code: function() {
          var pixelDensityRatio = $.pixelDensityRatio;
          var viewportSize = this.viewport.getContainerSize();
          return {
              // canvas width and height are integers
              x: Math.round(viewportSize.x * pixelDensityRatio),
              y: Math.round(viewportSize.y * pixelDensityRatio)
          };
      }
docs: private