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Using the AlphaBlend function

, 1 Feb 2000
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A sample application that uses the AlphaBlend function to produce a transparent splash screen
  • Download source files - 35 Kb
  • Sample Image - alphablend.gif

    <!-- Article Starts --> Note: The code in this article is restricted to win98 and win2000

    Do you want to cool splash window?. Do you think the general splash window is not good enough for your app? Then this sample source is for you.

    My semi-transparent splash window uses the AlphaBlend function. When I found this function, I was so surprised! The function works just like BitBlt for bitmaps that have transparent or semitransparent pixels. Here is the AlphaBlend function's syntax

    BOOL AlphaBlend( HDC hdcDest,
      int nXOriginDest,
      int nYOriginDest,
      int nWidthDest,
      int nHeightDest,
      HDC hdcSrc,
      int nXOriginSrc,
      int nYOriginSrc,
      int nWidthSrc,
      int nHeightSrc,
      BLENDFUNCTION blendFunction
    );
    

    The important parameter is last one, BLENDFUNCTION.

    typedef struct _BLENDFUNCTION {
        BYTE     BlendOp;
        BYTE     BlendFlags;
        BYTE     SourceConstantAlpha;
        BYTE     AlphaFormat;
    }BLENDFUNCTION;
    
    • BlendOp must be AC_SRC_OVER
    • BlendFlags must be 0
    • SourceConstantAlpha must be between 0 (transparent) and 255 (semi-transparent).
    • AlphaFormat must be AC_SRC_ALPHA
    MSND states:  The SourceConstantaAlpha member of BLENDFUNCTION specifies an alpha transparancy value to be used on the entire source bitmap. The SourceConstantAlpha value is combined with any per-pixel alpha values. If you set SourceConstantAlpha to 0, it is assumed that your image is transparent. Set the SourceConstantAlpha value to 255 (indicates that the image is opaque) when you only want to use per-pixel alpha values.

    See the sample application for a demonstration.

    Just enjoy!!

    Ajou University C.C. 4th member.

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    About the Author

    Wooseok Seo
    Software Developer (Senior)
    Korea (Republic Of) Korea (Republic Of)
    Woo Seok Seo have been a Microsoft MVP for 7 years and have translated several books into Korean. Author of C# Programming for Beginner (DevPress, 2001), he is interested in Debugging techniques and .NET technology. Get in touch with Woo Seok Seo at wooseok.seo@gmail.com

    Comments and Discussions

     
    QuestionAlphaBlend mode using Borland C++ 5.0 PinmemberMember 1091480330-Jun-14 8:33 
    GeneralMy vote of 3 PingroupMahdi Nejadsahebi30-Apr-11 21:24 
    GeneralMy vote of 2 PinmemberMember 3186846-Jan-10 0:41 
    QuestionAlphaBlend draws over the existing backgruound making it darker. gradually losing transaprency PinmemberVC++Maniac20-Apr-09 21:15 
    GeneralAbout OnPaint with the AlphaBlend(); [modified] PinmemberTed Lin16-Aug-07 22:12 
    GeneralAlphaBlend wrong formula ?! PinmemberOctopod23-Sep-06 10:17 
    GeneralRe: AlphaBlend wrong formula ?! PinmemberOctopod23-Sep-06 10:50 
    GeneralThank you PinmemberNick Z.23-May-05 10:41 
    GeneralProblem with AlphaBlend Pinmemberacidutzu23-Mar-05 23:13 
    GeneralRe: Problem with AlphaBlend Pinmemberjgarnett27-Oct-05 15:59 
    GeneralQuestion Pinmemberone_eddie1-Oct-04 11:40 
    GeneralGreat stuff! PinmemberJustDan24-Jan-04 17:36 
    GeneralRe: Great stuff! Pinmemberanothermxw4-Apr-04 19:08 
    GeneralRe: Great stuff! PinsussAnonymous5-Apr-04 14:18 
    GeneralNo with Dialog Pinmembermojster17-May-03 5:42 
    GeneralAlgorithm Code PinmemberJack Rabbit27-Feb-03 17:34 
    GeneralRe: Algorithm Code PinmemberHenry P.27-Feb-03 17:57 
    GeneralRe: Algorithm Code PinmemberJack Rabbit28-Feb-03 19:38 
    GeneralRe: Algorithm Code PinsussAnonymous3-Mar-03 6:27 
    GeneralRe: Algorithm Code PinmemberJack Rabbit8-Mar-03 4:50 
    GeneralRe: Algorithm Code PinmemberHenry P.31-Mar-03 19:22 
    GeneralRe: Algorithm Code PinmemberB2kguga25-Feb-07 10:04 
    GeneralWin95/98/ME vs. WinNT/2000/XP PinmemberHenry P.27-Feb-03 16:57 
    GeneralRe: Win95/98/ME vs. WinNT/2000/XP PinmemberChristian Graus27-Feb-03 17:57 
    GeneralRe: Win95/98/ME vs. WinNT/2000/XP PinmemberHenry P.3-Mar-03 9:21 

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