Conditional Collision Problem « cocos2d for iPhone

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Conditional Collision Problem

(6 posts) (3 voices)

Started 1 year ago by sunflower
Latest reply from mobilebros

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sunflower
Member

Hi,

I have problem with chipmunk collision. I have conditional collision of two physic shape. In certain conditon collision method should execute and in certain case it should ignore and there should not be any affect (force) of cllision. I am using following statement when i want to ignore collision in "Begin" and "Pre Solved" collision callback handler. I have tried same in all four callback handler but doesn't work.

cpArbiterIgnor(arb)
return 0;

It does ignore "Pre Solved" and "Solved" but not "Separate". and the problem is one object gets so much of force/impulse after collision that it goes out of screen very quick. I just want to ignore collision like both object never collide.

Please help me. I would really appreciate if you can guide me in right direction.

Thanks
Sunflower

Posted 1 year ago #
jd
Member

An alternate solution may be this:
When you create the body you add a collision pair. If you know ahead of time you don't want two objects to register collisions, you don't set those to collide. But it looks like you want them to collide sometimes but not others. Maybe it's possible to turn on/off that collision pair. I never tried it though.

The good thing about this method, if you can do it, is you save chipmunk from even checking those collisions when you toggle off. It should help with performance to some extent.

Posted 1 year ago #
sunflower
Member

thanks for response jd.

i only know weather i have to do collision or not is after checking contact point. so i am not sure at that time on "Begin" collision method i can toggle collision pair.

what i want is just ignore collision force if i ignore the collision. and object should behave like nothing happened.

Thanks
Sunflower

Posted 1 year ago #
mobilebros
Moderator

According to the chipmunk documentation:

Begin: Two shapes just started touching for the first time this step. Return false from the callback to make Chipmunk permanently ignore the collision. Chipmunk will not calculate collision forces for this collision, and the preSolve() and postSolve() callbacks will never be called. When the shapes stop touching the separate() callback will still be called however.

So it seems like all you need to worry about is the separate callback getting called... I suppose you'd have to flag the shape somehow.

Posted 1 year ago #
sunflower
Member

HI Mobilebros,

I didn't get what you are trying to say about worry about separate callback. And flagging the shape. Can you please write me in detail.

Yes, PreSolve and PostSolve never get called when i return 0 from begin with cpArbiterIgnore(arb). but it still calculate the force and apply to collided object.

Thanks
Sunflower

Posted 1 year ago #
mobilebros
Moderator

Chipmunk documentation says and my experience has been that if you return zero from Begin it will not register the collision and it will not apply any impulses to the objects of the collision.

However, the separate callback is always called no matter what (according to the documentation). By flagging the shape I just meant you would need to identify that it should be ignored somehow...

Posted 1 year ago #

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