[Герыч]

Сделал проверку на нулевую длину для связей:

package gerich.verlet
{
	import flash.display.Shape;
	import flash.display.Sprite;
	import flash.events.Event;
	import flash.events.MouseEvent;
 
	public class Main extends Sprite{
		private var pt:Array = new Array();
		private var joints:Array = new Array();
		private var particles:Sprite = new Sprite();
		private var canvas:Shape = new Shape();
		private var grav:Number = 500;
		private var timeSqr:Number;
 
		// ========================================================== //
		public function Main():void{
			stage.frameRate = 40;
 
			timeSqr=1/stage.frameRate;timeSqr*=timeSqr;
 
			addChild(canvas);
 
			addChild(particles);
 
			pt.push(new Particle(270,150,true));
 
			for (var j:int=0;j<30;j++)
			{
				pt.push(new Particle(270,150));
				joints.push(new RangeJoint(pt[j], pt[j+1], 8, 20));
			}
 
 
			for (var i in pt){
				particles.addChild(pt[i]);
			}
 
			addEventListener(Event.ENTER_FRAME, checkJoints);
			addEventListener(Event.ENTER_FRAME, ptMouse);
		}
		// ========================================================== //
 
		private function checkJoints(event:Event):void{
			var dx:Number;
			var dy:Number;
 
			canvas.graphics.clear();
 
			// Gravity
 
			for (var i in pt){
				dx = (pt[i].xx - pt[i].old_x);
				dy = (pt[i].yy - pt[i].old_y);
				pt[i].old_x = pt[i].xx;
				pt[i].old_y = pt[i].yy;
				pt[i].xx += dx;
				pt[i].yy += (dy+grav*timeSqr);
			}
 
			// Joints
 
 
			for (var z:int=0; z<30; z++){
				for (var i in joints){
					joints[i].Apply();
				}
 
				for (var i in pt){
					pt[i].xx=Math.max(pt[i].xx,0);
					pt[i].xx=Math.min(pt[i].xx,stage.stageWidth);
					pt[i].yy=Math.max(pt[i].yy,0);
					pt[i].yy=Math.min(pt[i].yy,stage.stageHeight);
				}
			}
 
			for (var i in pt){
				pt[i].x = pt[i].xx;
				pt[i].y = pt[i].yy;
			}
			// Lines
			for (var i in joints){
				joints[i].Draw(canvas);
			}
		}
		// ========================================================== //
		private function ptMouse(event:Event):void{
			for (var i in pt){
				if(pt[i].isMouse){
					pt[i].x=mouseX;
					pt[i].y=mouseY;
					pt[i].xx=mouseX;
					pt[i].yy=mouseY;
				}
			}
			canvas.graphics.clear();
			// Lines
			for (var i in joints){
				joints[i].Draw(canvas);
			}
		}
	}
}
 
// ***** [ Particle Class ] ***************************************** //
 
	import flash.display.Sprite;
 
	internal class Particle extends Sprite{
		public var old_x:Number;
		public var old_y:Number;
		public var xx:Number;
		public var yy:Number;
		public var isMouse:Boolean;
 
		// ========================================================== //
		public function Particle(_x:int, _y:int, _isMouse:Boolean=false):void{
			x = _x;
			y = _y;
 
			xx = _x;
			yy = _y;
 
			old_x = _x;
			old_y = _y;
 
			isMouse=_isMouse;
 
			graphics.lineStyle(1, 0x000000);
			graphics.beginFill(0xFFD22B);
			graphics.drawCircle(0,0,5);
			graphics.endFill();
		}
		// ========================================================== //
	}
 
	import flash.display.Shape;
 
	internal class Joint{
		public var p1:Particle;
		public var p2:Particle;
		public var len:Number;
 
		// ========================================================== //
		public function Joint(_p1:Particle, _p2:Particle, _len:Number):void{
			p1=_p1;
			p2=_p2;
			len=_len;
		}
		// ========================================================== //
 
		public function Draw(canvas:Shape):void{
			canvas.graphics.lineStyle(1,0x000000);
			canvas.graphics.moveTo(p1.x, p1.y);
			canvas.graphics.lineTo(p2.x, p2.y);
		}
		// ========================================================== //
 
		public function Apply():void{
			var dx:Number;
			var dy:Number;
			var d_len:Number;
			var diff:Number;
 
			dx = p2.xx-p1.xx;
			dy = p2.yy-p1.yy;
			d_len = Math.sqrt(dx*dx + dy*dy);
			if(d_len==0){
				dx=Math.random();
				dy=Math.random();
				d_len = Math.sqrt(dx*dx + dy*dy);
			}
			diff = (d_len-len)/d_len;
			dx *= 0.5*diff;
			dy *= 0.5*diff;
 
			if(!p2.isMouse){
				p2.xx -= dx;
				p2.yy -= dy;
			}
			if(!p1.isMouse){
				p1.xx += dx;
				p1.yy += dy;
			}
 
		}
		// ========================================================== //
	}
 
	internal class WeakJoint extends Joint
	{
		// ========================================================== //
		public function WeakJoint(_p1:Particle, _p2:Particle, _len:Number):void{
			super(_p1,_p2,_len);
		}
 
		// ========================================================== //
		override public function Apply():void{
			var dx:Number;
			var dy:Number;
			var d_len:Number;
			var diff:Number;
 
			dx = p2.xx-p1.xx;
			dy = p2.yy-p1.yy;
			d_len = Math.sqrt(dx*dx + dy*dy);
			if(d_len==0){
				dx=Math.random();
				dy=Math.random();
				d_len = Math.sqrt(dx*dx + dy*dy);
			}
			if(d_len>len){
				diff = (d_len-len)/d_len;
				dx *= diff;
				dy *= diff;
 
				if(!p2.isMouse){
					p2.xx -= dx;
					p2.yy -= dy;
				}
				if(!p1.isMouse){
					p1.xx += dx;
					p1.yy += dy;
				}
			}
		}
 
		// ========================================================== //
	}
 
	internal class RangeJoint extends Joint
	{
		public var lenmax:Number;
		public var lenmin:Number;
		// ========================================================== //
		public function RangeJoint(_p1:Particle, _p2:Particle, _lenmin:Number, _lenmax:Number):void
		{
			lenmax=_lenmax;
			lenmin=_lenmin;
			super(_p1,_p2,_lenmax);
		}
 
		// ========================================================== //
		override public function Apply():void
		{
			var dx:Number;
			var dy:Number;
			var d_len:Number;
			var diff:Number;
 
			dx = p2.xx-p1.xx;
			dy = p2.yy-p1.yy;
			d_len = Math.sqrt(dx*dx + dy*dy);
			if(d_len==0){
				dx=Math.random();
				dy=Math.random();
				d_len = Math.sqrt(dx*dx + dy*dy);
			}
			if((d_len>lenmax)||(d_len<lenmin)){
				if(d_len>lenmax)
					diff = (d_len-lenmax)/d_len;
				if(d_len<lenmin)
					diff = (d_len-lenmin)/d_len;
				dx *= diff;
				dy *= diff;
 
				if(!p2.isMouse){
					p2.xx -= dx;
					p2.yy -= dy;
				}
				if(!p1.isMouse){
					p1.xx += dx;
					p1.yy += dy;
				}
			}
		}
		// ========================================================== //
	}

Добавлено через 12 часов 1 минуту
Вопрос ко всем, а как реализовать трение о поверхность(границы нашего квадрата). Как я понимаю, если частица "проникла" в другой объект, то надо добавить силу трения, направленную в противоположную сторону скорости.. но как это сделать? Есть ли у кого хорошие статейки по теме?