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# blendshadow.cpp Example File
graphicsview/portedcanvas/blendshadow.cpp

    /****************************************************************************
    **
    ** Copyright (C) 2006-2006 Trolltech ASA. All rights reserved.
    **
    ** This file is part of the example classes of the Qt Toolkit.
    **
    ** Licensees holding valid Qt Preview licenses may use this file in
    ** accordance with the Qt Preview License Agreement provided with the
    ** Software.
    **
    ** See http://www.trolltech.com/pricing.html or email sales@trolltech.com for
    ** information about Qt Commercial License Agreements.
    **
    ** Contact info@trolltech.com if any conditions of this licensing are
    ** not clear to you.
    **
    ** This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
    ** WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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    #include <qimage.h>
    #include <qcolor.h>

    static inline int blendComponent( int v, int av, int s, int as )
    {
        return as*s + av*v -(av*as*s)/255;
    }

    static inline QRgb blendShade( QRgb v, QRgb s )
    {
        //shadow image is already reduced and blurred
        int as = qAlpha(s);
        int av = qAlpha(v);
        if ( as == 0 || av == 255 )
            return v;

        int a = as + av -(as*av)/255;

        int r = blendComponent( qRed(v),av, qRed(s), as)/a;
        int g = blendComponent( qGreen(v),av, qGreen(s), as)/a;
        int b = blendComponent( qBlue(v),av, qBlue(s), as)/a;

        return qRgba(r,g,b,a);
    }

    int main( int*, char**)
    {
        QImage image( "out.png" );
        image.convertDepth( 32 );
        QImage shade( "outshade.png" );
        shade.convertDepth( 32 );
        int dx = 10;
        int dy = 5;

        int w = image.width();
        int h = image.height();

        QImage img( w+dx, h+dy, 32 );
        img.setAlphaBuffer( TRUE );

        for ( int y = 0; y < h+dy; y++ ) {
            for ( int x = 0; x < w+dx; x++ ) {
                QRgb sh =  (x<dx||y<dy) ? 0 : shade.pixel( x-dx, y-dy );
                QRgb pixel = (x<w&y<h) ? image.pixel( x, y ) : 0;
                img.setPixel( x, y, blendShade( pixel, sh ) );
            }
        }
        img.save("blend.png", "PNG" );
    }