Unity handles collision between GameObjects with colliders, which attach to GameObjects and define the shape of a GameObjectThe 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 for the purposes of physical collisions. A collider is invisible, and does not need to be the exact same shape as the GameObject’s meshThe main graphics primitive of Unity. Meshes make up a large part of your 3D worlds. Unity supports triangulated or Quadrangulated polygon meshes. Nurbs, Nurms, Subdiv surfaces must be converted to polygons. More info
See in Glossary. A rough approximation of the mesh is often more efficient and indistinguishable in gameplay.
The simplest (and least processor-intensive) colliders are primitive collider types. In 3D, these are the Box ColliderA cube-shaped collider component that handles collisions for GameObjects like dice and ice cubes. More info
See in Glossary, Sphere ColliderA sphere-shaped collider component that handles collisions for GameObjects like balls or other things that can be roughly approximated as a sphere for the purposes of physics. More info
See in Glossary and Capsule ColliderA capsule-shaped collider component that handles collisions for GameObjects like barrels and character limbs. More info
See in Glossary. In 2D, you can use the Box Collider 2D and Circle Collider 2D. You can add any number of these to a single GameObject to create compound colliders.
Compound colliders approximate the shape of a GameObject while keeping a low processor overhead. To get further flexibility, you can add additional colliders on child GameObjects. For instance, you can rotate boxes relative to the local axes of the parent GameObject. When you create a compound collider like this, you should only use one RigidbodyA component that allows a GameObject to be affected by simulated gravity and other forces. More info
See in Glossary component, placed on the root GameObject in the hierarchy.
Primitive colliders do not work correctly with shear transforms. If you use a combination of rotations and non-uniform scales in the Transform hierarchy so that the resulting shape is no longer a primitive shape, the primitive collider cannot represent it correctly.
There are some cases, however, where even compound colliders are not accurate enough. In 3D, you can use Mesh CollidersA free-form collider component which accepts a mesh reference to define its collision surface shape. More info
See in Glossary to match the shape of the GameObject’s mesh exactly. In 2D, the Polygon Collider 2D does not match the shape of the spriteA 2D graphic objects. If you are used to working in 3D, Sprites are essentially just standard textures but there are special techniques for combining and managing sprite textures for efficiency and convenience during development. More info
See in Glossary graphic perfectly but you can refine the shape to any level of detailThe Level Of Detail (LOD) technique is an optimization that reduces the number of triangles that Unity has to render for a GameObject when its distance from the Camera increases. More info
See in Glossary you like.
These colliders are much more processor-intensive than primitive types, so use them sparingly to maintain good performance. Also, a mesh collider cannot collide with another mesh collider (i.e., nothing happens when they make contact). You can get around this in some cases by marking the mesh collider as Convex in the InspectorA Unity window that displays information about the currently selected GameObject, asset or project settings, allowing you to inspect and edit the values. More info
See in Glossary. This generates the collider shape as a “convex hull” which is like the original mesh but with any undercuts filled in.
The benefit of this is that a convex mesh collider can collide with other mesh colliders so you can use this feature when you have a moving character with a suitable shape. However, a good rule is to use mesh colliders for sceneA Scene contains the environments and menus of your game. Think of each unique Scene file as a unique level. In each Scene, you place your environments, obstacles, and decorations, essentially designing and building your game in pieces. More info
See in Glossary geometry and approximate the shape of moving GameObjects using compound primitive colliders.
You can add colliders to a GameObject without a Rigidbody component to create floors, walls and other motionless elements of a Scene. These are referred to as static colliders. At the opposite, colliders on a GameObject that has a Rigidbody are known as dynamic colliders. Static colliders can interact with dynamic colliders but since they don’t have a Rigidbody, they don’t move in response to collisions.
