Geometry Engine and Rasterizer
If we look at the Evans & Sutherland Lightning 1200 and the two 3DLabs cards, we immediately notice the architectural differences to mainstream 3D cards. The three graphics cards use several graphics chips on the same board. In these products the graphics processors execute the stages of the OpenGL graphics pipeline separately. There also is a differentiation between the geometry engine and the rasterizer. Most of you are probably only familiar with the DirectX terminology from the 3D game world. Therefore we are going to explain the most important terms at this point.
Despite the different terminology the similarity between the Direct3D and the OpenGL pipeline is quite astounding. From a historical point of view the OpenGL API is older than the Direct3D API that is often used in games. But the Direct3D game API, formerly seen as a cheap solution, has come of age. Now it almost offers the same functions that OpenGL has had for years. Nevertheless, Direct3D was unable to conquer the workstation market despite the competitive functions. The main problem: Direct3D does not enable 3D hardware acceleration under NT 4.0. OpenGL, on the other hand, works on all Windows, Unix and Linux platforms. No wonder that programmers of workstation applications support the real standard OpenGL instead of Microsoft's proprietary Direct3D interface. OpenGL also simplifies porting applications to other platforms.
Both interfaces divide the necessary computing steps into two main areas: geometry and rasterization. The geometry stage converts the coordinate systems for a 3D scene, in relation to the position of the 3D objects in the room as well as the viewing angle (or 'camera position') of the user. If necessary, the effects of the light sources must also be calculated. What is simply called geometry in the OpenGL world was named transform and lighting under DirectX and Direct3D, respectively. There are two possibilities for geometry computations under OpenGL: Either the CPU of the workstation runs the calculations, or the computing-intensive steps are outsourced to a special graphics chip, the geometry engine. For quite some time now the OpenGL card manufacturers rely on these geometry engines to take load of the workstation CPU. In the game world under Direct3D this option has been available since the introduction of DirectX 7. Before that the CPU always had to do the task. Formerly nobody was very interested in geometry chips for mainstream cards because of the associated higher costs. This situation changed last year. With the GeForce Nvidia presented the first 3D game chip that integrates geometry and rasterizer on one chip. Shortly after a version for OpenGL cards followed: the Quadro. The latter is used by the company Elsa for the Gloria II.