qt - Drawing extra item in QGraphicsItem during hover event -

i create coordinate points on qgraphicsview. when mouse hovers on point, coordinate shown.

i draw coordinates qgraphicsellipseitem. in order enable hover event, need re-implement qgraphicsellipseitem. however, because size of qgraphicsellipseitem fixed when constructed, hover text not shown properly. how can deal this?

here code:

the mainwindow:

mainwindow::mainwindow(qwidget *parent)     : qmainwindow(parent) {     view = new qgraphicsview(this);     view->setrenderhint(qpainter::antialiasing);      scene = new qgraphicsscene(this);     view->fitinview(scene->scenerect(), qt::keepaspectratio);     view->setscene(scene);     setcentralwidget(view);      (int y = 0; y < 900; y += 100)         for(int x = 0; x < 1400; x += 100)             drawpoint(x, y); }  void mainwindow::drawpoint(int x, int y) {     coordinatepoint* point = new coordinatepoint();     point->setrect(qrect(x, y, 3, 3));     point->setpen(qpen(qt::red, 3, qt::solidline));     point->setbrush(qt::red);     scene->additem(point); } 

the re-implement qgraphicsellipseitem:

coordinatepoint::coordinatepoint(qgraphicsitem* parent)     :qgraphicsellipseitem(parent) {     setaccepthoverevents(true); }   void coordinatepoint::hoverenterevent(qgraphicsscenehoverevent* event) {     hover = true;     mx = event->pos().x();     = event->pos().y();     update(); }  void coordinatepoint::hoverleaveevent(qgraphicsscenehoverevent* event) {     hover = false;     update(); }  void coordinatepoint::paint(qpainter* painter, const qstyleoptiongraphicsitem* option, qwidget* widget) {     qgraphicsellipseitem::paint(painter, option, widget);     if (hover)     {         painter->save();         painter->setpen(qt::black);         painter->setbrush(qt::black);         painter->drawtext(mx + 2, + 2,                           "(" + qstring::number(mx) + "," +                           qstring::number(my) + ")");         painter->restore();     } } 

i think using separate child item text make life lot easier:

#include <qtwidgets>  class coordinatepoint : public qgraphicsellipseitem { public:     coordinatepoint(qgraphicsitem* parent = q_nullptr) :         qgraphicsellipseitem(parent),         coordinatetext(q_nullptr)     {         setaccepthoverevents(true);     }      void hoverenterevent(qgraphicsscenehoverevent*)     {         if (!coordinatetext) {             coordinatetext = new qgraphicstextitem(this);             coordinatetext->setplaintext("(" + qstring::number(x())                 + "," + qstring::number(y()) + ")");             coordinatetext->setx(2);             coordinatetext->sety(2);         }          coordinatetext->setvisible(true);     }      void hoverleaveevent(qgraphicsscenehoverevent*)     {         if (coordinatetext) {             coordinatetext->setvisible(false);         }     }  private:     qgraphicstextitem *coordinatetext; };  int main(int argc, char *argv[]) {     qapplication a(argc, argv);      qmainwindow window;      qgraphicsview *view = new qgraphicsview(&window);     view->setrenderhint(qpainter::antialiasing);      qgraphicsscene *scene = new qgraphicsscene(&window);     view->fitinview(scene->scenerect(), qt::keepaspectratio);     view->setscene(scene);     window.setcentralwidget(view);      (int y = 0; y < 900; y += 100) {         for(int x = 0; x < 1400; x += 100) {             coordinatepoint* point = new coordinatepoint();             point->setrect(qrect(0, 0, 3, 3));             point->setx(x);             point->sety(y);             point->setpen(qpen(qt::red, 3, qt::solidline));             point->setbrush(qt::red);             scene->additem(point);         }     }      window.show();      return a.exec(); } 

if having qgraphicstextitem each coordinate worries you, construct 1 of them , share amongst them all, reparenting each 1 hovered. should work fine, there can ever 1 coordinate hovered @ time.

if try draw text part of ellipse item, you'd have to:

• increase size of item it's large enough contain text, means overriding boundingrect().
• only draw ellipse within part of area.
• in hoverenterevent(), check mouse cursor within ellipse's area.
• a bunch of other stuff, probably.