The contact points generated by the physics engine.
Every contact contains a contact point, normal and the two colliders that collided (see ContactPoint). From inside OnCollisionStay or OnCollisionEnter you can always be sure that contacts has at least one element.
function OnCollisionStay(collision : Collision) {
// Check if the collider we hit has a rigidbody
// Then apply the force
for (var contact : ContactPoint in collision.contacts) {
print(contact.thisCollider.name + " hit " + contact.otherCollider.name);
// Visualize the contact point
Debug.DrawRay(contact.point, contact.normal, Color.white);
}
}
// A grenade
// - instantiates a explosion prefab when hitting a surface
// - then destroys itself
var explosionPrefab : Transform;
function OnCollisionEnter(collision : Collision) {
// Rotate the object so that the y-axis faces along the normal of the surface
var contact = collision.contacts[0];
var rot = Quaternion.FromToRotation(Vector3.up, contact.normal);
var pos = contact.point;
Instantiate(explosionPrefab, pos, rot);
// Destroy the projectile
Destroy (gameObject);
}