创建透明图片(利用API)

Option Explicit

 

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

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 CreateBitmap Lib "gdi32" _
  (ByVal nWidth As Long, _
   ByVal nHeight As Long, _
   ByVal nPlanes As Long, _
   ByVal nBitCount As Long, _
   lpBits As Any) As Long

Private Declare Function SetBkColor Lib "gdi32" _
   (ByVal hdc As Long, _
    ByVal crColor As Long) As Long

Private Declare Function SelectObject Lib "gdi32" _
  (ByVal hdc As Long, _
   ByVal hObject 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 CreateCompatibleDC Lib "gdi32" _
   (ByVal hdc As Long)As Long

Private Declare Function DeleteDC Lib "gdi32" _
   (ByVal hdc As Long) As Long

Private Declare Function DeleteObject Lib "gdi32" _
   (ByVal hObject As Long) As Long>
  

        
Private Sub Command1_Click()

  Dim rc As RECT

  With rc
   .Left = 0
   .Top = 0
   .Right = Picture1.ScaleWidth
   .Bottom = Picture1.ScaleHeight
  End With

  TransparentBlt Form1.hdc, Form1.hdc, Picture1.hdc, rc, 20, 20, vbWhite

End Sub


Private Sub TransparentBlt(OutDstDC As Long, _
                           DstDC As Long, _
                           SrcDC As Long, _
                           SrcRect As RECT, _
                           DstX As Integer, _
                           DstY As Integer, _
                           TransColor As Long)
  
   'DstDC- Device context into which image must be
   'drawn transparently
 
   'OutDstDC- Device context into image is actually drawn,
  'even though it is made transparent in terms of DstDC

   'Src- Device context of source to be made transparent
   'in color TransColor

   'SrcRect- Rectangular region within SrcDC to be made
   'transparent in terms of DstDC, and drawn to OutDstDC

   'DstX, DstY - Coordinates in OutDstDC (and DstDC)
   'where the transparent bitmap must go. In most
   'cases, OutDstDC and DstDC will be the same
   Dim nRet As Long, W As Integer, H As Integer
   Dim MonoMaskDC As Long, hMonoMask As Long
   Dim MonoInvDC As Long, hMonoInv As Long
   Dim ResultDstDC As Long, hResultDst As Long
   Dim ResultSrcDC As Long, hResultSrc As Long
   Dim hPrevMask As Long, hPrevInv As Long
   Dim hPrevSrc As Long, hPrevDst As Long
   Dim OldBC As Long
  
   W = SrcRect.Right - SrcRect.Left + 1
   H = SrcRect.Bottom - SrcRect.Top + 1
  
  'create monochrome mask and inverse masks
   MonoMaskDC = CreateCompatibleDC(DstDC)
   MonoInvDC = CreateCompatibleDC(DstDC)
   hMonoMask = CreateBitmap(W, H, 1, 1, ByVal 0&)
   hMonoInv = CreateBitmap(W, H, 1, 1, ByVal 0&)
   hPrevMask = SelectObject(MonoMaskDC, hMonoMask)
   hPrevInv = SelectObject(MonoInvDC, hMonoInv)
  
  'create keeper DCs and bitmaps
   ResultDstDC = CreateCompatibleDC(DstDC)
   ResultSrcDC = CreateCompatibleDC(DstDC)
   hResultDst = CreateCompatibleBitmap(DstDC, W, H)
   hResultSrc = CreateCompatibleBitmap(DstDC, W, H)
   hPrevDst = SelectObject(ResultDstDC, hResultDst)
   hPrevSrc = SelectObject(ResultSrcDC, hResultSrc)
  
  'copy src to monochrome mask
   OldBC = SetBkColor(SrcDC, TransColor)
   nRet = BitBlt(MonoMaskDC, 0, 0, W, H, SrcDC, _
                 SrcRect.Left, SrcRect.Top, vbSrcCopy)
   TransColor = SetBkColor(SrcDC, OldBC)
  
  'create inverse of mask
   nRet = BitBlt(MonoInvDC, 0, 0, W, H, _
                 MonoMaskDC, 0, 0, vbNotSrcCopy)
  
  'get background
   nRet = BitBlt(ResultDstDC, 0, 0, W, H, _
                 DstDC, DstX, DstY, vbSrcCopy)
  
  'AND with Monochrome mask
   nRet = BitBlt(ResultDstDC, 0, 0, W, H, _
                 MonoMaskDC, 0, 0, vbSrcAnd)
  
  'get overlapper
   nRet = BitBlt(ResultSrcDC, 0, 0, W, H, SrcDC, _
                SrcRect.Left, SrcRect.Top, vbSrcCopy)
  
  'AND with inverse monochrome mask
   nRet = BitBlt(ResultSrcDC, 0, 0, W, H, _
                 MonoInvDC, 0, 0, vbSrcAnd)
  
  'XOR these two
   nRet = BitBlt(ResultDstDC, 0, 0, W, H, _
                 ResultSrcDC, 0, 0, vbSrcInvert)
  
  'output results
   nRet = BitBlt(OutDstDC, DstX, DstY, W, H, _
                 ResultDstDC, 0, 0, vbSrcCopy)
  
  'clean up
   hMonoMask = SelectObject(MonoMaskDC, hPrevMask)
   DeleteObject hMonoMask

   hMonoInv = SelectObject(MonoInvDC, hPrevInv)
   DeleteObject hMonoInv

   hResultDst = SelectObject(ResultDstDC, hPrevDst)
   DeleteObject hResultDst

   hResultSrc = SelectObject(ResultSrcDC, hPrevSrc)
   DeleteObject hResultSrc

   DeleteDC MonoMaskDC
   DeleteDC MonoInvDC
   DeleteDC ResultDstDC
   DeleteDC ResultSrcDC

End Sub