Painting the inside of a shape in QGraphicsItem

[wysota]

For this I subclassed QGraphicsItem with my_Item as parent. So in the mousePressEvent I set the item subclass to visible

You don't set classes to visible. At some point you must have created an instance of that class and this instance must have had boundingRect() (and hence shape()) defined. If you didn't redefine shape() then it by default equals to the boundingRect() hence everywhere inside that boundingRect (so in the bounding area of the item) is considered "inside" the item.

[xtraction]

Thanks for clearing that up.

If I can't set classes to Visible, what would be the right way to implement something like a rubberband to select an area of an image, except that I don't want a rubberband because I need to be able to define the shape of the selection with the mouse having a 'free hand' way of drawing. And If I don't like the selection I made, click, have it dissapear, and start again until I draw something I want.

I would really appreciate your advice.

[wysota]

I don't see how this functionality is related to "setting classes to visible". There is a myriad of ways you could implement lasso selection. The easiest one is to reimplement mouse events of the view, build an internal painter path as the user moves his mouse (possibly drawing that path on the view) and then apply that path to selecting items.

[xtraction]

So the lasso selection would just be the QPainterPath object, so there is no need to have a GraphicsItem to draw the path like in my case? I am doing something similar, I am creating a painterpath in the mouse events, but this is giving somewhat random behavior, sometimes I run the application and it draws fine, and sometimes it doesn't.

[wysota]

There is no need for any extra graphics items.

#include <QtGui>
 
 
class View : public QGraphicsView {
public:
    View() : QGraphicsView(){}
protected:
    void mousePressEvent(QMouseEvent *event) {
        foreach(QGraphicsItem *i, scene()->items())
            i->setSelected(false);
        m_path.setFillRule(Qt::WindingFill);
        m_path.moveTo(event->posF());
    }
    void mouseMoveEvent(QMouseEvent *event) {
        m_path.lineTo(event->posF());
        viewport()->update();
    }
    void mouseReleaseEvent(QMouseEvent *event) {
        m_path.closeSubpath();
 
        QList<QGraphicsItem*> it = scene()->items(mapToScene(m_path));
        foreach(QGraphicsItem *i, it)
            i->setSelected(true);
        viewport()->update();
        m_path = QPainterPath();
 
    }
 
void paintEvent(QPaintEvent *event) {
    QGraphicsView::paintEvent(event);
    if(m_path.isEmpty())
        return;
    QPainter p(viewport());
    QPen pen(QColor(Qt::red));
    pen.setWidth(4);
    p.setPen(pen);
    p.setRenderHint(QPainter::Antialiasing);
    p.setBrush(QColor(255,0,0,100));
 
    p.drawPath(m_path);
}
 
private:
    QPainterPath m_path;
};
 
int main(int argc, char **argv) {
    QApplication app(argc, argv);
    QGraphicsScene scene;
    qsrand(QDateTime::currentDateTime().toTime_t());
    for(int i=0;i<50;i++) {
        QColor c(qrand() % 255, qrand() % 255, qrand() % 255);
        scene.addEllipse(qrand() % 500, qrand() % 500, qrand() % 100, qrand() % 100, c, c)->setFlag(QGraphicsItem::ItemIsSelectable);
    }
    View view;
    view.setRenderHint(QPainter::Antialiasing);
    view.setScene(&scene);
    view.show();
    return app.exec();
}

#include <QtGui>


class View : public QGraphicsView {
public:
    View() : QGraphicsView(){}
protected:
    void mousePressEvent(QMouseEvent *event) {
        foreach(QGraphicsItem *i, scene()->items())
            i->setSelected(false);
        m_path.setFillRule(Qt::WindingFill);
        m_path.moveTo(event->posF());
    }
    void mouseMoveEvent(QMouseEvent *event) {
        m_path.lineTo(event->posF());
        viewport()->update();
    }
    void mouseReleaseEvent(QMouseEvent *event) {
        m_path.closeSubpath();

        QList<QGraphicsItem*> it = scene()->items(mapToScene(m_path));
        foreach(QGraphicsItem *i, it)
            i->setSelected(true);
        viewport()->update();
        m_path = QPainterPath();

    }

void paintEvent(QPaintEvent *event) {
    QGraphicsView::paintEvent(event);
    if(m_path.isEmpty())
        return;
    QPainter p(viewport());
    QPen pen(QColor(Qt::red));
    pen.setWidth(4);
    p.setPen(pen);
    p.setRenderHint(QPainter::Antialiasing);
    p.setBrush(QColor(255,0,0,100));

    p.drawPath(m_path);
}

private:
    QPainterPath m_path;
};

int main(int argc, char **argv) {
    QApplication app(argc, argv);
    QGraphicsScene scene;
    qsrand(QDateTime::currentDateTime().toTime_t());
    for(int i=0;i<50;i++) {
        QColor c(qrand() % 255, qrand() % 255, qrand() % 255);
        scene.addEllipse(qrand() % 500, qrand() % 500, qrand() % 100, qrand() % 100, c, c)->setFlag(QGraphicsItem::ItemIsSelectable);
    }
    View view;
    view.setRenderHint(QPainter::Antialiasing);
    view.setScene(&scene);
    view.show();
    return app.exec();
}

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