Cleanups to webagg & friends.

FigureCanvasWebAgg and FigureCanvasNbAgg empty subclasses of
FigureCanvasWebAggCore.  They only differed in that WebAggCore did not
define the (common) timer class, which is easily fixed (but the
TimerTornado definition needs to be moved above the
FigureCanvasWegAggCore definition), and that WebAgg explicitly redefined
`show` to use the module's `show`, whereas WebAggCore's `show` uses
`pyplot.show`... but `pyplot.show` is defined as calling the backend
module's `show`, so it comes down to the same.

Still it's useful for them to be subclasses rather than straight
aliases, to keep the possibility of a canvas->manager mapping.

No need to explicitly mark WebAggCore as `supports_blit`, as that's
autodetected now (one can easily check that
`FigureCanvasWebAggCore.supports_blit` is still True).

Saving `pgf` to a BytesIO actually works fine nowadays, and can indeed
by manually tested on WebAgg.

Author: anntzer

lib/matplotlib/backends/backend_nbagg.py

@@ -142,7 +142,7 @@ def remove_comm(self, comm_id):
 
 
 class FigureCanvasNbAgg(FigureCanvasWebAggCore):
-    _timer_cls = TimerTornado
+    pass
 
 
 class CommSocket:

lib/matplotlib/backends/backend_webagg.py

@@ -48,12 +48,7 @@ def run(self):
 
 
 class FigureCanvasWebAgg(core.FigureCanvasWebAggCore):
-    _timer_cls = TimerTornado
-
-    def show(self):
-        # show the figure window
-        global show  # placates pyflakes: created by @_Backend.export below
-        show()
+    pass
 
 
 class WebAggApplication(tornado.web.Application):

lib/matplotlib/backends/backend_webagg_core.py

@@ -117,8 +117,43 @@ def _handle_key(key):
     return key
 
 
+class TimerTornado(backend_bases.TimerBase):
+    def __init__(self, *args, **kwargs):
+        self._timer = None
+        super().__init__(*args, **kwargs)
+
+    def _timer_start(self):
+        self._timer_stop()
+        if self._single:
+            ioloop = tornado.ioloop.IOLoop.instance()
+            self._timer = ioloop.add_timeout(
+                datetime.timedelta(milliseconds=self.interval),
+                self._on_timer)
+        else:
+            self._timer = tornado.ioloop.PeriodicCallback(
+                self._on_timer,
+                max(self.interval, 1e-6))
+            self._timer.start()
+
+    def _timer_stop(self):
+        if self._timer is None:
+            return
+        elif self._single:
+            ioloop = tornado.ioloop.IOLoop.instance()
+            ioloop.remove_timeout(self._timer)
+        else:
+            self._timer.stop()
+        self._timer = None
+
+    def _timer_set_interval(self):
+        # Only stop and restart it if the timer has already been started
+        if self._timer is not None:
+            self._timer_stop()
+            self._timer_start()
+
+
 class FigureCanvasWebAggCore(backend_agg.FigureCanvasAgg):
-    supports_blit = True
+    _timer_cls = TimerTornado
 
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
@@ -478,8 +513,7 @@ def get_javascript(cls, stream=None):
         for filetype, ext in sorted(FigureCanvasWebAggCore.
                                     get_supported_filetypes_grouped().
                                     items()):
-            if ext[0] != 'pgf':  # pgf does not support BytesIO
-                extensions.append(ext[0])
+            extensions.append(ext[0])
         output.write("mpl.extensions = {0};\n\n".format(
             json.dumps(extensions)))
 
@@ -499,41 +533,6 @@ def _send_event(self, event_type, **kwargs):
             s.send_json(payload)
 
 
-class TimerTornado(backend_bases.TimerBase):
-    def __init__(self, *args, **kwargs):
-        self._timer = None
-        super().__init__(*args, **kwargs)
-
-    def _timer_start(self):
-        self._timer_stop()
-        if self._single:
-            ioloop = tornado.ioloop.IOLoop.instance()
-            self._timer = ioloop.add_timeout(
-                datetime.timedelta(milliseconds=self.interval),
-                self._on_timer)
-        else:
-            self._timer = tornado.ioloop.PeriodicCallback(
-                self._on_timer,
-                max(self.interval, 1e-6))
-            self._timer.start()
-
-    def _timer_stop(self):
-        if self._timer is None:
-            return
-        elif self._single:
-            ioloop = tornado.ioloop.IOLoop.instance()
-            ioloop.remove_timeout(self._timer)
-        else:
-            self._timer.stop()
-        self._timer = None
-
-    def _timer_set_interval(self):
-        # Only stop and restart it if the timer has already been started
-        if self._timer is not None:
-            self._timer_stop()
-            self._timer_start()
-
-
 @_Backend.export
 class _BackendWebAggCoreAgg(_Backend):
     FigureCanvas = FigureCanvasWebAggCore