cards like the Voodoo Graphics card allowed the card to do flat shading and simple texturing to the pixel. The advent of the TNT allowed two textures a clock to be applied to each pixel. The GeForce 256 card was the first commercially successful 3D card to be able to perform some limited shading with its NSR (NVIDIA Shader Rasterizer) such as bump mapping (emboss, Dot Product 3), shadow volumes, volumetric explosion, elevation maps, vertex blending, waves, specular lighting on a per-pixel basis.

The advent of the GeForce3 brought limited programmable pixel shaders into the limelight, as it was the basis for the graphics chip on the Xbox as well as a PC graphics chip. The GeForce DDR did the shading with fixed-function hardware, that couldn't be used for other features. The GeForce 3 could do up to 4 texture address operations for fetching texels (4 texels in a pass), and 8 texture blending operations per pass, totaling 12 pixel shader operations per program. The RADEON 8500 was capable of 22 pixel shader operations in a single pass. The next step was the RADEON 9700 Pro and Shader Model 2.0. The advantages SM 2.0 include up to 96 Pixel Shader operations per pass (65,536 operations in SM 2.0+ on the GeForce 5 series but that's another story altogether), introduced such features as 96-bit precision color, HDR, and many other features. Vertex Shader 2.0 introduced long VS programs (65,535+ via dynamic branching) and other features.