QGraphicsItem selection on opaque area

Question

I have these flags set on a QGraphicsPixmapItem:

setFlag(QGraphicsItem::ItemIsMovable, true)
setFlag(QGraphicsItem::ItemIsSelectable, true);

When I click and move the item, I want the selection dotted lines to be highlighting the opaque area of the item only and not include the transparent background.

Current behavior - On click - dotted lines surround the Item in a rectangle:

Desired behavior - dotted lines surround the diamond.

How do I do this?

Answer 1

The following method only works when the image has a transparent external part as shown in the following part:

The solution is to overwrite the paint() method and draw the shape().

#include <QApplication>
#include <QGraphicsView>
#include <QGraphicsPixmapItem>
#include <QStyleOptionGraphicsItem>

class GraphicsPixmapItem: public QGraphicsPixmapItem{
public:
    GraphicsPixmapItem(const QPixmap & pixmap, QGraphicsItem * parent = 0): QGraphicsPixmapItem(pixmap, parent){
        setFlag(QGraphicsItem::ItemIsMovable, true);
        setFlag(QGraphicsItem::ItemIsSelectable, true);
    }
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *){
        painter->setRenderHint(QPainter::SmoothPixmapTransform, (transformationMode() == Qt::SmoothTransformation));
        painter->drawPixmap(offset(), pixmap());
        if (option->state & QStyle::State_Selected){
            painter->setPen(QPen(option->palette.windowText(), 0, Qt::DashLine));
            painter->setBrush(Qt::NoBrush);
            painter->drawPath(shape());
        }
    }
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QGraphicsView w;
    QGraphicsScene scene;
    GraphicsPixmapItem *item = new GraphicsPixmapItem(QPixmap(":/image.png"));
    scene.addItem(item);
    w.setScene(&scene);
    w.show();

    return a.exec();
}

The complete example can be found in the following link.