Re: [Algorithms] FPS Questions

[Stephen J B. <sj...@li...>]

On Mon, 31 Jul 2000, Jim Offerman wrote:

> > 60fps is the ideal target.
> 
> I blindly follow the masses here, but I can't help wondering why... Anything
> above 24-25 fps will not be noticed by the human eye, 30 fps animations look
> _really_ smooth.

AAAAARRRRRGGGGGHHHHHH!!!!!

30Hz (on a 60Hz monitor) looks *terrible* compared to 60Hz.

Whenever anything moves quickly in the scene, you get
double imaging!  Yuk!

Try this:

while ( 1 )
{
  Clear screen to black ;
  Draw (say) a 10x10 pixel white square at coordinate (x, 100) ;
  x += 15 pixels ;
  if ( x > screen_width ) x = 0 ;
  swapbuffers
  delay for a while
}

Set your card up to swapbuffers on a vertical retrace, then
adjust the delay to run this at 60Hz and again at 30Hz. (or
at 72Hz and 36Hz if you have a 72Hz monitor).

Now imagine you are trying to shoot at the white square.

At 30Hz you are seeing double.  If you see double at 60Hz,
you probably still have a hangover from last night - the
effects are pretty similar.

20Hz is even worse because you get TRIPLE-imaging - although
a few people see only a very jerky image - it depends on
the individual.

At 24Hz, you are going to see that horizontal tear moving
rapidly up and down the screen whenever the eye is in motion
because you can't possibly be locked to the vertical retrace
as you should be at reasonable frame rates.

Steve Baker                      (817)619-2657 (Vox/Vox-Mail)
L3Com/Link Simulation & Training (817)619-2466 (Fax)
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