实现画线、矩形、椭圆等功能，其中实现了简单的橡皮筋方法。-Achieve drawing lines, rectangles, ellipses and other functions, which implement a simple rubber band method.

MFC 橡皮筋法绘制直线 矩形 圆 多边形 右击后换颜色-MFC rubber band method to draw a straight line rectangle round polygon right-click to change color

RectTracker 橡皮筋拖画矩形，可以直接运行使用，用到自己项目中作少许修改即可-RectTracker rubber band Drag a rectangle, you can run directly, use their own projects to make some modification