Forked from:: makc3d's forked from: Double Pendulum Symplectic Euler

Double Pendulum in QuickBox2D

forked:5
favorite:4
lines:77
license : MIT License
modified : 2010-03-13 18:07:29

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// forked from makc3d's forked from: Double Pendulum Symplectic Euler
// forked from aont's Double Pendulum
package {
	import com.actionsnippet.qbox.*;
	import flash.display.Bitmap;
	import flash.display.BitmapData;
	import flash.display.MovieClip;
	import flash.display.Sprite;
	import flash.events.Event;
	import flash.events.MouseEvent;
	import flash.events.TimerEvent;
	import flash.geom.ColorTransform;
	import flash.geom.Matrix;
	import flash.geom.Point;
	import flash.utils.Timer;
    [SWF(backgroundColor=0x3f7f00)]
	public class DoublePendulum extends MovieClip
	{
		private var circle:Sprite;
		private var circleObject:QuickObject;
		private var circleCoords:Array = [];
		private var line_ratio:Number;
		private var length_1:Number = 0.5;
		private var length_2:Number = 0.25;
		private var radius:Number = 2;
		
		private var mass_1:Number = 0.05;
		private var mass_2:Number = 0.01;
		private var color_3:Number = 0xff7f00;
		private var center:Number;
		private var bd:BitmapData;
		private var ct:ColorTransform;
		public function DoublePendulum()
		{
			this.center = 230;
			this.line_ratio = center /  (this.length_1+this.length_2);

bd = new BitmapData (465, 465, true, 0); addChild (new Bitmap (bd));
			ct = new ColorTransform; ct.color = color_3;
			ct.alphaMultiplier = 1 - 1e-3;

circle = new Sprite; circle.graphics.beginFill (0xffffff);
			circle.graphics.drawCircle (0, 0, radius);

var sim:QuickBox2D = new QuickBox2D(this, { debug:false } );
			var circleA:QuickObject = sim.addCircle({x:465/2/30, y:465/2/30,
				radius:6/30, density:0});
			var circleB:QuickObject = sim.addCircle({x:465/2/30, y:(465/2 + this.length_1*line_ratio)/30,
				radius:6/30, density:mass_1});
			circleObject = sim.addCircle({x:465/2/30, y:(465/2 + (this.length_1 + this.length_2)*line_ratio)/30,
				radius:6/30, density:mass_2});

sim.addJoint({type:"distance", a:circleA.body, b:circleB.body});
			sim.addJoint({type:"distance", a:circleB.body, b:circleObject.body});

sim.start();
			sim.mouseDrag();

addEventListener (Event.ENTER_FRAME, ReDraw);
		}
		private function ReDraw(e:Event=null):void
		{
			if (circleCoords.length == 4) circleCoords.shift ();
			while (circleCoords.length != 4) circleCoords.push (new Point (circleObject.x*30, circleObject.y*30));
			var m:Matrix = new Matrix, n:Number = 40 / radius;
			for (var i:int = 1; i < n + 1; i++) {
				var p:Point = spline (circleCoords [0], circleCoords [1], circleCoords [2], circleCoords [3], i / n);
				m.tx = p.x; m.ty = p.y;
				bd.draw (circle, m);
			}
			bd.colorTransform (bd.rect, ct);
		}
        /* 
        * Calculates 2D cubic Catmull-Rom spline.
        * @see http://www.mvps.org/directx/articles/catmull/ 
        */ 
        private function spline (p0:Point, p1:Point, p2:Point, p3:Point, t:Number):Point {
            return new Point (
				0.5 * ((          2*p1.x) +
					t * (( -p0.x           +p2.x) +
					t * ((2*p0.x -5*p1.x +4*p2.x -p3.x) +
					t * (  -p0.x +3*p1.x -3*p2.x +p3.x)))),
				0.5 * ((          2*p1.y) +
					t * (( -p0.y           +p2.y) +
					t * ((2*p0.y -5*p1.y +4*p2.y -p3.y) +
					t * (  -p0.y +3*p1.y -3*p2.y +p3.y))))
			);
        }
	}
}

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