风中的树(递归建树)

package 
{
	import flash.display.*;
	import flash.events.*;
	import flash.geom.Point;
	import flash.filters.GlowFilter;
	[SWF(backgroundColor = "0xFFFFFF",frameRate = "100")] 

	public class Main extends Sprite
	{
		private var shape:Shape;
		private var source:BitmapData;
		public function Main()
		{
			shape = new Shape  ;        
			source = new BitmapData(1000,1000,false,0xFFFFFF);
			addChild(new Bitmap(source));
			this.addEventListener(Event.ENTER_FRAME,onEnterFrame);
		}
		private function onEnterFrame(e:Event):void
		{
			shape.graphics.clear();
			creatTree(shape.graphics,400,850,90,180,5);
			creatTree(shape.graphics,400,850,45,100,4);
			creatTree(shape.graphics,400,850,135,100,4);
			step +=  Math.PI / 80 % Math.PI;
			source.fillRect(source.rect,0xFFFFFF);
			source.draw(shape);
		}
		private var step:Number = 0.0;
		private static const toRadian:Number = Math.PI / 180;

		private function creatTree(g:Graphics,px:Number,py:Number,angle:Number,len:Number,n:int):void
		{
			if (n > 0)
			{
				angle +=  3 * Math.cos(step) - 2;
				var x1:Number = px + 0.1 * len * Math.cos(angle * toRadian);
				var y1:Number = py - 0.1 * len * Math.sin(angle * toRadian);
				var x2:Number = px + len * Math.cos(angle * toRadian);
				var y2:Number = py - len * Math.sin(angle * toRadian);
				drawLine(g,n - 1,px,py,x2,y2);
				var a_l:Number = angle + 25;
				var a_r:Number = angle - 25;
				var lenlen = len * 2 / 3;
				creatTree(g,x2,y2,angle - 3 * Math.sin(step),len,n - 1);
				creatTree(g,x1,y1,a_l,len * 2 / 3,n - 1);
				creatTree(g,x1,y1,a_r,len * 2 / 3,n - 1);
				creatTree(g,x2,y2,a_l,len * 2 / 3,n - 1);
				creatTree(g,x2,y2,a_r,len * 2 / 3,n - 1);
			}
		}

		private function drawLine(g:Graphics,n:int,x1:Number,y1:Number,x2:Number,y2:Number):void
		{
			g.lineStyle(n,0x006600);
			g.moveTo(x1,y1);
			g.lineTo(x2,y2);
		}
	}
}