//BOIDS
//(c) 2010 by Tomasz Lubinski
//www.algorytm.org

var boids = new Array(20);
var r = 50.0;
var degree = 120.0;
var d_min = 20.0;
var weigth_v = 0.1;
var weigth_d = 0.15;
var weigth_min = 0.15;
var weigth_p = 0.1;
var v_max = 4.0;

var width = 600;
var height = 400;

//calculate new speed and direction
function modify_speed_and_direction()
{
  var dist = 0.0;
  var deg = 0.0;
  
	for (i=0; i<boids.length; i++)
	{
		boids[i].alg_mean_vx = boids[i].alg_vx;
    boids[i].alg_mean_vy = boids[i].alg_vy;
    boids[i].alg_mean_d = 0;
    boids[i].alg_num = 1;
    for (j=0; j<boids.length; j++)
		{
			if (j==i) continue;
			dist = Math.sqrt(Math.pow(boids[i].alg_x-boids[j].alg_x,2)+Math.pow(boids[i].alg_y-boids[j].alg_y,2));
			deg = Math.acos(
			   boids[i].alg_vx/Math.sqrt(boids[i].alg_vx*boids[i].alg_vx+boids[i].alg_vy*boids[i].alg_vy) *
			   ((boids[j].alg_x-boids[i].alg_x)/dist) +
			   boids[i].alg_vy/Math.sqrt(boids[i].alg_vx*boids[i].alg_vx+boids[i].alg_vy*boids[i].alg_vy) *
			   ((boids[j].alg_y-boids[i].alg_y)/dist));
			deg = Math.abs((180*deg)/Math.PI);
			if (dist < r && deg < degree)
			{
				boids[i].alg_num++;
				boids[i].alg_mean_vx += boids[j].alg_vx;
				boids[i].alg_mean_vy += boids[j].alg_vy;
				boids[i].alg_mean_d += dist;
			}
		}
	}
	
	for (i=0; i<boids.length; i++)
	{	
		//adjust speed to neighbours speed
		boids[i].alg_vx += (weigth_v*((boids[i].alg_mean_vx/boids[i].alg_num)-boids[i].alg_vx));
    boids[i].alg_vy += (weigth_v*((boids[i].alg_mean_vy/boids[i].alg_num)-boids[i].alg_vy));
    
		//pertubation
		boids[i].alg_vx += (weigth_p*((Math.random()-0.5)*v_max));
		boids[i].alg_vy += (weigth_p*((Math.random()-0.5)*v_max));
		
    if (boids[i].alg_num > 1) boids[i].alg_mean_d /= (boids[i].alg_num-1);
    for (j=0; j<boids.length; j++)
		{
			if (j==i) continue;
			dist = Math.sqrt(Math.pow(boids[i].alg_x-boids[j].alg_x,2)+Math.pow(boids[i].alg_y-boids[j].alg_y,2));
			deg = Math.acos(
			   boids[i].alg_vx/Math.sqrt(boids[i].alg_vx*boids[i].alg_vx+boids[i].alg_vy*boids[i].alg_vy) *
			   ((boids[j].alg_x-boids[i].alg_x)/dist) +
			   boids[i].alg_vy/Math.sqrt(boids[i].alg_vx*boids[i].alg_vx+boids[i].alg_vy*boids[i].alg_vy) *
			   ((boids[j].alg_y-boids[i].alg_y)/dist));
			deg = Math.abs((180*deg)/Math.PI);
			if (dist < r && deg < degree)
			{
      	if (Math.abs(boids[j].alg_x-boids[i].alg_x) > d_min)
        {
           boids[i].alg_vx += (weigth_d/boids[i].alg_num)*(((boids[j].alg_x-boids[i].alg_x)*(dist-boids[i].alg_mean_d))/dist);
           boids[i].alg_vy += (weigth_d/boids[i].alg_num)*(((boids[j].alg_y-boids[i].alg_y)*(dist-boids[i].alg_mean_d))/dist);
        }
        else //neighbours are too close
        {
           boids[i].alg_vx -= (weigth_min/boids[i].alg_num)*((((boids[j].alg_x-boids[i].alg_x)*(d_min))/dist)-(boids[j].alg_x-boids[i].alg_x));
           boids[i].alg_vy -= (weigth_min/boids[i].alg_num)*((((boids[j].alg_y-boids[i].alg_y)*(d_min))/dist)-(boids[j].alg_y-boids[i].alg_y));
			  }
	   	}
    }
    
    //check speed is not too high
    if (Math.sqrt(boids[i].alg_vx*boids[i].alg_vx+boids[i].alg_vy*boids[i].alg_vy)>v_max)
    {
    	boids[i].alg_vx *= 0.75;
			boids[i].alg_vy *= 0.75;
		}
	}
}

//move and displat boids
function move_and_display()
{
  //first modify speed and direction
  modify_speed_and_direction();
  
	for (i=0; i<boids.length; i++)
	{
	   //move boid
	   boids[i].alg_x += boids[i].alg_vx;
	   boids[i].alg_y += boids[i].alg_vy;
	   
	   //check if outside window
	   if (boids[i].alg_x > width) boids[i].alg_x -= width;
	   else if (boids[i].alg_x < 0) boids[i].alg_x += width;
	   if (boids[i].alg_y > height) boids[i].alg_y -= height;
	   else if (boids[i].alg_y < 0) boids[i].alg_y += height;
	   
	   //display new position of boid
	   boids[i].attr({path: "M" + boids[i].alg_x + " " + boids[i].alg_y + "l0 8m0 -1 l-3 -7 l6 0l-3 7"})
	   if (boids[i].alg_vx < 0)
     {
	      boids[i].rotate(90.0 + Math.atan(boids[i].alg_vy/boids[i].alg_vx)*180.0/Math.PI, true);
     }
     else
     {
        boids[i].rotate(-90.0 + Math.atan(boids[i].alg_vy/boids[i].alg_vx)*180.0/Math.PI, true);
     }
	}
	setTimeout("move_and_display()",20);
	
}

//initialize data
function start()
{
	var paper = Raphael("canvas", width, height);
	var background = paper.rect(0, 0, width, height);
	background.attr({fill: "#3490c9"});
	paper.text(width - 70, height - 20, "www.algorytm.org");
	
	
	for (i=0; i<boids.length; i++)
	{
	   boids[i] = paper.path("M0 0l0 8m0 -1 l-3 -7 l6 0l-3 7");
	   boids[i].alg_x = Math.floor(Math.random()*width);
	   boids[i].alg_y = Math.floor(Math.random()*height);
	   boids[i].alg_vx = Math.random()*4.0 - 2.0;
	   boids[i].alg_vy = Math.random()*4.0 - 2.0;
	}
	
	setTimeout("move_and_display()",100); 
}