How can I only instantiate if mouse over?

Questions & Answers
1

I am working on a game where I have a particle system prefab that instantiates on MouseButtonDown but I only want it to instantiate if the mouse is over a clickable object. I need to have the script on the camera so I believe I need to use raycasting but can’t work out how to do this. Here is the code I have. How would I go about making this script work only when over my object? Any help would be much appreciated!

var box : Transform;
function Update ()
{
    if (Input.GetMouseButtonDown(0))
        {
                var mousePos : Vector3 = Input.mousePosition;
                mousePos.z = 10.0;
                var worldPos : Vector3 = GetComponent.<Camera>().ScreenToWorldPoint(mousePos);
                Debug.Log("Mouse pos: " + mousePos + "   World Pos: " + worldPos + "   Near Clip Plane: " + GetComponent.<Camera>().nearClipPlane);
                clone = Instantiate(box, worldPos, Quaternion.identity);
    }
}
2

Indeed you can use RayCasting. Take a look at the Scripting API for Input.mousePosition; it has an example.

You have to attach a collider to the GameObject you want to click on.

var box : Transform;
 function Update ()
 {
     if (Input.GetMouseButtonDown(0))
         {
                 var mousePos : Vector3 = Input.mousePosition;
                 mousePos.z = 10.0;
                 var worldPos : Vector3 = GetComponent<Camera>().ScreenToWorldPoint(mousePos);
                 Debug.Log("Mouse pos: " + mousePos + "   World Pos: " + worldPos + "   Near Clip Plane: " + GetComponent<Camera>().nearClipPlane);

                 Ray ray = GetComponent<Camera>().ScreenPointToRay (Input.mousePosition);
                 if (Physics.Raycast(ray)) {
                       clone = Instantiate(box, worldPos, Quaternion.identity);
                 }
                
     }
 }

Also take a look at the Scripting API for Physics.Raycast and Ray for information about using LayerMask etc. so you have more control over what your ray can hit.
Note that the GetComponent<>() function needs no “.” after the GetComponent. I corrected it in my sample code.