function Rope()
{    
}

Rope.prototype = 
{
    onLoad: function (control, userContext, rootElement)
    {        
        // initialize timer and control
        this.control = control;
        this.timer = rootElement.findName('timer');
        this.timer.addEventListener("completed", Silverlight.createDelegate(this, this.onTick));
                      
        // initialize particles
        this.particles = new Array();
        var offset = this.control.width / 2;
        for( var i = 0; i < 12; i++)
        {
            this.particles[i] = new Particle(control, rootElement, i * 32 + offset, 2);
            if(i == 0)
            {
                // first particle is constained to its starting position
                var startElement  =
                {
                    left : function() { return  offset; },                    
                    top  : function() { return 2; }
                }
                this.particles[i].constraints.push(new Constraint(startElement, 4));
            }
            else
            {   // all other particles constained to the previous particle
                this.particles[i].constraints.push(new Constraint(this.particles[i-1], 30));
            }
            
        }                 
        
        // initialize forces and time (its all relative)
        this.gravityVector = new Point(0,0.9);
        this.timeStep = 0.25 // lower values to slow down
        this.canvas = rootElement;                       
        this.wind = false;
        this.windVector = new Point(0,0);
        
        // start the show
        this.timer.begin();
    },
    
    onTick: function(sender, eventArgs)
    {
        // the main loop - verlet algorithm
        // 
        this.accumulateForces();
        this.verlet();
        this.satisfyConstraints();
        this.updateAll();           
        this.timer.begin();
    },
    
    toggleWind: function()
    {
        this.wind = !this.wind
        // add a little horizontal disturbance...
        if(this.wind)
        {
            this.windVector.x = 1.2; // = Math.random();
            this.windVector.y = 0;
        }
    },
 
    accumulateForces: function()
    {
        for( var i = 0; i < this.particles.length; i++)
        {
            this.particles[i].forcePoint.init();                
            this.particles[i].forcePoint.add(this.gravityVector);
            if(this.wind)
            {
                this.particles[i].forcePoint.add(this.windVector);
            }
        }
    },
    
    verlet: function()
    {
        for( var i = 0; i < this.particles.length; i++)
        {            
            this.particles[i].verlet(this.timeStep);            
        }
    },
    
    satisfyConstraints: function()
    {
        // hack: assume all particles of same size
        var maxy = this.control.height - this.particles[0].height;
        var maxx = this.control.width - this.particles[0].width;
        
        // one of the keys to verlet is picking the right number 
        // of iterations for the scene. not sure what works best
        // for this, but < 15 seems pretty unstable...
        for( var iterations = 0; iterations < 17; iterations++)
        {
            for( var i = 0; i < this.particles.length; i++)
            {                                        
                this.particles[i].satisfyConstraints();                                
                this.particles[i].currentPoint.min(0,0);    
                this.particles[i].currentPoint.max(maxx, maxy);
            }        
        }
    },
    
    updateAll: function()
    {
       for( var i = 0; i < this.particles.length; i++)
       {            
            this.particles[i].update();
       }
    }
}