Q: Why do the glxgears stop after a while

Q: Why do the glxgears stop after a while

Post by Antonio Bl » Wed, 20 Oct 2004 19:09:25



Hi,

have you installed the nvidia drivers from www.nvidia.com ?
Have you installed the latest version? (cat /proc/driver/nvidia/version).
The latest driver version available is 1.0-6111. Did you read the
nvidia README concerning you XF86Config tuning (lots of useful hints there)?

Regards,

Toni


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Q: Why do the glxgears stop after a while

Post by Rainer Koe » Wed, 20 Oct 2004 19:50:47

Antonio Bleile < XXXX@XXXXX.COM > writes:


Sure. But as I mentioned, this problem is not depending on nVidia drivers
since I also can reproduce it with a Matrox G450 card. But anyway, I get
it on all nVidia drivers I tried (even the ones only released for OEMs).

Regards
Rainer
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Q: Why do the glxgears stop after a while

Post by Philipp Kl » Wed, 20 Oct 2004 20:33:15

Rainer Koenig schrieb:

If you look at the glxgears source you can see that it uses and
32 bit floating point variable to hold the angle. For every frame the
angle is incremented by 2.0. For a big enough floating point number
adding 2.0 is a noop, since they have finite precision.

I'll make a patch to it tonight and send it to the mesa3d-dev list.
Keeping angle between 0 and 360 degrees should solve the problem.

Philipp
 
 
 

Q: Why do the glxgears stop after a while

Post by Antonio Bl » Wed, 20 Oct 2004 21:24:02


hihihi :-) Sure this is not a driver bug lol...

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Q: Why do the glxgears stop after a while

Post by Philipp Kl » Thu, 21 Oct 2004 04:10:10

Rainer Koenig schrieb:

There's a floating-point number in the glxgears source representing the
anglefor turning the gears. Each frame 2.0 is added to it. Adding
2.0 to a big enough floating point variable is a noop due to limited
precision. Thus the geras stop turning.
To me it seems this is a bug. I'll send a patch to the author.

Philipp
 
 
 

Q: Why do the glxgears stop after a while

Post by Philipp Kl » Thu, 21 Oct 2004 04:14:39

Sorry for sending it twice. I didn't see my first post appear
on the group.
 
 
 

Q: Why do the glxgears stop after a while

Post by Rainer Koe » Thu, 21 Oct 2004 14:21:12

Philipp Klaus Krause < XXXX@XXXXX.COM > writes:


Thanks a lot. That really explains the thing, even until now I thought
that an "overflow" would just have ment that the variable is "reset" to
another value. But looks like for floats this is not what I have
expected. That shows me that I really need to brush up my programming
skills. :-)

Regards
Rainer
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* experience and knowledge. So it's NOT necessarily shared by my *
* employer or anyone else. All rights of being wrong reserved :-) *
 
 
 

Q: Why do the glxgears stop after a while

Post by ray » Thu, 21 Oct 2004 22:50:13


As I understand, it's not really overflow, it's just a matter of exceeding
the precision. Basically, a float has about 7 digits of precision (and a
double about 14, but the idea is the same). To 7 digits of precision, the
following is true

12345678 + 2 = 12345678

the amount being added is smaller than the least significant digit, so it
contributes nothing.
 
 
 

Q: Why do the glxgears stop after a while

Post by Arto Viita » Fri, 22 Oct 2004 19:11:01

>>>>> "Rainer" == Rainer Koenig < XXXX@XXXXX.COM > writes:

Rainer> But looks like for floats this is not what
Rainer> I have expected. That shows me that I really need to brush up my
Rainer> programming skills. :-)

Check "What Every Computer Scientist Should Know About Floating-Point
Arithmetic" by David Goldberg, in ACM Computing Survers, March 1991. It is
on web at http://www.yqcomputer.com/

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Q: Why do the glxgears stop after a while

Post by Rainer Koe » Fri, 22 Oct 2004 22:56:35

Arto Viitanen < XXXX@XXXXX.COM > writes:


Thanks a lot for this really interesting link. If I only had time to
read all those things... :-)

Regards
Rainer
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* experience and knowledge. So it's NOT necessarily shared by my *
* employer or anyone else. All rights of being wrong reserved :-) *