Technical Q&A QD3D61

Apple Accelerator Card & Textures

Q: I have an Apple Accelerator card in my PowerMac 9500. I'm seeing great acceleration with small models (without textures). However, I noticed with large models, performance actually gets worse! Yes, it is faster without the card! Can you explain this?

A: You will find the Apple card is good when you have very limited texture requirements, and only a few triangles in the scene (i.e., it is good at Gerbils), but it will quickly get bogged down when the triangle count goes up. This is because it doesn't start rendering until all the triangles are available - it can take up many megabytes of system memory to store them and you get no concurrency between the application and the rasterization.

Using a more traditional Z-buffered graphics architecture overcomes these limitations. That is not to say the Apple scanline method does not have some advantages.

There are several good high quality QD3D accelerator cards based on the defacto standard OpenGL chip (GLINT 500TX from 3Dlabs) in the PC market. They are generally more expensive than the Apple card, so they are probably not a "home" purchase. However, "you get what you pay for" is as true for 3D graphics as in other walks of life.