Shooting with a locked camera position

Questions & Answers
1

I’m making a FPS on rails. The camera is locked in a single position so the player can’t look around, but can move their cursor around the screen. I have a script for moving the crosshair around the screen. I just can’t figure out how I could expand this to instantiate objects (shoot) from the crosshair. Any help is greatly appreciated.

private var screenPoint : Vector3;
private var offset : Vector3;

function Update() {
	screenPoint = Camera.main.WorldToScreenPoint (gameObject.transform.position);
	offset = gameObject.transform.position - Camera.main.ScreenToWorldPoint (new Vector3(Input.mousePosition.x, Input.mousePosition.y, screenPoint.z));
}

function OnMouseDrag() {
	var curScreenPoint : Vector3 = new Vector3(Input.mousePosition.x, Input.mousePosition.y, screenPoint.z);
	var curPosition : Vector3 = Camera.main.ScreenToWorldPoint (curScreenPoint) + offset;
	transform.position = curPosition;
}
2

Raycasting is the typical way to solve the problem. Note that a ray does not necessarily hit anything, so you have to calculate a default distance along the ray. Assuming you Instantiated() your projectile just in front of your crosshairs, you can do something like (untested):

var v3LookPoint : Vector3;
var ray : Ray = camera.main.ViewportPointToRay(Input.mousePosition);
var hit : RaycastHit;
 
if (Physics.Raycast(ray, hit))
    v3LookPoint = hit.point;
else
  v3LookPoint = ray.GetPoint(distance); 
 
projectile.gameObject.transform.LookAt(v3LookPoint);
projectile.AddRelativeForce(transform.forward * 2000);

Note if you have gravity in the scene, your projectile will hit low since it will drop some on its way to the target. It is complicated to do a real fix for this problem, but you can fudge the hit point a bit fairly easily.