Unity Collisions

The aim of this post is to summarize:

• What’s required for collisions in Unity
• How to set up some basic collision detection
• When OnTrigger and OnCollision are called, and when they aren’t

What’s required for a collision to occur?

For collisions to be detected by Unity, there are 2 components of particular importance:

1. Rigidbody

• Allows an object to react to physics
• A key property to note is isKinematic
• If you do not require the object to have physics-based interactions with other objects (i.e. isKinematic is true), a Rigidbody is still required (on at least 1 object) for any collision to occur

2. Collider

• Used to define the shape of the object (or rather an approximation of it) which will be used for collisions
• There are various types of colliders, namely Box, Sphere, Capsule, Mesh, etc.
• A key property to note is isTrigger

How do you set up basic collision detection?

1. When you need two solid objects to interact with each other

Object 1:

Object 2:

Notes:

• At least one Rigidbody needs to be non-kinematic (i.e. isKinematic = false)

Callbacks that will be called:

• OnCollisionEnter
• OnCollisionExit

2. When you want to do something when a collision occurs (i.e. a trigger) on a non-physical object

Object 1:

Object 2:

Notes:

• At least one object requires a Rigidbody — isKinematic can be either true or false
• At least 1 Collider needs to have isTrigger = true — both cannot be set to isTrigger = true

Callbacks that will be called:

• OnTriggerEnter
• OnTriggerExit