JS1k: The JavaScript code golfing competition

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function Vector(x, y){
    this.x = x;
    this.y = y;

    this.sub = function(other){
        return new Vector(
            this.x - other.x,
            this.y - other.y
        );
    }
    this.isub = function(other){
        this.x -= other.x;
        this.y -= other.y;
    }
    this.iadd = function(other){
        this.x += other.x;
        this.y += other.y;
    }
    this.size = function(){
        return Math.sqrt(this.x*this.x + this.y*this.y);
    }
    this.idiv = function(scalar){
        this.x /= scalar;
        this.y /= scalar;
    }
    this.zero = function(){
        this.x = this.y = 0;
    }
    this.validate = function(){
        if(isNaN(this.x+this.y)){
            this.x = this.y = 0;
        }
    }
}

function Particle(canvas){
    this.acceleration = new Vector(0, 0);
    this.velocity = new Vector(
        Math.random() - 0.5,
        Math.random() - 0.5
    )
    this.position = new Vector(
        Math.random() * canvas.width,
        Math.random() * canvas.height
        
    )

    this.step = function(context){
        this.acceleration.validate();
        this.velocity.iadd(this.acceleration);
       
        speed = this.velocity.size();
        if(speed > 4){
            this.velocity.idiv(speed/4);
            speed = 4;
        }
        this.position.iadd(this.velocity);
        this.acceleration.zero();

        // border bounce
        if(this.position.x < 0){
            this.position.x = 0;
            this.velocity.x /= -2;
        }
        else if(this.position.x > canvas.width){
            this.position.x = canvas.width;
            this.velocity.x /= -2;
        }

        if(this.position.y < 0){
            this.position.y = 0;
            this.velocity.y /= -2;
        }
        else if(this.position.y > canvas.height){
            this.position.y = canvas.height;
            this.velocity.y /= -2;
        }
    
        color = Math.round(speed*128);
        context.fillStyle = 'rgba(' + (color-50) + ',' + (300-color) + ',0,1)';
        context.beginPath();
        context.arc(this.position.x, this.position.y, speed+2, 0, Math.PI*2, false);
        context.fill();
    }
}

gc='globalCompositionOperation';

new (function System(){
    var canvas = document.getElementById('c');
    canvas.width = canvas.height = 300;
    var context = canvas.getContext('2d');
        
    var particles = [];
    for(var i=0; i<30; i++){
        particles.push(new Particle(canvas));
    }
    

    setInterval(function(){
        // fading
        context[gc] = 'source-over';
        context.fillStyle = 'rgba(0,0,0,0.2)';
        context.fillRect(0, 0, canvas.width, canvas.height);

        // dot drawing style
        context[gc] = 'lighter';

        // nbody code acceleration accumulation
        for(var i=0, il=30; i<il; i++){
            var a = particles[i];
            for(var j=i+1; j<30; j++){
                var b = particles[j];
                var vec = a.position.sub(b.position);
                vec.idiv(Math.pow(Math.max(10, vec.size()), 3)/5); // scale the vector to the inverse square distance
                b.acceleration.iadd(vec);
                a.acceleration.isub(vec);
            }
            a.step(context);
        }
    }, 40);
})