Re: [Algorithms] FPS Questions

[Jim O. <j.o...@in...>]

I gave my original query some more thought, and I think I have found a
plausible explanation as to why 60 fps might be perceived as being smoother
than 30 fps.

The human eye in many ways works like a camera (note: actually, it is the
other way around): the retina is exposed to light for a small period of time
and then the accumulated light signal is transmitted to the brain before the
retina is exposed again.

Let's assume for a while that the eyes record at a steady 30 fps. If our
game also runs at 30 fps, the eye sees one frame at the time. However, if
the game runs at 60 fps, the eye sees two frames at the time, which are
blurred together, resulting in a form of motion blur.

Another important aspect is that your eyes will _never_ be in sync with the
frame rate of your game, so it is possible that there exists a moment where
your eye records a frame, but there is nothing to record (since the monitor
is doing a vblank). This will certainly be perceived as a discontinuity of
the ongoing motion on the screen. The higher the framerate, the less likely
that such situations occur.

Finally, I must agree with the lower latency factor, since while our eyes
may be relatively slow, our responses (generally) are _really_ fast.
Specially, if someone is trained in some response, then it becomes a
reflex... An experienced FPS player might be using his brain as little as
25% of the time, the rest of the time, his actions are merely reflexes.
Hence the phrase 'mindless killer' ;-).

> Why not just ask the player what they want and then scale the engine to
that
> speed.  If they want 'liquidity' at high frame rates then scale back and
use
> lower level of detail models.  If they can't tell the difference then
> they'll pull the frame rate down to 30fps and get better looking visuals.

We usually achieve this by offering the player some controls over detail.
Though it might be nice if your engine includes a little util which finds
the optimum detail settings to get n fps on a given machine... but I can
tell you that _won't_ be very easy, so better put that on the 'things to do
when I have time left' list ;-).

Jim Offerman

Innovade
- designing the designer