在客户端客户区绘制的图元可以同步绘制到服务器上的客户区上，支持撤销和恢复，支持插入文本，多线程、文件传输、断点续传双缓冲画图等。-On the client side of the client area map of yuan can synchronize on the client area of the drawing to the server, support undo and restore, support inserting text, multithreading, file