So I have a pretty good PC. I'm getting a smooth 60 FPS in most places, at highest settings, and I have the FPS setting in Options set to cap at 60.
However, the game is frequently setting the FPS cap to 30 (as verified by my FRAPS readout in the corner of my screen). It's not so much that I'm entering an area my computer can't handle (though that may provide some input for the problem), but that the game is simply taking my framecap from 60, down to 30. Sometimes it goes back up. It seems to be largely irregular.
I don't have any resource-intensive programs running in the background. What's going on here?
EDIT: Setting all of my video settings down to Low (I typically run at highest) has no effect. I still get frequent slowdowns to a smooth 30 FPS.
Best Answer
While it certainly could be an enforced cap by design (dynamic shadows are "expensive"), this sounds like it could be vsync as well.
Basically (and inaccurately), there is a frame which you see, and a frame which is drawn on. When the drawn one is complete, the contents are passed to the screen for you to see while a new frame is drawn.
In the "olden" days, video was drawn line by line at the upper corner and moving to the lower corner and then there was a delay when the "cursor" reset to the upper corner. The reset happens during a "wait state" (aka swap interval, vertical sync command etc) and the frame would be swapped during this very brief window.
vsync ON means wait for this to swap frames. You get FPS capped at the refresh rate of the monitor, a very stable picture, but fast movement feels choppy.
vsync OFF means don't wait. You get FPS capped at the computer's ability to render it, but you get frames being swapped out while the image is partially rendered (aka "tearing"), but fast movement feels smoother.
With vsync on, if you can't meet or exceed the refresh rate, then the hardware has to pause and wait for the next cycle. This means you wait 2 frames-worth of time to swap. In games, this tends to happen in extended bursts because large amounts of staffage, explosions, etc. taxes hardware. The result is the FPS appears to drop from locked 60 to locked 30.
Plenty of psuedo-technical info here, but that's the gist of it.