Hover Tool for plots in Pyqtgraph

I want to have data information shown when hovering over a line in pyqtgraph plots, but can’t get my sigpointsHovered to emit any signal. Here is a simple example of what i tried to do:

from PySide6.QtWidgets import QMainWindow, QWidget, QApplication, QVBoxLayout
import pyqtgraph as pg

def hovered(self, points, ev):
    print("FOOO")
    
x = [1,2,3,4,5,6,7,8,9]
y = [0,1,2,3,4,5,6,7,8]

app = QApplication([])
window = QWidget()
layout = QVBoxLayout()

plot_widget = pg.PlotWidget()
plot_item = plot_widget.getPlotItem()
line = plot_item.plot(x,y)
line.sigPointsHovered.connect(hovered)

layout.addWidget(plot_widget)
window.setLayout(layout)
       
window.show()
app.exec_()

I have already tried setting "hoverable" = True and read the docs several times, but I honestly have no clue why the sigPointsHovered is not working.

Answer

Why sigPointsHovered is not working

In short: There is no way to set “hoverable” argument for PlotDataItem class’s ScatterPlotItem right now. Therefore, it is not possible to use sigPointsHovered.

You could see this in the source code of PlotDataItem class’s function updateItems.

Workarounds

1. If you really want something like sigPointsHovered right now, instead of using a PlotWiget, use a ScatterPlotItem and set hoverable = True when you initialize it or when you use setData function. Run python -m pyqtgraph.examples and find the scatter plot example to see some example codes.

2. However, from your description, I think you actually want to do something when you hover over a “cruve” (instead of points). Currently, PlotCurveItem doesn’t implement a hoverEvent, so you may try to make a class that inherits the PlotCurveItem and add a hoverEvent to it.

Let me show you how to do this.

In this example, when the cursor enters the curve, the color changes to blue, and turn back to white when it leave the curve.

import pyqtgraph as pg
from pyqtgraph import QtCore, QtGui


class HoverableCurveItem(pg.PlotCurveItem):
    sigCurveHovered = QtCore.Signal(object, object)
    sigCurveNotHovered = QtCore.Signal(object, object)

    def __init__(self, hoverable=True, *args, **kwargs):
        super(HoverableCurveItem, self).__init__(*args, **kwargs)
        self.hoverable = hoverable
        self.setAcceptHoverEvents(True)

    def hoverEvent(self, ev):
        if self.hoverable:
            if self.mouseShape().contains(ev.pos()):
                self.sigCurveHovered.emit(self, ev)
            else:
                self.sigCurveNotHovered.emit(self, ev)


class MainWindow(QtGui.QMainWindow):
    def __init__(self, *args, **kwargs):
        super(MainWindow, self).__init__(*args, **kwargs)

        self.view = pg.GraphicsLayoutWidget()
        self.setCentralWidget(self.view)
        self.makeplot()

    def makeplot(self):
        x = [1, 2, 3, 4, 5, 6, 7, 8, 9]
        y = [0, 1, 2, 3, 4, 5, 6, 7, 8]
        plot = self.view.addPlot()
        self.plotitem = HoverableCurveItem(x, y, pen=pg.mkPen('w', width=10))
        self.plotitem.setClickable(True, width=10)
        self.plotitem.sigCurveHovered.connect(self.hovered)
        self.plotitem.sigCurveNotHovered.connect(self.leaveHovered)
        plot.addItem(self.plotitem)

    def hovered(self):
        print("cursor entered curve")
        self.plotitem.setPen(pg.mkPen('b', width=10))

    def leaveHovered(self):
        self.plotitem.setPen(pg.mkPen('w', width=10))


if __name__ == '__main__':
    import sys

    app = QtGui.QApplication(sys.argv)
    w = MainWindow()
    w.show()
    sys.exit(app.exec())

Edit

Need to setAcceptHoverEvent to Ture

Also, in the updated example, when the cursor enters the curve, the color changes to blue, and turn back to white when it leave the curve.