利用LINE命令画矩形的问题。

[lufeng112]

本人是一个初学者，看到书中有如下代码，是利用line命令画矩形的。
Dim xp1 As Single, yp1 As Single
Dim xp2 As Single, yp2 As Single
Dim drawing As Boolean 'boolean表示布尔型变量（只有True（真）和False（假）两种值）

Private Sub Form_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single)
If Not drawing Then
xp1 = X: yp1 = Y
xp2 = X: yp2 = 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 (xp1, yp1)-(xp2, yp2), , B
Line (xp1, yp1)-(X, Y), , B
xp2 = X: yp2 = Y
End If
End Sub

Private Sub Form_MouseUp(Button As Integer, Shift As Integer, X As Single, Y As Single)
If drawing Then
DrawMode = vbBlackness
DrawStyle = 0
Line (xp1, yp1)-(X, Y), , B
drawing = False
End If

End Sub

我想问一下，各位高手。 一、为什么要添加DrawMode = vbInvert
二、Line (xp1, yp1)-(xp2, yp2), , B
Line (xp1, yp1)-(X, Y), , B
为什么写两次矩形框的代码？
小弟实在搞不懂，望各位高手不惜赐教！谢谢

[lufeng112]

请大家一定帮帮我啊，大家都来说说。在这里小弟先谢谢大家了

[threenewbee]

DrawMode = vbInvert '用反色笔画，便于擦除

Line每次只能画一条线，要画矩形需要画出4条线。

[lufeng112]

line命令后面加了B的是表示利用左上角和右下角的坐标来画矩形。
caozhy还是谢谢你，关于你最后的“Line每次只能画一条线，要画矩形需要画出4条线。”是否有点牵强了？？

[Tiger_Zhao]

DrawMode = vbInvert 表示每画一次就是将图形上的每个像素进行反色，两次反色正好抵消。所以在这个模式下相同的图形画一次为显示图形，再画一次等于擦除（取消）图形。

Line (xp1, yp1)-(xp2, yp2), , B '将上次的坐标图形画第二次，等于擦除Line (xp1, yp1)-(X, Y), , B '用新的坐标画第一次
xp2 = X: yp2 = Y '记录新坐标，用于下次擦除

[熊孩子开学喽]

既然发在水版,只好灌水回复啦.

[贝隆]

画矩形？为什么不用 Rectangle？

Private Declare Function Rectangle Lib "gdi32" (ByVal hdc As Long, ByVal X1 As Long, ByVal Y1 As Long, ByVal X2 As Long, ByVal Y2 As Long) As Long

[lufeng112]

Tiger_Zhao
谢谢你了，嗯搞懂了。谢谢，当然也感谢回复我帖子的人。

[lufeng112]

ByVal是传递值的意思吗，如果是字符，是否就是传递字符的意思？贝隆哥，求解

[几罗星人]

[Quote=引用 6 楼 veron_04 的回复:]
画矩形？为什么不用 Rectangle？

Private Declare Function Rectangle Lib "gdi32" (ByVal hdc As Long, ByVal X1 As Long, ByVal Y1 As Long, ByVal X2 As Long, ByVal Y2 As Long) As Long
[/Quote]
同意此条答复。