package {
        import flash.display.Sprite;
        import flash.display.StageAlign;
        import flash.display.StageScaleMode;
        import flash.display.DisplayObject;
        import flash.events.Event;

        public class @ax-lib-flex-animation-code-01-GridCollision-GridCollision3 extends Sprite
        {
                private const GRID_SIZE:Number = 80;
                private const RADIUS:Number = 25;
                
                private var _balls:Vector.<DisplayObject>;
                private var _grid:CollisionGrid;
                private var _numBalls:int = 100;
                
                public function @ax-lib-flex-animation-code-01-GridCollision-GridCollision3()
                {
                        stage.align = StageAlign.TOP_LEFT;
                        stage.scaleMode = StageScaleMode.NO_SCALE;
                        
                        _grid = new CollisionGrid(stage.stageWidth, stage.stageHeight, GRID_SIZE);
                        _grid.drawGrid(graphics);
                        
                        makeBalls();
                        addEventListener(Event.ENTER_FRAME, onEnterFrame);
                }
                
                function onEnterFrame(event:Event):void
                {
                        updateBalls();
                        _grid.check(_balls);
                        var numChecks:int = _grid.checks.length;
                        for(var j:int = 0; j < numChecks; j += 2)
                        {
                                checkCollision(_grid.checks[j] as Ball, _grid.checks[j + 1] as Ball);
                        }
                }
                
                
                private function makeBalls():void
                {
                        _balls = new Vector.<DisplayObject>(_numBalls);
                        for(var i:int = 0; i < _numBalls; i++)
                        {
                                var ball:Ball = new Ball(RADIUS);
                                ball.x = Math.random() * stage.stageWidth;
                                ball.y = Math.random() * stage.stageHeight;
                                ball.vx = Math.random() * 4 - 2;
                                ball.vy = Math.random() * 4 - 2;
                                addChild(ball);
                                _balls[i] = ball;
                        }
                }
                
                private function updateBalls():void
                {
                        for(var i:int = 0; i < _numBalls; i++)
                        {
                                var ball:Ball = _balls[i] as Ball;
                                ball.update();
                                if(ball.x < RADIUS)
                                {
                                        ball.x = RADIUS;
                                        ball.vx *= -1;
                                }
                                else if(ball.x > stage.stageWidth - RADIUS)
                                {
                                        ball.x = stage.stageWidth - RADIUS;
                                        ball.vx *= -1;
                                }
                                if(ball.y < RADIUS)
                                {
                                        ball.y = RADIUS;
                                        ball.vy *= -1;
                                }
                                else if(ball.y > stage.stageHeight - RADIUS)
                                {
                                        ball.y = stage.stageHeight - RADIUS;
                                        ball.vy *= -1;
                                }
                                ball.color = 0xffffff;
                        }
                }
                
                private function checkCollision(ballA:Ball, ballB:Ball):void
                {
                        var dx:Number = ballB.x - ballA.x;
                        var dy:Number = ballB.y - ballA.y;
                        var dist:Number = Math.sqrt(dx * dx + dy * dy);
                        if(dist < ballA.radius + ballB.radius)
                        {
                                ballA.color = 0xff0000;
                                ballB.color = 0xff0000;
                        }
                }
        }
}