When colliders interact, their surfaces need to simulate the properties of the material they are supposed to represent. For example, a sheet of ice will be slippery while a rubber ball will offer a lot of friction and be very bouncy. Although the shape of colliders is not deformed during collisions, their friction and bounce can be configured using Physics Materials. Getting the parameters just right can involve a bit of trial and error. A slippery material like ice, for example, has zero (or very low) friction. A grippy material like rubber has high friction and near-perfect bounciness. See the reference pages for Physic Material and Physics Material 2D for further details on the available parameters. Note that for historical reasons, the 3D asset is actually called Physic MaterialA physics asset for adjusting the friction and bouncing effects of colliding objects. More info
See in Glossary (without the S) but the 2D equivalent is called Physics Material 2DUse to adjust the friction and bounce that occurs between 2D physics objects when they collide More info
See in Glossary (with the S).
The scripting system can detect when collisions occur and initiate actions using the OnCollisionEnter
function. However, you can also use the physics engineA system that simulates aspects of physical systems so that objects can accelerate correctly and be affected by collisions, gravity and other forces. More info
See in Glossary simply to detect when one collider enters the space of another without creating a collision. A collider configured as a Trigger (using the Is Trigger property) does not behave as a solid object and will simply allow other colliders to pass through. When a collider enters its space, a trigger will call the OnTriggerEnter
function on the trigger object’s scriptsA piece of code that allows you to create your own Components, trigger game events, modify Component properties over time and respond to user input in any way you like. More info
See in Glossary.
When collisions occur, the physics engine calls functions with specific names on any scripts attached to the objects involved. You can place any code you like in these functions to respond to the collision event. For example, you might play a crash sound effect when a car bumps into an obstacle.
On the first physics update where the collision is detected, the OnCollisionEnter
function is called. During updates where contact is maintained, OnCollisionStay
is called and finally, OnCollisionExit
indicates that contact has been broken. Trigger colliders call the analogous OnTriggerEnter
, OnTriggerStay
and OnTriggerExit
functions. Note that for 2D physics, there are equivalent functions with 2D appended to the name, eg, OnCollisionEnter2D
. Full details of these functions and code samples can be found on the Script Reference page for the MonoBehaviour class.
With normal, non-trigger collisions, there is an additional detail that at least one of the objects involved must have a non-kinematic Rigidbody (ie, Is Kinematic must be switched off). If both objects are kinematic Rigidbodies then OnCollisionEnter
, etc, will not be called. With trigger collisions, this restriction doesn’t apply and so both kinematic and non-kinematic Rigidbodies will prompt a call to OnTriggerEnter
when they enter a trigger collider.
Colliders interact with each other differently depending on how their Rigidbody components are configured. The three important configurations are the Static Collider (ie, no Rigidbody is attached at all), the Rigidbody Collider and the Kinematic Rigidbody Collider.
A static collider is a GameObject that has a Collider but no Rigidbody. Static colliders are mostly used for level geometry which always stays at the same place and never moves around. Incoming Rigidbody objects collide with static colliders but don’t move them.
In particular cases, the physics engine optimizes for static colliders that never move. For instance, a vehicle resting on top of a static collider remains asleep even if you move this static collider. You can enable, disable, or move static colliders in runtime without specially affecting the physics engine computation speed. Also, you can safely scale a static Mesh Collider as long as the scale is uniform (not skewed).
This is a GameObject with a Collider and a normal, non-kinematic Rigidbody attached. Rigidbody colliders are fully simulated by the physics engine and can react to collisions and forces applied from a script. They can collide with other objects (including static colliders) and are the most commonly used Collider configuration in games that use physics.
This is a GameObject with a Collider and a kinematic Rigidbody attached (ie, the IsKinematic property of the Rigidbody is enabled). You can move a kinematic rigidbody object from a script by modifying its Transform ComponentA Transform component determines the Position, Rotation, and Scale of each object in the scene. Every GameObject has a Transform. More info
See in Glossary but it will not respond to collisions and forces like a non-kinematic rigidbody. Kinematic rigidbodies should be used for colliders that can be moved or disabled/enabled occasionally but that should otherwise behave like static colliders. An example of this is a sliding door that should normally act as an immovable physical obstacle but can be opened when necessary. Unlike a static collider, a moving kinematic rigidbody will apply friction to other objects and will “wake up” other rigidbodies when they make contact.
