//What is our forward direction?  Our spaceship moves in the positive y direction.
  var forwardDirection : Vector3 = Vector3 (0.0, 1.0, 0.0);
  
  // Below we create two helper classes, MovementSettings and SpecialEffects
  // Although the helper classes are not necessary, it makes for nice clean code and usage.
  
  class MovementSettings {
          // What is the maximum speed of this movement?
          var maxSpeed : float;
          
          // What's the acceleration in the positive and negative directions associated with this movement?
          var positiveAcceleration : float;
          var negativeAcceleration : float;
          
          // How much drag should we apply when there isn't input for this movement?
          var dragWhileCoasting : float;
          
          // How much drag should we apply to slow down the movement for speeds above maxSpeed?
          var dragWhileBeyondMaxSpeed : float;
          
          // When neither of the above drag factors are in play, how much drag should there normally be?  (Usually very small.)
          var dragWhileAcceleratingNormally : float;
          
          // This function determines which drag variable to use and returns one.
          function ComputeDrag (input : float, velocity : Vector3) {
                  //Is the input not zero (the 0.01 allows for some error since we're working with floats and they aren't completely precise)
                  if (Mathf.Abs (input) > 0.01) {
                          // Are we greater or less than our max speed? Then return the appropriate drag.
                          if (velocity.magnitude > maxSpeed)
                                  return dragWhileBeyondMaxSpeed;
                          else
                                  return dragWhileAcceleratingNormally;
                  } else
                          //If the input is zero, use dragWhileCoasting
                          return dragWhileCoasting;
          }
  }
  
  class SpecialEffects {
          // There are four possible special effects that can be assigned.
          var positiveThrustEffect : GameObject;
          var negativeThrustEffect : GameObject;
          var positiveTurnEffect : GameObject;
          var negativeTurnEffect : GameObject;
          
          // How loud should collision sounds be? This is used in the OnCollisionEnter () function.
          var collisionVolume = 0.01;
  }
  
  // We create two instances using our MovementSettings helper class.
  // One will be for translational (position) movement, the other for rotational.
  var positionalMovement : MovementSettings;
  var rotationalMovement : MovementSettings;
  
  // We create an instance using our SpecialEffects helper class.
  var specialEffects : SpecialEffects;
  
  // Can the user control the spaceship currently?  This will be toggled by another script that also toggles what the camera should track.
  var canControl = true;
  
  //FixedUpdate () is advantageous over Update () for working with rigidbody physics.
  function FixedUpdate () {
          // Retrieve input.  Note the use of GetAxisRaw (), which in this case helps responsiveness of the controls.
          // GetAxisRaw () bypasses Unity's builtin control smoothing.
          thrust = Input.GetAxisRaw ("Vertical");
          turn = Input.GetAxisRaw ("Horizontal");
          
          if (!canControl) {
                  thrust = 0.0;
                  turn = 0.0;
          }
          
          //Use the MovementSettings class to determine which drag constant should be used for the positional movement.
          //Remember the MovementSettings class is a helper class we defined ourselves. See the top of this script.
          rigidbody.drag = positionalMovement.ComputeDrag (thrust, rigidbody.velocity);
  
          //Then determine which drag constant should be used for the angular movement.
          rigidbody.angularDrag = rotationalMovement.ComputeDrag (turn, rigidbody.angularVelocity);
          
          //Determines which direction the positional and rotational motion is occurring, and then modifies thrust/turn with the given accelerations. 
          //If you are not familiar with the ?: conditional, it is basically shorthand for an "if..else" statement pair.  See http://www.javascriptkit.com/jsref/conditionals.shtml
  	thrust *= (thrust > 0.0) ? positionalMovement.positiveAcceleration : positionalMovement.negativeAcceleration;
          turn *= (turn > 0.0) ? rotationalMovement.positiveAcceleration : rotationalMovement.negativeAcceleration;
          
