1.以鼠标左键的按下为"起点",保持按下状态,移动鼠标,直到放开鼠标键作为"终点",画一条静态直线.
2.在鼠标移动过程中应该从"起点"向鼠标的"当前位置"画一条动态的直线.绘制动态直线的方法是,先删除前一条直线,然后画一条新的直线.在鼠标移动过程中会不断接收到许多WM_MOUSEMOVE消息,其中LOWORD(lParam)和HIWORD(lParam)分别存放鼠标的当前X,Y值.(1. press the left mouse button as the starting point, keep the pressed state, move the mouse until the mouse button is released as the end line, draw a static straight line

2. in the mouse in the process should be from the "starting point" to the "current position" to draw a straight line. The dynamic method of drawing dynamic line is removed first before a straight line, and then draw a new line. In the process of moving the mouse will continue to receive many WM_MOUSEMOVE messages, including LOWORD (lParam) and HIWORD (lParam) at X, respectively. The Y value of the mouse store)