先来介绍几个画矩形的函数：
DrawFocusRect()：画一个焦点矩形；
Rectangle()：用当前选定的画笔描绘矩形，并用当前选定的画刷填充；
DrawEdge()：用指定的样式描绘一个矩形的边框；
RoundRect()：用当前选定的画笔画一个圆角矩形，并用当前选定的画刷填充。
今天用的是DrawFocusRect()函数，函数原型如下
Private Declare Function DrawFocusRect Lib "user32" Alias "DrawFocusRect"
(
ByVal hDC As Long,
lpRect As RECT
) As Long
hDc: Long //设备的句柄
lpRect: RECT结构，绘制矩形的坐标。
返回值为0，表示失败，不为0，则成功
示例：绘制矩形
Option Explicit Private Type RECT Left As Long Top As Long Right As Long Bottom As Long End Type ‘类型声明 Private Declare Function DrawFocusRect Lib "user32" (ByVal hdc As Long, lpRect As RECT) As Long Dim Flag As Boolean Dim Start As Boolean Dim Pos As RECT Dim tempPos As RECT Private Sub Command1_Click() Flag = True ‘开始绘图 End Sub Private Sub Command2_Click() Flag = False Picture1.Cls ‘结束绘图 End Sub Private Sub Form_Load() Flag = False Start = False ‘禁止绘图 Me.ScaleMode = 3 Me.Picture1.ScaleMode = 3 ‘设置对象坐标的度量单位为像素 End Sub Private Sub Picture1_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) If Flag Then Start = True Pos.Left = X Pos.Top = Y Else Start = False End If End Sub Private Sub Picture1_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single) If Start Then DrawFocusRect Me.Picture1.hdc, Pos ‘擦除原有焦点矩形 Pos.Right = X Pos.Bottom = Y DrawFocusRect Me.Picture1.hdc, Pos ‘绘制新的焦点矩形 End If End Sub Private Sub Picture1_MouseUp(Button As Integer, Shift As Integer, X As Single, Y As Single) If Start Then DrawFocusRect Me.Picture1.hdc, Pos ‘擦除原有焦点矩形 Pos.Right = X Pos.Bottom = Y DrawFocusRect Me.Picture1.hdc, Pos ‘绘制新的焦点矩形 Start = False End If End Sub