r canvas = document.getElementById('canvas');

          // As a default initial behavior, pop up an alert when webgl context is lost. To make your
          // application robust, you may want to override this behavior before shipping!
          // See http://www.khronos.org/registry/webgl/specs/latest/1.0/#5.15.2
          canvas.addEventListener("webglcontextlost", (e) => { alert('WebGL context lost. You will need to reload the page.'); e.preventDefault(); }, false);

          return canvas;
        })(