Collider

Summary

A Collider is a component that defines the physical boundaries of a GameObject in the scene. Thus, Colliders define the shape of an object for the physics engine, so without one, there’s no collision detection or response, the object is non-blocking. This means that other objects — including the player — can pass through it as if it doesn’t exist physically.

Here are some typical configurations using a collider:

Indication

Non-Blocking
- Other objects can pass through
- Useful for: decoration or props that are not in the player’s way
- Component: No collider
- Function: ⌀
Non-Blocking with Trigger
- Other objects can pass through, - but the collider detects when a GameObject passes through
- Useful for: the finish line in a car race, a trap in a cave
- Set: Collider + Trigger
- Function: void OnTriggerEnter(Collider other)
Blocking
- Other objects can bump into it - remains immobile
- Useful for: walls, floor
- Set: Collider
- Function: None

Colliders Shape

Setup

Navigate to Assets > Scenes

Create a new folder named « PhysX »

Create a new scene called « Colliders »

Double click to open it

Create a Sphere and assign it a color

Select the sphere

In the Inspector, notice that a Collider is already present

Sphere collider

Uncheck the checkbox of the Mesh Renderer

Notice that the collider of the sphere is now visible on the screen

Activate the sphere Mesh Renderer

Other colliders

We introduce the colliders of the other standard 3D objects:

Shape	Collider Type
Sphere	Sphere Collider
Capsule	Capsule Collider
Cylinder	Capsule Collider
Cube	Box Collider

Two remarks:

All basic 3D objects are delivered with a collider

The cylinder uses a capsule collider (Lower computational cost)

Collider

Scene Setup

Navigate to Assets > Scenes > PhysX

Create a new Scene named Detection

Create a sphere, assign it a color and a RigidBody with gravity

Move the sphere upwards

Collider Setup

In the Hierarchy, right click and select Create Empty gameobject

Rename the object « BCollider »

At the bottom of the Inspector, press the Add Component button

Select Box Collider

In the Inspector, activate the Is Trigger option

In the Inspector, click on the Edit Collider icon:

Use the face gizmos to

Enlarge the box

Make it larger and thicker than the sphere

Collider script setup

A collider trigger provides multiple functions to handle collisions:

In the PhysX folder, create a new script named « Colliz »

Select the GameObject BCollider

Drag and drop the script into the Inspector

Copy paste the following code into the script
using UnityEngine;

public class Colliz : MonoBehaviour
{
        public Material Mat_in,Mat_out;

        void OnTriggerEnter(Collider other)
        {
                Renderer objectRenderer = other.gameObject.GetComponent<Renderer>();
                objectRenderer.material = Mat_in;
        }

        void OnTriggerExit(Collider other)
        {
                Renderer objectRenderer = other.gameObject.GetComponent<Renderer>();
                objectRenderer.material = Mat_out;
        }
}
Drag and drop two Solid Color Materials into the Inspector

Avertissement

By reading the script, you can see that we change the sphere’s color via its Collider, using the reference named other. But why not place this script directly on the sphere? Because any object that activates the trigger option of its collider becomes a non-blocking object and that’s not the behavior we want for a 3D sphere.

Display collider

It is possible to display the collider in Play mode:

Select the Game window (by clicking on the tab, not by activating Play mode)

On the right of the Game tab, click on Gizmos to show the collider during Play mode

In the Hierarchy, select the BCollider

Test

Enter Play mode: