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

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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" );
 }


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Qt 4.3.5