Drag object relative to camera

Question

I'm using the Vuforia AR library and I'm trying to let the user drag the object across the screen with their finger. I've tried all sorts of different methods but everything I've found only drags the object along the axis defined by the object and not the camera.

I've tried using Camera.main.tranform.forward which I think is the key, but I haven't been able to implement it properly. Can someone kindly point me in the right direction?

Edit: This is the code I ended up using thanks to robertbu

[SOLVED]

 using UnityEngine;
 using System.Collections;
  
 public class DragObject : MonoBehaviour 
 {
     private float maxPickingDistance = 10000;// increase if needed, depending on your scene size
     
     private Vector3 startPos;
                  
     private Transform pickedObject = null;
      
     // Update is called once per frame
     void Update () 
     {
         foreach (Touch touch in Input.touches) 
         {
             //Create horizontal plane
             Plane horPlane = new Plane(Vector3.up, Vector3.zero);
             
             //Gets the ray at position where the screen is touched
             Ray ray = Camera.main.ScreenPointToRay(touch.position);
              
             if (touch.phase == TouchPhase.Began) 
             {
                 RaycastHit hit = new RaycastHit();
                 if (Physics.Raycast(ray, out hit, maxPickingDistance)) 
                 { 
                     pickedObject = hit.transform;
                     startPos = touch.position;
                 } 
                 else
                 {
                     pickedObject = null;
                 }
             } 
             else if (touch.phase == TouchPhase.Moved) 
             {
                 if (pickedObject != null) 
                 {
                     float distance1 = 0f;
                     if (horPlane.Raycast(ray, out distance1))
                     {
                         pickedObject.transform.position = ray.GetPoint(distance1);
                     }
                 }
             } 
             else if (touch.phase == TouchPhase.Ended) 
             {
                 pickedObject = null;
             }
         }
     }
 }

Answer 1

Best Answer

Answer by robertbu · Oct 30, 2013 at 03:57 PM

One solution is to use Unity's mathematical Plane class. You construct the plane using the Camera's forward and then use Plane.Raycast() to find the point on the plane. You should be able to borrow code from this answer (though you will need to make a few changes):

http://answers.unity3d.com/questions/486097/mouse-clicking-on-the-plane-and-drag-to-other-posi.html

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falantar14 · Oct 30, 2013 at 03:59 PM 0

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Thanks, I will look into it and accept your answer if it works.

robertbu · Oct 30, 2013 at 04:16 PM 0

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Here is some sample code that implements a drag and drop relative to the camera. Attach it to the object(s) you want to drag:

 using UnityEngine;
 using System.Collections;
  
 public class Drag: $$anonymous$$onoBehaviour {
     private float dist;
     private Vector3 v3Offset;
     private Plane plane;
     
     void On$$anonymous$$ouseDown() {
         plane.SetNormalAndPosition(Camera.main.transform.forward, transform.position);
         Ray ray = Camera.main.ScreenPointToRay (Input.mousePosition);
         float dist;
         plane.Raycast (ray, out dist);
         v3Offset = transform.position - ray.GetPoint (dist);         
     }
     
     void On$$anonymous$$ouseDrag() {
          Ray ray = Camera.main.ScreenPointToRay (Input.mousePosition);
          float dist;
          plane.Raycast (ray, out dist);
          Vector3 v3Pos = ray.GetPoint (dist);
          transform.position = v3Pos + v3Offset;    
     }
 }

falantar14 · Oct 30, 2013 at 04:25 PM 0

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Thanks I was actually able to tweak the code from your original answer to suit my needs. I'll post it here.

itsmealex100 · Mar 05, 2015 at 05:15 PM 0

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For anyone who needs this for 2 vectors (2D), it can be easily modified. As follows:

 using UnityEngine;
 using System.Collections;
 
 [RequireComponent(typeof(BoxCollider2D))]
 
 public class Drag : $$anonymous$$onoBehaviour {
     private Vector2 screenPoint;
     private Vector2 offset;
     
     void On$$anonymous$$ouseDown() {
         
         offset = gameObject.transform.position - Camera.main.ScreenToWorldPoint(new Vector2(Input.mousePosition.x, Input.mousePosition.y));
     }
     
     void On$$anonymous$$ouseDrag()
     {
         Vector2 curScreenPoint = new Vector2(Input.mousePosition.x, Input.mousePosition.y);
         Vector2 curPosition = Camera.main.ScreenToWorldPoint(curScreenPoint);
         transform.position = curPosition;
     }
     
 }

Drag object relative to camera

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