[osg-users] High event times

[Mathias Fröhlich]

Hi Robert,

On Saturday, October 31, 2015 18:02:24 Robert Osfield wrote:
> I have had a look at the revision and vaguely remember hunting double a
> long time troublesome bug, but can't recall the details of the recreating
> the bug off hand.  I'd have to look up what stuff I was doing around March
> this year.   The r14805 commit message was "Fixed resize dimensions of X11
> window".
> 
> At a guess, perhaps we can just do this check when we suspect a resize.
That is what I expect too. If this is required at all. Sadly I do not know exactly what
type of event is guaranteed to arrive.

> What are the event times you are seeing?  What platform are you testing on?
Fedora 22 x86_64. I now looked up the implementation in libX11 and it seems to
introduce 3 round trips in total to the X server. That results in 0.6ms-0.8ms
down to <= 0.2ms using the event visitor that just gets switched off completely
by setting it to no traversal mode. That does not sound too much time, but if you
want to squeeze the last out of your application you do not want to have a
single round trip if it is not needed.

Also, if you think about the 80Hz frame rate with an oculus for example, this
round trip time difference of about 0.5ms turns already in 0.0005/(1/80)=0.04
that is 4% reduced available cull time (or draw time) to hit the target frame
rate - without having drawn a single pixel. And having a round trip here makes
you much more prone to scheduling decisions in the system as the X server needs
to be started up to to answer your request which makes these times much more
jittery and increases the probability of a missed frame.

Greetings

Mathias
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