想利用VB编程实现屏幕变暗的效果（像关闭Win95时的效果），只要按下面的步骤来做：
    1.     在Form1中加入两个CommandButton和一个PictureBox.
    
    2.     在Form1的代码窗口中添加以下代码：
    Private Type RECT
    Left As Long
    Top As Long
    Right As Long
    Bottom As Long
    End Type
    
    Private Declare Function GetDC Lib "user32" (ByVal hwnd As Long) As Long
    Private Declare Function ReleaseDC Lib "user32" (ByVal hwnd As Long, ByVal hdc As Long) As Long
    Private Declare Function CreatePatternBrush Lib "gdi32" (ByVal hBitmap As Long) As Long
    Private Declare Function PatBlt Lib "gdi32" (ByVal hdc As Long, ByVal x As Long, ByVal y As Long, ByVal nWidth As Long, ByVal nHeight As Long, ByVal dwRop As Long) As Long
    Private Declare Function DeleteObject Lib "gdi32" (ByVal hObject As Long) As Long
    Private Declare Function CreateBitmap Lib "gdi32" (ByVal nWidth As Long, ByVal nHeight As Long, ByVal nPlanes As Long, ByVal nBitCount As Long, lpBits As Any) As Long
    Private Declare Function SelectObject Lib "gdi32" (ByVal hdc As Long, ByVal hObject As Long) As Long
    Private Declare Function InvalidateRect Lib "user32" (ByVal hwnd As Long, ByVal lpRect As Long, ByVal bErase As Long) As Long
    Private bybits(1 To 16) As Byte
    Private hBitmap As Long, hBrush As Long
    Private hDesktopWnd As Long
    
    Private Sub Command1_Click()
    Dim rop As Long, res As Long
    Dim hdc5 As Long, width5 As Long, height5 As Long
    hdc5 = GetDC(0)
    width5 = Screen.Width \ Screen.TwipsPerPixelX
    height5 = Screen.Height \ Screen.TwipsPerPixelY
    rop = &HA000C9
    Call SelectObject(hdc5, hBrush)
    res = PatBlt(hdc5, 0, 0, width5, height5, rop)
    Call DeleteObject(hBrush)
    res = ReleaseDC(0, hdc5)
    End Sub
    
    Private Sub Command2_Click()
    Dim aa As Long
    aa = InvalidateRect(0, 0, 1)
    End Sub
    Private Sub Form_Load()
    Dim ary
    Dim i As Long
    ary = Array(&H55, &H0, &HAA, &H0, _
    &H55, &H0, &HAA, &H0, _
    &H55, &H0, &HAA, &H0, _
    &H55, &H0, &HAA, &H0)
    For i = 1 To 16
    bybits(i) = ary(i - 1)
    Next i
    hBitmap = CreateBitmap(8, 8, 1, 1, bybits(1))
    hBrush = CreatePatternBrush(hBitmap)
    Picture1.ForeColor = RGB(0, 0, 0)
    Picture1.BackColor = RGB(255, 255, 255)
    Picture1.ScaleMode = 3
    End Sub
    
    运行程序，按Command1就可以使屏幕暗下来，按Command2恢复。