code: function update(dt) {
           // move things forward independent of the current frame rate
           var skew = dt * this._deltaInv; // Decrease particle life
  
           this.life = this.life > dt ? this.life - dt : 0; // Calculate the particle Age Ratio
  
           var ageRatio = this.life / this.startLife; // Resize the particle as particle Age Ratio
  
           var scale = this.startScale;
  
           if (this.startScale > this.endScale) {
             scale *= ageRatio;
             scale = scale < this.endScale ? this.endScale : scale;
           } else if (this.startScale < this.endScale) {
             scale /= ageRatio;
             scale = scale > this.endScale ? this.endScale : scale;
           } // Set the particle opacity as Age Ratio
  
  
           this.alpha = ageRatio; // Adjust the particle velocity
  
           this.vel.x += this.wind * skew;
           this.vel.y += this.gravity * skew; // If necessary update the rotation of particle in accordance the particle trajectory
  
           var angle = this.followTrajectory ? Math.atan2(this.vel.y, this.vel.x) : this.angle;
           this.pos.x += this.vel.x * skew;
           this.pos.y += this.vel.y * skew; // Update particle transform
  
           this.currentTransform.setTransform(scale, 0, 0, 0, scale, 0, this.pos.x, this.pos.y, 1).rotate(angle); // Return true if the particle is not dead yet
  
           return (this.inViewport || !this.onlyInViewport) && this.life > 0;
         }
docs: Update the Particle <br>
  This is automatically called by the game manager {@link me.game}
  @name update
  @memberOf me.Particle
  @function
  @ignore
  @param {Number} dt time since the last update in milliseconds