说明：  入门级2D绘图CAD程序，包括画线、画圆、画三角形、画矩形，以及拾取、平移、旋转、镜像等功能，同时配备详细的文档实现说明（为《工程计算机图形学》一书的一章节）
(entry-level 2D CAD drawing procedures, including line drawing, Circle, Triangle painting, drawing rectangles, and pick up, translation, rotation, Mirror, and so on with detailed documentation to achieve ( "Computer Graphics," a book of a chapter))