How to make drag and throw (2D)

Questions & Answers
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1

Hi, I need to do drag and throw and I know there are lots of identical questions and generally the answer is SpringJoint or its types.

I tried joints but Im not satisfied with them, they stretch too much and/or circle around the mouse. I haven’t found any way to fix this anywhere on internet.

I have 2 questions:

  1. How do Imake trully rigid spring joint?
  2. And if I can’t, what should I use for drag and throw?
2

I never really tried making a drag and throw kind of mechanic, so I thought it would be a nice challenge. Not saying this is the best or only solution, but it is a solution. Hope it helps you out.

I didn’t use any joints, just the Rigidbody and the mouse input. It’s a bit of a 10-min code jam, so embrace the jank I guess. What I did was use a raycast to detect the object and a mouse button to grab. While holding the object, store the previous’ frame position and the current frames position. When releasing the mouse button use the two positions to calculate the drag direction and the distance (distance per frame = speed) and add some force to the Rigidbody. Things I noticed already is that you might want to clamp the distance value so it doesn’t fly off.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
  
public class MouseDragThrow : MonoBehaviour
{
    public GameObject currentlyDraggedObject = null;
    private float savedZPosition = 0;
    public Camera cam;
  
    private Vector3 previousDragPosition;
    private Vector3 currentDragPosition;
  
    public void Update()
    {
        RaycastHit hit;
        Ray ray = cam.ScreenPointToRay(Input.mousePosition);
        Vector2 mousePosition = Input.mousePosition;
  
        if(Input.GetMouseButtonDown(0))
        {
            if(Physics.Raycast(ray, out hit))
            {
                if(hit.collider.gameObject.tag == "Draggable")
                {
                    currentlyDraggedObject = hit.collider.gameObject;
                    savedZPosition = Mathf.Abs(cam.transform.position.z - currentlyDraggedObject.transform.position.z);
                    currentlyDraggedObject.GetComponent<Rigidbody>().isKinematic = true;
                    currentDragPosition = currentlyDraggedObject.transform.position;
                }
            }
        }         
  
        if(currentlyDraggedObject != null)
        { 
            currentlyDraggedObject.transform.position = cam.ScreenToWorldPoint(new Vector3(mousePosition.x, mousePosition.y, savedZPosition));
            previousDragPosition = currentDragPosition;
            currentDragPosition = currentlyDraggedObject.transform.position;
  
            if(Input.GetMouseButtonUp(0))
            {
                Vector3 direction = currentDragPosition - previousDragPosition;
                float distance = Vector3.Distance(previousDragPosition, currentDragPosition);
                currentlyDraggedObject.GetComponent<Rigidbody>().isKinematic = false;
                currentlyDraggedObject.GetComponent<Rigidbody>().AddForce(direction * distance * 10f, ForceMode.Impulse);
                currentlyDraggedObject = null;
            }  
        }
    }  
}
3

This is actually brilliant, Some people overlook that you can take 3d objects and put them in 2d scenes, using 3d object to achieve this effect would be brilliant as long as you lock it on the forward back axis (Z for me)

4 
using UnityEngine;
public class DragObject : MonoBehaviour
{
    void OnMouseDrag()
    {
        GetComponent<Rigidbody2D>().AddForce(new Vector2(Input.GetAxis("Mouse X"),Input.GetAxis("Mouse Y"))*40);
    }
}
5

Well a SpringJoint2D is meant to stretch otherwise it wouldn’t be much of a spring. :wink:

Well that answer isn’t correct, it’s not the joint for the job!

You can use the TargetJoint2D to perform drag/drop operations. You can configure it to be a stiff or loose “drag” operation too. The joint allows you to specify a target you wish to move to whether that be a path or a specific position of the mouse etc.

You don’t need to use 3D physics; everything that can be done in 3D can be done in 2D physics anyway.

Anyway, it’s what is used in all my physics examples.

You can see the basic drag/drop operation here:

This shows it being used to “loosely” follow path: