How to show labels for markers on hover when using animation?

Question

I'm trying to use matplotlib inside PyQt5 GUI, and be able to move points by clicking on a point and after that on the place i want to move it, and for that i use FuncAnimation. I want to be able to see some details on the point before i'm picking it when hovering the point.

I found the mplcursors library and tried it, but because i uses the FuncAnimation option i can't make it work together. Also, because i'm not using scatter i couldn't understood how to use the mpld3 library. I tried to set the blit option in the animation to False but none off the things above worked for me.

This is how my code looks like:

import sys
import matplotlib

matplotlib.use('Qt5Agg')
import mplcursors
from PyQt5 import QtCore, QtWidgets
from PyQt5.QtWidgets import QApplication, QMainWindow, QMenu, QVBoxLayout, QHBoxLayout, QSizePolicy, QWidget, \
    QTextBrowser, QLineEdit
from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg as FigureCanvas
from matplotlib.figure import Figure
from matplotlib.animation import FuncAnimation
from Entities import Soldier, CompanyCommander, BTW, FieldObjects


class MyMplCanvas(FigureCanvas):
    fig = Figure(figsize=(5, 4), dpi=200)
    ax = fig.add_subplot(1, 1, 1)
    def __init__(self, parent=None):

        FigureCanvas.__init__(self, MyMplCanvas.fig)
        self.setParent(parent)
        FigureCanvas.setSizePolicy(self,
                                   QtWidgets.QSizePolicy.Expanding,
                                   QtWidgets.QSizePolicy.Expanding)
        FigureCanvas.updateGeometry(self)


class ApplicationWindow(QtWidgets.QMainWindow):
    soldiers = []
    picked_soldier = []

    s1 = Soldier(1, (3, 4), 100)
    s2 = Soldier(2, (5, 6), 100)
    s3 = Soldier(3, (1, 6), 100)
    s4 = BTW(1, (2, 3), 100)
    s5 = BTW(2, (3, 3.5), 100)
    s6 = BTW(3, (4.2, 3.7), 100)
    s7 = Soldier(1, (5.3, 4), 100)
    s8 = Soldier(2, (2.6, 4.3), 100)
    s9 = Soldier(3, (7, 5.2), 100)

    soldiers = [s1, s2, s3, s4, s5, s6, s7, s8, s9]

    def __init__(self):
        QtWidgets.QMainWindow.__init__(self)
        self.setAttribute(QtCore.Qt.WA_DeleteOnClose)
        self.setWindowTitle("application main window")
        self.main_widget = QtWidgets.QWidget(self)

        vbox = QtWidgets.QVBoxLayout(self.main_widget)

        self.canvas = MyMplCanvas(self.main_widget)  ###attention###
        vbox.addWidget(self.canvas)

        hbox = QtWidgets.QHBoxLayout(self.main_widget)

        self.setLayout(vbox)

        self.main_widget.setFocus()
        self.setCentralWidget(self.main_widget)

        self.ani = FuncAnimation(self.canvas.figure, self.animate, interval=1000, blit=False)
        self.curs = mplcursors.cursor(hover=True, highlight=True).connect("add", lambda sel: sel.annotation.set_text(sel.artist.get_label()))
        self.canvas.figure.canvas.mpl_connect('pick_event', ApplicationWindow.on_pick)

    def animate(self, i):
        self.canvas.ax.clear()
        self.create_plot()

    def create_plot(self):
        for s in self.soldiers:
            if s.company_number == 1:
                if type(s) == Soldier:
                    self.canvas.ax.plot(s.x, s.y, marker='o', markersize=5, color="blue", picker=5, label=s.__str__())
                else:
                    self.canvas.ax.plot(s.x, s.y, marker='*', markersize=5, color="blue", picker=5, label=s.__str__())

            elif s.company_number == 2:
                if type(s) == Soldier:
                    self.canvas.ax.plot(s.x, s.y, marker='o', markersize=5, color="red", picker=5, label=s.__str__())
                else:
                    self.canvas.ax.plot(s.x, s.y, marker='*', markersize=5, color="red", picker=5, label=s.__str__())

