CODEWITHSUNDEEP
c#unity-game-enginetransform
Gabe Tucker
Gabe Tucker

Reputation: 55

Unity C#: transform.up is not updating as object rotates

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class PlayerMovement : MonoBehaviour
{
    public GameObject player;
    public Rigidbody2D playerRB;
    public Transform playerTF;

    public float moveForce;
    public float rotateForce;

    private string currentMoveKey = "";
    private string currentRotateKey = "";

    void Update()
    {
        //move
        if(Input.GetKey("w") && currentMoveKey == "")
        {
            currentMoveKey = "w";

            playerRB.AddForce(transform.up * moveForce * Time.deltaTime);
        }

        if (Input.GetKeyUp("w") && currentMoveKey == "w")
        {
            playerRB.velocity = new Vector2(0, 0);//resets when keyup and not already reset

            currentMoveKey = "";
        }

        if (Input.GetKey("s") && currentMoveKey == "")
        {
            currentMoveKey = "s";

            playerRB.AddForce(transform.up * -moveForce * Time.deltaTime);
        }

        if (Input.GetKeyUp("s") && currentMoveKey == "s")
        {
            playerRB.velocity = new Vector2(0, 0);

            currentMoveKey = "";
        }
        //rotate
        if (Input.GetKeyDown("a") && currentRotateKey == "")
        {
            currentRotateKey = "a";
        }
        if (Input.GetKey("a") && currentRotateKey == "a")
        {
            playerTF.Rotate(transform.forward * rotateForce * Time.deltaTime);
        }
        if (Input.GetKeyUp("a") && currentRotateKey == "a")
        {
            currentRotateKey = "";
        }

        if (Input.GetKeyDown("d") && currentRotateKey == "")
        {
            currentRotateKey = "d";
        }
        if (Input.GetKey("d") && currentRotateKey == "d")
        {
            playerTF.Rotate(transform.forward * -rotateForce * Time.deltaTime);
        }
        if (Input.GetKeyUp("d") && currentRotateKey == "d")
        {
            currentRotateKey = "";
        }
    }
}

Hey there! For some reason, in the lines where I AddForce to the RigidBody2D, if I rotate the player at the same time as he's moving- thus altering where transform.up would be pointed- the player continues moving in the direction that he was pointed at originally. In other words, he looks like he's sliding, and I have to stop moving and start moving again to update the direction in which he's pointed. What can I do to fix this, so that as he rotates, the direction he's moving updates simultaneously?

Upvotes: 1

Views: 717

Answers (1)

NSJacob1
NSJacob1

Reputation: 537

Adding force just keeps adding momentum to the rigidbody; you've already figured this out since you've been reseting your velocity when you raise the key. When you turn but keep holding move forward down your rigid body velocity isn't being reset, just being changed additively.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class PlayerMovement : MonoBehaviour
{
    public GameObject player;
    public Rigidbody2D playerRB;
    public Transform playerTF;

    public float moveForce;
    public float rotateForce;

    private Vector3 movement;

    private string currentRotateKey = "";

    void Update()
    {
        //move in Local space
        if (Input.GetKeyDown(KeyCode.W))
        {
            movement += Vector3.up;
        }

        if (Input.GetKeyUp(KeyCode.W))
        {
            movement -= Vector3.up;
        }

        if (Input.GetKeyDown(KeyCode.S))
        {
            movement -= Vector3.up;
        }

        if (Input.GetKeyUp(KeyCode.S))
        {
            movement += Vector3.up;
        }

        //rotate
        if (Input.GetKeyDown("a") && currentRotateKey == "")
        {
            currentRotateKey = "a";
        }
        if (Input.GetKey("a") && currentRotateKey == "a")
        {
            playerTF.Rotate(transform.forward * rotateForce * Time.deltaTime);
        }
        if (Input.GetKeyUp("a") && currentRotateKey == "a")
        {
            currentRotateKey = "";
        }

        if (Input.GetKeyDown("d") && currentRotateKey == "")
        {
            currentRotateKey = "d";
        }
        if (Input.GetKey("d") && currentRotateKey == "d")
        {
            playerTF.Rotate(transform.forward * -rotateForce * Time.deltaTime);
        }
        if (Input.GetKeyUp("d") && currentRotateKey == "d")
        {
            currentRotateKey = "";
        }

        // Implicit cast from Vector3 to Vector2, takes X and Ys
        ApplyMovement(movement);
    }

    public void ApplyMovement(Vector2 movement)
    {
        playerRB.velocity = player.transform.TransformDirection(movement.x, movement.y, 0) * moveForce * Time.deltaTime;
    }
}

I find it a little cleaner to use the KeyCode enums instead of string values, and I like to track a local Vector3 movement for the class instead of checking currentMovementKey. This lets you press multiple keys at a time, and catch spelling errors at compile time.

Moving where you "apply" your movement into it's own method helps change your behaviour when you want to.

movement is handled in local space, using Vector3.up instead of transform.up to avoid errors while rotating, then when applied to the playerRB.velocity we can convert back into world space using player.transform.TransformDirection(movement.x, movement.y, 0) (which could also be transform.TransformDirection(movement.x, movement.y, 0) if this component was on the same GameObject as the RigidBody2D component).

If you wanted to still have acceleration instead of jumping up and falling back down in speed, but did not want any drift like a real object things get a little trickier, here is one way of how to solve that problem: 

    public void ApplyMovement(Vector3 movement)
    {
        if (movement.sqrMagnitude > Mathf.Epsilon)
        {
            playerRB.drag = 0; // or some other small value
            if (playerRB.velocity.sqrMagnitude > Mathf.Epsilon)
            {
                playerRB.velocity = player.transform.TransformDirection(movement.normalized) * playerRB.velocity.magnitude;
            }

            playerRB.AddRelativeForce(movement * moveForce * Time.deltaTime);
        }
        else
        {
            playerRB.drag = 100f; // or some other value larger than the small one
        }
    }

What we're doing now is checking to see if we have a non-negligible (basically 0) amount of movement to apply, and if we are then we're not going to apply drag because then we'd be slowing our positive acceleration and that makes it difficult to predict what values you should have when setting up the game.

Since we now have no drag on the object, it should drift according to physics. That's what you're currently seeing. If we don't want that we can check if we have a non-negligible (basically 0) amount of velocity, and align that to our desired movement direction. Don't forget that movement is in local space still, and playerRB.velocity is in world space.

Then since we have movement to apply we should apply our local movement to our body using AddRelativeVelocity to continue accelerating in the desired direction. Currently this keeps going forever but you probably want to clamp your maximum speed eventually.

If we aren't applying movement, we want physics to apply drag and slow down the player. If we make physics do the work you should get reasonable(ish) acceleration to speed up and slow down (depending on your drag values and applied forces), but since we're ignoring drift you should get immediate turns.

Upvotes: 2

Related Questions