在图形编辑应用中常会用到橡皮筋线，如选择图形的某个区域等，这里用Qt来实现一个简单的橡皮筋线。-Frequently used in graphics editing application rubber band line, such as choosing an area such as graphics, where the use of Qt to implement a simple rubber band line.

使用跨平台专业图形库Qt进行2D图形开发。使用双缓冲区进行优化。-Using the cross-platform Qt graphics library specializing in 2D graphics development. Optimize the use of double buffering.