The FPS things is definitely a display problem.
I performed this simple test:
1) Pause the game.
2) Go up and down levels, each time waiting for the FPS to stabilize.
Results:
(game FPS is capped at 100, display FPS at 30)
When on level 0 of the map, the FPS is 100 when I'm cruising along random places on the map, however (and I think this is the important part), as soon as I'm looking at a place that isn't instantly visible (ie, there's a layer of rock above my current viewport), the game slows down to 38-40. I move aside and it instantly climbs back to 100. If there's only small amount of rocks visible than it can stay on 70 or 80. If the entire view is just "there are rocks above" (like if I go to a completely undug layer, or on layer 0 I'm looking under a tall mountain) its 30. If I'm so "high" that I can only see the blue mist, its 30 again, ditto for just being high enough to barely see the layer below, with the exception that it doesn't happen when I'm on layer 0.
To sum up for Toady One:
The game runs properly when I'm looking at layer 0.
The game runs crappily when I'm looking at any other layer, but the amount of crappiness is directly related to the type of area I'm looking at:
I) If I'm looking at ground that is really on the current layer (ie, no blue mist, no undug-blackness and no its-just-one-level-below-dots), it runs properly
II) Otherwise it runs like crap.
III) The overall speed at which it runs depends on the ratio between I and II. If its mostly I than it will run at 70-100, if its mostly II than it will run at 40-50, if its just II than it will run at 25-30.
EDIT: Changing the display FPS limitation has no effect on the FPS at which the game plays.
EDIT: What I said in the part before the summation is slightly self-contradictory. The summation is the part that's got it right.
[ October 30, 2007: Message edited by: Slartibartfast ]
[ October 30, 2007: Message edited by: Slartibartfast ]