MatterJS allow bodies to pass through yet still trigger collision

Question

I want certain rigid bodies to be able to pass through eachother, i.e. no collision response. Though I still want the collision to detect, and trigger an event for collisionsActive: Events.on('collisionActive') so that I can execute some code when they collide with eachother.

Events.on(engine, 'collisionActive', (event) => {
  for (const body of event.pairs) {
    if (body.a collides with body.b) doSomeStuff(body.a, body.b)
  }
});

These rigid bodies sit on 'floors' or 'platforms', so they need to collide with these walls or floors, but pass through other bodies. One option is to give the bodies a category in the collisionFilter but this doesn't seem to trigger the collisionActive event.

What can I do here?

Answer 1

I solved this by manually going over the Bodies and comparing their bounds using Bounds.contains.

if (Bounds.contains(bodyA.bounds, bodyB.position)) doSomeStuff()

Answer 2

When you create a body you can pass the option isSensor as true, that way the body will pass through anything and will trigger the collision event

{ 
 isSensor:true 
}