WebAgg performance improvements

lib/matplotlib/backend_bases.py

@@ -3125,7 +3125,7 @@ def draw(self):
 
             for loc in locators:
                 loc.refresh()
-        self.canvas.draw()
+        self.canvas.draw_idle()
 
     def _update_view(self):
         """Update the viewlim and position from the view and
@@ -3146,7 +3146,7 @@ def _update_view(self):
             a.set_position(pos[i][0], 'original')
             a.set_position(pos[i][1], 'active')
 
-        self.draw()
+        self.draw_idle()
 
     def save_figure(self, *args):
         """Save the current figure"""

lib/matplotlib/backends/backend_webagg.py

@@ -253,7 +253,6 @@ def handle_event(self, event):
             elif e_type == 'key_release':
                 self.key_release_event(key)
         elif e_type == 'toolbar_button':
-            print('Toolbar button pressed: ', event['name'])
             # TODO: Be more suspicious of the input
             getattr(self.toolbar, event['name'])()
         elif e_type == 'refresh':
@@ -296,8 +295,10 @@ def remove_web_socket(self, web_socket):
         self.web_sockets.remove(web_socket)
 
     def refresh_all(self):
-        for s in self.web_sockets:
-            s.send_image()
+        if self.web_sockets:
+            diff = self.canvas.get_diff_image()
+            for s in self.web_sockets:
+                s.send_diff_image(diff)
 
     def send_event(self, event_type, **kwargs):
         for s in self.web_sockets:
@@ -473,6 +474,8 @@ def open(self, fignum):
             _, _, w, h = manager.canvas.figure.bbox.bounds
             manager.resize(w, h)
             self.on_message('{"type":"refresh"}')
+            if hasattr(self, 'set_nodelay'):
+                self.set_nodelay(True)
 
         def on_close(self):
             Gcf.get_fig_manager(self.fignum).remove_web_socket(self)
@@ -484,6 +487,15 @@ def on_message(self, message):
             # whole.
             if message['type'] == 'supports_binary':
                 self.supports_binary = message['value']
+            elif message['type'] == 'ack':
+                # Network latency tends to decrease if traffic is
+                # flowing in both directions.  Therefore, the browser
+                # sends back an "ack" message after each image frame
+                # is received.  This could also be used as a simple
+                # sanity check in the future, but for now the
+                # performance increase is enough to justify it, even
+                # if the server does nothing with it.
+                pass
             else:
                 canvas = Gcf.get_fig_manager(self.fignum).canvas
                 canvas.handle_event(message)
@@ -493,9 +505,7 @@ def send_event(self, event_type, **kwargs):
             payload.update(kwargs)
             self.write_message(json.dumps(payload))
 
-        def send_image(self):
-            canvas = Gcf.get_fig_manager(self.fignum).canvas
-            diff = canvas.get_diff_image()
+        def send_diff_image(self, diff):
             if self.supports_binary:
                 self.write_message(diff, binary=True)
             else:

lib/matplotlib/backends/web_backend/mpl.js

@@ -66,6 +66,11 @@ figure.prototype.finalize = function (canvas_id_prefix, toolbar_id_prefix, messa
     onload_creator = function(fig) {return function() {fig.context.drawImage(fig.imageObj, 0, 0);};};
     this.imageObj.onload = onload_creator(fig);
 
+
+    this.imageObj.onunload = function() {
+        this.ws.close();
+    }
+
     this.ws.onmessage = gen_on_msg_fn(this);
 };
 
@@ -88,11 +93,13 @@ function gen_on_msg_fn(fig)
                 }
                 fig.imageObj.src = (window.URL || window.webkitURL).createObjectURL(
                     evt.data);
+                fig.ws.send('{"type": "ack"}')
                 return;
             }
         } else {
             if (evt.data.slice(0, 21) == "data:image/png;base64") {
                 fig.imageObj.src = evt.data;
+                fig.ws.send('{"type": "ack"}')
                 return;
             }
         }
@@ -132,6 +139,9 @@ function gen_on_msg_fn(fig)
                 fig.rubberband_canvas.width = size[0];
                 fig.rubberband_canvas.height = size[1];
                 fig.ws.send(JSON.stringify({type: 'refresh'}));
+                fig.ws.send(JSON.stringify(
+                    {type: 'supports_binary',
+                     value: fig.supports_binary}));
             }
             break;