利用VB捕捉并保存屏幕图象

2008-02-23 06:52:36来源:互联网 阅读 ()

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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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