Colliders and rigidbodies

Related: Triggers

Colliders

component that defines the shape of an object for the purposes of physical collisions https://docs.unity3d.com/ScriptReference/Collider.html

private void OnCollisionEnter(Collision other)
{
	Debug.Log("Bumped!");
	//component name in <>
	GetComponent<MeshRenderer>().material.color = Color.yellow;
}
 
// other functions
OnCollisionStay()
OnCollisionExit()

Lots of colliders
- Rigidbody is needed to be able to bump
  - Not all components need Rigidbody (ex. if there is a ball and a wall, only the ball can have rigidbody)
It’s a good idea to freeze components too so that it doesn’t do crazy stuff
- Freeze Position: Y (you don’t want it flying)
- Freeze Rotation: X,Y,Z (you don’t want player to rotate at all)
OnCollisionEnter is a callback (used when 2 colliders collide)
sphere, capsule, box
For more complex objects
- combine several primitive colliders to different parts of the game object
- mesh collider (often gets too detailed, impacting efficiency)
- combine shaders AND use mesh collider

Collision detection messages

https://docs.unity3d.com/Manual/collider-types-interaction.html When a pair of colliders make contact, they generate collision detection msgs if the following are both true:

There is at least one dynamic collider.
The other collider is a static collider, a kinematic collider, or another dynamic collider.
- static collider = collider
- dynamic collider = collider + rigidbody
- kinematic collider = collider + (is kinematic option) rigidbody

Collision generates trigger messages

Trigger messages occur in the following circumstances:

A dynamic or kinematic trigger collider collides with any collider type.
A static trigger collider collides with any dynamic or Kinematic collider.
So you can just make your ship have a dymanic trigger collider (doesn’t matter if its kinematic or not) so it can collide with everything lol

Making a collider into a trigger

We make a collider into a trigger by checking isTrigger
Objects can pass through the collider and can be detected through code
Make your trigger objects static

OnTriggerEnter(Collider other)
OnTriggerStay(Collider other)
OnTriggerExit(Collider other)

Sample script

using UnityEngine;
 
// on the player ship
public class CollisionHandler : MonoBehaviour
{
    // Start is called before the first frame update
    void OnCollisionEnter(Collision other)
    {
        Debug.Log(this.name + " -- collided with -- " + other.gameObject.name);
    }
 
    void OnTriggerEnter(Collider other)
    {
        // OnTriggerEnter
        // String interpolation
        Debug.Log($"{this.name} ** triggered by ** {other.gameObject.name}");
    }
}

For Argon Assault, put the rididbody and collider on the ship, and just put the colliders on the obstacles/enemies!

Rigidbody

component that gives an object the ability to move, fall, or be affected by physics (like gravity, forces, and collisions).

Adding a rigidbody to an object enables Unity’s physics engine to control the movement and collisions of that object.
Without a rigidbody, an object will stay where it is, even if you apply forces or try to simulate gravity.
As a general rule, moving objects should be rigidbody objects

public Rigidbody rb;
 
void Start()
{
	rb.AddForce
}

must also have collider attached
Mass: how much force is required to move, stop, or change the motion of that object
Drag: How quickly it will slow down (air resistance)
Angular velocity: How quickly it will slow its rotation
isKinematic: manual scripting (not affected by physics)

Use case

Box falling to ground

The Box
- the box should have both a collider and a rigidbody if you want it to fall and interact with other objects physically
The Ground
- the ground only needs a collider, not a rigidbody, because you generally don’t want the ground to move or be affected by gravity
- In Unity, objects without a rigidbody but with a collider are considered static objects, which can be collided with but do not move themselves.

leejunkim

Explorer