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DO NOT MERGE: Patch WebAgg backend for pyodide #29568

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5c8845d
Patch WebAgg backend
ianthomas23 Jan 31, 2025
55117ee
Improve python to javascript conversion
ianthomas23 May 6, 2025
38e9e52
Add Timer class to support animations
ianthomas23 May 7, 2025
94bde9b
Import alert from js [skip ci]
ianthomas23 May 12, 2025
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289 changes: 47 additions & 242 deletions lib/matplotlib/backends/backend_webagg.py
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Original file line number Diff line number Diff line change
Expand Up @@ -20,31 +20,14 @@
import signal
import threading

try:
import tornado
except ImportError as err:
raise RuntimeError("The WebAgg backend requires Tornado.") from err

import tornado.web
import tornado.ioloop
import tornado.websocket
from js import document
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We don't support matplotlib in Node.js anyways, but importing document in Node.js or other Node.js-like environments will fail.

from pyodide.code import run_js
from pyodide.ffi import create_proxy

import matplotlib as mpl
from matplotlib.backend_bases import _Backend
from matplotlib._pylab_helpers import Gcf
from . import backend_webagg_core as core
from .backend_webagg_core import ( # noqa: F401 # pylint: disable=W0611
TimerAsyncio, TimerTornado)


@mpl._api.deprecated("3.7")
class ServerThread(threading.Thread):
def run(self):
tornado.ioloop.IOLoop.instance().start()


webagg_server_thread = threading.Thread(
target=lambda: tornado.ioloop.IOLoop.instance().start())


class FigureManagerWebAgg(core.FigureManagerWebAgg):
Expand All @@ -54,278 +37,100 @@ class FigureManagerWebAgg(core.FigureManagerWebAgg):
def pyplot_show(cls, *, block=None):
WebAggApplication.initialize()

url = "http://{address}:{port}{prefix}".format(
address=WebAggApplication.address,
port=WebAggApplication.port,
prefix=WebAggApplication.url_prefix)
managers = Gcf.get_all_fig_managers()
for manager in managers:
manager.show()

def show(self):
fignum = str(self.num)

if mpl.rcParams['webagg.open_in_browser']:
import webbrowser
if not webbrowser.open(url):
print(f"To view figure, visit {url}")
else:
print(f"To view figure, visit {url}")
js_code = \
"""
var websocket_type = mpl.get_websocket_type();
var fig = new mpl.figure(fig_id, new websocket_type(fig_id), null, document.body);
fig;
"""
js_code = f"var fig_id = '{fignum}';" + js_code

WebAggApplication.start()
self.js_fig = run_js(js_code)
web_socket = WebAggApplication.MockPythonWebSocket(self, self.js_fig.ws)
web_socket.open(fignum)


class FigureCanvasWebAgg(core.FigureCanvasWebAggCore):
manager_class = FigureManagerWebAgg


class WebAggApplication(tornado.web.Application):
class WebAggApplication():
initialized = False
started = False

class FavIcon(tornado.web.RequestHandler):
def get(self):
self.set_header('Content-Type', 'image/png')
self.write(Path(mpl.get_data_path(),
'images/matplotlib.png').read_bytes())

class SingleFigurePage(tornado.web.RequestHandler):
def __init__(self, application, request, *, url_prefix='', **kwargs):
self.url_prefix = url_prefix
super().__init__(application, request, **kwargs)

def get(self, fignum):
fignum = int(fignum)
manager = Gcf.get_fig_manager(fignum)

ws_uri = f'ws://{self.request.host}{self.url_prefix}/'
self.render(
"single_figure.html",
prefix=self.url_prefix,
ws_uri=ws_uri,
fig_id=fignum,
toolitems=core.NavigationToolbar2WebAgg.toolitems,
canvas=manager.canvas)

class AllFiguresPage(tornado.web.RequestHandler):
def __init__(self, application, request, *, url_prefix='', **kwargs):
self.url_prefix = url_prefix
super().__init__(application, request, **kwargs)

def get(self):
ws_uri = f'ws://{self.request.host}{self.url_prefix}/'
self.render(
"all_figures.html",
prefix=self.url_prefix,
ws_uri=ws_uri,
figures=sorted(Gcf.figs.items()),
toolitems=core.NavigationToolbar2WebAgg.toolitems)

class MplJs(tornado.web.RequestHandler):
def get(self):
self.set_header('Content-Type', 'application/javascript')

js_content = core.FigureManagerWebAgg.get_javascript()

self.write(js_content)

class Download(tornado.web.RequestHandler):
def get(self, fignum, fmt):
fignum = int(fignum)
manager = Gcf.get_fig_manager(fignum)
self.set_header(
'Content-Type', mimetypes.types_map.get(fmt, 'binary'))
buff = BytesIO()
manager.canvas.figure.savefig(buff, format=fmt)
self.write(buff.getvalue())

class WebSocket(tornado.websocket.WebSocketHandler):
class MockPythonWebSocket:
supports_binary = True

def __init__(self, manager, js_web_socket):
self.manager = manager
self.js_web_socket = js_web_socket
self.on_message_proxy = None

def open(self, fignum):
self.on_message_proxy = create_proxy(self.on_message)
self.js_web_socket.open(self.on_message_proxy)
self.fignum = int(fignum)
self.manager = Gcf.get_fig_manager(self.fignum)
self.manager.add_web_socket(self)
if hasattr(self, 'set_nodelay'):
self.set_nodelay(True)

def on_close(self):
self.manager.remove_web_socket(self)
self.on_message_proxy.destroy()
self.on_message_proxy = None

def on_message(self, message):
message = json.loads(message)
message = message.as_py_json()
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Makes sense, assuming that we get a JavaScript JSON object (mix of arrays, objects, numbers, strings, and bools) as input.


