Quaternion Angle

Questions & Answers
1

Hello,

I am new to Unity and a beginner at programming. I am playing around with Unity to create an RTS control scheme. The script is supposed to detect when the player right-clicks a position, after which the player’s unit should rotate to face in the direction of the click, and once it has finished rotating, it begins moving towards it. After following several tutorials and searching forum posts, I have been able to implement it through a Quaternion.Slerp within a coroutine loop. Problem is, once the ship is facing the correct direction, it doesn’t move.

Here is the code:

using System.Collections;
using UnityEngine;
using UnityEngine.AI;

public class PlayerController : MonoBehaviour
{
    public Camera cam;
    public NavMeshAgent agent;  

    [SerializeField]
    private float rotationSpeed = 0.3f;

    private Vector3 moveOrder;
    private Quaternion targetDirection = default;
    private RaycastHit hit;
    private bool isRotating;

    private void Start()
    {
        agent.updateRotation = false;
    }

    // Update is called once per frame
    void Update() 
    {
        if (Input.GetMouseButtonDown(1))
        {            
            Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
            if (Physics.Raycast(ray, out hit, Mathf.Infinity))
            {
                StartCoroutine(rotateShip(transform.rotation, targetDirection));
                if (isRotating == false)
                {
                    agent.SetDestination(hit.point);
                }   
            }
        }
    }
    IEnumerator rotateShip(Quaternion currentRotation, Quaternion targetDirection)
    {
        isRotating = true;
        
        while (currentRotation != targetDirection)
        {
            targetDirection = Quaternion.LookRotation(hit.point - transform.position);
            transform.rotation = Quaternion.Slerp(transform.rotation, targetDirection, rotationSpeed * Time.deltaTime);
            yield return 1;
        }
        isRotating = false;
    }
}

The script seems to be stuck in the coroutine loop because the while loop condition is never met (i.e. currentrotation != targetRoation).

I saw this tutorial for calculating angles in unity, and tried my hand at implementing something similar: calculate the angle using the Inverse Tangent as shown in the video (except using the y axis for rotation instead of z, since my game uses 3D coordinates), then change the condition of the loop so it stops once the angle is acute enough. The code didn’t work, it would always output a negative right angle “-90.” I also tried my hand at Quaternion.Angle, but I couldn’t wrap my head around it.

I would appreciate if someone could shed some light into how to go about solving this. I am not just interested in a solution but in developing the thinking process to troubleshoot this sort of thing myself in the future. Thank you in advance!

2

you are using Slerp wrong

using System.Collections;
using UnityEngine;
using UnityEngine.AI;

public class PlayerController : MonoBehaviour
{
    public Camera cam;
    public NavMeshAgent agent;  

    [SerializeField]
    private float rotationSpeed = 0.3f;

    private Vector3 moveOrder;
    private Quaternion targetDirection = default;
    private RaycastHit hit;
    private bool isRotating;

    private void Start()
    {
        agent.updateRotation = false;
    }

    // Update is called once per frame
    void Update() 
    {
        if (Input.GetMouseButtonDown(1))
        {            
            Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
            if (Physics.Raycast(ray, out hit, Mathf.Infinity))
            {
                StartCoroutine(rotateShip(transform.rotation, targetDirection));
            }
        }
    }

     IEnumerator rotateShip(Quaternion currentRotation, Quaternion targetDirection)
     {
         isRotating = true;
         float amount = 0;
         while (currentRotation != targetDirection)
         {
             targetDirection = Quaternion.LookRotation(hit.point - transform.position);
             transform.rotation = Quaternion.Slerp(transform.rotation, targetDirection, amount);
             amount += rotationSpeed * Time.deltaTime;
             yield return null;
         }

         isRotating = false;
         agent.SetDestination(hit.point);
     }
3

For future reference, I was able to solve it. The Code ended up being the following:

  void Update()
     {
         if (Input.GetMouseButtonDown(1))
         {
             Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
             Plane plane = new Plane(Vector3.up, new Vector3(0f, transform.position.y, 0));
             float distanceToPlane;
             if (plane.Raycast(ray, out distanceToPlane))
             {                
                 moveOrder = ray.GetPoint(distanceToPlane);
                 targetDirection = Quaternion.LookRotation(moveOrder - transform.position);
                 StartCoroutine(rotateShip(transform.rotation, targetDirection));
             }
 
         }
     }
 
     IEnumerator rotateShip(Quaternion currentRotation, Quaternion targetDirection)
     {
         while (Quaternion.Angle(targetDirection, transform.rotation) > 1f)
         {
             targetDirection = Quaternion.LookRotation(moveOrder - transform.position);
             transform.rotation = Quaternion.Slerp(transform.rotation, targetDirection, rotationSpeed * Time.deltaTime);
             yield return null;
         }
         agent.SetDestination(moveOrder);
     }

This code has several of adjustments from my original code.

  1. The first one is the use of of a plane to shoot the ray at. Because the ground is lower than the GameObject, it was trying to orient itself towards the ground constantly, causing some wiggling. By creating a plane at the same height as the ship, this is no longer a problem:

Plane plane = new Plane(Vector3.up, new Vector3(0f, transform.position.y, 0));

  1. The second issue, and the biggest, was floating point inaccuracy. Because computers always have some inaccuracies in comparing floating point calculations, it was always returning false when comparing two quaternion rotations, even though at a glance they seemed identical.
    To solve this, I used the while (Quaternion.Angle(targetDirection, transform.rotation) > 1f) which simply measures the angle between both rotations and, if it’s within 1 degree, it considers it good enough.