Disable collision on the fly in Box2D: does not work when entity is already colliding

Question

I'm writing a game with impactjs and i'm using Box2D as physics-engine (Box2DFlash to be specific). So there is a move off the player where he should not collide with the enemys. To achieve this Collision Filtering seems to be the best method.

So I set for the enemy fixture:

 var shapeDef = new b2.PolygonDef();
 shapeDef.filter.categoryBits = 0x0002;

And for the player:

var shapeDef = new b2.PolygonDef();
shapeDef.filter.categoryBits = 0x0004;

When I want to turn on/off the collision of the player with the enemys i call these functions:

ghost: function(){
 this.setMaskBits( 0x0001 ); // only collide with boundary
},
deghost: function () {
  this.setMaskBits( 0xFFFF ); // collide with everything
},
setMaskBits: function (bits) {
  this.body.GetShapeList().m_filter.maskBits = bits;
}

And it is working... but only when they are not colliding with each other. The same problem occurs when i'm facing a wall and I set the categoryBits to 0x0000.

UPDATE

Ok, I fixed it with a dirty hack: The Problem was, that contacts were still existing, so I'd have to delete them somehow. I tried to delete them at first manually but failed.

In the Manual of Box2D is written:

Contacts are destroyed with the AABBs cease to overlap.

So I wrote a function that moves the player about 6px (the smallest amount that seem to work) in the directory he is facing (if he's not colliding with a wall at that moment), this would overlap the entities and solve the problem.

Here is the function in question:

  changePosition: function (x,y) {
    this.facingWall = false;
    this.collision(); // will set facingWall to true if he's facing a wall.
    if(!this.facingWall) {
      this.body.m_xf.position.x = x;
      this.body.m_xf.position.y = y;
    }
  } 

Answer 1

You can call Refilter() on the fixtures for which the collision settings were changed.

Answer 2

Ok, I fixed it with a dirty hack: The Problem was, that contacts were still existing, so I'd have to delete them somehow. I tried to delete them at first manually but failed.

In the Manual of Box2D is written:

Contacts are destroyed with the AABBs cease to overlap.

So I wrote a function that moves the player about 6px (the smallest amount that seem to work) in the directory he is facing (if he's not colliding with a wall at that moment), this would overlap the entities and solve the problem.

Here is the function in question:

  changePosition: function (x,y) {
    this.facingWall = false;
    this.collision(); // will set facingWall to true if he's facing a wall.
    if(!this.facingWall) {
      this.body.m_xf.position.x = x;
      this.body.m_xf.position.y = y;
    }
  }