Check pressed mouse buttons in pan/zoom drag handlers.

Sometimes, the mouse_release_event ending a pan/zoom can be lost, if it
occurs while the canvas does not have focus (a typical case is when a
context menu is implemented on top of the canvas, see example below);
this can result in rather confusing behavior as the pan/zoom continues
which no mouse button is pressed.  To fix this, always check that the
correct button is still pressed in the motion_notify_event handlers.

To test, use e.g.
```
from matplotlib import pyplot as plt
from matplotlib.backends.qt_compat import QtWidgets

def on_button_press(event):
    if event.button != 3:  # Right-click.
        return
    menu = QtWidgets.QMenu()
    menu.addAction("Some menu action", lambda: None)
    menu.exec(event.guiEvent.globalPosition().toPoint())

fig = plt.figure()
fig.canvas.mpl_connect("button_press_event", on_button_press)
fig.add_subplot()
plt.show()
```
enter pan/zoom mode, right-click to open the context menu, exit the
menu, and continue moving the mouse.

Author: anntzer

lib/matplotlib/backend_bases.py

@@ -3059,6 +3059,11 @@ def press_pan(self, event):
 
     def drag_pan(self, event):
         """Callback for dragging in pan/zoom mode."""
+        if event.buttons != {self._pan_info.button}:
+            # Zoom ended while canvas not in focus (it did not receive a
+            # button_release_event); cancel it.
+            self.release_pan(None)  # release_pan doesn't actually use event.
+            return
         for ax in self._pan_info.axes:
             # Using the recorded button at the press is safer than the current
             # button, as multiple buttons can get pressed during motion.
@@ -3092,7 +3097,7 @@ def zoom(self, *args):
         for a in self.canvas.figure.get_axes():
             a.set_navigate_mode(self.mode._navigate_mode)
 
-    _ZoomInfo = namedtuple("_ZoomInfo", "direction start_xy axes cid cbar")
+    _ZoomInfo = namedtuple("_ZoomInfo", "button start_xy axes cid cbar")
 
     def press_zoom(self, event):
         """Callback for mouse button press in zoom to rect mode."""
@@ -3117,11 +3122,17 @@ def press_zoom(self, event):
             cbar = None
 
         self._zoom_info = self._ZoomInfo(
-            direction="in" if event.button == 1 else "out",
-            start_xy=(event.x, event.y), axes=axes, cid=id_zoom, cbar=cbar)
+            button=event.button, start_xy=(event.x, event.y), axes=axes,
+            cid=id_zoom, cbar=cbar)
 
     def drag_zoom(self, event):
         """Callback for dragging in zoom mode."""
+        if event.buttons != {self._zoom_info.button}:
+            # Zoom ended while canvas not in focus (it did not receive a
+            # button_release_event); cancel it.
+            self._cleanup_post_zoom()
+            return
+
         start_xy = self._zoom_info.start_xy
         ax = self._zoom_info.axes[0]
         (x1, y1), (x2, y2) = np.clip(
@@ -3150,6 +3161,7 @@ def release_zoom(self, event):
         self.remove_rubberband()
 
         start_x, start_y = self._zoom_info.start_xy
+        direction = "in" if self._zoom_info.button == 1 else "out"
         key = event.key
         # Force the key on colorbars to ignore the zoom-cancel on the
         # short-axis side
@@ -3161,8 +3173,7 @@ def release_zoom(self, event):
         # "cancel" a zoom action by zooming by less than 5 pixels.
         if ((abs(event.x - start_x) < 5 and key != "y") or
                 (abs(event.y - start_y) < 5 and key != "x")):
-            self.canvas.draw_idle()
-            self._zoom_info = None
+            self._cleanup_post_zoom()
             return
 
         for i, ax in enumerate(self._zoom_info.axes):
@@ -3174,11 +3185,18 @@ def release_zoom(self, event):
                         for prev in self._zoom_info.axes[:i])
             ax._set_view_from_bbox(
                 (start_x, start_y, event.x, event.y),
-                self._zoom_info.direction, key, twinx, twiny)
+                direction, key, twinx, twiny)
+
+        self._cleanup_post_zoom()
+        self.push_current()
 
+    def _cleanup_post_zoom(self):
+        # 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()
         self.canvas.draw_idle()
         self._zoom_info = None
-        self.push_current()
 
     def push_current(self):
         """Push the current view limits and position onto the stack."""

lib/matplotlib/backend_bases.pyi

@@ -429,7 +429,7 @@ class NavigationToolbar2:
     def zoom(self, *args) -> None: ...
 
