Click here to Skip to main content
Click here to Skip to main content

AlphaBlending

, 12 Dec 2005
Rate this:
Please Sign up or sign in to vote.
This articles illustrates alpha-blending two bitmaps.

AlphaBlending

Introduction

This code snippet shows how to alpha-blend two bitmaps by using the linear interpolation formula.

Background

Using the code

Here is a function which can be used in OnPaint() or OnDraw(). Actually, in the sample project, I didn't prepare a function, I put the code directly in the OnPaint() method. In this function, the new blended bitmap is placed on a second bitmap. You can implement the code and create a third bitmap for the new bitmap if you need.

The second parameter, double blend, must be in [0,1). This number is for the first bitmap, and the second number is 1-blend for the second bitmap.

void CAlphaBlendingDlg::AlphaBlend(CDC *pDC, double blend) 
{
    BITMAP bmpX,bmpY;
    
    CBitmap bmp1,bmp2;
    bmp2.LoadBitmap(IDB_BITMAP2);
    bmp1.LoadBitmap(IDB_BITMAP1);

    bmp1.GetBitmap(&bmpX);
    UINT* bmpBuffer=(UINT*) GlobalAlloc(GPTR, 
                            bmpX.bmWidthBytes * bmpX.bmHeight);
    bmp1.GetBitmapBits(bmpX.bmWidthBytes * bmpX.bmHeight, bmpBuffer);

    bmp2.GetBitmap(&bmpY);
    UINT* bmpBuffer2=(UINT*) GlobalAlloc(GPTR, 
                             bmpY.bmWidthBytes * bmpY.bmHeight);
    bmp2.GetBitmapBits(bmpY.bmWidthBytes * bmpY.bmHeight, bmpBuffer2);

    int nSize = bmpY.bmWidth * bmpY.bmHeight;

    for (int i = 0; i < nSize; i++)
    {
        int abR = (int) (GetR(bmpBuffer[i]) * blend + 
                        (1-blend) * GetR(bmpBuffer2[i]));
        int abG = (int) (GetG(bmpBuffer[i]) * blend + 
                        (1-blend) * GetG(bmpBuffer2[i]));
        int abB = (int) (GetB(bmpBuffer[i]) * blend + 
                        (1-blend) * GetB(bmpBuffer2[i]));

        bmpBuffer2[i] = RGB(abB, abG, abR);
    }

    bmp2.SetBitmapBits(bmpX.bmWidthBytes * bmpX.bmHeight, bmpBuffer2);

    CDC memdc;
    memdc.CreateCompatibleDC(pDC);
    memdc.SelectObject(bmp2);
    pDC->BitBlt(10,10,bmpX.bmWidthBytes, 
                bmpX.bmHeight, &memdc, 0, 0, SRCCOPY);

    GlobalFree((HGLOBAL)bmpBuffer);
    GlobalFree((HGLOBAL)bmpBuffer2);
    memdc.DeleteDC();
}

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

Share

About the Author

Ozge Colak
Software Developer Ibtech
Turkey Turkey
mathematician-programmer

Comments and Discussions

 
QuestionHow to alpha-blend three (or more) bitmaps? PinmemberTee Moore4-Dec-07 23:30 
AnswerRe: How to alpha-blend three (or more) bitmaps? Pinmemberengelbert16-Jan-08 21:00 
GeneralVery cool article! PinmemberSavior99923-Nov-06 2:48 
GeneralYou forgot to cap each color PinmemberCBasicNet12-Dec-05 22:52 
GeneralRe: You forgot to cap each color - No, they are capped PinmemberOzge Colak13-Dec-05 1:27 

General General    News News    Suggestion Suggestion    Question Question    Bug Bug    Answer Answer    Joke Joke    Rant Rant    Admin Admin   

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.

| Advertise | Privacy | Terms of Use | Mobile
Web02 | 2.8.141220.1 | Last Updated 12 Dec 2005
Article Copyright 2005 by Ozge Colak
Everything else Copyright © CodeProject, 1999-2014
Layout: fixed | fluid