Verlet Structure

based on AdvancED ActionScript 3.0 Animation | Keith Peters
http://amzn.to/10s5J

by k__ 31 Jul 2010

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kinetic
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/**
 * Copyright k__ ( http://wonderfl.net/user/k__ )
 * MIT License ( http://www.opensource.org/licenses/mit-license.php )
 * Downloaded from: http://wonderfl.net/c/bPwM
 */

package {
	import flash.display.*;
	import flash.events.*;
	import flash.geom.Rectangle;

        /*
        based on AdvancED ActionScript 3.0 Animation | Keith Peters
        http://amzn.to/10s5J
        */
	public class Main extends Sprite {
		private var points:Vector.<VerletPoint>;
		private var sticks:Vector.<VerletStick>;
		private var rect:Rectangle;
		private var acc:uint=1;
		private var len:uint=15;

		public function Main() {
			points=new Vector.<VerletPoint>  ;
			sticks=new Vector.<VerletStick>  ;
			rect=new Rectangle(0,0,stage.stageWidth,stage.stageHeight);

			for (var i:uint = 0; i < len; i ++) {
				if (i>=1) {
					points.push(new VerletPoint(Math.random() * 100 - 50 + points[i - 1].x, Math.random() * 100 - 50 + points[i - 1].y));
					points[i].constrain(rect);
					sticks.push(new VerletStick(points[i], points[i - 1]));
				} else {
					points.push(new VerletPoint(Math.random() * stage.stageWidth, Math.random() * stage.stageHeight));
				}
				if (Math.random()<0.5&&i>=2) {
					sticks.push(new VerletStick(points[i], points[Math.floor(Math.random() * (i - 2))]));
				}

				points[i].x+=Math.random()*7-4;
				points[i].y+=Math.random()*7-4;
			}
			addEventListener(Event.ENTER_FRAME, h_enterFrame);
		}

		private function h_enterFrame(evt:Event):void {
			var i:uint,j:uint;
			for (i = 0; i < points.length; i ++) {
				points[i].update();
			}
			for (i = 0; i < points.length; i ++) {
				for (j = 0; j < acc; j ++) {
					points[i].constrain(rect);
				}
			}
			for (i = 0; i < sticks.length; i ++) {
				for (j = 0; j < acc; j ++) {
					sticks[i].update();
				}
			}

			graphics.clear();
			for (i = 0; i < points.length; i ++) {
				points[i].render(graphics);
			}

			for (i = 0; i < sticks.length; i ++) {
				sticks[i].render(graphics);
			}
		}

	}
}

import flash.display.Graphics;
import flash.geom.Rectangle;

class VerletPoint {
	public var x:Number;
	public var y:Number;
	private var ox:Number;
	private var oy:Number;

	public function VerletPoint(x:Number, y:Number) {
		setPos(x, y);
	}
	public function update():void {
		var tx:Number=x;
		var ty:Number=y;
		x+=vx;
		y+=vy;
		ox=tx;
		oy=ty;
	}
	public function setPos(x:Number, y:Number):void {
		this.x=ox=x;
		this.y=oy=y;
	}
	public function constrain(rect:Rectangle):void {
		x=Math.max(rect.left,Math.min(rect.right,x));
		y=Math.max(rect.top,Math.min(rect.bottom,y));
	}
	public function set vx(n:Number):void {
		ox=x-n;
	}
	public function set vy(n:Number):void {
		oy=y-n;
	}
	public function get vx():Number {
		return x - ox;
	}
	public function get vy():Number {
		return y - oy;
	}
	public function render(g:Graphics):void {
		g.beginFill(0xFF6600, 0.5);
		g.drawCircle(x, y, 3);
		g.endFill();
	}
}

class VerletStick extends Array {
	private var pa:VerletPoint;
	private var pb:VerletPoint;
	private var len:Number;

	public function VerletStick(pa:VerletPoint, pb:VerletPoint, len:Number = -1) {
		this.pa=pa;
		this.pb=pb;
		if (len==-1) {
			var dx:Number=pa.x-pb.x;
			var dy:Number=pa.y-pb.y;
			this.len=Math.sqrt(dx*dx+dy*dy);
		} else {
			this.len=len;
		}
	}

	public function update():void {
		var dx:Number=pb.x-pa.x;
		var dy:Number=pb.y-pa.y;
		var d:Number=Math.sqrt(dx*dx+dy*dy);
		var diff:Number=len-d;
		var offsetX:Number = (diff * dx / d) / 2;
		var offsetY:Number = (diff * dy / d) / 2;
		pa.x-=offsetX;
		pa.y-=offsetY;
		pb.x+=offsetX;
		pb.y+=offsetY;
	}
	public function render(g:Graphics):void {
		g.lineStyle(0,0xFF6600,0.5);
		g.moveTo(pa.x, pa.y);
		g.lineTo(pb.x, pb.y);
	}
}