MousePointer

using UnityEngine;

public class MousePointer : MonoBehaviour
{
    private Vector2 mouseDownStart;
    private Vector3 objectStart;
    private Vector2 mouseDelta;

    private bool dragging = false;
    public float pixelWorldRatio;

    void Update ( )
    {
        if ( Input.GetMouseButtonDown ( 0 ) )
        {
            mouseDownStart = Input.mousePosition;
            mouseDelta = Vector2.zero;
            objectStart = transform.localPosition;
            dragging = true;
        }

        if ( Input.GetMouseButtonUp ( 0 ) )
        {
            mouseDelta = Vector2.zero;
            dragging = false;
        }

        if ( dragging )
        {
            mouseDelta = ( Vector2 ) Input.mousePosition - mouseDownStart;
            gameObject.transform.localPosition = new Vector3 ( objectStart.x + ( mouseDelta.x * pixelWorldRatio ), objectStart.y, objectStart.z + ( mouseDelta.y * pixelWorldRatio ) );
        }
    }
}