Objetc in mouse position

Hello, I need a code that make a object (ex: sphere) stay at mouse position in X and Y axis and at 0 position in Z axis.
I need this to make my Gun in 2.5D sidescroller shooter, the gun is already facing the object, I just need to make it stay at crosshair position.

Already tried ScreenToWorldPoint, but no sucess... ;/

 

You were on the right track, ScreenToWorldPoint is what you need.

Code (csharp):

1. // totally untested made-up-on-the-spot code...
2. Vector3 gunPosition = Input.mousePosition;
3. Camera cam = Camera.mainCamera;
4. gunPosition.z = -cam.position.z;
5. gunPosition = cam.ScreenToWorldPoint(gunPosition);
6. myGunObject.transform.position = gunPosition;

 

Thanks Cameron, It worked almost perfectly, with some adjustments its now this way:

Code (csharp):

1. function Update () {
2.     gunPosition = Input.mousePosition;
3.     gunPosition.z = -Camera.mainCamera.transform.position.z;
4.     gunPosition = Camera.mainCamera.ScreenToWorldPoint(gunPosition);
5.     transform.position = gunPosition;
6.     transform.position.z = 0;

And the arm script is

Code (csharp):

1.  
2. var fpc : GameObject;
3. function Update () {
4.     transform.LookAt(fpc.transform.position);
5. }
6.