[osg-users] osgParticle behavior with discontinuous and reversed time

[Robert Spearman]

I have a simulator where time can go forward or backward and I am 
integrating an osgParticle system which draws line particles.  My 
particle lifetimes are under 1 second.

I am looking for suggestions on the following problems:

When I jump ahead in simulation time (by a week, for example) the 
currently live particles stick around for that week plus their remaining 
lifetimes.  I would expect them to die immediately because the delta 
time that just elapsed is much greater than their lifetimes.

When I jump backwards a similar issue occurs.  But as I jump back in 
time before the simulation time when the particle system was 
initialized, the start and end of the particle lines seem to grow apart 
until I have enormously long particles (presumably from the parent node 
moving with time).  Only going past the start time again resolves the 
issue.  I would expect particles to work normally at any time in my 
simulation as long as time is going forward.

When time is in reverse weird things happen as well, but less severe.  I 
would be fine if nothing drew while time is reversed since obviously 
there is no way to easily reverse a particle system.

So...  I've tried turning off the particle system node while time is 
jumping but it doesn't resolve anything.  I've tried modifying 
osgParticle to kill the particles when dt is zero (since negative dt is 
not allowed by the particle updater).  I then get no particles at all 
until time is again after the startup time, which is some improvement.  
But I don't see what is storing the particle system initialization time 
or why.

Wondering if anyone has any ideas.

Thanks!
Rob