拖拽/跟踪一条线-The example of draging and following in drawing a line

LineTracker源码，实现类似CRectTracker的功能。-LineTracker source, CRectTracker to achieve similar functionality.

常用的CRectTracker类在使用翻转时，坐标会发生相应的变化。选择直线是，问题就更加明显。使用KLineTracker类就能解决这个问题。-CRectTracker common classes in the use of flip coordinates will change accordingly. Select the line, the problem is even more pronounced. Use KLineTracker class can solve this p