title: Unity3D UI, calculation for position dragging an item?
body: <p>These days it's incredibly easy to drag UI elements in Unity: Make a few UI items. Add Component -> Event -> <strong>Event Trigger</strong>. Drop on the script below. Click to add the four obvious triggers. You're done.</p>
  
  <p>However.</p>
  
  <p>I'm totally lost in the relationship between <strong>pointer coordinates</strong> and <strong>UI coordinates</strong> (as seen in RectTransform and so on).</p>
  
  <p>In <code>DragIt</code> below: how the hell do you move a UI panel correctly under the finger?</p>
  
  <p>Say you have one large panel, with ten UIButton sitting in the panel with <code>Dragster</code> on the buttons. What is the relationship between the RectTransform coords and the mouse pointer ...</p>
  
  <p>in short how do you move one of the button around at DragIt() below?</p>
  
  <pre><code>/* modern Unity drag of UI element */
  using UnityEngine;
  using UnityEngine.UI;
  using UnityEngine.Events;
  using UnityEngine.EventSystems;
  public class Dragster:MonoBehaviour
      {
      public int index; // number each of your UI items
      static bool beingDragged = false;
      static int dragFrom;
      public void DragStart()
          {
          beingDragged = true; dragFrom = index;
          }
      public void DragIt()
          {
          ? ? W T F ? ?
          }
      public void DragEnd()
          {
          beingDragged = false;
          }
      public void DroppedBra()
          {
          Debig.Log("Drag: from/to " +dragFrom +" --&gt; " +index);
          }
      }
  </code></pre>