private Vector3 initialPos;
 private Vector3 finalPos;

 // Update is called once per frame
 void Update () {
  if(Input.GetMouseButtonDown(0)){
   print(Input.mousePosition);
   initialPos = Input.mousePosition;
   print("initial to screen" + Camera.main.ScreenPointToRay(initialPos).origin);
  }
  if (Input.GetMouseButtonUp (0)) {
   print(Input.mousePosition);

   finalPos = Input.mousePosition;
   print("final to screen" + Camera.main.ScreenPointToRay(finalPos).origin);
   DrawLine (Camera.main.ScreenPointToRay(initialPos).origin , Camera.main.ScreenPointToRay(finalPos).origin, Color.red, 100f);
  }

 }



 void DrawLine(Vector3 start, Vector3 end, Color color, float duration = 0.2f)
 {
  start.z = 0;
  end.z = 0;
  GameObject myLine = new GameObject();
  myLine.transform.position = start;
  myLine.AddComponent<LineRenderer>();
  LineRenderer lr = myLine.GetComponent<LineRenderer>();
  lr.material = new Material(Shader.Find("Particles/Alpha Blended Premultiply"));
  lr.SetColors(color, color);
  lr.SetWidth(0.1f, 0.1f);
  lr.SetPosition(0, start);
  lr.SetPosition(1, end);
  GameObject.Destroy(myLine, duration);
 }