Increase margin for detecting tooltip events of QGraphicsLineItem?

[norobro]

. . . So, you can implement shape() for your line to return a path containing a "fat" line (a QPolygon probably would work) that is as wide as it needs to be to give a good margin for the tooltip detection.

If I'm not mistaken that's what the OP is saying doesn't work. Returning shape() as the bounding rect seems to work:

#include <QtGui>
 
class LineItem : public QGraphicsLineItem
{
public:
    LineItem(qreal x, qreal y, qreal w, qreal h): QGraphicsLineItem(x,y,w,h){}
    QPainterPath shape() const{
        QPainterPath path;
        QPainterPathStroker stroker;
        path.moveTo(line().p1());
        path.lineTo(line().p2());
        stroker.setWidth(50);
        return stroker.createStroke(path);
    }
    QRectF boundingRect() const{
        return shape().boundingRect();
    }
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget){ 
        painter->fillPath(shape(),QBrush(QColor(0,0,0,10)));
        QGraphicsLineItem::paint(painter, option, widget);
    }
};
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QGraphicsView view;
    QGraphicsScene scene;
    LineItem horizontalLine(0,0,200,0);
    horizontalLine.setToolTip("horizontal line tool tip");
    scene.addItem(&horizontalLine);
    LineItem diagonalLine(0,100,200,300);
    diagonalLine.setToolTip("diagonal line tool tip");
    diagonalLine.setFlag(QGraphicsItem::ItemIsMovable);
    scene.addItem(&diagonalLine);
    view.setScene(&scene);
    view.setMinimumSize(300,400);
    view.show();    
    return a.exec();
}

#include <QtGui>

class LineItem : public QGraphicsLineItem
{
public:
    LineItem(qreal x, qreal y, qreal w, qreal h): QGraphicsLineItem(x,y,w,h){}
    QPainterPath shape() const{
        QPainterPath path;
        QPainterPathStroker stroker;
        path.moveTo(line().p1());
        path.lineTo(line().p2());
        stroker.setWidth(50);
        return stroker.createStroke(path);
    }
    QRectF boundingRect() const{
        return shape().boundingRect();
    }
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget){ 
        painter->fillPath(shape(),QBrush(QColor(0,0,0,10)));
        QGraphicsLineItem::paint(painter, option, widget);
    }
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QGraphicsView view;
    QGraphicsScene scene;
    LineItem horizontalLine(0,0,200,0);
    horizontalLine.setToolTip("horizontal line tool tip");
    scene.addItem(&horizontalLine);
    LineItem diagonalLine(0,100,200,300);
    diagonalLine.setToolTip("diagonal line tool tip");
    diagonalLine.setFlag(QGraphicsItem::ItemIsMovable);
    scene.addItem(&diagonalLine);
    view.setScene(&scene);
    view.setMinimumSize(300,400);
    view.show();    
    return a.exec();
}

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Note: I just threw the paint function in there to show the area where the tool tip will be shown. It is not necessary.

[d_stranz]

Returning shape() as the bounding rect seems to work

I guess my point is that because the bounding rect is always aligned with the horizontal and vertical, the further you tilt the line away from horizontal or vertical, the bigger the bounding rect becomes. If a line goes diagonally from topLeft to bottomRight of a window, then the bounding rect covers the entire window, which means the tooltip will be triggered from anywhere in the whole window, not just near the line.

I am not sure why the stroker didn't work in the OP. Perhaps the stroker doesn't have any "real" width (i.e. doesn't actually describe an enclosed area in terms of a path). That's why I suggested using a QPolygon instead, or maybe a path described by two half-circles at each end of the line, connected by two parallel lines to create a closed area.