boids.js

// Javascript implementation of Boids
// Requires http://raphaeljs.com/raphael.js
// Ben Dowling - Oct 2008
// www.coderholic.com

// Modified slightly for proceduralgraphics.blogspot.com

var Boid = function(x, y, size, maxVelocity) {
	this.x = x;
	this.y = y;
	this.maxVelocity = maxVelocity;
	this.xVelocity = 1;
	this.yVelocity = -1;
}

Boid.prototype.move = function() {
	this.x += this.xVelocity;
	this.y += this.yVelocity;
}

Boid.prototype.constrain = function(width,height) {
	var border = -100; // negative will allow boids to fly a bit offscreen
	if(this.x <= border || this.x >= width - border) {
		this.x -= this.xVelocity;					
		this.x = Math.max(this.x, border);
		this.x = Math.min(this.x, width - border);
		this.xVelocity = -this.xVelocity;
		this.x += this.xVelocity;
	}
	if(this.y <= border || this.y >= height - border) {
		this.y -= this.yVelocity;
		this.y = Math.max(this.y, border);
		this.y = Math.min(this.y, height - border);
		this.yVelocity = -this.yVelocity;
		this.y += this.yVelocity;
	}
}
	
Boid.prototype.distance = function(boid) {
    var distX = this.x - boid.x;
	var distY = this.y - boid.y;
	return Math.sqrt(distX * distX + distY * distY);
}
	
Boid.prototype.moveAway = function(boids, minDistance) {
	var distanceX = 0;
	var distanceY = 0;
	var numClose = 0;

	for(var i = 0; i < boids.length; i++) {
		var boid = boids[i];
		
		if(boid.x == this.x && boid.y == this.y) continue;
		
		var distance = this.distance(boid)
		if(distance < minDistance) {
			numClose++;
			var xdiff = (this.x - boid.x);
			var ydiff = (this.y - boid.y);

			if(xdiff >= 0) xdiff = Math.sqrt(minDistance) - xdiff;
			else if(xdiff < 0) xdiff = -Math.sqrt(minDistance) - xdiff;

			if(ydiff >= 0) ydiff = Math.sqrt(minDistance) - ydiff;
			else if(ydiff < 0) ydiff = -Math.sqrt(minDistance) - ydiff;

			distanceX += xdiff;
			distanceY += ydiff;
			boid = null; 
		}
	}
	
	if(numClose == 0) return;
	
	this.xVelocity -= distanceX / 5;
	this.yVelocity -= distanceY / 5;
}
	
Boid.prototype.moveCloser = function(boids, distance) {
    if(boids.length < 1) return				

	var avgX = 0;
	var avgY = 0;
	for(var i = 0; i < boids.length; i++) {
		var boid = boids[i];
		if(boid.x == this.x && boid.y == this.y) continue;
		if(this.distance(boid) > distance) continue;
		
		avgX += (this.x - boid.x);
		avgY += (this.y - boid.y);
		boid = null;
	}
		

	avgX /= boids.length;
	avgY /= boids.length;

	distance = Math.sqrt((avgX * avgX) + (avgY * avgY)) * -1.0
	if(distance == 0) return;
	
	this.xVelocity= Math.min(this.xVelocity + (avgX / distance) * 0.15, this.maxVelocity)
	this.yVelocity = Math.min(this.yVelocity + (avgY / distance) * 0.15, this.maxVelocity)
}
	
Boid.prototype.moveWith = function(boids, distance) {
    if(boids.length < 1) return

	// calculate the average velocity of the other boids
	var avgX = 0;
	var avgY = 0;
	for(var i = 0; i < boids.length; i++) {
		var boid = boids[i];
		if(boid.x == this.x && boid.y == this.y) continue;
		if(this.distance(boid) > distance) continue;
		
		avgX += boid.xVelocity;
		avgY += boid.yVelocity;
		boid = null;
	}
	avgX /= boids.length;
	avgY /= boids.length;

	distance = Math.sqrt((avgX * avgX) + (avgY * avgY)) * 1.0
	if(distance == 0) return;

	this.xVelocity= Math.min(this.xVelocity + (avgX / distance) * 0.05, this.maxVelocity)
	this.yVelocity = Math.min(this.yVelocity + (avgY / distance) * 0.05, this.maxVelocity)						
}


Boid.prototype.getHeading = function() {
	return Math.atan2(this.yVelocity, this.xVelocity);
}