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makeimg.cpp Example File
graphicsview/portedcanvas/makeimg.cpp

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 #include <qimage.h>
 #include <qcolor.h>

 static inline int blendComponent( int v, int av, int s, int as )
 {
     //shadow gets a color inversely proportional to the
     //alpha value
     s = (s*(255-as))/255;
     //then do standard blending
     return as*s + av*v -(av*as*s)/255;
 }

 static inline QRgb blendShade( QRgb v, QRgb s )
 {
     //pick a number: shadow is 1/3 of object
     int as = qAlpha(s)/3;
     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 *img;

     img = new QImage( "in.png" );
     int w,h;
     int y;
     img->setAlphaBuffer( TRUE );
     *img = img->convertDepth( 32 );
     w = img->width();
     h = img->height();
 #if 0
     for ( y = 0; y < h; y ++ ) {
         uint *line = (uint*)img->scanLine( y );
         for ( int x = 0; x < w; x++ ) {
             uint pixel = line[x];
             int r = qRed(pixel);
             int g = qGreen(pixel);
             int b = qBlue(pixel);
             int min = QMIN( r, QMIN( g, b ) );
             int max = QMAX( r, QMAX( g, b ) );
             r -= min;
             g -= min;
             b -= min;
             if ( max !=min ) {
                 r = (r*255)/(max-min);
                 g = (g*255)/(max-min);
                 b = (b*255)/(max-min);
             }
             int a = 255-min;
             a -=  (max-min)/3; //hack more transparency for colors.
             line[x] = qRgba( r, g, b, a );
         }
     }
 #endif
     *img = img->smoothScale( w/2, h/2 );

     qDebug( "saving out.png");
     img->save( "out.png", "PNG" );

     w = img->width();
     h = img->height();

     QImage *img2 = new QImage( w, h, 32 );
     img2->setAlphaBuffer( TRUE );
     for ( y = 0; y < h; y++ ) {
         for ( int x = 0; x < w; x++ ) {
             QRgb shader = img->pixel( x, y );

             int as = qAlpha(shader)/3;

             int r = (qRed(shader)*(255-as))/255;
             int g = (qGreen(shader)*(255-as))/255;
             int b = (qBlue(shader)*(255-as))/255;

             img2->setPixel( x, y, qRgba(r,g,b,as) );
         }
     }

     img2->save( "outshade.png", "PNG" );

 }


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Qt 4.6.3