More on the GeForce 256

Pixels or Texels?

With paranoid fears aside, let us go to the other good feature of the GF256 - its quad pixel pipeline. The GF256 runs at the relatively slow speed of 120MHz, yet delivers 480 million pixels per second (480MP/s.) This is about 130 million pixels more than more than the fastest TNT2 and 113 million more than the Voodoo3 3500's texel number. Which, unfortunately, brings us to a very, very bad point about the GF256.

The GeForce 256 doesn't have the texel fill rate of other next generation cards. While the GeForce has a respectable pixel fill rate, the texel fill rate is below average. Since the Voodoo2 came out, texels have been a standard feature on 3D accelerators. While the V2 could only do 90MP/s, it could to 180MTexels/s. This translated to a doubling of performance (theoretical) when texel support was enabled in software (GLQuake and Quake2 were the first - in fact, the only recent engine that doesn't have texel support is the LithTech engine used in Shogo and Blood 2.)

Stop Hurting Me!

So what's the big deal? Well, let's put it this way. Since I've joined FiringSquad, I've played some of the best Quake players around and I've learned to get every single advantage I can get. I play in 640x480,I turn off all the extra display options and attempt to squeeze the most performance out of my system. While 30fps is fine for television, this is because all frames are done "in transition", ie, there is motion blur. One frame moves to another smoothly and your eye doesn't have to compensate. Now, in a game, there is no motion blur. Every model, wall, line, texture is drawn in perfect crispness. When you turn quickly with the mouse in Quake3, you notice it 30fps or not. Your target "skips" approximately 12 degrees per frame if you were to turn all 360 degrees of a circle in one second. As any mouse using Quake player knows, turning a full circle is far faster than 1 second. If you're slow, you might do it in a quarter, that means your target would skip 48 degrees in one second, and that's if he was simply standing still! That's about 1/8th of a circle. Again, it's very hard to rail somebody if you're turning quickly and getting only 30fps.

Now imagine your opponent has the top of the line ungodly bastard of a video card that can do 90fps in Quake3. This means he's getting only 1/3 the choppy motion feeling that you get, so if he was turning as quickly as you, you'd be moving only 16 degrees, or 1/24th of a circle to him. In a rail match between two equal players with equal lag, this is the deciding factor.

How does this relate to the GF256? Well, like I said, it can push 15 million triangles per second, compared to about 3 million for a Pentium III. However, at 640x480 with full detail, a TNT2 Ultra already maxes out by said Pentium III. In that case, the fill rate (millions of texels/second) becomes the limiting factor, not the processor. This is because with the extra passes, fill rate gets gobbled up. (A pass is the number of times an accelerator 'paints' a scene internally before displaying it as a frame. Having a dual-texel pipeline lets you effectively do two passes at the same time.)