Using Win32 functions in Visual FoxPro Image Gallery
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Displaying bitmap using the AlphaBlend function

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Before you begin:
The AlphaBlend function displays bitmaps that have transparent or semitransparent pixels.

See also:
  • Bitmap Class for Visual FoxPro application
  • Semi-transparent Form
  • Form Magnifier
  • GDI+: Color Transparency
  • #DEFINE LR_LOADFROMFILE 16
    #DEFINE AC_SRC_OVER 0
    #DEFINE AC_SRC_ALPHA 1
    #DEFINE AC_SRC_NO_ALPHA 2
    #DEFINE IMAGE_BITMAP 0
    #DEFINE SRCCOPY 0xCC0020
    #DEFINE BITMAP_STRU_SIZE 24
    
    DO declare
    
    LOCAL lcBitmap
    *lcBitmap = "C:\WinNT\system32\setup.bmp"
    lcBitmap = "C:\Windows\Forest.bmp"
    = LoadAndShowBitmap(lcBitmap, LR_LOADFROMFILE, 20,100)
    * end of main
    
    PROCEDURE LoadAndShowBitmap(lcBitmap, lnLoadOptions, lnX,lnY)
        LOCAL hBitmap
        hBitmap = LoadImage(0, lcBitmap, IMAGE_BITMAP,;
            0,0, lnLoadOptions)
    
        IF hBitmap <> 0
            = ShowBitmap(hBitmap, lnX,lnY)
            = DeleteObject(hBitmap)
        ELSE
            = MESSAGEBOX(lcBitmap + Chr(13) + Chr(13) +;
                "Check if this is a valid bitmap file.",;
                32, " Unable to load an image from file")
        ENDIF
    
    PROCEDURE ShowBitmap(hBitmap, lnX, lnY)
    *|typedef struct _BLENDFUNCTION {
    *|  BYTE     BlendOp;
    *|  BYTE     BlendFlags;
    *|  BYTE     SourceConstantAlpha;
    *|  BYTE     AlphaFormat;
    *|}BLENDFUNCTION, *PBLENDFUNCTION, *LPBLENDFUNCTION;
    
        LOCAL hWindow, hDC, hMemDC, lnWidth, lnHeight
        STORE 0 TO lnWidth, lnHeight
        = GetBitmapSize(hBitmap, @lnWidth, @lnHeight)
    
        hWindow = GetActiveWindow()
        hDC = GetWindowDC(hWindow)
    
        hMemDC = CreateCompatibleDC(hDC)
        = SelectObject(hMemDC, hBitmap)
    
        LOCAL lnAlphaBlend, lnResult,;
            lnBlendOp, lnBlendFlags, lnSrcConstAlpha, lnAlphaFormat
    
        lnBlendOp = AC_SRC_OVER  && always
        lnBlendFlags = 0         && always
        lnSrcConstAlpha = 48     && intensity, up to 255
        lnAlphaFormat = 0        && try AC_SRC_ALPHA on non-white background
    
        * assembling the BLENDFUNCTION structure 
        lnAlphaBlend = lnBlendOp +;
            BitLShift(lnBlendFlags, 8) +;
            BitLShift(lnSrcConstAlpha, 16) +;
            BitLShift(lnAlphaFormat, 24)
    
        lnResult = AlphaBlend(hDC, lnX,lnY, lnWidth,lnHeight,;
            hMemDC, 0,0, lnWidth,lnHeight,;
            lnAlphaBlend)
    
        IF lnResult = 0
        *  6 = The handle is invalid
        * 87 = The parameter is incorrect
            ? "Error:", GetLastError()
        ENDIF
    
        = DeleteDC(hMemDC)
        = ReleaseDC(hWindow, hDc)
    RETURN .T.
    
    FUNCTION GetBitmapSize(hBitmap, lnWidth, lnHeight)
        LOCAL lcBuffer
        lcBuffer = Repli(Chr(0), BITMAP_STRU_SIZE)
    
        IF GetObjectA(hBitmap, BITMAP_STRU_SIZE, @lcBuffer) <> 0
            lnWidth  = buf2dword(SUBSTR(lcBuffer, 5,4))
            lnHeight = buf2dword(SUBSTR(lcBuffer, 9,4))
           ENDIF
    
    FUNCTION buf2dword(lcBuffer)
    RETURN Asc(SUBSTR(lcBuffer, 1,1)) + ;
        BitLShift(Asc(SUBSTR(lcBuffer, 2,1)),  8) +;
        BitLShift(Asc(SUBSTR(lcBuffer, 3,1)), 16) +;
        BitLShift(Asc(SUBSTR(lcBuffer, 4,1)), 24)
    
    PROCEDURE declare
        DECLARE INTEGER CreateCompatibleDC IN gdi32 INTEGER hdc
        DECLARE INTEGER DeleteDC IN gdi32 INTEGER hdc
        DECLARE INTEGER GetActiveWindow IN user32
        DECLARE INTEGER GetWindowDC IN user32 INTEGER hWindow
        DECLARE INTEGER ReleaseDC IN user32 INTEGER hWindow, INTEGER dc
        DECLARE INTEGER DeleteObject IN gdi32 INTEGER hObject
        DECLARE INTEGER SelectObject IN gdi32 INTEGER hdc, INTEGER hObject
    
        DECLARE INTEGER LoadImage IN user32;
            INTEGER hinst, STRING lpszName, INTEGER uType,;
            INTEGER cxDesired, INTEGER cyDesired, INTEGER fuLoad
    
        DECLARE INTEGER GetObject IN gdi32 AS GetObjectA;
            INTEGER hgdiobj, INTEGER cbBuffer, STRING @lpvObject
    
        DECLARE INTEGER AlphaBlend IN Msimg32;
            INTEGER hDestDC, INTEGER x, INTEGER y,;
            INTEGER nWidth, INTEGER nHeight, INTEGER hSrcDC,;
            INTEGER xSrc, INTEGER ySrc, INTEGER nWidthSrc,;
            INTEGER nHeightSrc, INTEGER blendFunction
    
        DECLARE INTEGER GetLastError IN kernel32
    
    
    

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    3476 bytes  
    Created: 2002-03-23 10:43:13  
    Modified: 2009-01-17 11:17:30  
    Visits in 7 days: 40  
    Listed functions:
    AlphaBlend
    CreateCompatibleDC
    DeleteDC
    DeleteObject
    GetActiveWindow
    GetLastError
    GetObject
    GetWindowDC
    LoadImage
    ReleaseDC
    SelectObject
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