Collider 2D - Official Unity Tutorial

To have any physical presence in the scene

a game object must use one of the

collider components to define it's physical shape

and to interact with the relevant physics engine.

Unity has 2 physics engines.

One for 3D and one for 2D.

These two physics engines do not interact with each other.

For more information on physics and physics 2D

please see the information linked below.

When using the 2D physics engine

a collider 2D component must be used.

There are 4 collider 2D components to choose from.

The circle collider 2D,

the box collider 2D,

the polygon collider 2D

and the edge collider 2D.

All of these collider components share many properties

as they all derive from the same generic

base collider 2D.

Each collider 2D component however is

optimised for a particular shape.

The circle collider 2D works with

round circular objects.

The box collider 2D works well with rectangular objects.

The polygon collider 2D work

best with complex shapes.

And the edge collider 2D works well for surfaces.

The edge collider and polygon colliders are very similar.

They are created by several points, or vertices,

with edges connecting them.

The main difference between them is that the polygon collider

must be a closed shape covering an area.

And the edge collider must be open,

defining an edge of one or more segments.

One good use of the edge collider

is to make a single solid surface

rather than a series of 2D colliders

even if several sprites are used to create

the visual aspect of the surface.

When comparing all 2D colliders

there are 2 properties exposed in the inspector

that they all share.

Is Trigger and Material.

The other unique properties are for defining

the shape of that particular 2D collider.

The Is Trigger property will set the collider

to behave as a trigger collider.

With normal 2D physics collisions

the 2D physics engine will prevent

2D colliders from passing through each other.

2D trigger colliders will not participate

in physical collisions and will send 2D

trigger messages rather than 2D collision messages.

These trigger messages can be used to

initiate new actions in the scene.

For more information on Is Trigger

and the messages sent by colliders

please see the information linked below.

The material property is a reference to the

physics material 2D being used by the collider 2D

and this can be none.

Physics materials define how colliders

will react when they collider

and define both the bounciness and

the friction of the collider's surface.

To make a bouncy ball or slippery ice covered platform

use a different physics material 2D

with each collider 2D.

For more information on physics material 2D

please see the information linked below.

To use a collider 2D it must be attached

to a game object.

One way of attaching a collider 2D component

is to use the Add Component button

and select Physics 2D

and select a Collider 2D Component.

For more information on game objects,

components and how to use them

please see the information linked below.

When a collider 2D component is attached

Unity will try to size the collider 2D to the sprite.

If the size and shape of the collider 2D

is undesirable then the shape can be edited by either

changing the values in the inspector

or changing the collider 2D itself in the scene view.

To edit a collider 2D in the scene view

hold down the shift key.

This will display handles on the 2D collider's

gizmo in the scene view.

These handles are drag-able.

In the case of the edge collider and the polygon collider

dragging an existing handle will move

the collider's vertex, and change the collider's shape

rather than resizing the collider.

By moving the cursor over an empty edge

on either the edge collider or the polygon collider

a new vertex can be created by clicking.

This is indicated by a new handle appearing

and the edge highlighting in green.

In the case of the edge collider and the polygon collider

holding the control key will allow a

vertex to the be deleted when clicked.

This is indicated by the handle

and the edge highlighting in red.

A game object does not need a rigidbodied

2D to use a collider 2D.

To participate in 2D collision and trigger events

however at least 1 of the game objects

involved must have a rigidbody 2D attached.

A common pattern for best performance

would be to attach collider 2D components

but not rigidbody components

to all of the static, or non-moving game objects

that need to interact with 2D physics.

And attach a collider 2D and a rigidbody 2D

to the dynamic, or moving, game object

that need to interact in the scene.

For more information on physics 2D

collider 2D, collisions and triggers

please see the information linked below.