destroy() {
        //force unloading of current canvas (1x1 will be gc later, trick not necessarily needed)
        this.canvas.width  = 1;
        this.canvas.height = 1;
        this.sketchCanvas = null;
        this.sketchContext = null;
        this.container.removeChild(this.canvas);
    }
Destroy the drawer (unload current loaded tiles)