Add ModifiedEvent listener for ipyvtk plotter (#1264)

pyvista/jupyter/notebook.py

@@ -21,6 +21,8 @@
 except ImportError:  # pragma: no cover
     raise ImportError('Install IPython to display an image in a notebook')
 
+from pyvista import _vtk
+
 PANEL_EXTENSION_SET = [False]
 
 
@@ -92,6 +94,9 @@ def show_ipyvtk(plotter, return_viewer):
     disp = ViewInteractiveWidget(plotter.ren_win, on_close=plotter.close,
                                  transparent_background=plotter.image_transparent_background)
 
+    for renderer in plotter.renderers:
+        renderer.AddObserver(_vtk.vtkCommand.ModifiedEvent, lambda *args: disp.update_canvas())
+
     if return_viewer:
         return disp
     display.display_html(disp)