matplotlib · greglucas · Mar 5, 2022 · Nov 28, 2021 · Nov 27, 2021 · Jan 9, 2022
diff --git a/lib/matplotlib/backends/backend_macosx.py b/lib/matplotlib/backends/backend_macosx.py
@@ -30,27 +30,64 @@ def __init__(self, figure):
         FigureCanvasBase.__init__(self, figure)
         width, height = self.get_width_height()
         _macosx.FigureCanvas.__init__(self, width, height)
+        self._draw_pending = False
+        self._is_drawing = False
 
     def set_cursor(self, cursor):
         # docstring inherited
         _macosx.set_cursor(cursor)
 
-    def _draw(self):
-        renderer = self.get_renderer()
-        if self.figure.stale:
-            renderer.clear()
-            self.figure.draw(renderer)
-        return renderer
-
     def draw(self):
-        # docstring inherited
-        self._draw()
-        self.flush_events()
+        """Render the figure and update the macosx canvas."""
+        # The renderer draw is done here; delaying causes problems with code
+        # that uses the result of the draw() to update plot elements.
+        if self._is_drawing:
+            return
+        with cbook._setattr_cm(self, _is_drawing=True):
+            super().draw()
+        self.update()
 
-    # draw_idle is provided by _macosx.FigureCanvas
+    def draw_idle(self):
+        # docstring inherited
+        if not (getattr(self, '_draw_pending', False) or
+                getattr(self, '_is_drawing', False)):
+            self._draw_pending = True
+            # Add a singleshot timer to the eventloop that will call back
+            # into the Python method _draw_idle to take care of the draw
+            self._single_shot_timer(self._draw_idle)
+
+    def _single_shot_timer(self, callback):
+        """Add a single shot timer with the given callback"""
+        # We need to explicitly stop (called from delete) the timer after
+        # firing, otherwise segfaults will occur when trying to deallocate
+        # the singleshot timers.
+        def callback_func(callback, timer):
+            callback()
+            del timer
+        timer = self.new_timer(interval=0)
+        timer.add_callback(callback_func, callback, timer)
+        timer.start()
+
+    def _draw_idle(self):
+        """
+        Draw method for singleshot timer
+
+        This draw method can be added to a singleshot timer, which can
+        accumulate draws while the eventloop is spinning. This method will
+        then only draw the first time and short-circuit the others.
+        """
+        with self._idle_draw_cntx():
+            if not self._draw_pending:
+                # Short-circuit because our draw request has already been
+                # taken care of
+                return
+            self._draw_pending = False
+            self.draw()
 def _draw_idle(self): 
     with self._idle_draw_cntx(): 
         if not self._draw_pending: 
             return 
         self._draw_pending = False 
         if self.height() < 0 or self.width() < 0: 
             return 
         try: 
             self.draw() 
         except Exception: 
             # Uncaught exceptions are fatal for PyQt5, so catch them. 
             traceback.print_exc() 
 def _draw_idle(self): 
     with self._idle_draw_cntx(): 
         if not self._draw_pending: 
             return 
         self._draw_pending = False 
         if self.height() < 0 or self.width() < 0: 
             return 
         try: 
             self.draw() 
         except Exception: 
             # Uncaught exceptions are fatal for PyQt5, so catch them. 
             traceback.print_exc() 
 
     def blit(self, bbox=None):
-        self.draw_idle()
+        # docstring inherited
+        super().blit(bbox)
+        self.update()
 
     def resize(self, width, height):
         # Size from macOS is logical pixels, dpi is physical.

