constructor(pos,rect,type){

    this.pos = pos;

    this.rect = rect;

    this.type = type;

    //step 1 define body

    let bd = new box2d.b2BodyDef();

    if(this.type=="dynamic"){//b2_staticBody

      bd.type = box2d.b2BodyType.b2_dynamicBody;

    }else if(this.type=="static"){

      bd.type = box2d.b2BodyType.b2_staticBody; 

    }

    bd.position = scaleToWorld(this.pos.x,this.pos.y);

    //step 2 create body

    this.body = world.CreateBody(bd);

    //step 3 create shape

    let ps = new box2d.b2PolygonShape();

    ps.SetAsBox(scaleToWorld(this.rect/2),scaleToWorld(this.rect/2));

    //step 4 create fixture

    let fd = new box2d.b2FixtureDef();

    fd.density = 19.35;

    fd.friction = 2.3;

    fd.restitution = 0.2;

    //step 5 attach shape to body 

    fd.shape = ps;

    this.body.CreateFixture(fd);

    //some additional stuff

    if(this.type == "dynamic"){

      this.body.SetLinearVelocity(new box2d.b2Vec2(0, 9.807));//gravity

    }

    //this.body.SetAngularVelocity(random(-5, 5));//rotation

  }

  applyForce(){

    let pos = box2d.b2Vec2(0,0); 

    this.body.applyForce(pos,new box2d.b2Vec2(200,0));

  }

  display(){

    let pos = scaleToPixels(this.body.GetPosition());

    let a = this.body.GetAngleRadians();

    noStroke()

    rectMode(CENTER);

    push();

    translate(pos.x,pos.y);

    rotate(a);

    fill("grey");

    rect(0,0,this.rect,this.rect);

    pop();

  }

}