几个窗口操作

1、dev_set_window — Activate a graphics window.  设置活动窗口

2、dev_open_window — Open a new graphics window. 打开活动窗口

3、dev_clear_window — Clear the contents of the active graphics window. 清除活动窗口的内容

4、dev_display — Displays image objects in the current graphics window. 在当前活动窗口显示对象