[ bzflag-Bugs-573488 ] Low FPS slow z movement

[<no...@so...>]

Bugs item #573488, was opened at 2002-06-24 21:27
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Category: BZFlag
Group: None
Status: Open
Resolution: None
Priority: 8
Submitted By: Dave Brosius (dbrosius)
Assigned to: Tim Riker (timriker)
Summary: Low FPS slow z movement

Initial Comment:
It has been reported that machines that have slow fps 
have slow jumping tanks. At the suggestion of chestal 
and cobra, I looked at the bug fix for falling thru 
buildings w/low fps.

Perhaps I am missing something, but I believe this is 
the cause of the problem.

The fix for falling thru platforms with low fps was to limit 
the timekeeper delta's between frames to at a maximum 
of 0.1s.

Problem is, if you really DO draw frames slower than 
this delta, you necessarily extend the time taken in 
jumping (or dropping)

For instance: say you have a 100  fps system, and 
jumping is supposed to take 1/2 second.

100 fps X 50 deltas = 1/2 second.
  -- each delta is .01 seconds

Now suppose you have a 10 fps second, you still want 
the jump to take 1/2 second

10 fps x 5 deltas = 1/2 second
-- each delta is .2

Yet, deltas are limited now to .1 so

10 fps x 10 deltas = 1 second

thus slower jumping

Seems like to prevent fall thru of buildings, we need to 
either specify a minimum fps to play bzflag, or perhaps, 
test the line from the old position to the new position for 
collisions with buildings.

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>Comment By: Chris Schoeneman (crs23)
Date: 2002-06-26 09:24

Message:
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there's a very simple solution to this... limit any given
timestep to X but run the update several times for each frame.

  const float dtMax = 0.1;
  float dt = /* whatever */;
  while (dt > 0.0) {
    float step = dt > dtMax ? dtMax : dt;
    dt -= step;
    /* update by step */
  }




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Comment By: Jeremiah (cobraa1)
Date: 2002-06-25 20:16

Message:
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user_id=25311

Since this affects gameplay, it really should be reverted 
until a better solution is found.

I second the idea to test the line from the old position to 
the new position for collisions.  That should be ideal for any 
framerate.

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https://sourceforge.net/tracker/?func=detail&atid=103248&aid=573488&group_id=3248