1．建立一个新项目，将其命名为DEMO3.vbp。
2．在Form1窗体的声明中加入以下代码：
Private Declare Function SystemParametersInfo Lib "user32" Alias "SystemParametersInfoA" (ByVal uAction As Long, ByVal uParam As Long, ByRef lpvParam As Any, ByVal fuWinIni As Long) As Long
Const SPI_SCREENSAVERRUNNING = 97
3． 在Form1窗口的Command1_Click中加入以下代码：
Private Sub Command1_Click()
Dim r As Integer
Dim p As Boolean
If Command1.Caption = "屏蔽" Then
r = SystemParametersInfo(SPI_SCREENSAVERRUNNING, True, p, 0)
Command1.Caption = "有效"
Else
r = SystemParametersInfo(SPI_SCREENSAVERRUNNING, False, p, 0)
Command1.Caption = "屏蔽"
End If
End Sub
4． 在Form1窗体的Form_Unload中加入以下代码：
Form1_Unload()
Dim r As Integer
Dim p As Boolean
r = SystemParametersInfo(SPI_SCREENSAVERRUNNING, False, p, 0)
运行效果如下图：
2） 示例二：抓屏演示
本示例程序将演示如何拷贝屏幕图象。
实现步骤：
1． 建立一个新项目，将其命名为Demo4.vbp。
2． 增加模块Demo4.bas，在Demo4.bas中加入如下代码：
Public Declare Function GetDC Lib "user32" (ByVal hwnd As Long) As Long
Public Declare Function StretchBlt Lib "gdi32" (ByVal hdc As Long, ByVal x As Long, ByVal y As Long, ByVal nWidth As Long, ByVal nHeight As Long, ByVal hSrcDC As Long, ByVal xSrc As Long, ByVal ySrc As Long, ByVal nSrcWidth As Long, ByVal nSrcHeight As Long, ByVal dwRop As Long) As Long
Public Const SRCCOPY = &HCC0020
3. 在窗体Form1的Command1_Click处理程序中加入以下代码：
Private Sub Command1_Click()
Dim i As Long
Dim wScreen As Long
Dim hscreen As Long
Dim w As Long
Dim h As Long
Picture1.Cls
wScreen = Screen.Width \ Screen.TwipsPERPixelX
hscreen = Screen.Height \ Screen.TwipsPerPixelY
w = Picture1.ScaleWidth
h = Picture1.ScaleHeight
hdcScreen = GetDC(0)
i = StretchBlt(Picture1.hdc, 0, 0, w, h, hdcScreen, 0, 0, wScreen,
hscreen, vbSrcCopy)
Picture1.Refresh
End Sub
运行效果如下图：
3．多媒体编程：
1） 示例一：百叶窗效果
实现步骤：
1．建立一个新项目，将其命名为Demo5.vbp。
2．增加模块Demo5.bas，在Demo5.bas中加入如下代码：
Public Const SRCCOPY = &HCC0020
Public Declare Function BitBlt Lib "gdi32" (ByVal hDestDC As Long, ByVal x As Long, ByVal y As Long, ByVal nWidth As Long, ByVal nHeight As Long, ByVal hSrcDC As Long, ByVal xSrc As Long, ByVal ySrc As Long, ByVal dwRop As Long) As Long
3．在窗体的声明部分加入代码：
Dim h, w As Integer
4．在窗体的Form_Load处理程序中加入代码：
Private Sub Form_Load()
Picture1.Move 0, 0
Picture2.Move 0, 0
h = Picture1.ScaleHeight
w = Picture1.ScaleWidth
Picture2.Width = Picture1.Width
Picture2.Height = Picture1.Height
End Sub
5．在窗体的Command1_Click处理代码中：
Private Sub Command1_Click()
Dim i, j, g As Integer
Picture2.Cls
For i = 0 To 50
For j = i To w Step 50
BitBlt Picture2.hDC, j, 0, 1, h, Picture1.hDC, j, 0, SRCCOPY
For g = 0 To 500
Next g
Next j
Next i
End Sub
6．在窗体的Command2_Click的处理程序中：
Private Sub Command2_Click()
Dim i, j, g As Integer
Picture2.Cls
For i = 0 To 50
For j = i To w Step 50
BitBlt Picture2.hDC, 0, j, w, 1, Picture1.hDC, 0, j, SRCCOPY
For g = 0 To 500
Next g
Next j
Next i
End Sub
7．在窗体的Picture1_Resize的处理程序中加入代码：
Private Sub Picture1_Resize()
Picture2.Width = Picture1.Width
Picture2.Height = Picture1.Height
End Sub
2）示例二：播放背景音乐
实现步骤：
1．建立一个新项目，将其命名为Demo6.vbp。
2．增加模块Demo6.bas，在Demo6.bas中加入如下代码：
Public Declare Function mciSendString Lib "winmm.dll" Alias "mciSendStringA" (ByVal lpstrCommand As String, ByVal lpstrReturnString As String, ByVal
uReturnLength As Long, ByVal hwndCallback As Long) As Long
3．在窗体的Form_load的处理程序中加入如下代码：
Private Sub Form_Load()
Dim back
back = mciSendString&("OPEN " App.Path "\TEST.MID" " TYPE
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