Unity: Adding impulse to a ball from a certain position - unity3d

Question

I'm making a 3d pool game and I stuck with this problem.
I can't find the needed function to add an impulse to a ball which will make the ball to spin.
In other words, how to set the AIM point from where I want to add the impulse?
If I use AddForce or AddTorque, it seems that it calculates it from the Center of the Ball.
But how to specify the aim point (Left english, Right english, etc...)?
And how to route the ball to the camera direction after a cue hit the ball?

Answer 1

At first look I think you should check Rigidbody.AddForceAtPosition. You should calculate the aim points somehow in world coordinates also.
I am relatively new on Unity but the main idea came to my mind first rotate the cue vector by y axis by a small amount angle, then calculate the hit point for each regions by casting physics ray then finally apply impulse by using Rigidbody.AddForceAtPosition. I tried to write a sample code:
public class SphereController : MonoBehaviour {
private Vector3 cueStartPoint;
void Start () {
cueStartPoint = new Vector3(0, 0.5f, -13f);
}
void Update () {
//direction from cue to center
var direction = transform.position - cueStartPoint;
//rotate cue to aim right english
var angleForRightEnglish = 5f;
var directionForRight = Quaternion.AngleAxis(angleForRightEnglish, Vector3.up) * direction;
Debug.DrawRay(cueStartPoint, directionForRight, Color.red, 10f);
//rotate cue to aim right english
var angleForLeftEnglish = -5f;
var directionForLeft = Quaternion.AngleAxis(angleForLeftEnglish, Vector3.up) * direction;
Debug.DrawRay(cueStartPoint, directionForLeft, Color.blue, 10f);
//try a sample hit from right
if (Input.GetKeyDown(KeyCode.RightArrow)) {
var forceMagnitude = 1f;
var hitForce = forceMagnitude * directionForRight.normalized;
//calculate right hit point on sphere surface
RaycastHit hitInfo;
if (Physics.Raycast(cueStartPoint, directionForRight, out hitInfo)) {
var rightHitPoint = hitInfo.point;
gameObject.GetComponent<Rigidbody>().AddForceAtPosition(hitForce, rightHitPoint, ForceMode.Impulse);
}
}
//try a sample hit from left
if (Input.GetKeyDown(KeyCode.LeftArrow)) {
var forceMagnitude = 1f;
var hitForce = forceMagnitude * directionForLeft.normalized;
//calculate left hit point on sphere surface
RaycastHit hitInfo;
if (Physics.Raycast(cueStartPoint, directionForLeft, out hitInfo)) {
var leftHitPoint = hitInfo.point;
gameObject.GetComponent<Rigidbody>().AddForceAtPosition(hitForce, leftHitPoint, ForceMode.Impulse);
}
}
}
}
this script should be added to ball as component of course, hope this helps.