请教一个vb的line问题

Question

Dim x1, y1, x2, y2 As Single
Dim drawing As Boolean
Private Sub form_mousedown(Button As Integer, Shift As Integer, X As Single, Y As Single)
If Not drawing Then
x1 = X: y1 = Y
x2 = X: y2 = Y
drawing = True
End If
End Sub
Private Sub Form_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single)
If drawing Then
DrawStyle = 2
DrawMode = vbInvert
Line (x1, y1)-(x2, y2), , B
Line (x1, y1)-(X, Y), , B
x2 = X: y2 = Y
End If
End Sub
Private Sub Form_MouseUp(Button As Integer, Shift As Integer, X As Single, Y As Single)
If drawing Then
DrawStyle = 0
DrawMode = vbBlackness
drawing = False
Line (x1, y1)-(X, Y), , B
End If
End Sub
为什么把Line (x1, y1)-(x2, y2), , B
Line (x1, y1)-(X, Y), , B 其中一个去掉后移动鼠标就一直画矩形？？
有点明白了
但是把line (x1,y1)-(X,Y),B去掉的话也会一直画矩形
这是什么原因啊？

Answer 1

同样的道理的！！因为
x1 = X: y1 = Y
x2 = X: y2 = Y

这个赋值，你看一下就知道了

呵呵，因为MouseMove过程是在鼠标不段移动中执行的
Line (x1, y1)-(x2, y2), , B
这句的意思是起始点-起始点，那么就是什么也没有，那么在鼠标移动的时候，是不会有任何线条的
而如果你去掉了的话，那你每移动一下，都会执行Line (x1, y1)-(X, Y), , B一次，（至于这句的意思，就是起始点-当前点，比如起始点为100，当前点为50，那么中间的那段50就会一线条连接起来。。。可能说的比较含糊，你理解一下就行了！！）所以线条再不段的画，就变的乱七八糟了