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  • vb教程之利用VB捕捉并保存屏幕图象

  • 2017-06-16 20:39 来源:未知
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

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

注释: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."
  注释: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

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

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

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

  注释: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)

  注释:获得屏幕属性
  RasterCapsScrn = GetDeviceCaps(hDCSrc, RASTERCAPS)
  HasPaletteScrn = RasterCapsScrn And RC_PALETTE
  PaletteSizeScrn = GetDeviceCaps(hDCSrc, SIZEPALETTE)

  注释:如果屏幕对象有调色板则获得屏幕调色板
  If HasPaletteScrn And (PaletteSizeScrn = 256) Then
    注释: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)
    注释: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

  注释: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

  注释:释放资源
  r = DeleteDC(hDCMemory)
  r = ReleaseDC(hWndSrc, hDCSrc)

  Set CaptureWindow = CreateBitmapPicture(hBmp, hPal)
End Function
注释:capturescreen函数捕捉整个屏幕图象
Public Function CaptureScreen() As Picture
  Dim hWndScreen As Long

  注释: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。有兴趣的读者可以到我的主页http://www.nease.net/~blackcat上下载源程序。

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