GPU Technologies - SmoothVision HD
In terms of the technology that makes up R420, nothing much has changed since R350, it's just been made more powerful, more able to scale and more efficient. SmoothVision, HyperZ, HydraVision, SmartShader, Overdrive and Videoshader are all present and correct in R420, just tweaked or upgraded slightly.SmoothVision, ATI's anti-aliasing engine, is the first that's worth covering.
R420 supports the same scattered grid multi-sampling that R3x0 did, using the same sample patterns and method of operation. Scattered/sparse grid AA, as pioneered by ATI in generally available, affordable consumer hardware, is widely recognised as giving the highest AA quality possible using multi-sampling, at good speed. With that in mind, ATI has little need to change it.
What they have done is to add in a new method of combining differing sparse sample patterns on alternate frames, giving effective higher quality AA at little to no performance loss.
Temporal Anti-aliasing
Called temporal anti-aliasing, it alternates the AA sample grid used to anti-alias a frame, per frame. With 2X or 3X temporal multiplier, it alternates between two or three distinct samples over two or three successive frames, giving effective AA quality that's higher than the standard method.With 2X temporal multiplier and 6X base AA, the resulting 6X2T mode has the effective image quality of a discrete 12X mode. The same method of calculation works with all other modes and multipliers. 6X3T is the highest effective new AA mode available. The big news is that it's not limited to R420, with R3x0 GPUs and their programmable AA patterns able to benefit from temporal AA as well.
Temporal AA has some limitations in practical use. It needs vsync to be enabled for the effect to work, so you don't 'stack up' the same sample grid for successive frames. That also means keeping the frame rate higher than the vsync refresh rate for it to work. Depending on your game title and its playable framerate range, it might not be practical to enable temporal AA and have the effect look good. When working sub-optimally, at lower than vsync framerates, geometry edges can be seen to creep or shimmer.
It's a rediculously hard AA method to demonstrate in a static medium like a webpage. Even a video of it working would be of little use unless you could sync your refresh rate to that of the captured video. Displaying the sample patterns changing is trivial, but its effect on a game title is much harder to demonstrate well.
