Simplify interactive zoom handling.

anntzer · anntzer · commit 9a9498438efd · 2020-04-08T07:40:35.000+02:00
- Stash all the relevant variables (start click position, start click
  button, list of axes, callback id) into a single dict (`_zoom_info`).
- start_x/start_y is the same for all axes (it's in screen coordinates)
  so just store it once (under `start_xy`) instead of repeatedly.
- Immediatedly exit if no axes are selected (`not axes`) instead of
  later checking `self._xypress`.
- Remove the "cancel zoom if another button is pressed feature": that
  second button is going to get released anyways, so the release_event
  for that second button is going to handle the cancellation just fine.
  (More specifically, the second button press will throw away the first
  zoom and start a new zoom session from the new starting point, and
  then the button release will be detected as a zoom cancelled because
  &lt;5px.)
- Simplify twinx/y detection.
- Resolve zoom direction from the beginning.
diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
@@ -2699,7 +2699,7 @@ def __init__(self, canvas):
         self._init_toolbar()
         self._id_drag = self.canvas.mpl_connect(
             'motion_notify_event', self.mouse_move)
-        self._id_zoom = None
+        self._zoom_info = None
 
         self._button_pressed = None  # determined by button pressed at start
 
@@ -2909,37 +2909,24 @@ def press_pan(self, event):
 
     def press_zoom(self, event):
         """Callback for mouse button press in zoom to rect mode."""
-        # If we're already in the middle of a zoom, pressing another
-        # button works to "cancel"
-        if self._id_zoom is not None:
-            self.canvas.mpl_disconnect(self._id_zoom)
-            self.release(event)
-            self.draw()
-            self._xypress = None
-            self._button_pressed = None
-            self._id_zoom = None
+        if event.button not in [1, 3]:
             return
-
-        if event.button in [1, 3]:
-            self._button_pressed = event.button
-        else:
-            self._button_pressed = None
+        if event.x is None or event.y is None:
+            return
+        axes = [a for a in self.canvas.figure.get_axes()
+                if a.in_axes(event) and a.get_navigate() and a.can_zoom()]
+        if not axes:
             return
-
         if self._nav_stack() is None:
-            # set the home button to this view
-            self.push_current()
-
-        x, y = event.x, event.y
-        self._xypress = []
-        for a in self.canvas.figure.get_axes():
-            if (x is not None and y is not None and a.in_axes(event) and
-                    a.get_navigate() and a.can_zoom()):
-                self._xypress.append((x, y, a))
-
-        self._id_zoom = self.canvas.mpl_connect(
-            'motion_notify_event', self.drag_zoom)
-
+            self.push_current()  # set the home button to this view
+        id_zoom = self.canvas.mpl_connect(
+            "motion_notify_event", self.drag_zoom)
+        self._zoom_info = {
+            "direction": "in" if event.button == 1 else "out",
+            "start_xy": (event.x, event.y),
+            "axes": axes,
+            "cid": id_zoom,
+        }
         self.press(event)
 
     def push_current(self):
@@ -2984,65 +2971,53 @@ def drag_pan(self, event):
 
     def drag_zoom(self, event):
         """Callback for dragging in zoom mode."""
-        if self._xypress:
-            x, y = event.x, event.y
-            lastx, lasty, a = self._xypress[0]
-            (x1, y1), (x2, y2) = np.clip(
-                [[lastx, lasty], [x, y]], a.bbox.min, a.bbox.max)
-            if event.key == "x":
-                y1, y2 = a.bbox.intervaly
-            elif event.key == "y":
-                x1, x2 = a.bbox.intervalx
-            self.draw_rubberband(event, x1, y1, x2, y2)
+        start_xy = self._zoom_info["start_xy"]
+        ax = self._zoom_info["axes"][0]
+        (x1, y1), (x2, y2) = np.clip(
+            [start_xy, [event.x, event.y]], ax.bbox.min, ax.bbox.max)
+        if event.key == "x":
+            y1, y2 = ax.bbox.intervaly
+        elif event.key == "y":
+            x1, x2 = ax.bbox.intervalx
+        self.draw_rubberband(event, x1, y1, x2, y2)
 
     def release_zoom(self, event):
         """Callback for mouse button release in zoom to rect mode."""
-        if self._id_zoom is not None:
-            self.canvas.mpl_disconnect(self._id_zoom)
-        self._id_zoom = None
+        if self._zoom_info is None:
+            return
 
+        # We don't check the event button here, so that zooms can be cancelled
+        # by (pressing and) releasing another mouse button.
+        self.canvas.mpl_disconnect(self._zoom_info["cid"])
         self.remove_rubberband()
 
-        if not self._xypress:
-            return
-
-        last_a = []
+        start_x, start_y = self._zoom_info["start_xy"]
 
-        for lastx, lasty, a in self._xypress:
+        for i, ax in enumerate(self._zoom_info["axes"]):
             x, y = event.x, event.y
             # ignore singular clicks - 5 pixels is a threshold
             # allows the user to "cancel" a zoom action
             # by zooming by less than 5 pixels
-            if ((abs(x - lastx) < 5 and event.key != "y") or
-                    (abs(y - lasty) < 5 and event.key != "x")):
+            if ((abs(x - start_x) < 5 and event.key != "y") or
+                    (abs(y - start_y) < 5 and event.key != "x")):
                 self._xypress = None
                 self.release(event)
                 self.draw()
                 return
 
-            # detect twinx, twiny axes and avoid double zooming
-            twinx, twiny = False, False
-            if last_a:
-                for la in last_a:
-                    if a.get_shared_x_axes().joined(a, la):
-                        twinx = True
-                    if a.get_shared_y_axes().joined(a, la):
-                        twiny = True
-            last_a.append(a)
-
-            if self._button_pressed == 1:
-                direction = 'in'
-            elif self._button_pressed == 3:
-                direction = 'out'
-            else:
-                continue
+            # Detect whether this axes is twinned with an earlier axes in the
+            # list of zoomed axes, to avoid double zooming.
+            twinx = any(ax.get_shared_x_axes().joined(ax, prev)
+                        for prev in self._zoom_info["axes"][:i])
+            twiny = any(ax.get_shared_y_axes().joined(ax, prev)
+                        for prev in self._zoom_info["axes"][:i])
 
-            a._set_view_from_bbox((lastx, lasty, x, y), direction,
-                                  event.key, twinx, twiny)
+            ax._set_view_from_bbox(
+                (start_x, start_y, x, y), self._zoom_info["direction"],
+                event.key, twinx, twiny)
 
         self.draw()
-        self._xypress = None
-        self._button_pressed = None
+        self._zoom_info = None
 
         self.push_current()
         self.release(event)
