FIX: Update blitting and drawing on the macosx backend

This inherits some of the drawing and blitting code from the
AGG canvas and leverages that to handle when a full AGG re-render
should happen. The macosx code always grabs the full AGG buffer
when doing the draw to the GUI window.

Author: greglucas

lib/matplotlib/backends/backend_macosx.py

@@ -30,27 +30,37 @@ 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 (getattr(self, '_draw_pending', False) or
+                getattr(self, '_is_drawing', False)):
+            return
+        self._draw_pending = True
+        with self._idle_draw_cntx():
+            self._draw_pending = False
+            self.draw()
 
     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.

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;
@@ -485,12 +478,8 @@ 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 +1252,7 @@ -(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;