Stop object rotation

To freeze the aim, you could use a bool variable and toggle its value when the button is pressed, and place the aim code inside an if - but you must declare the variable targetPoint outside the function, so it can "remember" the last point aimed when you freeze the aim.

private var lineRenderer : LineRenderer;

function Start() { lineRenderer = GetComponent(LineRenderer); lineRenderer.SetWidth(4,3); lineRenderer.SetVertexCount(2); }

// speed is the rate at which the object will rotate var speed = 4.0; var targetPoint: Vector3; // save the target point even when freezed var freeze = false; // tells if aim is freezed or not

function Update () {

 if (Input.GetMouseButtonDown(1){ // freeze/unfreeze the aim with Right Mouse Button
     freeze = !freeze;
 }
 if (freeze){ // if aim freezed...
     if (Input.GetMouseButtonDown(0)){ // allow firing with Left Mouse Button
         // place here the cannon shoot code
         // and finish unfreezing the aim
         freeze = false; // unfreeze aim after shooting
     }
 }
 else { // if not freezed...
     // Generate a plane that intersects the transform's position with an upwards normal.
     var playerPlane = new Plane(Vector3.up, transform.position);
     // Generate a ray from the cursor position
     var ray = Camera.main.ScreenPointToRay (Input.mousePosition);
     // Determine the point where the cursor ray intersects the plane.
     // This will be the point that the object must look towards to be looking at the mouse.
     // Raycasting to a Plane object only gives us a distance, so we'll have to take the distance,
     //   then find the point along that ray that meets that distance.  This will be the point
     //   to look at.
     var hitdist = 0.0;
     // If the ray is parallel to the plane, Raycast will return false.
     if (playerPlane.Raycast (ray, hitdist)) {
         // Get the point along the ray that hits the calculated distance.
         targetPoint = ray.GetPoint(hitdist);
         // Determine the target rotation.  This is the rotation if the transform looks at the target point.
         var targetRotation = Quaternion.LookRotation(targetPoint - transform.position);
         // Smoothly rotate towards the target point.
         transform.rotation = Quaternion.Slerp(transform.rotation, targetRotation, speed * Time.deltaTime);
         // shorten the ray if it's hitting some obstacle:
         var hit: RaycastHit;
         if (Physics.Linecast(transform.position, targetPoint, hit)){
             targetPoint = hit.point;
         }
     } else {
         targetPoint = transform.position;
     }
 }
 lineRenderer.SetPosition(0, transform.position);
 lineRenderer.SetPosition(1, targetPoint);

}