利用VB捕捉并保存屏幕图像

利用VB捕捉并保存屏幕图像 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 　　Dim hBmp As Long 　　Dim hBmpPrev As Long 　　Dim r As Long 　　Dim hDCSrc As Long 　　Dim hPal As Long 　　Dim hPalPrev As Long 　　Dim RasterCapsScrn As Long 　　Dim HasPaletteScrn As Long 　　Dim PaletteSizeScrn As Long 　　Dim LogPal As LOGPALETTE 　　If Client Then 　　　　hDCSrc = GetDC(hWndSrc) 　　Else 　　　　hDCSrc = GetWindowDC(hWndSrc) 　　End If 　　hDCMemory = CreateCompatibleDC(hDCSrc) 　　hBmp = CreateCompatibleBitmap(hDCSrc, WidthSrc, HeightSrc) 　　hBmpPrev = SelectObject(hDCMemory, hBmp) 　　'获得屏幕属性 　　RasterCapsScrn = GetDeviceCaps(hDCSrc, RASTERCAPS) 　　HasPaletteScrn = RasterCapsScrn And RC_PALETTE 　　PaletteSizeScrn = GetDeviceCaps(hDCSrc, SIZEPALETTE) 　　'如果屏幕对象有调色板则获得屏幕调色板 　　If HasPaletteScrn And (PaletteSizeScrn = 256) Then 　　　　'建立屏幕调色板的拷贝 　　　　LogPal.palVersion = &H300 　　　　LogPal.palNumEntries = 256 　　　　r = GetSystemPaletteEntries(hDCSrc, 0, 256, LogPal.palPalEntry(0)) 　　　　hPal = CreatePalette(LogPal) 　　　　'将新建立的调色板选如建立的内存绘图句柄中 　　　　hPalPrev = SelectPalette(hDCMemory, hPal, 0) 　　　　r = RealizePalette(hDCMemory) 　　End If 　　'拷贝图象 　　r = BitBlt(hDCMemory, 0, 0, WidthSrc, HeightSrc, hDCSrc, LeftSrc, TopSrc, vbSrcCopy) 　　hBmp = SelectObject(hDCMemory, hBmpPrev) 　　If HasPaletteScrn And (PaletteSizeScrn = 256) Then 　　　　hPal = SelectPalette(hDCMemory, hPalPrev, 0) 　　End If 　　'释放资源 　　r = DeleteDC(hDCMemory) 　　r = ReleaseDC(hWndSrc, hDCSrc) 　　Set CaptureWindow = CreateBitmapPicture(hBmp, hPal) End Function 'capturescreen函数捕捉整个屏幕图象 Public Function CaptureScreen() As Picture 　　Dim hWndScreen As Long 　　'获得桌面的窗口句柄 　　hWndScreen = GetDesktopWindow() 　　Set CaptureScreen = CaptureWindow(hWndScreen, False, 0, 0, Screen.Width _ 　　　　\ Screen.TwipsPerPixelX, Screen.Height \ Screen.TwipsPerPixelY) End Function Public Function CaptureActiveWindow() As Picture 　　Dim hWndActive As Long 　　Dim r As Long 　　Dim RectActive As RECT 　　 　　hWndActive = GetForegroundWindow() 　　r = GetWindowRect(hWndActive, RectActive) 　　Set CaptureActiveWindow = CaptureWindow(hWndActive, False, 0, 0, _ 　　　　RectActive.Right - RectActive.Left, RectActive.Bottom - RectActive.Top) End Function Public Sub PrintPictureToFitPage(Prn As Printer, Pic As Picture) 　　Const vbHiMetric As Integer = 8 　　Dim PicRatio As Double 　　Dim PrnWidth As Double 　　Dim PrnHeight As Double 　　Dim PrnRatio As Double 　　Dim PrnPicWidth As Double 　　Dim PrnPicHeight As Double 　　 　　If Pic.Height >= Pic.Width Then 　　　　Prn.Orientation = vbPRORPortrait 　　Else 　　　　Prn.Orientation = vbPRORLandscape 　　End If 　　 　　PicRatio = Pic.Width / Pic.Height 　　 　　PrnWidth = Prn.ScaleX(Prn.ScaleWidth, Prn.ScaleMode, vbHiMetric) 　　PrnHeight = Prn.ScaleY(Prn.ScaleHeight, Prn.ScaleMode, vbHiMetric) 　　PrnRatio = PrnWidth / PrnHeight 　　 　　If PicRatio >= PrnRatio Then 　　　　PrnPicWidth = Prn.ScaleX(PrnWidth, vbHiMetric, Prn.ScaleMode) 　　　　PrnPicHeight = Prn.ScaleY(PrnWidth / PicRatio, vbHiMetric, Prn.ScaleMode) 　　Else 　　　　PrnPicHeight = Prn.ScaleY(PrnHeight, vbHiMetric, Prn.ScaleMode) 　　　　PrnPicWidth = Prn.ScaleX(PrnHeight * PicRatio, vbHiMetric, Prn.ScaleMode) 　　End If 　　 　　Prn.PaintPicture Pic, 0, 0, PrnPicWidth, PrnPicHeight End Sub Private Sub Command4_Click() 　　CommonDialog1.DefaultExt = ".BMP" 　　CommonDialog1.Filter = "Bitmap Image (*.bmp)|*.bmp" 　　CommonDialog1.ShowSave 　　If CommonDialog1.FileName <> "" Then 　　　　SavePicture Picture1.Picture, CommonDialog1.FileName 　　End If End Sub Private Sub Command5_Click() 　　PrintPictureToFitPage Printer, Picture1.Picture 　　Printer.EndDoc End Sub Private Sub Form_Load() 　　Command1.Caption = "捕捉整个屏幕" 　　Command2.Caption = "两秒钟后捕捉活动窗口" 　　Command3.Caption = "清除图象" 　　Command4.Caption = "保存图象" 　　Command5.Caption = "打印图象" End Sub 　　运行程序，点击command1或者Command2就可以捕捉成个屏幕或者窗口到Picture1中，然后点击Command4或者Command5就可以保存或打印图象。 　　上面的程序中最重要的是CaptureWindow函数以及CreateBitmapPicture函数，CaptureWindow函数建立与要捕捉的窗口的绘图设备（Device Context）句柄相兼容的绘图设备（Device Context）句柄，然后建立相应的调色板，最后将绘图设备（Device Context）中的图象拷贝到一个hBitmap对象句柄中。CreateBitmapPicture函数则根据传递过来的hBitmap对象句柄和调色板句柄建立一个Picture对象。在将这个对象赋予PictureBox的Picture属性，然后就可以使用SavePicture函数来保存图象了。 　　OleCreatePictureIndirect函数支持的不仅有BMP图象，同时也支持Ico图标，所以利用该函数和ExtractIcon函数也可以提取并保存Windows文件中的图标。