Dynamically enabling and disabling collision detection of an object

Dynamically enabling and disabling collision detection of an object

Gameon 20 Apr 2008 17:39

I was wondering what is the best way to enable and disable collision detection.

What I need to do is for some world objects to be passable (no collision) by the player at certain times, and impassable (has collision detection) at other times. My world objects are triangle meshes and the player are made out of primitive boxes as the collision skin.

The only way I can see of doing this is to add and remove the collision skins in the physics system depending on what I want, but I am afraid I will get some performance issue. Also, I don't want the passable object to turn back on its collision detection when a player is still inside the object. If I remove the collision skins from the physics system, then there's no way for me to test whether the player is inside a disabled collision skin.

Any suggestions as to how I may be able to approach this problem?

Thanks!

Re: Dynamically enabling and disabling collision detection of an object

Gameon 20 Apr 2008 20:17

Walking through the engine code a bit, I thought I had find the solution but it's not working as I thought it should.

What I've found out is the CollisionSystem class has this DetectAllCollisions method that does the collision detection calculation (as far as I could tell). It takes in a list of bodies that are currently active as a parameter and I'm assuming those are the bodies that get detected for collisions. There is a SetActive and SetInactive method for the body objects and I thought if I set the bodies to inactive, the collision detection won't be performed. But I was wrong and even though the bodies are inactive, collision detection is still being calculated.

Hmmmm…I thought I was close :(

Re: Dynamically enabling and disabling collision detection of an object

Anonymous (91.44.56.x) 21 Apr 2008 07:34

Two possibilities:

CollisionSkin.NonCollidables … add collision skins which should not collide

or

Use the callback function of the collisionSkin to get a callback everytime a collision is detected. Than you can decide if you want to have collision or not.

body.CollisionSkin.callbackFn += new CollisionCallbackFn(CollisionSkin_callbackFn);

bool CollisionSkin_callbackFn(CollisionSkin skin0, CollisionSkin skin1)
{
     // return true/false for keeping/dropping collision informations
     throw new Exception("The method or operation is not implemented.");
}

Re: Dynamically enabling and disabling collision detection of an object

quintonv 22 May 2008 07:40

Thanks, this really helped me :D

Re: Dynamically enabling and disabling collision detection of an object

Jezze (guest) 10 Dec 2008 10:44

Hi guys!

I have a problem when using two callback function on one CollisionSkin.

// in controller A
body.CollisionSkin.callbackFn += new CollisionCallbackFn(First);

...

// in controller B (same body)
body.CollisionSkin.callbackFn += new CollisionCallbackFn(Second);

If the second function returns true the collision is never ignored, even if the first function already returned false. But i want that if just one function returns false the collision should be ignored - like (false && true) == false.

Thanks in advance!