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Posted 1 Feb 2000

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Using the AlphaBlend Function

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3.63/5 (18 votes)
1 Feb 2000
A sample application that uses the AlphaBlend function to produce a transparent splash screen

Sample Image - alphablend.gif

Note: The code in this article is restricted to win98 and win2000.

Do you want a 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.

C++
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 the last one, BLENDFUNCTION.

C++
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

MSDN states: The SourceConstantaAlpha member of BLENDFUNCTION specifies an alpha transparency 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

 
QuestionGotcha with 64-bit OS and AlphaBlend Pin
Snuff Daddy12-Jun-15 12:33
MemberSnuff Daddy12-Jun-15 12:33 
QuestionAlphaBlend mode using Borland C++ 5.0 Pin
Member 1091480330-Jun-14 8:33
MemberMember 1091480330-Jun-14 8:33 
GeneralMy vote of 3 Pin
Mahdi Nejadsahebi30-Apr-11 21:24
MemberMahdi Nejadsahebi30-Apr-11 21:24 
GeneralMy vote of 2 Pin
Anaghir6-Jan-10 0:41
MemberAnaghir6-Jan-10 0:41 
QuestionAlphaBlend draws over the existing backgruound making it darker. gradually losing transaprency Pin
VC++Maniac20-Apr-09 21:15
MemberVC++Maniac20-Apr-09 21:15 
AnswerRe: AlphaBlend draws over the existing backgruound making it darker. gradually losing transaprency Pin
Snuff Daddy12-Jun-15 12:41
MemberSnuff Daddy12-Jun-15 12:41 
GeneralAbout OnPaint with the AlphaBlend(); [modified] Pin
Ted Lin16-Aug-07 22:12
MemberTed Lin16-Aug-07 22:12 
GeneralAlphaBlend wrong formula ?! Pin
Octopod23-Sep-06 10:17
MemberOctopod23-Sep-06 10:17 
GeneralRe: AlphaBlend wrong formula ?! Pin
Octopod23-Sep-06 10:50
MemberOctopod23-Sep-06 10:50 
GeneralThank you Pin
Nick Z.23-May-05 10:41
MemberNick Z.23-May-05 10:41 
GeneralProblem with AlphaBlend Pin
Petru Dumitrache23-Mar-05 23:13
MemberPetru Dumitrache23-Mar-05 23:13 
GeneralRe: Problem with AlphaBlend Pin
jgarnett27-Oct-05 15:59
Memberjgarnett27-Oct-05 15:59 
GeneralRe: Problem with AlphaBlend Pin
Snuff Daddy12-Jun-15 12:31
MemberSnuff Daddy12-Jun-15 12:31 
GeneralQuestion Pin
one_eddie1-Oct-04 11:40
Memberone_eddie1-Oct-04 11:40 
GeneralGreat stuff! Pin
JustDan24-Jan-04 17:36
MemberJustDan24-Jan-04 17:36 
GeneralRe: Great stuff! Pin
anothermxw4-Apr-04 19:08
Memberanothermxw4-Apr-04 19:08 
GeneralRe: Great stuff! Pin
Anonymous5-Apr-04 14:18
MemberAnonymous5-Apr-04 14:18 
GeneralNo with Dialog Pin
Person_17-May-03 5:42
MemberPerson_17-May-03 5:42 
GeneralAlgorithm Code Pin
27-Feb-03 17:34
suss27-Feb-03 17:34 
GeneralRe: Algorithm Code Pin
Henry P.27-Feb-03 17:57
MemberHenry P.27-Feb-03 17:57 
GeneralRe: Algorithm Code Pin
Jack Puppy28-Feb-03 19:38
MemberJack Puppy28-Feb-03 19:38 
GeneralRe: Algorithm Code Pin
Anonymous3-Mar-03 6:27
MemberAnonymous3-Mar-03 6:27 
GeneralRe: Algorithm Code Pin
Jack Puppy8-Mar-03 4:50
MemberJack Puppy8-Mar-03 4:50 
GeneralRe: Algorithm Code Pin
Henry P.31-Mar-03 19:22
MemberHenry P.31-Mar-03 19:22 
GeneralRe: Algorithm Code Pin
B2kguga25-Feb-07 10:04
MemberB2kguga25-Feb-07 10:04 

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