dev-notes/DotNet/Unity/Collisions.md

Collisions (Physics)

Rigidbody Component

Enables physics on the game objects.

Rigidbodies collide with other objects instead of going through them.

Avoid object rotation on collisions:

1. Assign Rigidbody component to object
2. Enable Freeze Rotation in Rigidbody > Constraints

using UnityEngine;
using System.Collections;

public class GameObject : MonoBehaviour {

    Rigidbody = rigidbody;  // game object rigidbody reference container

    void Start()
    {
        rigidbody = GetComponent<Rigidbody>();  // get rigidbody reference
    }

    void Update()
    {
    }

    // FixedUpdate is calls every x seconds (not influenced by FPS instability)
    // used for physics calculations which should be FPS independent
    void FixedUpdate()
    {
        Time.fixedDeltaTime;  // fixed amount of time
        Time.timeDelta;  // if called inside FIxedUpdate() behaves like fixedDeltaTime
    }

}

Box Collider Component

Enable Is Trigger to register the collision but avoid blocking the movement of the objects. The trigger can generate a event to signal the contact with the object.

One of the colliding GameObjects must have the Rigidbody component and the other Is Trigger enabled. To detect the collision but avoid computing the physics Is Kinematic must be enabled in the Rigidbody component.

using UnityEngine;
using System.Collections;

public class GameObject : MonoBehaviour {

    Rigidbody = rigidbody;  // game object rigidbody reference container

    void Start()
    {
        rigidbody = GetComponent<Rigidbody>();  // get rigidbody reference
    }

    // FixedUpdate is calls every x seconds (not influenced by FPS instability)
    // used for physics calculations which should be FPS independent
    void FixedUpdate()
    {
        Time.fixedDeltaTime;  // fixed amount of time
        Time.timeDelta;  // if called inside FixedUpdate() behaves like fixedDeltaTime
    }

    // called on box collision.
    void OnTriggerEnter(Collider triggerCollider) {

        // detect a collision with a particular GameObject(must have a TAG)
        if (triggerCollider.tag = "tag") {
            Destroy(triggerCollider.gameObject);  // destroy tagged item on collision
            //or
            Destroy(gameObject);  // destroy itself
        }
    }