Even when immobile, kinematic rigidbody colliders have different behavior to static colliders. For example, if the collider is set to as a trigger then you also need to add a rigidbody to it in order to receive trigger events in your script. If you don’t want the trigger to fall under gravity or otherwise be affected by physics then you can set the IsKinematic property on its rigidbody.
A Rigidbody component can be switched between normal and kinematic behavior at any time using the IsKinematic property.
A common example of this is the “ragdoll” effect where a character normally moves under animation but is thrown physically by an explosion or a heavy collision. The character’s limbs can each be given their own Rigidbody component with IsKinematic enabled by default. The limbs move normally by animation until IsKinematic is switched off for all of them and they immediately behave as physics objects. At this point, a collision or explosion force will send the character flying with its limbs thrown in a convincing way.
When two objects collide, a number of different script events can occur depending on the configurations of the colliding objects’ rigidbodies. The charts below give details of which event functions are called based on the components that are attached to the objects. Some of the combinations only cause one of the two objects to be affected by the collision, but the general rule is that physics will not be applied to an object that doesn’t have a Rigidbody component attached.
Collision detection occurs and messages are sent upon collision | ||||||
---|---|---|---|---|---|---|
Static Collider | Rigidbody Collider | Kinematic Rigidbody Collider | Static Trigger Collider | Rigidbody Trigger Collider | Kinematic Rigidbody Trigger Collider | |
Static Collider | Y | |||||
Rigidbody Collider | Y | Y | Y | |||
Kinematic Rigidbody Collider | Y | |||||
Static Trigger Collider | ||||||
Rigidbody Trigger Collider | ||||||
Kinematic Rigidbody Trigger Collider |
Trigger messages are sent upon collision | ||||||
---|---|---|---|---|---|---|
Static Collider | Rigidbody Collider | Kinematic Rigidbody Collider | Static Trigger Collider | Rigidbody Trigger Collider | Kinematic Rigidbody Trigger Collider | |
Static Collider | Y | Y | ||||
Rigidbody Collider | Y | Y | Y | |||
Kinematic Rigidbody Collider | Y | Y | Y | |||
Static Trigger Collider | Y | Y | Y | Y | ||
Rigidbody Trigger Collider | Y | Y | Y | Y | Y | Y |
Kinematic Rigidbody Trigger Collider | Y | Y | Y | Y | Y | Y |
When you visit any website, it may store or retrieve information on your browser, mostly in the form of cookies. This information might be about you, your preferences or your device and is mostly used to make the site work as you expect it to. The information does not usually directly identify you, but it can give you a more personalized web experience. Because we respect your right to privacy, you can choose not to allow some types of cookies. Click on the different category headings to find out more and change our default settings. However, blocking some types of cookies may impact your experience of the site and the services we are able to offer.
More information
These cookies enable the website to provide enhanced functionality and personalisation. They may be set by us or by third party providers whose services we have added to our pages. If you do not allow these cookies then some or all of these services may not function properly.
These cookies allow us to count visits and traffic sources so we can measure and improve the performance of our site. They help us to know which pages are the most and least popular and see how visitors move around the site. All information these cookies collect is aggregated and therefore anonymous. If you do not allow these cookies we will not know when you have visited our site, and will not be able to monitor its performance.
These cookies may be set through our site by our advertising partners. They may be used by those companies to build a profile of your interests and show you relevant adverts on other sites. They do not store directly personal information, but are based on uniquely identifying your browser and internet device. If you do not allow these cookies, you will experience less targeted advertising. Some 3rd party video providers do not allow video views without targeting cookies. If you are experiencing difficulty viewing a video, you will need to set your cookie preferences for targeting to yes if you wish to view videos from these providers. Unity does not control this.
These cookies are necessary for the website to function and cannot be switched off in our systems. They are usually only set in response to actions made by you which amount to a request for services, such as setting your privacy preferences, logging in or filling in forms. You can set your browser to block or alert you about these cookies, but some parts of the site will not then work. These cookies do not store any personally identifiable information.