package {
          import flash.display.Sprite;
          import flash.display.StageAlign;
          import flash.display.StageScaleMode;
          import flash.events.Event;
          import flash.events.KeyboardEvent;
          import flash.ui.Keyboard;
          
          [SWF(backgroundColor=0x000000)]
          public class @ax-animation-ch15-Trees extends Sprite
          {
                  private var trees:Array;
                  private var num@ax-animation-ch15-Trees:uint = 100;
                  private var fl:Number = 250;
                  private var vpX:Number = stage.stageWidth / 2;
                  private var vpY:Number = stage.stageHeight / 2;
                  private var floor:Number = 50;
                  private var vz:Number = 0;
                  private var friction:Number = 0.98;
                  
                  public function @ax-animation-ch15-Trees()
                  {
                          init();
                  }
                  
                  private function init():void
                  {
                          stage.align = StageAlign.TOP_LEFT;
                          stage.scaleMode = StageScaleMode.NO_SCALE;
                          
                          trees = new Array();
                          for(var i:uint = 0; i < num@ax-animation-ch15-Trees; i++)
                          {
                                  var tree:animation_ch15_Tree = new animation_ch15_Tree();
                                  trees.push(tree);
                                  tree.xpos = Math.random() * 2000 - 1000;
                                  tree.ypos = floor;
                                  tree.zpos = Math.random() * 10000;
                                  addChild(tree);
                          }
                          addEventListener(Event.ENTER_FRAME, onEnterFrame);
                          stage.addEventListener(KeyboardEvent.KEY_DOWN, onKeyDown);
                  }
                  
                  private function onEnterFrame(event:Event):void
                  {
                          for(var i:uint = 0; i < num@ax-animation-ch15-Trees; i++)
                          {
                                  var tree:animation_ch15_Tree = trees[i];
                                  move(tree);
                          }
                          vz *= friction;
                          sortZ();
                  }
                  
                  private function onKeyDown(event:KeyboardEvent):void
                  {
                          if(event.keyCode == Keyboard.UP)
                          {
                                  vz -= 1;
                          }
                          else if(event.keyCode == Keyboard.DOWN)
                          {
                                  vz += 1;
                          }
                  }
                  
                  private function move(tree:animation_ch15_Tree):void
                  {
                          tree.zpos += vz;
                          
                          if(tree.zpos < -fl)
                          {
                                  tree.zpos += 10000;
                          }
                          if(tree.zpos > 10000 - fl)
                          {
                                  tree.zpos -= 10000;
                          }
                          
                          var scale:Number = fl / (fl + tree.zpos);
                          tree.scaleX = tree.scaleY = scale;
                          tree.x = vpX + tree.xpos * scale;
                          tree.y = vpY + tree.ypos * scale;
                          tree.alpha = scale;
                  }
                  
                  private function sortZ():void
                  {
                          trees.sortOn("zpos", Array.DESCENDING | Array.NUMERIC);
                          for(var i:uint = 0; i < num@ax-animation-ch15-Trees; i++)
                          {
                                  var tree:animation_ch15_Tree = trees[i];
                                  setChildIndex(tree, i);
                          }
                  }
          }
  }