cocos2d for iPhone

A fast, easy to use, free, and community supported 2D game engine

1. 

   mster50
   Member

   Hello all, been a while.

   Having an unfortunate issue I can't seem to combat - it's an inconsistent problem. After making a simple shape removal call, if there are resting shapes above that which was removed, shapes that are stacked will not react to the removal. They will stay motionless and dormant.

   My hunch is that it has something to do with sleeping bodies, but I can't be certain. Not much to really trace back on.

   Does anyone have any ideas? Thank you in advance for your help, I appreciate it greatly and will award cookies to my helpers.

   Kind regards,
   Mster50

   Posted 5 months ago #
2. 

   razvan_b
   Member

   ok, what physics engine do you use? box2d or the chipmunk ? My hunch is also that the shapes are asleep.
   in box2d you can get the list of b2body's that the body getting removed is in contact with and try setting them awake, or you can set all of them awake.

   Posted 5 months ago #
3. 

   mster50
   Member

   Hi Raz, thanks for your response.

   Yeah, I was pretty certain it had to be a sleeping issue. I'm using Chipmunk, for reference, and Spacemanager as an Objective-C (or more specifically, Cocos2d) wrapper. I spent a little bit of time yesterday trying to find a method to force all bodies in the space awake, but didn't find any results. Do you offhand know of a way? If not, I'm sure I could just handle it. Interesting problem, though.

   Posted 5 months ago #
4. 

   mster50
   Member

   Ah, just had a second to check the sleeping api for chipmunk. Looks like just forcing a single body to wake up will wake everything else sleeping in the group up. Will have to try this tonight.

   Posted 5 months ago #
5. 

   slembcke
   Administrator

   Yes, it's almost certainly a sleeping issue. Both Chipmunk 5 and 6 try to handle the issue as well as possible. Although in Chipmunk 6 is rewrote most of the sleeping code to try and make it as rare as possible. Both 5 and 6, should wake up the group when removing a body/shape/joint. Chipmunk 5 also performs a shape query and wakes up all the things it's overlapping. Chipmunk 6 uses the contact graph instead which is much more reliable if things get moved.

   However, it's still possible for objects to fall asleep slightly after losing contact with each other, and that is generally what causes the "floating objects" issue. Try adjusting the sleep time and velocity thresholds, or increasing the collision slop to ensure better better stability of the contact set.

   Posted 5 months ago #
6. 

   mster50
   Member

   Awesome. Scott, you are always super helpful. Thanks for the tips. I swear I will have my wife bake some cookies and mail them to you sometime.

   I am unfamiliar with the collision slop, would you mind a short explanation?

   Thanks again.

   Posted 5 months ago #
7. 

   slembcke
   Administrator

   Collision slop is how much overlap Chipmunk allows shapes to overlap. It defaults to 0.1, which is pretty small if you are using pixel coords. The idea is that by allowing things to overlap slightly, you don't end up with the case where a contact doesn't disappear every other frame allowing the physics to run more stably. 0.1 usually works Ok, but if you increase it to be a pixel or two, it probably still won't be noticeable but will help immensely with the jittering problem.

   Posted 5 months ago #
8. 

   mster50
   Member

   Roger that. Appreciate it greatly. You rock, as always.

   Posted 5 months ago #

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