            elif s.company_number == 3:
                if type(s) == Soldier:
                    self.canvas.ax.plot(s.x, s.y, marker='o', markersize=5, color="green", picker=5, label=s.__str__())
                else:
                    self.canvas.ax.plot(s.x, s.y, marker='*', markersize=5, color="green", picker=5, label=s.__str__())
            else:
                continue


    def on_pick(event):
        this_point = event.artist
        x_data = this_point.get_xdata()
        y_data = this_point.get_ydata()
        ind = event.ind

        for soldier in ApplicationWindow.soldiers:
            if soldier.x == x_data and soldier.y == y_data:
                index = soldier.ID - 1
                ApplicationWindow.picked_soldier.append(soldier)
                break

        print(str(float(x_data[ind])) + ", " + str(float(y_data[ind])))
        print(str(ApplicationWindow.soldiers[index].__str__()))

        MyMplCanvas.fig.canvas.mpl_connect('button_press_event', ApplicationWindow.on_click)
        MyMplCanvas.fig.canvas.mpl_disconnect(MyMplCanvas.fig.canvas.mpl_connect
                                                           ('pick_event', ApplicationWindow.on_pick))

    def on_click(event):
        x_data = event.xdata
        y_data = event.ydata
        if len(ApplicationWindow.picked_soldier) > 0:
            soldier = ApplicationWindow.picked_soldier.pop(0)
            soldier.update_location(x_data, y_data)

        print(x_data, y_data)
        MyMplCanvas.fig.canvas.mpl_connect('pick_event', ApplicationWindow.on_pick)
        MyMplCanvas.fig.canvas.mpl_disconnect(MyMplCanvas.fig.canvas.mpl_connect('button_press_event', ApplicationWindow.on_click))

if __name__ == "__main__":
    App = QApplication(sys.argv)
    aw = ApplicationWindow()
    aw.show()
    sys.exit(App.exec_())

I would like to know if there is a better way the show the labels on hovering a point or what else i can try to make the labels work when usin FuncAnimation and PyQt5 GUI together.

Answer 1

Since markers are used and your constantly clearing and redrawing the plot, you need to cycle through the axes lines and check if it contains the current event; for the same reason, some persistent data about the annotation is required.

class ApplicationWindow(QtWidgets.QMainWindow):
    # ...
    def __init__(self):
        # ...
        self.tooltip_visible = False
        self.tooltip_coords = 0, 0
        self.tooltip_text = ''
        self.ani = FuncAnimation(self.canvas.figure, self.animate, interval=1000, blit=False)
        self.canvas.figure.canvas.mpl_connect('pick_event', ApplicationWindow.on_pick)
        self.canvas.mpl_connect("motion_notify_event", self.hover)

    def hover(self, event):
        if event.inaxes == self.canvas.ax:
            for line in self.canvas.ax.lines:
                contains, index = line.contains(event)
                if contains:
                    self.tooltip.set_text(line.get_label())
                    self.tooltip.set_x(line.get_xdata())
                    self.tooltip.set_y(line.get_ydata())
                    self.tooltip.set_visible(True)
                    self.tooltip_coords = line.get_xdata(), line.get_ydata()
                    self.tooltip_text = line.get_label()
                    break
            else:
                self.tooltip.set_visible(False)
        self.tooltip_visible = self.tooltip._visible
        # redraw the canvas to display or hide the label
        self.canvas.draw()

    def animate(self, i):
        self.canvas.ax.clear()
        self.tooltip = self.canvas.ax.annotate(self.tooltip_text, self.tooltip_coords)
        self.tooltip.set_visible(self.tooltip_visible)
        self.create_plot()

I have to warn you, though, that your implementation has some issues. The advantage of animation is to change properties of persistent objects, redrawing the whole plot at each pass is not a good solution. All markers can be created just once: you can create an internal list of markers and extend it for each canvas.ax.plot (which returns a list of markers created), then use the animation to set that data. Since you are using the blit argument, the animation function should return the new data about each object, otherwise there's no point in using it. Have a look at the animation api documentation.
Finally, I think you should youse instance methods for connections, and not class methods (since they won't let you access the instance attributes, including the canvas itself).