How can I display a key/value pair on a ToolTip across two graphs?

Question

I am using QCustomPlot to display to graphs, each with a different Key/Value Pairs. On the mouse hover, I am expecting to see the key/value pairs per graph, but instead, I am seeing the first graph on the right as shown on the picture

How can I do this to make it work better?

What I expected to be the behavior

For the graph to show the key/value pair for each graph, as the mouse cursor is placed on it.

What I have tried so far

Signal/Slot connection

connect(this,&QCustomPlot::mouseMove,this,&ChartWidget::showToolTip);

showToolTip slot implementation

   void ChartWidget::showToolTip(QMouseEvent *event){
      double x = xAxis->pixelToCoord(event->pos().x());
      double y = yAxis->pixelToCoord(event->pos().y());

     if(x>0&&y>0 && x<xAxis->range().upper) 
     setToolTip(tr("%1,%2").arg(x).arg(y));}

Answer 1

What you have to do is verify that QCPAxisRect is above the cursor. and then get the axes of each QCPAxisRect and then the values:

void showToolTip(QMouseEvent *event){
    for(QCPLayoutElement *element : plotLayout()->elements(true)){
        QCPAxisRect *axisRect = static_cast<QCPAxisRect *>(element);
        if(axisRect){
            if(axisRect->rect().contains(event->pos())){
                double x= axisRect->axis(QCPAxis::atBottom)->pixelToCoord(event->x());
                double y= axisRect->axis(QCPAxis::atLeft)->pixelToCoord(event->y());
                setToolTip(tr("%1,%2").arg(x).arg(y));
                break;
            }
        }
    }
}

Example:

#include "qcustomplot.h"

#include <QApplication>

class ChartWidget: public QCustomPlot{
public:
    ChartWidget(QWidget *parent=nullptr):QCustomPlot(parent){

        plotLayout()->clear();
        QCPAxisRect *leftAxisRect = new QCPAxisRect(this);
        QCPAxisRect *rightAxisRect = new QCPAxisRect(this);
        plotLayout()->addElement(0, 0, leftAxisRect);
        plotLayout()->addElement(0, 1, rightAxisRect);

        QVector<QCPGraphData> dataCos(100);

        for(int i=0; i<dataCos.size(); ++i){
            dataCos[i].key = i/(double)(dataCos.size()-1)*10-5.0;
            dataCos[i].value = qCos(dataCos[i].key);
        }

        QCPGraph *mainGraphCos = addGraph(leftAxisRect->axis(QCPAxis::atBottom), leftAxisRect->axis(QCPAxis::atLeft));
        mainGraphCos->data()->set(dataCos);
        mainGraphCos->valueAxis()->setRange(-1, 1);
        mainGraphCos->rescaleKeyAxis();
        mainGraphCos->setPen(QPen(QColor("blue"), 2));

        QVector<QCPGraphData> dataExp(100);

        for(int i=0; i<dataExp.size(); ++i){
            dataExp[i].key = i/(double)(dataExp.size()-1)*10-5.0;
            dataExp[i].value = qExp(dataExp[i].key)*qCos(dataExp[i].key);
        }

        QCPGraph *mainGraphExp = addGraph(rightAxisRect->axis(QCPAxis::atBottom), rightAxisRect->axis(QCPAxis::atLeft));
        mainGraphExp->data()->set(dataExp);
        mainGraphExp->keyAxis()->setRange(-5, 5);
        mainGraphExp->rescaleValueAxis();
        mainGraphExp->setPen(QPen(QColor("red"), 2));

        connect(this, &ChartWidget::mouseMove, this, &ChartWidget::showToolTip);
    }
private:
    void showToolTip(QMouseEvent *event){
        for(QCPLayoutElement *element : plotLayout()->elements(true)){
            QCPAxisRect *axisRect = static_cast<QCPAxisRect *>(element);
            if(axisRect){
                if(axisRect->rect().contains(event->pos())){
                    double x= axisRect->axis(QCPAxis::atBottom)->pixelToCoord(event->x());
                    double y= axisRect->axis(QCPAxis::atLeft)->pixelToCoord(event->y());
                    setToolTip(tr("%1,%2").arg(x).arg(y));
                    break;
                }
            }
        }
    }
};
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    ChartWidget w;
    w.resize(640, 480);
    w.show();

    return a.exec();
}

In the following link you can find the complete example