cocos2d for iPhone

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

1. 

   TwoHanded
   Member

   hello,
   -------------------------------------------
   -Question :
   is it possible to avoid collision between
   2 sprites being on different Z ?
   ( i mean, because they are on different Z, so they don't collide )
   -------------------------------------------
   -Explanation :
   i have 2 sprites, each on separate layers
   sprites and layers have different z from 1 to 4
   but they still get collision

   -------------------------------------------

   thank you for your help

   Posted 2 years ago #
2. 

   mhussa
   Member

   Box2D is strictly a 2D simulation model.

   Layers are a container object which uses Z for defining the rendering order of objects that it holds.

   Layers/Sprites/etc are what you use to display the physical model in box2D. The two exist in completely different worlds which is why the layer Z has no effect on box2D collisions.

   You need to disable collision in your box2D model for the sprites that are on different layers. The box2d online manual is your friend.

   Posted 2 years ago #
3. 

   PhilM
   Member

   As mhussa says. To expand on it a little, in a custom b2ContactFilter you could check the z level for the 2 colliding sprites and cancel/ignore the collision if their different.

   Posted 2 years ago #
4. 

   TwoHanded
   Member

   thank you
   reading both and then manuel,
   i used maskBits and categoryBits
   (still a little confusing these things but well have to work on)

   now it's working

   :=)

   thank you

   Posted 2 years ago #
5. 

   carlosh
   Member

   How about creating 4 worlds? The objects won't collide between worlds. Of course, that would depend on what you are trying to accomplish.

   Posted 2 years ago #
6. 

   MikeSz
   Member

   @ carlosh - there can be many wordls ? neat !

   @ OP - IIRC Chipmunk can handle many object layers just fine. won't check them by cocos2d Z, but you can use the Z when putting objects to different layers

   Posted 2 years ago #
7. 

   vimard
   Member

   @everyone - Box2D has something called the group index. If the bodies have a negative index they won't collide among each other.

   ex:

   In the following example, fixture1 and fixture2 always collide, but fixture3 and fixture4 never collide.

   fixture1Def.filter.groupIndex = 2;
   
   fixture2Def.filter.groupIndex = 2;
   
   fixture3Def.filter.groupIndex = -8;
   
   fixture4Def.filter.groupIndex = -8;

   Posted 1 year ago #
8. 

   steg90
   Member

   Hi,

   The groupIndex sounds great. Is it possible to do this on the fly/dynamically? If so, how do you get the fixtureDef from b2Fixture object or contact object as thinking of doing something similar in PreSolve method?

   Regards,
   Steve

   Posted 1 year ago #
9. 

   Questor
   Member

   Steve,

   For getting/setting filter data, you can use:
   b2Filter *myFilterData=someFixture->GetFilterData();
   and
   someFixture->SetFilterData(myFilterData);

   Regards,
   Q

   Posted 1 year ago #

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