Comments on: Scary Vines http://toddvanderlin.com/2009/04/scary-vines/ Design & Technology Fri, 06 Aug 2010 19:09:08 +0000 hourly 1 http://wordpress.org/?v=3.0 By: monoflow http://toddvanderlin.com/2009/04/scary-vines/comment-page-1/#comment-200297 monoflow Sat, 04 Apr 2009 14:26:22 +0000 http://toddvanderlin.com/?p=1160#comment-200297 Hi Todd, i worked with JBox2D an has a similar problem. The only solution for me was to delete and create a new Shape in a Body on each Frame. The only Problem was that my instruction to delete and create was triggert in a moment when the World.Step() phase was in action an so I got crazy exceptions in irregular intervalls. In my application I have 2 threads: on OpenGL Thread who triggers the World.step() method to update the simulation at the same intervall of the rendering and a second with my own code. So i made a hack: I extend the org.jbox2d.dynamics.World class from the sources of JBox2D with a method to get the m_lock variable. public Boolean getLock(){ return m_lock; } If you look in line 458 (step() method) you see that this is a flag to lock a lot of functions while the solver is working. With this extension I'm able to check in my code if the Physik-Engine is in a crucial phase and wait: My code: while(m_world.getLock()){ //nothing: } //go ahead //now i set a custom lock-flag to stop the call of the World.step() Method because my OpenGL Thread triggers this _lock= true; //now i can create and delete some shape or Body in the Physic-engine _lock= false;//release the flag. Now the Physic-engine gets updated. ..... if(_lock==False){ m_world.step(_timeStep,_settings.iterationCount); } Cheers Hi Todd,
i worked with JBox2D an has a similar problem. The only solution for me was to delete and create a new Shape in a Body on each Frame. The only Problem was that my instruction to delete and create was triggert in a moment when the World.Step() phase was in action an so I got crazy exceptions in irregular intervalls.
In my application I have 2 threads: on OpenGL Thread who triggers the World.step() method to update the simulation at the same intervall of the rendering and a second with my own code.
So i made a hack: I extend the org.jbox2d.dynamics.World class from the sources of JBox2D with a method to get the m_lock variable.

public Boolean getLock(){
return m_lock;
}
If you look in line 458 (step() method) you see that this is a flag to lock a lot of functions while the solver is working.
With this extension I’m able to check in my code if the Physik-Engine is in a crucial phase and wait:
My code:

while(m_world.getLock()){
//nothing:
}
//go ahead
//now i set a custom lock-flag to stop the call of the World.step() Method because my OpenGL Thread triggers this
_lock= true;
//now i can create and delete some shape or Body in the Physic-engine
_lock= false;//release the flag. Now the Physic-engine gets updated.
…..
if(_lock==False){ m_world.step(_timeStep,_settings.iterationCount);
}

Cheers

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