QGraphicsScene/QGraphicsView & QGradient



  • Hello,

    I intend to draw inside a QGraphicsScene a "life gauge", that is a rectangle whose length varies depending on your hit/life points. The user should be able to change their own hit/life points and the gauge should adapt nicely, matching the new value entered by the user.

    I would like to draw that gauge with a gradient (orange -> red for example), but I'm not sure what's the best way to do that. I've done some quick research and it looks like I could use a QPainter and make the appropriate QImage, which could then be converted to a QPixmap, and drawn into the QGraphicsScene/QGraphicsView.

    But wouldn't that be rather costly if I change the gauge via QPropertyAnimations? If for example I were to change the length of the gauge from 250 to 200 pixels within 1 second, Qt would probably decrease the length one by one (249, 248, 247, ...202, 201, 200) and as a result the setter that I specified with the property would be called 50 times, resulting in Qt using 50 times a QPainter.

    So basically my question is: do you know a better/smarter way to change the length of a gradiented rectangle?


  • Lifetime Qt Champion

    Hi,

    What about implementing your own QGraphicsItem and re-implement the paint method ? Depending on the geometry of your gauge, QGraphicsRectItem could also be used.

    Hope it helps



  • @SGaist thanks for replying.

    I'm not familiar with re-implementing paint yet :S Could you drop a very short example? For example if I wanted to paint an entirely black rectangle, what would that look like? I'll probably manage to take it from here afterward.


  • Lifetime Qt Champion

    It should be something like:

    void GaugeItem::paint(QPainter *painter,
                          const QStyleOptionGraphicsItem *option,
                          QWidget *widget)
    {
        painter->setPen(Qt::black);
        painter->setBrush(Qt::black);
        painter->drawRect(boundingRect());
    }
    


  • Thanks a lot SGaist :)


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