What Info is in the planck.js EndContact Event?

In planck.js—a 2D physics engine for JavaScript games and simulations—the EndContact event is triggered immediately after two fixtures stop touching. This article provides a quick breakdown of the specific information you can extract from this event, including access to the underlying Contact object, the colliding fixtures, the parent bodies, and why contact state data like manifolds are no longer available at this stage of the collision lifecycle.

Accessing the Contact Object

When the EndContact event fires, the listener receives a Contact object as its primary argument. This object is the gateway to understanding which elements in your physics world have just separated.

world.on('end-contact', function(contact) {
    // Your extraction code here
});

Key Data Extracted from the Event

• The Fixtures (getFixtureA() and getFixtureB()): You can determine exactly which parts of your shapes broke contact. This is crucial if a single rigid body has multiple fixtures (e.g., a character body fixture and a separate sensor fixture for detecting ground contact).
• The Bodies (getBody()): By calling contact.getFixtureA().getBody() and contact.getFixtureB().getBody(), you can access the parent Body objects. This allows you to update game logic, such as switching a character’s state from “grounded” to “jumping/falling” the moment they leave a platform.
• User Data (getUserData()): If you attached custom game properties, IDs, or labels to your fixtures or bodies during creation, you can retrieve them here to identify what game entities just separated.

Limitations: What You Cannot Extract

It is equally important to know what information is not reliable during an EndContact event. Because the shapes are no longer intersecting, the engine clears the geometric collision data.

• No Contact Manifolds: Methods like contact.getManifold() will not yield useful geometric data because the contact points no longer exist.
• No Impulse or Normal Vectors: If you need to know the final direction or force of the separation, you cannot get it from EndContact. That data must be captured during the preceding PostSolve or PreSolve steps while the objects are still touching.