实现用Bresenham算法及中点画线法画直线，并且画出网格图，判断对话框中输入的起点终点坐标是否在给定的范围内。若在范围内则画线，在单位像素点打点，直观的看出Bresenham算法及中点画线法的操作原理。-Bresenham algorithm implemented by the dotted line method and draw a straight line, and draw a grid chart to determine the coordinates of the dial