Detect mouse collision over an object

Question

Suppose there are 4 areas namely A1,A2,A3,A4 and each object is given a number(1,2,3,4). When I drag and drop the object(1) on A1, it should print a message "where the object is being dropped". (no need of mouse over... any mouse collision concept)

first set i=1 -----> o1

ie;logic

if(mousecollision == "L1" && i=1)
{
  mouseup
  score++;
}
else
{
  score--;
}

Answer 1

This a several-step answer and this is just a way of doing things, but certainly not the only one.

1. Both objects and areas must have a collider component attached.
2. Create the proper tags for each set to combine. In this case they're "Green" and "Purple".
3. Create a layer for the areas. In this case it's "DDArea".
4. Use the following script, attached to the D&D objects, as an example to your own. In this case I used spheres.

The train of thought goes as follows:

• Take advantage of the MonoBehaviour functions for handling mouse collision (OnMouseDrag and OnMouseUp) for moving the objects and detecting release, respectively.
• Move the object according to the position of the mouse.
• Cast a ray on release in order to know whether the mouse's position (thus, the object's position) is inside an area.
• If that's the case, then compare the area's and the object's tags (sets), so a decision can be made accordingly; reset the object to its initial position or increase the score.

Finally, here's my example running on Unity web player: https://dl.dropboxusercontent.com/u/4568142/unity/dragdrop/dragdrop.html

Inspector for the objects representing the areas

Inspector for the objects representing the objects (balls/spheres)

DragDropBall.cs:

using UnityEngine;
using System.Collections;
public class DragDropBall : MonoBehaviour
{
    public Camera mainCam;
    int layerMask;
    Vector3 initPosition;

    void Start()
    {
        if (mainCam == null)
            Debug.LogError("No camera attached");
        layerMask = 1 << LayerMask.NameToLayer("DDArea");
        initPosition = gameObject.transform.position;
    }

    void OnMouseDrag()
    {
        Vector3 newPosition = mainCam.ScreenToWorldPoint(Input.mousePosition);
        newPosition.z = transform.position.z;
        transform.position = newPosition;
    }

    void OnMouseUp()
    {      
        Vector3 origin = mainCam.ScreenToWorldPoint(Input.mousePosition);
        Ray ray = new Ray(mainCam.ScreenToWorldPoint(Input.mousePosition), Vector3.forward);
        RaycastHit[] hits = Physics.RaycastAll(ray, Mathf.Infinity, layerMask);
        foreach (RaycastHit h in hits)
        {
            string nameSphere = gameObject.name;
            string nameArea = h.collider.gameObject.name;
            string tagSphere = gameObject.tag;
            string tagArea = h.collider.gameObject.tag;
            Debug.Log(nameSphere + " dropped on " + nameArea);
            if (tagSphere.Equals(tagArea))
            {
                Debug.Log("Increment points");
                // further logic for your game here
            }
            else
            {
                // return the object to its inital position
                gameObject.transform.position = initPosition;
            }
        }
    }
}