The original Uncharted had a simple, but unrefined solution. It was double-buffered, with no v-sync. Put simply, the game is generating a new frame while the old one is still on-screen. If the new buffer isn't complete by the time the frame is supposed to render, it simply displays the unfinished image (creating a torn frame), purges the buffer and repeats the process. It can look ugly when the engine is under stress, but it ensures the fastest possible response from the controller, and ties in perfectly with the 100ms response time I measured for Uncharted.
V-sync can be deployed in a double-buffer situation, but there's a nasty side effect: if the complete frame isn't ready to be displayed, you'll wait until the next screen refresh to see it. During this time the GPU is effectively idle. It's a poor use of resources and it can be very impactful on the frame rate; the game will literally "switch" between 20FPS and 30FPS when the engine is under stress. Metal Gear Solid 4 is perhaps the most noteworthy example of the use of v-sync double-buffering and its impact on performance and controller response. Check out this FPS graph from Metal Gear Online, which uses the same engine:
Uncharted 2 is more ambitious. It aims to eliminate GPU idling and to maintain v-sync; effectively Naughty Dog wants to have its cake and eat it. Instead of flipping between two frames, it employs triple-buffering, holding one frame in reserve. Rather than produce a torn frame, it'll display the reserve frame instead.
The result is that we get the visual performance we always wanted from Uncharted... You get those spectacular visuals, and you get them without a single torn frame in the whole game. It's not really a case of being difficult to program as such, though there are memory implications; the trick is in doing so without impacting performance. As you can see from the level FPS graphs on all the Uncharted 2 vids in this feature, Naughty Dog has achieved it. Compare and contrast with Resident Evil 5 on PS3, which uses exactly the same triple-buffer technique but still has performance issues and the additional controller lag up against the double-buffered Xbox 360 version.
So kudos and various "big ups" to Naughty Dog for pulling it off. But to bring the discussion full circle, there has to be a cost for this level of advanced processing - and the price in this case is that the controller is less responsive. For the sake of visual quality, it's a price well worth paying, and we can demonstrate that in a pretty conclusive fashion. Check out this interesting "what if?" exercise. It's a montage of action from the original Uncharted, with a twist. Using a bit of our own coding magic, we can eliminate all the torn frames from the game's output. In effect, we can simulate Uncharted 2's v-sync on Uncharted 1 video to show the difference.