# The 'supports_binary' message is on a client-by-client
# basis. The others affect the (shared) canvas as a
# whole.
if message['type'] == 'supports_binary':
self.supports_binary = message['value']
else:
manager = Gcf.get_fig_manager(self.fignum)
manager = self.manager
# It is possible for a figure to be closed,
# but a stale figure UI is still sending messages
# from the browser.
if manager is not None:
manager.handle_json(message)

def send_json(self, content):
self.write_message(json.dumps(content))
self.js_web_socket.receive_json(json.dumps(content))

def send_binary(self, blob):
if self.supports_binary:
self.write_message(blob, binary=True)
self.js_web_socket.receive_binary(blob, binary=True)
else:
data_uri = "data:image/png;base64,{}".format(
blob.encode('base64').replace('\n', ''))
self.write_message(data_uri)

def __init__(self, url_prefix=''):
if url_prefix:
assert url_prefix[0] == '/' and url_prefix[-1] != '/', \
'url_prefix must start with a "/" and not end with one.'

super().__init__(
[
# Static files for the CSS and JS
(url_prefix + r'/_static/(.*)',
tornado.web.StaticFileHandler,
{'path': core.FigureManagerWebAgg.get_static_file_path()}),

# Static images for the toolbar
(url_prefix + r'/_images/(.*)',
tornado.web.StaticFileHandler,
{'path': Path(mpl.get_data_path(), 'images')}),

# A Matplotlib favicon
(url_prefix + r'/favicon.ico', self.FavIcon),

# The page that contains all of the pieces
(url_prefix + r'/([0-9]+)', self.SingleFigurePage,
{'url_prefix': url_prefix}),

# The page that contains all of the figures
(url_prefix + r'/?', self.AllFiguresPage,
{'url_prefix': url_prefix}),

(url_prefix + r'/js/mpl.js', self.MplJs),

# Sends images and events to the browser, and receives
# events from the browser
(url_prefix + r'/([0-9]+)/ws', self.WebSocket),

# Handles the downloading (i.e., saving) of static images
(url_prefix + r'/([0-9]+)/download.([a-z0-9.]+)',
self.Download),
],
template_path=core.FigureManagerWebAgg.get_static_file_path())
self.js_web_socket.receive_binary(data_uri)

@classmethod
def initialize(cls, url_prefix='', port=None, address=None):
if cls.initialized:
return

# Create the class instance
app = cls(url_prefix=url_prefix)
css = (Path(__file__).parent / "web_backend/css/mpl.css").read_text(encoding="utf-8")
style = document.createElement('style')
style.textContent = css
document.head.append(style)

cls.url_prefix = url_prefix

# This port selection algorithm is borrowed, more or less
# verbatim, from IPython.
def random_ports(port, n):
"""
Generate a list of n random ports near the given port.

The first 5 ports will be sequential, and the remaining n-5 will be
randomly selected in the range [port-2*n, port+2*n].
"""
for i in range(min(5, n)):
yield port + i
for i in range(n - 5):
yield port + random.randint(-2 * n, 2 * n)

if address is None:
cls.address = mpl.rcParams['webagg.address']
else:
cls.address = address
cls.port = mpl.rcParams['webagg.port']
for port in random_ports(cls.port,
mpl.rcParams['webagg.port_retries']):
try:
app.listen(port, cls.address)
except OSError as e:
if e.errno != errno.EADDRINUSE:
raise
else:
cls.port = port
break
else:
raise SystemExit(
"The webagg server could not be started because an available "
"port could not be found")
js_content = core.FigureManagerWebAgg.get_javascript()
set_toolbar_image_callback = run_js(js_content)
set_toolbar_image_callback(create_proxy(WebAggApplication.get_toolbar_image))

cls.initialized = True

@classmethod
def start(cls):
import asyncio
try:
asyncio.get_running_loop()
except RuntimeError:
pass
else:
cls.started = True

if cls.started:
return

"""
IOLoop.running() was removed as of Tornado 2.4; see for example
https://groups.google.com/forum/#!topic/python-tornado/QLMzkpQBGOY
Thus there is no correct way to check if the loop has already been
launched. We may end up with two concurrently running loops in that
unlucky case with all the expected consequences.
"""
ioloop = tornado.ioloop.IOLoop.instance()

def shutdown():
ioloop.stop()
print("Server is stopped")
sys.stdout.flush()
cls.started = False

@contextmanager
def catch_sigint():
old_handler = signal.signal(
signal.SIGINT,
lambda sig, frame: ioloop.add_callback_from_signal(shutdown))
try:
yield
finally:
signal.signal(signal.SIGINT, old_handler)

# Set the flag to True *before* blocking on ioloop.start()
cls.started = True

print("Press Ctrl+C to stop WebAgg server")
sys.stdout.flush()
with catch_sigint():
ioloop.start()


def ipython_inline_display(figure):
import tornado.template

WebAggApplication.initialize()
import asyncio
try:
asyncio.get_running_loop()
except RuntimeError:
if not webagg_server_thread.is_alive():
webagg_server_thread.start()

fignum = figure.number
tpl = Path(core.FigureManagerWebAgg.get_static_file_path(),
"ipython_inline_figure.html").read_text()
t = tornado.template.Template(tpl)
return t.generate(
prefix=WebAggApplication.url_prefix,
fig_id=fignum,
toolitems=core.NavigationToolbar2WebAgg.toolitems,
canvas=figure.canvas,
port=WebAggApplication.port).decode('utf-8')
def get_toolbar_image(cls, image):
filename = Path(__file__).parent.parent / f"mpl-data/images/{image}.png"
png_bytes = filename.read_bytes()
return png_bytes


@_Backend.export
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