Is there a way to refresh a matplotlib cursor on click?

Question

I'm plotting around 250k points with matplotlib so naturally when I'm moving my mouse to use/refresh a cursor widget, it lags a lot. Therefore, I was looking for one way to optimize the use of this widget and I thought of refreshing the cursor on click to reduce the number of freezes. I saw this extract from the matplotlib documentation and other examples of click events, however I didn't manage to find more information about specifically linking the cursor refresh to the mouse click event.

Is it even possible?

Screenshot of the graph and the cursor:

Code used to plot the graph and add the cursor:

import matplotlib.pyplot as plt
from matplotlib.widgets import Cursor

fig, ax = plt.subplots(figsize=(20, 8), num="Original Signal")
thismanager = plt.get_current_fig_manager()
thismanager.window.wm_iconbitmap("icon.ico")
thismanager = plt.get_current_fig_manager().window.state('zoomed')
plt.plot(Time, Ampl)
plt.xlabel("Time")
plt.ylabel("Amplitude")
plt.tight_layout()
plt.savefig(filepath[:-4] + "_OriginalSignal.jpeg")
cursor = Cursor(ax, color='r', horizOn=True, vertOn=True)
print('Original Signal file created: "', filepath[:-4], '_OriginalSignal.jpeg".', sep="")

What is this **cursor widget**? Is it a MPL element? Ideally, you could store a reference to your widget element and call its `refresh` function. — vyi, Dec 19 '22 at 13:34
@vyi According to the [documentation](https://matplotlib.org/stable/api/widgets_api.html#matplotlib.widgets.Cursor), `Cursor` is called like this: `matplotlib.widgets.Cursor` and takes multiple arguments but none of them affect it's refresh. [Click events](https://matplotlib.org/stable/gallery/event_handling/coords_demo.html) are a possible solution that I found while looking online, but I didn't manage to set it up for the `Cursor`. — Guillaume G, Dec 19 '22 at 13:45

score 1 · Accepted Answer · edited Dec 19 '22 at 15:04

If I understand your problem correctly, you wish to not draw the cursor as the mouse moves, but only when (and wherever) you do the left-click. Now your questions are:

Is it even possible?

Yes, using the active property of matplotlib.widgets.Widget base class. You will have to first make the cursor inactive and then activate it inside the on_click handler. You may also need to call fig.canvas.draw() once.

I didn't manage to find more information about specifically linking the cursor refresh to the mouse click event

This is a two-step process.

Make cursor inactive on mouse movement:

    def on_move(event):
        if cursor.active:
            cursor.active = False

Make cursor active on mouse click:

    def on_click(event):
        cursor.active = True
        cursor.canvas.draw():

Don't forget to link those events:

    plt.connect("motion_notify_event", on_move)
    plt.connect("button_press_event", on_click)

Thanks for your answer it worked perfectly (without the `fig.canvas.draw()` call)! — Guillaume G, Dec 19 '22 at 15:01
Done :). I also edited your answer to add details for dummies like me that would forget to link the events. — Guillaume G, Dec 19 '22 at 15:05

score 0 · Answer 2 · edited Dec 20 '22 at 03:37

0

You can use the Threading library. It will that allow a part of your program, in this case your plotting, to be run on a separate thread. I do this with my Tkinter GUIs were I plot data (around 2k point).

Are you doing real time plotting? If yes, it is not a good idea for that amount of points.

To be fair, with that amount of data it might be a bit too much.

++

Edit:

Ok, as I don't have the data and the parameters of the cursor try this:

from threading import Thread  

def newcursor():
    # Here place the code of your cursor 
    cursor = Cursor(ax, color='r', horizOn=True, vertOn=True)
    
# Before the print  
t=Thread(target=newcursor)
t.start()

edited Dec 20 '22 at 03:37

Guillaume G

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answered Dec 19 '22 at 12:54

Harith 75

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Thank you for your answer. However this seems like a heavy implementation. Isn't this possible within the matplotlib library (especially if I have too much data for the `threading` library/overall)? Also my data is static. – Guillaume G Dec 19 '22 at 13:19
It is not as heavy as you think. If you can provide some code it would be helpful. – Harith 75 Dec 19 '22 at 13:55
Okay, then I'm going to edit my question to add more details. – Guillaume G Dec 19 '22 at 14:00
1

I edited my answer try something like this – Harith 75 Dec 19 '22 at 14:37
Thanks it looks more clear. But how would you link the click on the plot to the thread start? – Guillaume G Dec 19 '22 at 14:43
Note that [Matplotlib is not thread safe](https://stackoverflow.com/questions/34764535)! – vyi Dec 19 '22 at 14:49
Yes. But I think multiprocessing here would be a bit hard for what he is asking. Since the memory is not shared it will be necessary to create communication tunnels (Queue) – Harith 75 Dec 19 '22 at 15:00
I went for @vyi answer but thanks for taking the time to try to solve my problem. – Guillaume G Dec 19 '22 at 15:05
1

No problem ! Indeed it is faster and easy – Harith 75 Dec 19 '22 at 15:09

Is there a way to refresh a matplotlib cursor on click?

2 Answers2