Delving Deeper into SMOOTHVISION
The above SMOOTHVISION analysis is pretty straightforward but it doesn't address the main issue we have with the ATI implementation. With a GeForce3, we can enable AA and use the card at any resolution, assuming your system can take the performance hit. With the RADEON 8500 and SMOOTHVISION, this is not the case and each of the various AA modes imposes a limitation on the game resolution. For example, enabling 4X Performance will display a maximum resolution of 1280x1024, while moving this up to the 4X Quality cuts this down to only 1024x768. Once you hit 5X and 6X Quality, you're limited to 800x600.
Thinking that these were simply "recommended settings" we set about testing the limitations of the SMOOTHVISION engine. The results were both varied and sometimes confusing. Depending on the system and game tested, our attempts to supercede the "maximum resolution" spelled out by the SMOOTHVISION driver tab ranged from the game actually working at one resolution higher than allowed, to a total game crash or lock if we really got zany.
On our Pentium 4/i850 and AMD/761 configurations, running a game over it's SMOOTHVISION maximums usually resulting in the game running without AA enabled at all, though sometimes it would just crash out. On our AMD/KT133A system the results were a bit worse. Either the game would crash out to the desktop, or even lock hard and require a reboot. In fact, on one occasion we set SMOOTHVISION to 6X Quality and tried to boot Quake 3 preconfigured at 1600x1200 with MAX detail settings. The result was a black screen with no way to exit from the game or OS without a reset. Even then, Windows started "finding" various hardware devices like the keyboard and motherboard resources, which gave us a bit of a scare.
Problems aside, we really started wondering what was causing these imposed resolution limits and the game problems we encountered when trying to overstep them. The word from ATI was that SMOOTHVISION enacted serious memory requirements on the card and that the maximum resolutions were a result of this. While truthful on the surface, something just didn't add up, since a GeForce3 can easily pass the same Quake 3 1600x1200/32-bit test that brought down the RADEON 8500. The only possible explanations were that the SMOOTHVISION implementation was not fully tuned, the RADEON 8500 has serious bandwidth concerns, or that ATI was somehow transferring a lot more data across the memory bus than NVIDIA. After witnessing the impressive 3D benchmark scores put in by the RADEON 8500, none of these made any real sense.
As has become apparent of late, the SMOOTHVISION anti-aliasing solution does not employ multi-sampling as we originally thought, but instead uses a method of supersampling. This is an important distinction and fits the scenario we described above perfectly. Instead of taking multiple samples of the same data like the GeForce3, SMOOTHVISION theoretically renders higher-resolution pixel data, which are then sampled, processed/blended and sent to a buffer. This process can really eat up buffer memory and tax the memory bus as well.
This translates into a high quality anti-aliased image, but with an extra step needed in the supersampling process, whereby the pixel up-sampling takes place. This makes supersampling a relatively simple and easy to implement anti aliasing technique, but one that places a great deal of strain on the hardware, not to mention wasting GPU clock cycles that could be better used elsewhere. Just don't confuse Supersampling with the simplistic Oversampling, which simply pre-processes the image at a higher resolution and then filters the image down to the size of the screen resolution.
Depending on the SMOOTHVISION methodology, supersampling can occur at different levels and use sampling methods such as ordered, adaptive or jittered. We don't have enough technical information on the RADEON 8500's SMOOTHVISION technology to made a precise call, but no matter which way the ball bounces, it amounts to a large amount of data being processed, stored and sent across the memory bus of the RADEON 8500.
Supersampling technology has been around for awhile now in various incarnations (Voodoo5, GeForce, RADEON, etc.), and usually entails a huge drain on memory bandwidth when anti-aliasing rates are increased. Hence, the maximum resolutions ATI has imposed at each SMOOTHVISION setting make a lot more sense when viewed from this perspective.
What this allows ATI to do is surpass the GeForce3 in terms of overall anti-aliasing image quality (especially at 4X Quality) but at a noticeable cost to framerates. Which is the better anti-aliasing option is dependent on your point of view, but it does bring up some serious SMOOTHVISION concerns for upcoming games. For example, SMOOTHVISION 4X Quality may be playable on games like Quake 3 and CounterStrike, but will performance constraints appear when we try it with Unreal 2? Whatever the answer, it would seem that SMOOTHVISION, while being a great anti-aliasing option for current games, might run into some potholes down the road.
