Mouse movement across canvas seems to trigger events even though all callbacks are cleared

Hello, I must be missing something fundamental here, but the issue is the following:

Consider this MWE:

%matplotlib widget

import matplotlib.pyplot as plt

plt.ioff()
fig, ax = plt.subplots(figsize=(2, 2))
fig.canvas.toolbar_visible = False
fig.canvas.header_visible = False
fig.canvas.resizable = False

# Remove all callbacks
fig.canvas.callbacks.callbacks.clear()
fig.callbacks.callbacks.clear()
ax._propobservers = {}

ax.plot([1, 2, 3])
display(fig.canvas)

As expected, it draws a simple figure without header and toolbar into the notebook. However, even though I removed all callbacks that might be associated with this figure, its canvas, and the axes, moving the mouse cursor across the figure causes communication between front- and backend, which results in considerable data transfer (and, hence, jerkiness) when used over the internet. See this screen recording that demonstrates the issue:

https://youtu.be/M5mMzIGXT1s

It can also be seen that mouse clicks (indicated by the black circle) inside the canvas trigger communication as well.

How can I disable this behavior?

My system specifications:

• ipympl 0.5.6
• JupyterLab 2.0.1
• Browser: Safari 13.1
• OS: macOS Catalina 10.15.4

[hoechenberger]

I am wondering how other Matplotlib back-ends are behaving

No idea, I’m relatively inexperienced when it comes to Matplotlib internals. In any case, since ipympl is specifically designed for Jupyter Notebook use, and since Jupyter Notebooks are often deployed online on remote servers, behavior that might be unproblematic for other (locally running) backends could become an issue due to network latency and data transfer time. This just to say that: Even if other backends do act like I demonstrated in my MWE, ipympl should probably opt for a slightly different approach that’s more responsive and generates fewer data transfers.

[martinRenou]

Hello, thanks for opening an issue!

Indeed your code will not cancel the communication between the back-end and the front-end. I did not know there was an API for that in Matplotlib, and it’s not plugged to the widgets communication AFAIK.

@tacaswell do you think doing fig.canvas.callbacks.callbacks.clear() should cancel communication? If yes, should it only cancel mouse-related communication or all communication (resize, redraw etc).