code: function (width, height, canvas) {
              // XXX This should probably be a configurable option
              var match;
              match = this._pxregex.exec(height);
              if (match) {
                  this.pixelHeight = match[1];
              } else {
                  this.pixelHeight = $(canvas).height();
              }
              match = this._pxregex.exec(width);
              if (match) {
                  this.pixelWidth = match[1];
              } else {
                  this.pixelWidth = $(canvas).width();
              }
          }
docs: Calculate the pixel dimensions of the canvas