Pixel Shaders and Moore's Law

In my post on 64-bit computing and X-Plane, there's a point that's implicit: there is a cost (in development time) to adopting any new technology, and it takes away from other things. I've been slow to work on 64-bit X-Plane because it would take away from things like texture paging and generic instruments. Similarly, there is a cost every time we do a build to supporting more configurations, so we pay for 64-bit continuously, by supporting six platforms instead of 3 (3 operating systems x 2 "bit-widths" of 32 and 64 bits).

We have a similar problem with graphics hardware, but it's even more evil. Moore's Law more or less says that in a given period of time, computer technology gets twice as fast. In the case of graphics cards, each generation of cards (coming out about every 12-18 months) is twice as fast as the last.

This has some scary implications for X-Plane. Consider these stats for video cards (taken from Wikipedia):

Card      Date        fill rate       Bus         Memory bw
GF3       01Q4        1920 MT/S       4x          8 GB/S
GF4 Ti    03Q1        2400 MT/S       8x          10 GB/S
GF5950    03Q4        3800 MT/S       8x          30.4 GB/S
GF6800    04Q2        7200 MT/S       PCIe16      35.2 GB/S
GF7900    06Q1        15600 MT/S      PCIe16      51.2 GB/S
GF8800    06Q4        36800 MT/S      PCIe16      86.4 GB/S
GF9800    08Q2        47232 MT/S      PCIe16/2    70.4 GB/S

Let's assume we support any video card in the last 5 years (in truth we support more than that). The difference between the best card and the oldest in w006 was 13,680 MT of fill rate.

Now in 2008 the difference is 43,432 megatexels per second!

In other words, the gap between the best and worst cards we might support is over 3x larger in only 3 years!

This is no surprise - since cards get twice as fast with every revision, the gap for a given number of generations also gets twice as wide.

What this means for us, programming X-Plane, is that coming up with a single simulator that runs on the very best and worst hardware is becoming increasingly more difficult, as the performance gains at the high end run away.