Fix show logic in pyplot visualizer (RobotLocomotion#12658)

The show arguments passed into the recording methods were doing nothing (they were accidentally setting self.show instead of self._show).  And it was too late, anyhow, to prevent a window being drawn in the jupyter workflow.  This commit does the shenanigans necessary to avoid that extra plot.

Unfortunately, the drawing/not drawing is not something we currently test.

bindings/pydrake/systems/planar_scenegraph_visualizer.py

@@ -72,7 +72,8 @@ def __init__(self,
                  ylim=[-1, 1],
                  facecolor=[1, 1, 1],
                  use_random_colors=False,
-                 ax=None):
+                 ax=None,
+                 show=None):
         """
         Args:
             scene_graph: A SceneGraph object.
@@ -90,13 +91,16 @@ def __init__(self,
             ax: If supplied, the visualizer will draw onto those axes instead
                 of creating a new set of axes. The visualizer will still change
                 the view range and figure size of those axes.
+            show: Opens a window during initialization / publish iff True.
+                Default is None, which implies show=True unless
+                matplotlib.get_backend() is 'template'.
         """
         default_size = matplotlib.rcParams['figure.figsize']
         scalefactor = (ylim[1]-ylim[0]) / (xlim[1]-xlim[0])
         figsize = (default_size[0], default_size[0]*scalefactor)
 
         PyPlotVisualizer.__init__(self, facecolor=facecolor, figsize=figsize,
-                                  ax=ax, draw_period=draw_period)
+                                  ax=ax, draw_period=draw_period, show=show)
         self.set_name('planar_multibody_visualizer')
 
         self._scene_graph = scene_graph

bindings/pydrake/systems/pyplot_visualizer.py

@@ -1,8 +1,8 @@
 import matplotlib
 import matplotlib.animation as animation
 import matplotlib.pyplot as plt
-from matplotlib.widgets import Slider
 import numpy as np
+from warnings import warn
 
 from pydrake.systems.framework import LeafSystem, PublishEvent, TriggerType
 from pydrake.systems.primitives import SignalLogger
@@ -26,7 +26,7 @@ class PyPlotVisualizer(LeafSystem):
     """
 
     def __init__(self, draw_period=1./30, facecolor=[1, 1, 1],
-                 figsize=None, ax=None):
+                 figsize=None, ax=None, show=None):
         LeafSystem.__init__(self)
 
         self.set_name('pyplot_visualization')
@@ -41,14 +41,22 @@ def __init__(self, draw_period=1./30, facecolor=[1, 1, 1],
             self.ax = ax
             self.fig = ax.get_figure()
 
+        if show is None:
+            show = (matplotlib.get_backend().lower() != 'template')
+        self._show = show
+
         self.ax.axis('equal')
         self.ax.axis('off')
 
+        if not show:
+            # This is the preferred way to support the jupyter notebook
+            # animation workflow and the `inline` backend grabbing an
+            # extraneous render of the figure.
+            plt.close(self.fig)
+
         self._is_recording = False
         self._recorded_contexts = []
 
-        self._show = (matplotlib.get_backend().lower() != 'template')
-
         def on_initialize(context, event):
             if self._show:
                 self.fig.show()
@@ -77,13 +85,16 @@ def draw(self, context):
         """
         raise NotImplementedError
 
-    def start_recording(self, show=True):
-        self.show = show
+    def start_recording(self, show=None):
+        if show is not None:
+            warn("The `show` argument of this `start_recording()` method "
+                 "actually never worked.  Pass `show` to the class "
+                 "constructor instead.  This argument will be removed on or "
+                 "after 2020-04-01.")
         self._is_recording = True
 
     def stop_recording(self):
         self._is_recording = False
-        self.show = (matplotlib.get_backend().lower() != 'template')
 
     def reset_recording(self):
         self._recorded_contexts = []  # Reset recorded data.

tutorials/pyplot_animation_multibody_plant.ipynb

@@ -112,7 +112,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "def run_pendulum_example(duration=1., playback=True):\n",
+    "def run_pendulum_example(duration=1., playback=True, show=True):\n",
     "    \"\"\"\n",
     "    Runs a simulation of a pendulum.\n",
     "\n",
@@ -134,7 +134,7 @@
     "                     [0., 0., 0., 1.]])\n",
     "    visualizer = builder.AddSystem(PlanarSceneGraphVisualizer(\n",
     "        scene_graph, T_VW=T_VW,\n",
-    "        xlim=[-1.2, 1.2], ylim=[-1.2, 1.2]))\n",
+    "        xlim=[-1.2, 1.2], ylim=[-1.2, 1.2], show=show))\n",
     "    builder.Connect(pose_bundle_output_port, visualizer.get_input_port(0))\n",
     "    if playback:\n",
     "        visualizer.start_recording()\n",
@@ -239,6 +239,23 @@
     "if animation.writers.is_available(\"ffmpeg\"):\n",
     "    display(HTML(ani.to_html5_video()))"
    ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "If you do not want to render the image (only the animation), then pass `show=False` in to the constructor of `PlanarSceneGraphVisualizer()`."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "ani = run_pendulum_example(playback=True, show=False)\n",
+    "HTML(ani.to_jshtml())"
+   ]
   }
  ],
  "metadata": {