OnCollision events

Collision events occur when two non-trigger colliders make contact.

Example uses for collision events include:

• When a projectile hits a target, destroy both the projectile and the enemy.
• When a player character touches a door, trigger an animation to open the door.
• When a player character touches a power-up, increase the player’s size.

Working with collision events primarily involves the following API functions:

• Collider.OnCollisionEnter: Unity calls this function on each collider when two colliders first make contact.
• Collider.OnCollisionStay: Unity calls this function on each collider once per physics update while two colliders are in contact.
• Collider.OnCollisionExit: Unity calls this function on each collider when two colliders cease contact.

For collision events, at least one of the objects involved must have a dynamic physics body (that is, a Rigidbody or ArticulationBody that has Is Kinematic disabled). If both GameObjectsThe fundamental object in Unity scenes, which can represent characters, props, scenery, cameras, waypoints, and more. A GameObject’s functionality is defined by the Components attached to it. More info
See in Glossary in a collision are kinematic physics bodies, the collision does not call OnCollision functions.

The following example prints a message to the console when Unity calls each function.

using UnityEngine;
using System.Collections;

public class DoorObject : MonoBehaviour
{
    // “other” refers to the collider that is touching this collider
    void OnCollisionEnter (Collision other)
    {
        Debug.Log ("A collider has made contact with the DoorObject Collider");
    }

    void OnCollisionStay (Collision other)
    {
        Debug.Log ("A collider is in contact with the DoorObject Collider");
    }
    
    void OnCollisionExit (Collision other)
    {
        Debug.Log ("A collider has ceased contact with the DoorObject Collider");
    }
}

For examples of practical applications for OnCollision events, refer to example scripts for collider events.

Additional resources

• Collider interactions
• CollisionA collision occurs when the physics engine detects that the colliders of two GameObjects make contact or overlap, when at least one has a Rigidbody component and is in motion. More info
  See in Glossary
• ColliderAn invisible shape that is used to handle physical collisions for an object. A collider doesn’t need to be exactly the same shape as the object’s mesh - a rough approximation is often more efficient and indistinguishable in gameplay. More info
  See in Glossary