package {
    import flash.display.Sprite;
    import flash.display.StageAlign;
    import flash.display.StageScaleMode;
    import flash.display.DisplayObject;
    import flash.events.Event;
     
    public class GridCollision3 extends Sprite {
        private const GRID_SIZE:Number=20;
        private const RADIUS:Number=10;
        private var _balls:Vector.<DisplayObject>;
        private var _grid:CollisionGrid;
        private var _numBalls:int=100;
        public function 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.assign(_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;
            }
        }
    }
}