The current mouse position delta in pixel coordinates. (Read Only).
Input.mousePositionDelta is a Vector3 for compatibility with functions that have Vector3 arguments. The z component of the Vector3 is always 0.
Note: You should use Input.mousePositionDelta instead of [[Input.mousePosition] when Cursor.lockState is set to CursorLockMode.Locked, since when cursor is locked, the mouse position remains stationary when moving the mouse, thus only position delta gives you the information about mouse movement.