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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.
     **
     ** This file may be used under the terms of the GNU General Public
     ** License version 2.0 as published by the Free Software Foundation
     ** and appearing in the file LICENSE.GPL included in the packaging of
     ** this file.  Please review the following information to ensure GNU
     ** General Public Licensing requirements will be met:
     ** http://www.trolltech.com/products/qt/opensource.html
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     ** review the following information:
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     ** 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" );
     }