一幅圖片上，但是這幅圖象不是完全將原來的圖象覆蓋，而是能夠部分的透過疊加的圖象顯示
出來，下面我就介紹如何在VB中編程實現這樣的功能。
首先在建立兩個大小相等的圖象文件，將它們保存成BMP文件，VB5以上的版本支
持JPEG顯示，也可以保存為Jpg文件。在Form中加入兩個PictureBox控件，將它們的大小設置成
同圖象文件相同的大小。注意這兩個PictureBox控件不要相互重疊，也不要和Form中的其它控件
產生重疊。將兩幅圖象分別加入到兩個PictureBox控件中。然后在Form中加入一個CommandButton
控件。最后在Form的代碼窗口中加入以下代碼：
Private Type LOGBRUSH
lbStyle As Long
lbColor As Long
lbHatch As Long
End Type
Private Type RECT
Left As Long
Top As Long
Right As Long
Bottom As Long
End Type
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 SelectObject Lib "gdi32" (ByVal hdc As Long, _
ByVal hObject As Long) As Long
Private Declare Function FillRect Lib "user32" (ByVal hdc As Long, _
lpRect As RECT, ByVal hBrush As Long) As Long
Private Declare Function BitBlt Lib "gdi32" (ByVal hDestDC As Long, _
ByVal x As Long, ByVal y As Long, ByVal nWidth As Long, _
ByVal nHeight As Long, ByVal hSrcDC As Long, ByVal xSrc _
As Long, ByVal ySrc As Long, ByVal dwRop As Long) As Long
Private Declare Function CreateBrushIndirect Lib "gdi32" (lpLogBrush _
As LOGBRUSH) As Long
Private Declare Function DeleteDC Lib "gdi32" (ByVal hdc As Long) As Long
Const SRCPAINT = &HEE0086
Const SRCAND = &H8800C6
Const BS_SOLID = 0
Const gColor = &HFFFFFF
Private Sub Command1_Click()
Dim pDstDC As Long
Dim dcCompatible As Long
Dim pBitmapOld As Long
Dim bm As Long
Dim rectTemp As RECT
Dim lBrush As Long
Dim tLog As LOGBRUSH
dcCompatible = CreateCompatibleDC(Picture1.hdc)
bm = CreateCompatibleBitmap(Picture1.hdc, Picture1.Width \ 15, _
Picture1.Height \ 15)
pBitmapOld = SelectObject(dcCompatible, bm)
rectTemp.Left = 0: rectTemp.Top = 0
rectTemp.Right = Picture1.Width \ 15: rectTemp.Bottom = _
Picture1.Height \ 15
tLog.lbColor = gColor
tLog.lbStyle = BS_SOLID
tLog.lbHatch = 0
lBrush = CreateBrushIndirect(tLog)
FillRect dcCompatible, rectTemp, lBrush
BitBlt Picture1.hdc, 0, 0, Picture1.Width \ 15, _
Picture1.Height \ 15, dcCompatible, 0, 0, SRCAND
SelectObject dcCompatible, pBitmapOld
BitBlt Picture1.hdc, 0, 0, Picture1.Width \ 15, _
Picture1.Height \ 15, Picture2.hdc, 0, 0, SRCPAINT
DeleteDC dcCompatible
End Sub
運行程序，點擊Command1，你就可以看到Picture2上的圖象疊加到了Picture1上面了。改變上面
源程序中的 Const gColor = &HFFFFFF 一句中的gColor的值（在0到&HFFFFFFFF間變動），就可以
使圖象的疊加產生不同的透明效果。
以上程序在Win98、VB6.0下運行通過。
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