求大神帮帮忙，这代码每个的作用是啊啥var graph = this.ownerCt.ownerCt.mxGraph;
var xmlDoc = mxUtils.createXmlDocument();
var root = xmlDoc.createElement('graph');
xmlDoc.appendChild(root);
var xmlCanvas = new mxXmlCanvas2D(root);
var imgExport = new mxImageExport();
imgExport.drawState(graph.getView().getState(graph.model.root), xmlCanvas);
var bounds = graph.getGraphBounds();
var width = Math.round(bounds.x + bounds.width + 4);
var height = Math.round(bounds.y + bounds.height + 4);