temporal antialiasing

fiddling around with my ATI drivers a few days ago, i found this little gem.

from what i know, ATI cards are capable of using different "patterns" with AA, which will obviously result in slightly different results each time. apparently temporal AA merely cycles through these different patterns with each frame, and can give the illusion of higher AA if the card can push the framerates fast enough. for example, AAx2 with TAAx2 will give the illusion of AAx4, with the same performance hit as AAx2.

unfortunately, my HD2400PRO cannot push enough frames for this to become viable. by default, TAAx2 will only turn on if FPS is above 60. i forced it to enable at 30FPS, and got a flickery mess as a result. setting TAAx3 had no effect whatsoever, not even flickering.

has anyone else tried this feature before, preferably with a much faster card? does it really work as advertised?

What is Temporal Anti-Aliasing?

One of the impressive (but little discussed) features of ATi's R3x0 architecture is that it is capable of programmable AA patterns. Whereas most graphics boards only have pre-programmed sampling patterns, theoretically a developer (or indeed ATi themselves) could change to a different AA pattern whenever they chose. This feature has never really been explored by either ATi or developers... Until now, where it has become the basis for a new (and thus far only available via the registry) anti-aliasing mode.

So, how does it work? Basically, instead of using a single, static sampling pattern when AA is enabled, temporal AA allows the board to select from one of several patterns, which it can then switch between on a per frame basis. In other words, every rendered frame is antialiased slightly differently, using a different pattern. If at this point you are thinking that changing the pattern every frame would end up as a horrible, flickery mess, you'd be right. Until you examine the principle a little more closely that is....

What you need to remember here is that the user is not seeing a handful of frames every second, in most cases on a modern GPU you would hope to see some way over 60 frames per second being rendered by the card. When you reach these kinds of performance level, the changes in sampling pattern are happening so quickly, and so frequently, that the human eyes cannot detect the difference between the changes at all. Therefore, the eye sees all of the different patterns used to antialias the image at the same time, thus giving the impression of a higher level of AA than is actually in effect.

The one big potential caveat here is that if frame rates drop too low, then the effect becomes visible to the human eye and flickering will occur. Therefore, this new technique is obviously not going to be suitable for all titles, the user will need to pick and choose carefully those which will give sufficient performance for the method to function as it should. A side-effect of this is that V-sync has to be enabled when temporal AA is used (this is forced on in ATi's drivers when it is in use), and also requires a high refresh rate on your monitor to really do it justice (in the order of 100Hz seems to do the job nicely).

Heh - turn it on. If it cripples your FPS, turn it off. Otherwise, leave it on.

Does this render temporal-AA useless on most LCD displays? These typically run 60hz through a single DVI channel, particulary WUXGA.

actually, the effect is ENHANCED on LCDs. because of pixel decay, this effect is effective even at around 30 FPS.

or at least, it did back in 2005. no idea if current LCD technology eliminated pixel decay or not.

CRT's reqeuire higher refresh rates due to rapid pixel fade per strobe cycle, but LCD pixels have constant luminance. Perhaps you mean pixel response time between color shifts? I do know that these have gotten much faster (3ms on my display).

Most LCDs do 2ms now. But it's a cool feature. Too bad I'm using nvidia..

This LCD monitor is a 5ms response, my other LCD is an 8ms, never notice the difference heh.

I just use the AA that games provide me, I never turn it on in the Nvidia control panel as it has never worked for me, at least not in Guild Wars.