Scene Generation
This is the first stage, and what happens here is the that the CPU has to figure out what is going on in the scene, and how to draw it. All of the scene information and settings are recorded, so that geometry transformation can begin.

Geometry Transformation, And Culling
This step is done by the CPU, with the acception of some of the newer video cards which feature a dedicated Transform & Lighting processor. This step is responsible for the creation of the coordinate matrix for every object, and the scene. These data matrixes are used in the later pipeline stanges for calculations. All geometry information has to be recalculated everytime an object moves. All geometry which is out of view or behind the viewpoint is removed, called culling.

Lighting, And Clipping
This step is done by the CPU, with the exception of some of the newer video cards which feature a dedicated Transform & Lighting processor. This step is responsible for the basic appearance of all of the polygons which were created by the previous stage. But matrix multiplication and comparisons, base colours are assigned to each polygon based on their orientation to the light sources, opacity and reflectivity. Any geometry which is hidden behind another objects is removed now, called clipping.

Triangle Setup
Triangle setup is done by all video accelerators, and this involves the breakdown of each polygon into horizontal strips called spans based on what textures they use. This stage on is also refered to as rasterization. Each one of these spans is then sent individually to the next pipeline stage.

Texturing
This pipeline takes each span and pixel by pixel begins to texture it. Based on what type of texture filtering is needed, and how many textures are to be used, a pixel may have to spend up to three clock cycles before it is complete. Most current video cards are capable of applying 2 or even 3 textures to each pixel in a single clock. This is called multi-texturing, and it is one of the major advancements in computer gaming, creating life-like realism out of simple polygons. Once each pixel is complete, it is sent to the assembly stage.

Rendering Assembly
This stage takes each pixel and determines its position in the buffer. If a pixel based on the pixels x and y coordinates already exists, the z-buffer is compared. If the current pixel has a higher z buffer value than the current pixel, transparency is compared. If the pixel already in the frame buffer has less than 100% opacity, than the current pixel is blended with that pixel, called alpha blending. If the current pixel has a lower z-index value and 100% opacity, the buffer pixel is replaced, if not, the two are blended.

Screen Output
This stage involves transferring that image in the back buffer to the front buffer so that it can be displayed.

Pixel Information | 3D Pipeline