CFAA Performance

Unfortunately, custom filter AA doesn’t come free. You will see a performance hit. The premise though is simple: CFAA can be used to enhance the image quality of older and/or less-demanding games. Or if you’re on an LCD and stuck at a max resolution of say 1680x1050, where a card like the Radeon HD 4870 has plenty of extra memory bandwidth to spare, you could conceivably use CFAA to improve game visuals while hopefully still maintaining a playable frame rate.

That’s the theory at least. But does it pan out?

To test this we booted up our Half-Life 2: Episode Two timedemo as well as Quake Wars, and ran tests with Oblivion in our foliage area. The results were definitely mixed:

As you can see, the 4850 and 4870 cards took a huge hit in performance in Episode Two, but the performance hit wasn’t that great in Quake Wars or Oblivion. The Radeon 4850 saw a performance reduction of just 15% when going from 8xMSAA to 8xMSAA with edge detect filter (24xAA) in Quake Wars for instance. Why is that?

For starters, our Episode Two demo is taken in a large outdoor environment. Trees, bushes, and other foliage are everywhere. While our Oblivion foliage test also contains lots of foliage, we’re running in a smaller, more concentrated area that isn’t as expansive as our Episode Two demo where trees that are miles away have to be rendered. Oblivion is also getting old in the tooth, even at max settings a performance-oriented card like the 4850 is more than capable of handling it at 1920x1200 with HDR and 4xAA/16xAF.

Our Quake Wars timedemo is also outdoors, but it doesn’t contain nearly the amount of foliage as the other two games, hence the better CFAA performance.

Based on this, we feel pretty safe in surmising that the extent of the performance hit you’ll see from CFAA will not only vary from game-to-game, but it’s also very likely that it could vary from one level to the next. A game with a mixture of outdoor and indoor areas will see lots of performance fluctuations: in an area with large, open spaces and lots of foliage you’ll see a greater performance hit than a scene that takes place indoors with tight corridors.