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

	public class animation_ch11_Billiard3 extends Sprite
	{
		private var ball0:animation_ch11_Ball;
		private var ball1:animation_ch11_Ball;
		private var bounce:Number = -1.0;
		
		public function animation_ch11_Billiard3()
		{
			init();
		}
		
		private function init():void
		{
			stage.scaleMode = StageScaleMode.NO_SCALE;
			stage.align = StageAlign.TOP_LEFT;
			ball0 = new animation_ch11_Ball(150);
			ball0.mass = 2;
			ball0.x = stage.stageWidth - 200;
			ball0.y = stage.stageHeight - 200;
			ball0.vx = Math.random() * 10 - 5;
			ball0.vy = Math.random() * 10 - 5;
			addChild(ball0);

			ball1 = new animation_ch11_Ball(90);
			ball1.mass = 1
			ball1.x = 100;
			ball1.y = 100;
			ball1.vx = Math.random() * 10 - 5;
			ball1.vy = Math.random() * 10 - 5;
			addChild(ball1);

			addEventListener(Event.ENTER_FRAME, onEnterFrame);
		}
		
		private function onEnterFrame(event:Event):void
		{
			ball0.x += ball0.vx;
			ball0.y += ball0.vy;
			ball1.x += ball1.vx;
			ball1.y += ball1.vy;
			checkCollision(ball0, ball1);
			checkWalls(ball0);
			checkWalls(ball1);
		}
		
		private function checkWalls(ball:animation_ch11_Ball):void
		{
			if(ball.x + ball.radius > stage.stageWidth)
			{
				ball.x = stage.stageWidth - ball.radius;
				ball.vx *= bounce;
			}
			else if(ball.x - ball.radius < 0)
			{
				ball.x = ball.radius;
				ball.vx *= bounce;
			}
			if(ball.y + ball.radius > stage.stageHeight)
			{
				ball.y = stage.stageHeight - ball.radius;
				ball.vy *= bounce;
			}
			else if(ball.y - ball.radius < 0)
			{
				ball.y = ball.radius;
				ball.vy *= bounce;
			}
		}

		private function checkCollision(ball0:animation_ch11_Ball, ball1:animation_ch11_Ball):void
		{
			var dx:Number = ball1.x - ball0.x;
			var dy:Number = ball1.y - ball0.y;
			var dist:Number = Math.sqrt(dx*dx + dy*dy);
			if(dist < ball0.radius + ball1.radius)
			{
				// calculate angle, sine and cosine
				var angle:Number = Math.atan2(dy, dx);
				var sin:Number = Math.sin(angle);
				var cos:Number = Math.cos(angle);
				
				// rotate ball0's position
				var x0:Number = 0;
				var y0:Number = 0;
				
				// rotate ball1's position
				var x1:Number = dx * cos + dy * sin;
				var y1:Number = dy * cos - dx * sin;
				
				// rotate ball0's velocity
				var vx0:Number = ball0.vx * cos + ball0.vy * sin;
				var vy0:Number = ball0.vy * cos - ball0.vx * sin;
				
				// rotate ball1's velocity
				var vx1:Number = ball1.vx * cos + ball1.vy * sin;
				var vy1:Number = ball1.vy * cos - ball1.vx * sin;
				
				// collision reaction
				var vxTotal:Number = vx0 - vx1;
				vx0 = ((ball0.mass - ball1.mass) * vx0 + 2 * ball1.mass * vx1) / (ball0.mass + ball1.mass);
				vx1 = vxTotal + vx0;
				x0 += vx0;
				x1 += vx1;

				// rotate positions back
				var x0Final:Number = x0 * cos - y0 * sin;
				var y0Final:Number = y0 * cos + x0 * sin;
				var x1Final:Number = x1 * cos - y1 * sin;
				var y1Final:Number = y1 * cos + x1 * sin;

				// adjust positions to actual screen positions
				ball1.x = ball0.x + x1Final;
				ball1.y = ball0.y + y1Final;
				ball0.x = ball0.x + x0Final;
				ball0.y = ball0.y + y0Final;

				// rotate velocities back
				ball0.vx = vx0 * cos - vy0 * sin;
				ball0.vy = vy0 * cos + vx0 * sin;
				ball1.vx = vx1 * cos - vy1 * sin;
				ball1.vy = vy1 * cos + vx1 * sin;
			}
		}
	}
}