source: trunk/examples/graphicsview/portedcanvas/blendshadow.cpp@ 79

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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" );
}