          // Add torque and force to the rigidbody.  Torque will rotate the body and force will move it.
          // Always modify your forces by Time.deltaTime in FixedUpdate (), so if you ever need to change your Time.fixedTime setting,
          // your setup won't break.
           rigidbody.AddRelativeTorque (Vector3 (0.0, 0.0, -1.0) * turn * Time.deltaTime, ForceMode.VelocityChange);
          rigidbody.AddRelativeForce (forwardDirection * thrust * Time.deltaTime, ForceMode.VelocityChange);
  }
  
  // This function allows us to SendMessage to an object to set whether or not the player can control it
  function SetControllable (controllable : boolean) {
          canControl = controllable;
  }
  
  // The Update () function only serves to provide special effects in this case.
  function Update () {
          //Collecting appropriate input.
          thrust = Input.GetAxisRaw ("Vertical");
          turn = Input.GetAxisRaw ("Horizontal");
          
          if (!canControl) {
                  thrust = 0.0;
                  turn = 0.0;
          }
          
          // If the thrust effect slots aren't null in the inspector, send a message.
          // The message will be received by the component SpecialEffectHandler
          // If the boolean statement is true, (e.g. (thrust > 0.01)) then the special effects will be enabled.
          if (specialEffects.positiveThrustEffect)
                  specialEffects.positiveThrustEffect.SendMessage ("SetSpecialEffectActive", (thrust > 0.01));
  
          if (specialEffects.negativeThrustEffect)
                  specialEffects.negativeThrustEffect.SendMessage ("SetSpecialEffectActive", (thrust < -0.01));
  
          if (specialEffects.positiveTurnEffect)
                  specialEffects.positiveTurnEffect.SendMessage ("SetSpecialEffectActive", (turn > 0.01));
  
          if (specialEffects.negativeTurnEffect)
                  specialEffects.negativeTurnEffect.SendMessage ("SetSpecialEffectActive", (turn < -0.01));        
  }
  
  // The OnCollisionEnter () function only serves to provide special effects in this case.
  function OnCollisionEnter (collision : Collision) {
          // Get the component "CollisionSoundEffect" of the object we collided with.
          // The platforms in this tutorial have a CollisionSoundEffect component.
          var collisionSoundEffect : CollisionSoundEffect = collision.gameObject.GetComponent (CollisionSoundEffect);
  
          // If collisionSoundEffect isn't null, get the audio clip, set the volume, and play.
          if (collisionSoundEffect) {
                  audio.clip = collisionSoundEffect.audioClip;
                  // By multiplying by collision.relativeVelocity.sqrMagnitude, the sound will be louder for faster impacts.
                  audio.volume = collisionSoundEffect.volumeModifier * collision.relativeVelocity.sqrMagnitude * specialEffects.collisionVolume;
                  audio.Play ();                
          }
  }
  
  // The Reset () function is called by Unity when you first add a script, and when you choose Reset on the
  // gear popup menu for the script.
  function Reset () {
          // Set some nice default values for our MovementSettings.
          // Of course, it is always best to tweak these for your specific game.
          positionalMovement.maxSpeed = 3.0;
          positionalMovement.dragWhileCoasting = 3.0;
          positionalMovement.dragWhileBeyondMaxSpeed = 4.0;
          positionalMovement.dragWhileAcceleratingNormally = 0.01;
          positionalMovement.positiveAcceleration = 50.0;
          
          // By default, we don't have reverse thrusters.
          positionalMovement.negativeAcceleration = 0.0;
          
          rotationalMovement.maxSpeed = 2.0;
          rotationalMovement.dragWhileCoasting = 32.0;
          rotationalMovement.dragWhileBeyondMaxSpeed = 16.0;
          rotationalMovement.dragWhileAcceleratingNormally = 0.1;
  
          // For rotation, acceleration is usually the same in both directions.
          // It could make for interesting unique gameplay if it were significantly
          // different, however!
          rotationalMovement.positiveAcceleration = 50.0;
          rotationalMovement.negativeAcceleration = 50.0;
  }
  
  // In order for this script to work, the object its applied to must have a Rigidbody and AudioSource component.
  // This tells Unity to always have the components when this script is attached.
  @script RequireComponent (Rigidbody, AudioSource)