Avoid event accumulation in webagg backend. by raphaelquast · Pull Request #27160 · matplotlib/matplotlib · GitHub

PR summary

This PR is intended to address the problem of event-accumulation during image-processing in the webagg backend
which can result in an extreme lag that makes "fast updated" events like motion_notify_event etc. unusable at the moment.

Not 100% sure, but this might also improve problems concerning blitting in jupyter-notebooks (e.g. #19116) but would require sending "ack" messages in ipympl. The implementation is made in a way such that ipympl (or more generally backends that don't send "ack" messages) are not affected.

The following gifs show the outcome of this change: (left: current behavior, right: result of this PR)

🐍 code to run example

import matplotlib as mpl
mpl.use("webagg")
mpl.rcParams['webagg.port']=8988
mpl.rcParams['webagg.open_in_browser']=True

import matplotlib.pyplot as plt

fig, ax = plt.subplots(figsize=(14, 8))
ax.plot([0, 1], [0, 1], 'r')
ln, = ax.plot([0, 1], [0, 0], 'g', animated=True)
ax.figure.canvas.draw()

fig._last_blit_bg = fig.canvas.copy_from_bbox(ax.bbox)

def on_resize(event):
    ax.figure.canvas.draw()
    fig._last_blit_bg = fig.canvas.copy_from_bbox(ax.bbox)

def on_move(event):
    ax.figure.canvas.restore_region(fig._last_blit_bg)
    ln.set_ydata([event.ydata, event.ydata])
    ax.draw_artist(ln)
    ax.figure.canvas.blit(ax.bbox)

fig.canvas.mpl_connect('motion_notify_event', on_move)
fig.canvas.mpl_connect('resize_event', on_resize)

plt.show()

PR checklist

"closes #0000" is in the body of the PR description to link the related issue
new and changed code is tested
Plotting related features are demonstrated in an example
New Features and API Changes are noted with a directive and release note
Documentation complies with general and docstring guidelines

Co-authored-by: Tim Hoffmann <2836374+timhoffm@users.noreply.github.com>

Comments from call:

add ability to opt-in to this behavior with a string control (so we can support other stratgies)
look into de-bouncing in blit as well

attn @ianhi

I am using an interactive ipympl widget in an application, that would profit a lot from blitting, so i have been waiting for this PR to be merged. Thank you for the promising work done.
I just wanted to ask now, if we can expect this to be merged eventually, or if development has stopped, or is happening somewhere else, or ... ?

Hey, just a quick comment from my side:
I would be really happy if this PR is merged sometime soon...
Unfortunately however, I have absolutely no time right now to continue working on the remaining issues that need to be resolved and it will stay this way for a few months more...

I am happy if someone takes over in the meantime, otherwise I'll try to continue working on it as soon as i find some time (best guess is sometime early next year).

@sjmarwitz you could also monkey-patch the fix in the meantime to check if it does the job for you... I implemented a workaround for EOmaps ( see here)

@raphaelquast Thanks for your quick response and for pointing me to your monkey-path fix. I tried it and immediately hit the problem with ipympl, that was already mentioned in the PR summary. Actually, when using ipympl, after the initial display of a figure, it won't update the canvas/figure, not even zooming or panning is possible. It seems, no 'ack' messages are being received (and sent?).

I would have liked to contribute a fix somehow, given the limited amount of time i have, but looking into the ipympl code, i got lost, as i don't "speak" js and the like and are not familiar with web technologies.

Don't know what this comment means.

Co-authored-by: Elliott Sales de Andrade <quantum.analyst@gmail.com>

Avoid event accumulation in webagg backend.

809810b

raphaelquast mentioned this pull request Oct 20, 2023

[ENH] Proposal how to fix blitting in "webagg" (and potentially "ipympl") #27125

Closed

timhoffm reviewed Oct 20, 2023

View reviewed changes

Comment thread lib/matplotlib/backends/backend_webagg_core.py Outdated

Comment thread lib/matplotlib/backends/backend_webagg_core.py Outdated

Comment thread lib/matplotlib/backends/backend_webagg_core.py Outdated

raphaelquast and others added 4 commits October 21, 2023 11:51

Update lib/matplotlib/backends/backend_webagg_core.py

52c63de

Co-authored-by: Tim Hoffmann <2836374+timhoffm@users.noreply.github.com>

Update lib/matplotlib/backends/backend_webagg_core.py

52d1758

Co-authored-by: Tim Hoffmann <2836374+timhoffm@users.noreply.github.com>

rename sent_cnt and ack_cnt to num_ent_images and num_received_images

7fe7fb9

rename cnt_eq to pending_images and invert logic

d6e20d5

raphaelquast requested a review from timhoffm October 23, 2023 07:40

raphaelquast mentioned this pull request Oct 31, 2023

WebAgg for multiple clients #2620

Closed

raphaelquast mentioned this pull request Dec 7, 2023

EOmaps pyOpenSci/software-submission#138

Closed

14 of 30 tasks

QuLogic reviewed Oct 4, 2024

View reviewed changes

ianhi mentioned this pull request Oct 17, 2024

occasional graphical corruption when manipulating plots using the zoom and pan widgets matplotlib/ipympl#566

Open

Update lib/matplotlib/backends/backend_webagg_core.py

9110f10

Co-authored-by: Elliott Sales de Andrade <quantum.analyst@gmail.com>

github-actions Bot added the GUI: webagg label Mar 5, 2025

raphaelquast and others added 2 commits March 5, 2025 09:39

Update lib/matplotlib/backends/backend_webagg_core.py

8a91f7b

Co-authored-by: Elliott Sales de Andrade <quantum.analyst@gmail.com>

Update lib/matplotlib/backends/backend_webagg_core.py

7551b47

Co-authored-by: Elliott Sales de Andrade <quantum.analyst@gmail.com>

This was referenced Mar 6, 2025

Stale information drawn by nbAgg #19116

Open

WebAgg based jupyter notebook backend #29725

Closed

Avoid event accumulation in webagg backend. by raphaelquast · Pull Request #27160 · matplotlib/matplotlib · GitHub

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Avoid event accumulation in webagg backend. - #27160

Avoid event accumulation in webagg backend.#27160
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+                      # Keep track of the number of received ack messages.
+                      if self._num_received_images is None:
+                          self._num_received_images = 0  # To support no "ack" messages.

Avoid event accumulation in webagg backend. by raphaelquast · Pull Request #27160 · matplotlib/matplotlib · GitHub

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Avoid event accumulation in webagg backend. - #27160

Avoid event accumulation in webagg backend.#27160raphaelquast wants to merge 8 commits intomatplotlib:mainmatplotlib/matplotlib:mainfrom raphaelquast:webagg_blit_fixraphaelquast/matplotlib:webagg_blit_fixCopy head branch name to clipboard

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raphaelquast commented Oct 20, 2023

PR summary

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Avoid event accumulation in webagg backend.#27160
raphaelquast wants to merge 8 commits into
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raphaelquast:webagg_blit_fix

ghost commented Sep 26, 2024 •
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