diff --git a/lib/matplotlib/tests/test_backends_interactive.py b/lib/matplotlib/tests/test_backends_interactive.py
@@ -413,3 +413,72 @@ def _lazy_headless():
 @pytest.mark.backend('QtAgg', skip_on_importerror=True)
 def test_lazy_linux_headless():
     proc = _run_helper(_lazy_headless, timeout=_test_timeout, MPLBACKEND="")
+
+
+def _test_number_of_draws_script():
+    import matplotlib.pyplot as plt
+
+    fig, ax = plt.subplots()
+
+    # animated=True tells matplotlib to only draw the artist when we
+    # explicitly request it
+    ln, = ax.plot([0, 1], [1, 2], animated=True)
+
+    # make sure the window is raised, but the script keeps going
+    plt.show(block=False)
+    plt.pause(0.3)
+    # Connect to draw_event to count the occurrences
+    fig.canvas.mpl_connect('draw_event', print)
+
+    # get copy of entire figure (everything inside fig.bbox)
+    # sans animated artist
+    bg = fig.canvas.copy_from_bbox(fig.bbox)
+    # draw the animated artist, this uses a cached renderer
+    ax.draw_artist(ln)
+    # show the result to the screen
+    fig.canvas.blit(fig.bbox)
+
+    for j in range(10):
+        # reset the background back in the canvas state, screen unchanged
+        fig.canvas.restore_region(bg)
+        # Create a **new** artist here, this is poor usage of blitting
+        # but good for testing to make sure that this doesn't create
+        # excessive draws
+        ln, = ax.plot([0, 1], [1, 2])
+        # render the artist, updating the canvas state, but not the screen
+        ax.draw_artist(ln)
+        # copy the image to the GUI state, but screen might not changed yet
+        fig.canvas.blit(fig.bbox)
+        # flush any pending GUI events, re-painting the screen if needed
+        fig.canvas.flush_events()
+
+    # Let the event loop process everything before leaving
+    plt.pause(0.1)
+
+
+_blit_backends = _get_testable_interactive_backends()
+for param in _blit_backends:
+    backend = param.values[0]["MPLBACKEND"]
+    if backend == "gtk3cairo":
+        # copy_from_bbox only works when rendering to an ImageSurface
+        param.marks.append(
+            pytest.mark.skip("gtk3cairo does not support blitting"))
+    elif backend == "wx":
+        param.marks.append(
+            pytest.mark.skip("wx does not support blitting"))
+
+
+@pytest.mark.parametrize("env", _blit_backends)
+# subprocesses can struggle to get the display, so rerun a few times
+@pytest.mark.flaky(reruns=4)
+def test_blitting_events(env):
+    proc = _run_helper(_test_number_of_draws_script,
+                       timeout=_test_timeout,
+                       **env)
+
+    # Count the number of draw_events we got. We could count some initial
+    # canvas draws (which vary in number by backend), but the critical
+    # check here is that it isn't 10 draws, which would be called if
+    # blitting is not properly implemented
+    ndraws = proc.stdout.count("DrawEvent")
+    assert 0 < ndraws < 5
diff --git a/src/_macosx.m b/src/_macosx.m
@@ -345,14 +345,7 @@ static CGFloat _get_device_scale(CGContextRef cr)
 }
 
 static PyObject*
-FigureCanvas_draw(FigureCanvas* self)
-{
-    [self->view display];
-    Py_RETURN_NONE;
-}
-
-static PyObject*
-FigureCanvas_draw_idle(FigureCanvas* self)
+FigureCanvas_update(FigureCanvas* self)
 {
     [self->view setNeedsDisplay: YES];
     Py_RETURN_NONE;
@@ -361,6 +354,9 @@ static CGFloat _get_device_scale(CGContextRef cr)
 static PyObject*
 FigureCanvas_flush_events(FigureCanvas* self)
 {
+    // We need to allow the runloop to run very briefly
+    // to allow the view to be displayed when used in a fast updating animation
+    [[NSRunLoop currentRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:0.0]];
     [self->view displayIfNeeded];
     Py_RETURN_NONE;
 }
@@ -485,12 +481,8 @@ static CGFloat _get_device_scale(CGContextRef cr)
     .tp_new = (newfunc)FigureCanvas_new,
     .tp_doc = "A FigureCanvas object wraps a Cocoa NSView object.",
     .tp_methods = (PyMethodDef[]){
-        {"draw",
-         (PyCFunction)FigureCanvas_draw,
-         METH_NOARGS,
-         NULL},  // docstring inherited
-        {"draw_idle",
-         (PyCFunction)FigureCanvas_draw_idle,
+        {"update",
+         (PyCFunction)FigureCanvas_update,
          METH_NOARGS,
          NULL},  // docstring inherited
         {"flush_events",
@@ -1263,7 +1255,7 @@ -(void)drawRect:(NSRect)rect
 
     CGContextRef cr = [[NSGraphicsContext currentContext] CGContext];
 
-    if (!(renderer = PyObject_CallMethod(canvas, "_draw", ""))
+    if (!(renderer = PyObject_CallMethod(canvas, "get_renderer", ""))
         || !(renderer_buffer = PyObject_GetAttrString(renderer, "_renderer"))) {
         PyErr_Print();
         goto exit;