problem with Qgraphicspixmapitem

Hi all,

I need a QGraphicsPixmapItem that show pixel's value when you zoom. So I create my QGraphicsPixmapItem and reimplement paint method :

Code:

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MyPixmapGraphicsItem::MyPixmapGraphicsItem(QPixmap p , QGraphicsItem * parent)
    : pix(p)
    , QGraphicsItem(parent)
{
    image = pix.toImage();
}
 
 
 void MyPixmapGraphicsItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    const qreal lod = option->levelOfDetailFromTransform(painter->worldTransform());
 
    painter->drawPixmap (0,0, pix);
 
    if (lod >= 30)
    {
        QPen pen;
        int wStart, wLength;
        int hStart, hLength;
        int x1,y1;
        QRgb pixval;
        QString tr,tg,tb;
        QRectF boundbox = option->exposedRect;
 
        wStart  = (int) (boundbox.x());
        hStart  = (int) (boundbox.y());
        wLength = (int) (boundbox.width());
        hLength = (int) (boundbox.height());
 
        for(int i=hStart ; i<hStart+hLength ; i++)
        {
            for(int j=wStart ; j<wStart+wLength ; j++)
            {
                   pixval=20;image.pixel(j,i);
                   tr.setNum(qRed(pixval));
                   tg.setNum(qGreen(pixval));
                   tb.setNum(qBlue(pixval));
                   if(pix.depth()==8)
                   {
                        if(qRed(pixval)<140)
                            pen.setColor( QColor::fromRgb(255,255,255));
                        else
                            pen.setColor( QColor::fromRgb(0,0,0) );
 
                        painter->setPen( pen );
                        painter->drawText(j,(int) i,tr);
                   }
                   else
                   {
                        QColor color = QColor::fromRgb(pixval);
                        if(color.value()<140)
                            pen.setColor( QColor::fromRgb(255,255,255));
                        else
                            pen.setColor( QColor::fromRgb(0,0,0));
                        painter->setPen( pen );
                        tr.insert(0,"R:");tg.insert(0,"G:");tb.insert(0,"B:");
                        painter->drawText(j,i+2,tr);
                        painter->drawText(j,i+3,tg);
                        painter->drawText(j,i+4,tb);
                   }
               }
        }
    }
}

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"Pix" variable is my pixmap and "image" is a Qimage (pix copy) created by MyPixmapGraphicsItem constructor.

This code not work because I draw pixel value on the entire image. How can I draw pixel value on the display window only.

Thanks in advance

Quote:

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Originally Posted by skab

This code not work because I draw pixel value on the entire image. How can I draw pixel value on the display window only.

---

Can you explain the difference between "on the entire image" and "on the display window only"?

"display windows only" : When you zoom, scrollbar appears and you only see a small part of the entire image. I want to refresh pixel value only on that.

Currently, I think that is too long to refresh all the image (it freezes my application).

here's how I would do it:
subclass QGraphicsView and override paint(). Draw your number in that function and then call QGraphicsView::paint() to draw the zoomed scene.