Due to to the way that double buffering works, a v-sync enabled game that drops below 60 frames per second reverts to 30FPS, but id Software’s upcoming Rage intentionally allows screen tearing at the top of the screen when the frame rate drops slightly below the 60FPS threshold.
So what we do on the consoles, where we have this tight control, is we say, OK, you’re going 60FPS, it’s v-syncing, there are no tear lines. But if you miss by a tiny little bit, we’ll let it tear at the top of the screen and we adjust the resolutions dynamically to let it catch back up.
It’s a really novel idea, and one that id managed to convince vendors to implement:
We were able to convince all of the vendors to go ahead and implement that extension on Windows, so we’re now able to do that at 60FPS as long as you’ve got the horsepower. But if you get a hiccup, where it slows down a little bit, it reverts to tearing, which is exactly what we want for gameplay reasons.
You just have to love how id always strives to push graphical boundaries as far as possible.