FSAA Performance

The one thing that 3dfx failed to mention when they first started talking about FSAA was the performance hit. The Voodoo5 offers two forms of FSAA, 2 sample and 4 sample (the Voodoo4 will only offer 2 sample FSAA for performance reasons). The 2 sample FSAA essentially renders the scene twice and blends the two scenes in order to remove some of the "jaggies" while 4 sample FSAA renders the scene four times in order to remove most of the "jaggies" present in that particular scene.

Because it is simply re-rendering a scene x-number of times, 2 sample FSAA will reduce the fill rate to 1/2 of what it was without FSAA enabled and 4 sample FSAA will reduce the fill rate to 1/4 of what it was without FSAA. Now if you're running a game at a resolution that isn't hitting the peak fill rate of the Voodoo5, then the performance hit caused by moving to 2 or 4 sample FSAA should be noticeable but will still allow your game to play smoothly.

Racing and Flight Simulator games would fall into this category since they generally aren't fill rate limited and aren't that demanding on the fill rate of a video card.

However if you have a game that is beginning to expose the fill rate limitations of your card, such as Quake III Arena, then enabling 2 or 4 sample FSAA could be deadly to your frame rate and render your game virtually unplayable.

We chose Quake III Arena's demo001 benchmark in order to illustrate the worst case scenario effects of enabling 2 and 4 sample FSAA and what kind of performance hit you'll be taking because of it. Keep in mind that a first person shooter isn't the best place for FSAA, but because a first person shooter is also the most fill rate demanding type of game it represents the largest performance hit you can expect when enabling 2/4 sample FSAA.

As you can see, the performance hit is incredible in Quake III Arena, making enabling FSAA not too realistic of an option for Quake III or any other first person shooters. At the same time, FSAA doesn't really make that big of a difference in first person shooters because the action is at such a fast paced level that you don't really have the time to notice whether or not the bloody steps you're walking on are jagged or not.

Switching to 32-bit color only worsened the performance hit caused by 2/4 sample FSAA. The tests wouldn't even complete in 4 sample FSAA mode at some of the higher resolutions in 32-bit color mode.

The games that FSAA truly shines in don't need a video card with a 667MP/s fill rate, they don't even need a card with a 480MP/s fill rate, they run just fine on something like a Voodoo3 or a TNT2 which makes the performance hit caused by 2 or 4 sample FSAA much easier to bear.

We played Need for Speed 5: Porsche Unleashed at 800 x 600 with 4 sample FSAA enabled at very reasonable frame rates. We estimated the performance at 60 - 80fps at 800 x 600 x 16 with 4 sample FSAA enabled. Unfortunately, moving over to 32-bit color dropped the performance noticeably, we estimated it at around 25 - 45fps at 800 x 600 x 32.

Is it worth it? We think so, at least in games like NFS5, but because the final decision is up to you, we put together some screenshot comparisons for you all to have a look at.

At 16-bit color the GeForce2 GTS's 1.5 x 1.5 setting is faster than the Voodoo5 5500 with FSAA off, however the move to 32-bit color hurts the GeForce2 GTS quite a bit. The Voodoo5 5500's 4X FSAA is the slowest setting out of the bunch but depending on your perspective it is potentially the best looking. 3dfx would like to claim that their 2X FSAA is better than NVIDIA's 2x2 FSAA in terms of image quality, and these numbers show its faster as well. We'll have a more in depth comparison of the GeForce 2 GTS FSAA and the Voodoo5's FSAA in an upcoming FSAA comparison article.

Full Scene Anti-Aliasing (FSAA) FSAA Image Quality (OpenGL)
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