Originally posted by: hopeless
Since they bought 3dfx was/is there something bad about the way they did it back then, just splitting the screen between odd & even lines?
All 3dfx's cards and the implementation did was rasterise textured triangles.
Simple, and straightforward to divide the rendered scene up by scan lines. Easily used on any application across any number of chips.
nVidia could potentially have used a similar implementation but then VS/PS performance wouldn't scale at all, in fact it would be slower in an SLI system with the added overhead.
Clearly we're not about to go back to relying on the processor to do all the geometry work as we did in the Voodoo 2 SLI days and the Voodoo 5, and we obviously don't want to hamper VS/PS throughput at all in an SLI implementation as a GPU's geometry performance is becoming even more important then sheer pixel/texel fillrate in todays applications.
nVidia wants to scale geometry throughput as well as pure rasterization speed, so they need to ensure both GPU's are not calculating the same geometry workload. You can't do that if your dividing by scan lines, as 3dfx did so their stuck with splitting top/bottom half of the screen (Split Frame Rendering/SFR) which is the preferable solution.
It scales the best, but unfortunately it's not compatible with all games depending on rendering techniques used.
They can also use Alternate Frame Rendering (AFR) much the same as ATi did with the Rage Fury Maxx, a viable option though it doesn't scale quite as well as SFR, and it also doubles latency so response time to user actions is cut in half. It is more broadly compatible with applications then SFR however, though there will still be some games in which you'll have to resprt to single GPU mode due to compatibility issues.
The old alternate line way resulted in an image some deemed grainier. It was noticeable. (but still the thing to have- then and now!)
That was primarily due to the pass through cable, nVidia isn't using that so they likely could have used 3dfx's implementation with no impact on image quality at all.
As said, it's not a particularly ideal solution though as geometry performance wouldn't scale at all.... not a big deal in older games and even many current ones but is becoming an increasingly major factor in GPU performance.
The lone plus side to 3dfx's implemtnation is it would be easily compatible with any games though, which won't be true for nVidia's implementation unfortunately.
