famo.us access to collisionData upon collision event

Question

In the famo.us source I see that two things are emitted upon collision: the 'collision' string, and a variable called collisionData, like this: (physics/constraints/Collision.js, lines 112-122):

if (this._eventOutput) {
                var collisionData = {
                    target  : target,
                    source  : source,
                    overlap : overlap,
                    normal  : n
                };

                this._eventOutput.emit('preCollision', collisionData);
                this._eventOutput.emit('collision', collisionData);
            }

I know how to use the 'collision' string like so:

collision.on('collision', function() {
  // do stuff
};

But, it would be very helpful to know target and source for a collision event. How do I get access to collisionData? collision.collisionData returns 'undefined'.

It's passed as the first parameter to your callback function (probably). — Evan Trimboli, Dec 31 '14 at 01:29
Thanks Evan! `collision.on('collision', function(collisionData) { console.log(collisionData) }; ` will show the collision data. Unfortunately if doesn't give me agent id's or some other unique object identifier, unless I'm missing something. Back to the drawing board... — Dave Thomas, Dec 31 '14 at 01:39
Just had a look at the API documentation, it's pretty useless. — Evan Trimboli, Dec 31 '14 at 01:40

talves · Accepted Answer · 2015-01-01T00:02:29.400

Get the object from the return event object:

collision.on('collision', function(data) {
  // do stuff
  console.log('data', data);
  console.log('target', data.target);
  console.log('source', data.source);
});

The target and source returned are the particles of the body objects you attached to create collision.

Example Code here (not tested fully)

Just do something like the following to track a unique id of who bumped together.

// assuming your body is called body and body1 respectively
//   also, this is just partial code.
var uniqueID = 0;
body.particle = new Circle({
  radius: 50,
  position: [x, y, 0]
});
body1.particle = new Circle({
  radius: 50,
  position: [x, y, 0]
});

body.particle.uniqueID = 'body' + uniqueID;
uniqueID += 1;
body1.particle.uniqueID = 'body' + uniqueID;

collision.on('collision', function(data) {
  // do stuff
  console.log('target id', data.target.uniqueID);
  console.log('source id', data.source.uniqueID);
});

famo.us access to collisionData upon collision event

1 Answers1

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