Changing Vector direction without effecting speed

Unity Engine
1

Hi friends,

I’m using AddForce to have my object travel to my mouse input. However, I want the direction of force to always be in the direction of the mouse input. At the moment, when I try to change the direction of the object, I’m getting a lot of ‘over-shooting’ or ‘drag effect’.

I would like to know how I could approach this problem

Thanks! Here’s my code:

using UnityEngine;
using System.Collections;

public class Player : MonoBehaviour {

    float proxyAngle;
    float speed = 20;
    Vector3 vectorToTarget;
    Vector3 mouseLocal;


    void Start () {
   
    }
   
    void Update () {


        if(Input.GetMouseButton(0))
        {
            mouseLocal = Camera.main.ScreenToWorldPoint(Input.mousePosition);
            vectorToTarget = mouseLocal - transform.position;
            float angle = Mathf.Atan2(vectorToTarget.y, vectorToTarget.x) * Mathf.Rad2Deg;
            proxyAngle = angle;
            Quaternion q = Quaternion.AngleAxis(angle, Vector3.forward);
            transform.rotation = Quaternion.Slerp(transform.rotation, q, Time.deltaTime * speed);
        }
    }

    void OnCollisionEnter2D(Collision2D coll) {
        if(coll.gameObject.tag == "Floor")
        {
            Debug.Log ("FLOOR");
            Application.LoadLevel(0);

        }
        if(coll.gameObject.tag == "Goal")
        {
            Debug.Log ("GOAL YE");
            Application.LoadLevel(0);

        }
    }
    void OnTriggerStay2D(Collider2D coll){
        Debug.Log (coll.tag);
        if(coll.tag == "Ramp"){
            Rigidbody2D rb = gameObject.GetComponent<Rigidbody2D>();
            //Vector3 currentVelocity = rb.velocity;
            rb.AddForce(vectorToTarget * 5);
       
        }

    }
}
2

According to the laws of physics, changing direction is changing speed, so doing what you said shouldn’t be possible.

That said, if you want your object to move at a constant rate, maybe you don’t want to use the physics system at all, but rather make it kinematic and move it solely through your script.

3

I will just say that what you want seems like it’s negating much of the usefulness of actually using the physics engine so you may want to look into simpler (and more easily controlled) methods of moving objects. Also, you’re using smooth-lerping to slowly change your rotation, which seems counterproductive if your goal is to have immediate and absolute control over the vector of your object.

4

Yeah I guess you’re probably right. By the way, did you mean changing direction is changing velocity?

5

I actually want to keep the lerping (so yes there is a slight delay but not as strong as the addforce effect). I think I will scrap the physics engine and just adjust the players velocity directly instead, because that actually achieves the effect I want.

Thanks for the answers guys

6

Possibly. It’s been many years since I’ve had a physics class. The difference between speed and velocity escapes me.

You knew what I meant, though. :stuck_out_tongue:

1 Like
7

You want to maintain a constant speed regardless of the direction? This is actually relatively simple. Pseudo code as follows.

// Set these variables elsewhere
public Vector3 targetDirection;
public float targetSpeed;

void FixedUpdate (){
    // Cacheing your RigidBody is still a good idea
    GetComponent<RigidBody>().velocity = targetDirection.normalised * targetSpeed;
}
2 Likes
8

Speed is just a number… velocity is speed and direction… ie

rigidbody.velocity.magnitude = speed; // a float
//rigidbody.velocity; // is a vector3
[\code]
9

not a constant speed, but a changing speed due to addforce.

10

Actually, speed is ignorant of direction. Speed is just the rate at which an object covers a distance. What you are thinking of is velocity, which is both speed and direction. Therefore, changing direction would not affect the speed of the object, but rather the velocity of the object.

Edit: I see this was already addressed later in the thread… my bad

11

And also, that post was over two years ago. :stuck_out_tongue: