下面程序是由鼠标事件在窗体上画图，如果按下鼠标将可以画图，双击窗体可以清除所画图形。

问题：

下面程序是由鼠标事件在窗体上画图，如果按下鼠标将可以画图，双击窗体可以清除所画图形。补充完整下而的程序。
首先在窗体层定义如下变量：
Dim PaintStart As Boolean
编写如下事件过程：
Private Sub Form_Load()
　　DrawWidth=2
　　ForeColor=vbGreen
End Sub
Private Sub Form_MouseDown(Button As Integer，Shift As Integer,_X As Single，Y As Single)
　　PaintStart=True
End Sub
Private Sub Form_MouseMove(Button As Integer，Shift As Integer,_x As Single，Y As Single)
　　If PaintStart Then
　　　　PSet(X,Y)
　　End If
End Sub
Private Sub Form_MouseUp(Button As Integer，Shift As Integer,_X As Single，Y As Single)
　______
End Sub
Private Sub Form-DblClick()
　　Cls
End Sub