Wandering OT. Re: [TriLUG] hardware requirements for linux gaming computer

Tanner Lovelace lovelace at wayfarer.org
Tue Jun 24 10:55:41 EDT 2003


:On Tue, 2003-06-24 at 10:21, Chris Knowles wrote:
> While I am aware of this, the picture is actually very smooth and isn't
> a problem.  I would be willing to dare you to come over and see if you
> can detect the tearing.  (I can't, but I could be going blind...  if
> these hairy palms are any indication.)

Well, if you can't see the tearing, then you probably have vertical
sync enabled on your video card.  Try setting this environment variable
before running bzflag and tell me if you still can't see the tearing.

export __GL_SYNC_TO_VBLANK=0

> I'm reasonably certain that the BZ FPS counter is theoretical.  (Of
> course, we could go to source to figure it out.)  (In other words, it
> doesn't actually update the screen that much, but it could...)

It does actually calculate it.  The relevant code 
(from bzflag-1.7g0, source file src/bzflag/playing.cxx) is as follows:

      // compute fps
      frameCount++;
      cumTime += float(dt);
      if (cumTime >= 2.0) {
        if (showFPS) hud->setFPS(float(frameCount) / cumTime);
        cumTime = 0.0;
        frameCount = 0;
      }

For those who aren't C++ programmers, every couple of seconds it sets
the frames per second to be the number of frames drawn divided by the
elapsed time.

Of course, the question then becomes, since the card is synchronizing it
to the vertical refresh rate, how is bzflag thinking it's going at 150
fps.  My guess is that if a frame is done before the monitor refreshes
it just throws a frame away.  If it's not done before the monitor 
refreshes, the card displays the same frame twice.

> BTW, smiley faces usually indicate some tongue-in-cheek attitude.  I am
> aware that measuring frame rates is juvenile, but I just couldn't

And, perhaps I didn't make it clear enough, but my post was meant to
be fairly tongue-in-cheek.  I do know that you are quite knowledgeable 
about linux gaming and I don't seriously think you're full of it.  There
is, however, a lot of misconceptions about frame rates.  High frame
rates aren't the end-all be-all of a game, just like high MHz rates
don't tell everything about a processor.

> resist.  This game is ugly at low res and actually pretty at high res. 
> (The sunrise is particularly nice.)

Sure, but high res and high frame rates are two different things.  I can
program a very nice looking sunset that only updates once every second.
It will still be pretty even if it's not interactive.  But, that's a
bit beside the point.

Cheers,
Tanner
-- 
Tanner Lovelace | lovelace(at)wayfarer.org | http://wtl.wayfarer.org/
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