package
  {
          import flash.display.Sprite;
          import flash.events.Event;
          import flash.events.MouseEvent;
          
          public class @ax-animation-ch08-TripleSpring extends Sprite
          {
                  private var ball0:animation_ch08_Ball;
                  private var ball1:animation_ch08_Ball;
                  private var ball2:animation_ch08_Ball;
                  private var ball0Dragging:Boolean = false;
                  private var ball1Dragging:Boolean = false;
                  private var ball2Dragging:Boolean = false;
                  private var spring:Number = 0.05;
                  private var friction:Number = 0.95;
                  private var springLength:Number = 100;
                  
                  public function @ax-animation-ch08-TripleSpring()
                  {
                          init();
                  }
                  
                  private function init():void
                  {
                          ball0 = new animation_ch08_Ball(20);
                          ball0.x = Math.random() * stage.stageWidth;
                          ball0.y = Math.random() * stage.stageHeight;
                          ball0.addEventListener(MouseEvent.MOUSE_DOWN, onPress);
                          addChild(ball0);
                          
                          ball1 = new animation_ch08_Ball(20);
                          ball1.x = Math.random() * stage.stageWidth;
                          ball1.y = Math.random() * stage.stageHeight;
                          ball1.addEventListener(MouseEvent.MOUSE_DOWN, onPress);
                          addChild(ball1);
                          
                          ball2 = new animation_ch08_Ball(20);
                          ball2.x = Math.random() * stage.stageWidth;
                          ball2.y = Math.random() * stage.stageHeight;
                          ball2.addEventListener(MouseEvent.MOUSE_DOWN, onPress);
                          addChild(ball2);
                          
                          addEventListener(Event.ENTER_FRAME, onEnterFrame);
                          stage.addEventListener(MouseEvent.MOUSE_UP, onRelease);
                  }
  
                  
                  private function onEnterFrame(event:Event):void
                  {
                          if(!ball0Dragging)
                          {
                                  springTo(ball0, ball1);
                                  springTo(ball0, ball2);
                          }
                          if(!ball1Dragging)
                          {
                                  springTo(ball1, ball0);
                                  springTo(ball1, ball2);
                          }
                          if(!ball2Dragging)
                          {
                                  springTo(ball2, ball0);
                                  springTo(ball2, ball1);
                          }
                          graphics.clear();
                          graphics.lineStyle(1);
                          graphics.moveTo(ball0.x, ball0.y);
                          graphics.lineTo(ball1.x, ball1.y);
                          graphics.lineTo(ball2.x, ball2.y);
                          graphics.lineTo(ball0.x, ball0.y);
                  }
  
                  private function springTo(ballA:animation_ch08_Ball, ballB:animation_ch08_Ball):void
                  {
                          var dx:Number = ballB.x - ballA.x;
                          var dy:Number = ballB.y - ballA.y;
                          var angle:Number = Math.atan2(dy, dx);
                          var targetX:Number = ballB.x - Math.cos(angle) * springLength;
                          var targetY:Number = ballB.y - Math.sin(angle) * springLength;
                          ballA.vx += (targetX - ballA.x) * spring;
                          ballA.vy += (targetY - ballA.y) * spring;
                          ballA.vx *= friction;
                          ballA.vy *= friction;
                          ballA.x += ballA.vx;
                          ballA.y += ballA.vy;
                  }
                  
                  private function onPress(event:MouseEvent):void
                  {
                          event.target.startDrag();
                          if(event.target == ball0)
                          {
                                  ball0Dragging = true;
                          }
                          if(event.target == ball1)
                          {
                                  ball1Dragging = true;
                          }
                          if(event.target == ball2)
                          {
                                  ball2Dragging = true;
                          }
                  }
                  
                  private function onRelease(event:MouseEvent):void
                  {
                          ball0.stopDrag();
                          ball1.stopDrag();
                          ball2.stopDrag();
                          ball0Dragging = false;
                          ball1Dragging = false;
                          ball2Dragging = false;
                  }
          }
  }