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:

.. hint:: 

	* 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
	
		.. image:: sphere.png
			:scale: 40%
		
	* Select the sphere
	* In the Inspector, notice that a Collider is already present
	
		.. image:: spherecollider.png
			:scale: 40%
	
Sphere collider
---------------
	
	* Uncheck the checkbox of the *Mesh Renderer*
	
	* Notice that the collider of the sphere is now visible on the screen
		
		.. image:: spherecol.png
			:scale: 50%	
	
	* Activate the sphere *Mesh Renderer*	
	

Other colliders
---------------

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

		.. image:: otherscolliders.png
			:scale: 30%
		
+-----------+-------------------+
| 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 
		
			.. image:: add.png
				:scale: 50%
				 
			* Select **Box Collider**
			
			.. image:: box.png
				:scale: 50%
				
			.. image:: scene1.png
				:scale: 35%	
		
		* In the Inspector, activate the **Is Trigger** option
		
			.. image:: istri.png
				:scale: 50%
			
		
		* In the Inspector, click on the **Edit Collider** icon:
		
			.. image:: edit.png
				:scale: 40%
	 
			 
		
		* Use the face gizmos to
		
			* Enlarge the box 
			* Make it larger and thicker than the sphere 
			
		.. image:: enlarge.gif
			:scale: 70%
			
Collider script setup
---------------------

A collider trigger provides multiple functions to handle collisions:


	.. image:: onmethod.png
		:scale: 40%

	

		
	* In the PhysX folder, create a new script named "Colliz"
	
	* Select the GameObject *BCollider*

	* Drag and drop the script into the Inspector
	
		.. image:: script.png
			:scale: 50%
	
	
	* Copy paste the following code into the script
	
	.. code-block:: csharp


		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
	
		.. image:: plum.gif 
		
		
	.. warning:: 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
	
	.. image:: giz.png
		:scale: 60%
		
	.. image:: wire.png
		:scale: 60%

	
Test
----	
	
	* Enter Play mode:
	
		.. image:: fallll.gif
			:scale: 60%