Drag ridgid bodys. Problem with mouseposition input.

[XIVMohawk]

Hi, I’m trying to make a script which allows the player to drag the rigid body. My problem is that I don’t get the mouse position right.

using UnityEngine;
using System.Collections;

public class IfSelecting : MonoBehaviour {

    private Ray ray;
    private RaycastHit Hit;
    private CollisionBool Bool;
    private Vector3 move;

	// Update is called once per frame
	void Update ()
    {

        if (Input.GetMouseButtonDown(0))
        {
            ray = Camera.main.ScreenPointToRay(Input.mousePosition);
            
            if (Physics.Raycast(ray,out Hit) && !Hit.rigidbody.isKinematic)
            {
                move = new Vector3(Input.mousePosition.x,Input.mousePosition.y,0f);

                Hit.rigidbody.freezeRotation = true;

                Hit.rigidbody.MovePosition(Hit.rigidbody.position + move);

            }
        }
    }
}

It is a very simple way to do it and I’ve tried using ScreenToWorldPoint but it did not help me or enlighten me in anyway.

If you have better ways to acquire this feel free to post some examples.
Thanks!

Edit: The game is restricted to x and y axis Therefore the z in move is 0.

[robertbu]

Here is some additions to your code to implement a drag:

using UnityEngine;
using System.Collections;

public class Drag : MonoBehaviour {
    //private CollisionBool Bool;
	private Vector3 delta;
	private Rigidbody rb;
	private Transform trDrag;
	private bool dragging = false;
	private float zDist;
 
    void Update (){
        if (Input.GetMouseButtonDown(0)) {
			Ray ray;
   			RaycastHit hit;
            ray = Camera.main.ScreenPointToRay(Input.mousePosition);
            if (Physics.Raycast(ray,out hit) && hit.rigidbody != null && !hit.rigidbody.isKinematic) {
				dragging = true;
				rb = hit.rigidbody;
				trDrag = hit.collider.gameObject.transform;
                delta =  trDrag.position - hit.point;
				zDist = Mathf.Abs (Camera.main.transform.position.z - hit.point.z);
                rb.freezeRotation = true;
            }
        }
		
		if (Input.GetMouseButton(0)) {
			if (dragging) {
				Vector3 v3Pos = new Vector3(Input.mousePosition.x, Input.mousePosition.y, zDist);
				v3Pos = Camera.main.ScreenToWorldPoint(v3Pos);
				rb.MovePosition(v3Pos + delta);
			}
		}
		
		if (Input.GetMouseButtonUp(0)) {
			dragging = false;
		}
    }
}

[IR_Nifty]

I believe your problem is where your vector calculation code is. Input.GetMouseButtonDown() returns true only in the frame the input is registered and no longer. Meaning: if I click, it will only fire in that one frame I happened to click during. After that, it will not return true anymore. Allow me to propose a modified script:

using UnityEngine;
using System.Collections;
 
public class Draggable : MonoBehaviour {

    //How much does the difference in mouse position affect the drag?
    //Public allows this value to be modified in the component list of a game
    //object once affixed to it.
    public float dragPower = 50;

    private Ray ray;
    private RaycastHit Hit;
    private Rigidbody bodyToDrag;
    private float distToBody;
    private Vector3 moveDirection;
 
    // Update is called once per frame
    void Update ()
    {
        if (Input.GetMouseButton(0))
        {
            ray = Camera.main.ScreenPointToRay(Input.mousePosition);
 
            //Are we hitting a new object that isn't kinematic that we also
            //don't already know about?
            if (Physics.Raycast(ray,out Hit) && !Hit.rigidbody.isKinematic &&
                bodyToMove == null)
            {
                //Make sure we know about the body we're dragging.
                bodyToMove = Hit.rigidbody;

                //Get the distance to it. This is used to make sure one of the
                //3 axes of this and another point are the same later on,
                //since the game is 2D. Better explained later.
                distToBody = Vector3.Distance(bodyToMove.position, ray.origin);
 
                Hit.rigidbody.freezeRotation = true;
            }

            if (bodyTomove != null)
            {
                //This gets the 3D point of the mouse,
                //but with one of the axes being the same.
                //Since the game is 2D, one of the axes must
                //be equal on both points, or the object will be dragged in
                //the 3rd dimension. This distance should ensure that.
                //If it doesn't, add a comment to my post and I'll help
                //you make sure of it.
                Vector3 currentMousePos = ray.GetPoint(distToBody);

                //Gets the direction we want to drag the body,
                //including a small magnitude.
                moveDirection = currentMousePos - bodyToMove.position;

                //Adds force in the move direction. Since the included
                //magnitude is too small for any meaningful change in
                //position, we multiply that magnitude with a
                //configurable power.
		bodyToMove.AddForce(moveDirection * dragPower);
            }
        }
        else
        {
            bodyToMove = null;
        }
    }
}

This should enable any object to be dragged once attached to any game object. This is untested, so if you have problems or want to restrict dragging to a single object or group of objects, comment on this answer and I’ll help.

[XIVMohawk]

robertbu’s code works excellently moving the objects around, I just added things for rotation freezing and unfreezing correctly as well as isKinematic to avoid the objects gaining falling momentum as you hold them.

However, when dragging an object it ignores collision with the walls and the terrain in my scene. Which is really weird since the dragged object collides with other similar objects and the wall are constructed the exact same way using colliders and even rigidbodys.

The same problem occurs when using IR Nifty’s code example so I’m wondering if the manual moving of object could override the physics or something along those lines.

Any thoughts on this?