code: public void setVelocity(float dirx, float diry, float speed) {
  		this.velx = dirx * speed;
  		this.vely = diry * speed;
  	}
docs: Set the velocity of the particle
  
  @param dirx
  The x component of the new velocity
  @param diry
  The y component of the new velocity
  @param speed
  The speed in the given direction