Setting things into motion

We'll need to move the castle and the silhouettes to create an illusion of the dragon flying. We do this by updating their position after every tick, as shown here:

FairytaleManager.prototype.update = function() {
  this.updateCastle();
  this.updateSilhouette();
};

The update function will be called from the parent layer (MainMenu or GameWorld) on every tick. It is here that you will have to move your castle and the backdrop. The updateCastle and updateSilhouette functions are identical, so I will discuss the updateCastle function only:

FairytaleManager.prototype.updateCastle = function(){
  for(var i = 0; i < this.castleSprites.length; ++i)
  {
    // first update the position based on the scroll speed
    var castleSprite = this.castleSprites[i];
    castleSprite.setPosition(castleSprite.getPositionX() - MAX_SCROLLING_SPEED, castleSprite.getPositionY());

    // check if the sprite has gone completely out of the left edge of the screen
    if(castleSprite...