利用VB产生屏幕变暗的效果.
想利用VB编程实现屏幕变暗的效果（向关闭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。