When you design a 3-D application, you define the world in any units you find convenient, from microns to parsecs. Your application passes a description of that world to Direct3D. This description includes the sizes and relative positions of all of the objects in your world and the position and orientation of the viewer. Direct3D transforms this description into a series of pixels on the screen. This process—the transformation of the geometry you supply into a two-dimensional image—is the geometry pipeline, sometimes called the transformation pipeline.
This section provides a Direct3D-centered approach to discussing the geometry pipeline. The following topics introduce key concepts and make parallels from those concepts to their counterparts in the Direct3D API: