Dreamcast 3D performance

Of polygons and fillrate

With last week's announcement of PC 3D graphics chips offering 15 million polygons/sec and fillrates in the range of 800 MTexels/sec, it's easy to dismiss the Dreamcast graphics subsystem as being obsolete. While it is true that these new PC graphics chips, as well as the next generation Playstation are more powerful 3D accelerators, the Dreamcast is far from being deficient. Today's Pentium III processors still cannot produce a sustained throughput of 3 million polygons/sec. A quick look at these screenshots taken from a Japanese promotional demo disc for Shenmue can show you what 3 million polygons/sec can produce:

Facial Detail test 256 colof GIF only

FillRate

The remarkably low fillrate may also shock a few readers as it's even lower than last year's S3 Savage3D accelerator for the PC. Yet again, the numbers can be misleading. The first "special case" the Dreamcast has is that it is a console and not a PC, which means that it only needs to run at the NTSC limit of 640x480. Part of the reason why PC owners need such fast 3D accelerators is that PCs need to run games at high resolutions such as 1024x768 to reduce aliasing. On a TV, 640x480 is plenty. Remember that an average DVD only has 480 lines of resolution.

Detailed faces in real gameplay

Player models in real-time

The second distinction is that the PowerVR chip is an infinite-plane based deferred renderer rather than a conventional triangle renderer such as that with S3, NVIDIA, or Sony. The developers of the PowerVR, NEC and VideoLogic, have quoted performance as being "250-500 MPixels/sec" and on occasion even claimed a fillrate exceeding 1 gigapixel/sec! Though marketing hype is half of the situation, the PowerVR chip has been measured at a fill rate exceeding 1 gigapixel/sec in the past! To understand why these different numbers are being thrown around, you need to first understand how these numbers are determined.