这是一个小型的CAD程序，支持直线、矩形、椭圆和文字四种图形元素，实现了放置以及选中后删除、选中后改变大小、选中后移动三种功能。(This is a small CAD program, support lines, rectangles, ellipses and text four graphic elements, to achieve the placement, and after the election, delete, select, change the size, selec