程序实现划线功能，可以保存、重绘；然后判断所画直线间的几何关系：相交、重合、相离，相交的直线交点以绿点显示，重合部分以红色高亮显示-Program realization crossed feature, you can save, redraw then determine the geometrical relationship between painted lines: intersect, overlap, with leave, a straight line intersecti