利用VB捕捉并保存屏幕图象

大家知道在VB下利用API函数Bitblt可以将屏幕或者窗口上的图象拷贝到VB中的PictureBox对象中,但是如果简单的利用PictureBox的SavePicture函数来保存图象，会发现什么也保存不了。这篇文章就是介绍如何捕获并利用Windows下的OLE API函数保存图象。
　　 首先来看源程序，首先建立一个新的工程文件，然后在Form1中加入5个CommandButton对象和一个PictureBox对象，然后在Form1中加入以下代码：
Option Explicit
Option Base 0

Private Type PALETTEENTRY
　 peRed As Byte
　 peGreen As Byte
　 peBlue As Byte
　 peFlags As Byte
End Type

Private Type LOGPALETTE
　 palVersion As Integer
　 palNumEntries As Integer
　 palPalEntry(255) As PALETTEENTRY
End Type

Private Type GUID
　 Data1 As Long
　 Data2 As Integer
　 Data3 As Integer
　 Data4(7) As Byte
End Type

Private Const RASTERCAPS As Long = 38
Private Const RC_PALETTE As Long = &H100
Private Const SIZEPALETTE As Long = 104

Private Type RECT
　 Left As Long
　 Top As Long
　 Right As Long
　 Bottom As Long
End Type

Private Declare Function CreateCompatibleDC Lib "GDI32" (ByVal hDC As Long) As Long
Private Declare Function CreateCompatibleBitmap Lib "GDI32" (ByVal hDC As Long, _
　　　　 ByVal nWidth As Long, ByVal nHeight As Long) As Long
Private Declare Function GetDeviceCaps Lib "GDI32" (ByVal hDC As Long, ByVal _
　　　　 iCapabilitiy As Long) As Long
Private Declare Function GetSystemPaletteEntries Lib "GDI32" (ByVal hDC As Long, _
　　　　 ByVal wStartIndex As Long, ByVal wNumEntries As Long, lpPaletteEntries _
　　　　 As PALETTEENTRY) As Long
Private Declare Function CreatePalette Lib "GDI32" (lpLogPalette As LOGPALETTE) _
　　　　 As Long
Private Declare Function SelectObject Lib "GDI32" (ByVal hDC As Long, ByVal hObject _
　　　　 As Long) As Long
Private Declare Function BitBlt Lib "GDI32" (ByVal hDCDest As Long, ByVal XDest As _
　　　　 Long, ByVal YDest As Long, ByVal nWidth As Long, ByVal nHeight As Long, _
　　　　 ByVal hDCSrc As Long, ByVal XSrc As Long, ByVal YSrc As Long, ByVal dwRop _
　　　　 As Long) As Long
Private Declare Function DeleteDC Lib "GDI32" (ByVal hDC As Long) As Long
Private Declare Function GetForegroundWindow Lib "USER32" () As Long
Private Declare Function SelectPalette Lib "GDI32" (ByVal hDC As Long, ByVal hPalette _
　　　　 As Long, ByVal bForceBackground As Long) As Long
Private Declare Function RealizePalette Lib "GDI32" (ByVal hDC As Long) As Long
Private Declare Function GetWindowDC Lib "USER32" (ByVal hWnd As Long) As Long
Private Declare Function GetDC Lib "USER32" (ByVal hWnd As Long) As Long
Private Declare Function GetWindowRect Lib "USER32" (ByVal hWnd As Long, lpRect As _
　　　　 RECT) As Long
Private Declare Function ReleaseDC Lib "USER32" (ByVal hWnd As Long, ByVal hDC As _
　　　　 Long) As Long
Private Declare Function GetDesktopWindow Lib "USER32" () As Long

Private Type PicBmp
　 Size As Long
　 Type As Long
　 hBmp As Long
　 hPal As Long
　 Reserved As Long
End Type

Private Declare Function OleCreatePictureIndirect Lib "olepro32.dll" (PicDesc As _
　　　　 PicBmp, RefIID As GUID, ByVal fPictureOwnsHandle As Long, IPic As IPicture) As Long

'捕捉整个屏幕
Private Sub Command1_Click()
　 Set Picture1.Picture = CaptureScreen()
End Sub

'在两秒钟后捕捉当前的活动窗口
Private Sub Command2_Click()
　　 MsgBox "当你关闭这个对话框两秒钟之后程序会捕捉处于活动状态的窗口."
　　 '等待两秒钟
　　 Dim EndTime As Date
　　 EndTime = DateAdd("s", 2, Now)
　　 Do Until Now > EndTime
　　　 DoEvents
　　　 Loop
　　 Set Picture1.Picture = CaptureActiveWindow()

　　 Me.SetFocus
End Sub

Private Sub Command3_Click()
　　 Set Picture1.Picture = Nothing
End Sub

Public Function CreateBitmapPicture(ByVal hBmp As Long, ByVal hPal As Long) As Picture
　 Dim r As Long

　 Dim Pic As PicBmp
　 Dim IPic As IPicture
　 Dim IID_IDispatch As GUID

　 '填充IDispatch界面
　 With IID_IDispatch
　　　 .Data1 = &H20400
　　　 .Data4(0) = &HC0
　　　 .Data4(7) = &H46
　 End With

　 '填充Pic
　 With Pic
　　　 .Size = Len(Pic)　　　　　' Pic结构长度
　　　 .Type = vbPicTypeBitmap　 ' 图象类型
　　　 .hBmp = hBmp　　　　　　　' 位图句柄
　　　 .hPal = hPal　　　　　　　' 调色板句柄
　 End With

　 '建立Picture图象
　 r = OleCreatePictureIndirect(Pic, IID_IDispatch, 1, IPic)

　 '返回Picture对象
　 Set CreateBitmapPicture = IPic
End Function

Public Function CaptureWindow(ByVal hWndSrc As Long, ByVal Client As Boolean, ByVal _
　　 LeftSrc As Long, ByVal TopSrc As Long, ByVal WidthSrc As Long, ByVal HeightSrc _
　　 As Long) As Picture

　　 Dim hDCMemory As Long

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