     class _ZoomInfo(NamedTuple):
-        direction: Literal["in", "out"]
+        button: MouseButton
         start_xy: tuple[float, float]
         axes: list[Axes]
         cid: int

lib/matplotlib/tests/test_backend_bases.py

@@ -260,19 +260,21 @@ def test_interactive_colorbar(plot_func, orientation, tool, button, expected):
     # Set up the mouse movements
     start_event = MouseEvent(
         "button_press_event", fig.canvas, *s0, button)
+    drag_event = MouseEvent(
+        "motion_notify_event", fig.canvas, *s1, button, buttons={button})
     stop_event = MouseEvent(
         "button_release_event", fig.canvas, *s1, button)
 
     tb = NavigationToolbar2(fig.canvas)
     if tool == "zoom":
         tb.zoom()
         tb.press_zoom(start_event)
-        tb.drag_zoom(stop_event)
+        tb.drag_zoom(drag_event)
         tb.release_zoom(stop_event)
     else:
         tb.pan()
         tb.press_pan(start_event)
-        tb.drag_pan(stop_event)
+        tb.drag_pan(drag_event)
         tb.release_pan(stop_event)
 
     # Should be close, but won't be exact due to screen integer resolution
@@ -395,14 +397,17 @@ def test_interactive_pan(key, mouseend, expectedxlim, expectedylim):
     start_event = MouseEvent(
         "button_press_event", fig.canvas, *sstart, button=MouseButton.LEFT,
         key=key)
+    drag_event = MouseEvent(
+        "motion_notify_event", fig.canvas, *send, button=MouseButton.LEFT,
+        buttons={MouseButton.LEFT}, key=key)
     stop_event = MouseEvent(
         "button_release_event", fig.canvas, *send, button=MouseButton.LEFT,
         key=key)
 
     tb = NavigationToolbar2(fig.canvas)
     tb.pan()
     tb.press_pan(start_event)
-    tb.drag_pan(stop_event)
+    tb.drag_pan(drag_event)
     tb.release_pan(stop_event)
     # Should be close, but won't be exact due to screen integer resolution
     assert tuple(ax.get_xlim()) == pytest.approx(expectedxlim, abs=0.02)
@@ -510,6 +515,8 @@ def test_interactive_pan_zoom_events(tool, button, patch_vis, forward_nav, t_s):
 
     # Set up the mouse movements
     start_event = MouseEvent("button_press_event", fig.canvas, *s0, button)
+    drag_event = MouseEvent(
+        "motion_notify_event", fig.canvas, *s1, button, buttons={button})
     stop_event = MouseEvent("button_release_event", fig.canvas, *s1, button)
 
     tb = NavigationToolbar2(fig.canvas)
@@ -534,7 +541,7 @@ def test_interactive_pan_zoom_events(tool, button, patch_vis, forward_nav, t_s):
 
         tb.zoom()
         tb.press_zoom(start_event)
-        tb.drag_zoom(stop_event)
+        tb.drag_zoom(drag_event)
         tb.release_zoom(stop_event)
 
         assert ax_t.get_xlim() == pytest.approx(xlim_t, abs=0.15)
@@ -570,7 +577,7 @@ def test_interactive_pan_zoom_events(tool, button, patch_vis, forward_nav, t_s):
 
         tb.pan()
         tb.press_pan(start_event)
-        tb.drag_pan(stop_event)
+        tb.drag_pan(drag_event)
         tb.release_pan(stop_event)
 
         assert ax_t.get_xlim() == pytest.approx(xlim_t, abs=0.15)

lib/mpl_toolkits/mplot3d/tests/test_axes3d.py

@@ -2130,19 +2130,21 @@ def test_toolbar_zoom_pan(tool, button, key, expected):
     # Set up the mouse movements
     start_event = MouseEvent(
         "button_press_event", fig.canvas, *s0, button, key=key)
+    drag_event = MouseEvent(
+        "motion_notify_event", fig.canvas, *s1, button, key=key, buttons={button})
     stop_event = MouseEvent(
         "button_release_event", fig.canvas, *s1, button, key=key)
 
     tb = NavigationToolbar2(fig.canvas)
     if tool == "zoom":
         tb.zoom()
         tb.press_zoom(start_event)
-        tb.drag_zoom(stop_event)
+        tb.drag_zoom(drag_event)
         tb.release_zoom(stop_event)
     else:
         tb.pan()
         tb.press_pan(start_event)
-        tb.drag_pan(stop_event)
+        tb.drag_pan(drag_event)
         tb.release_pan(stop_event)
 
     # Should be close, but won't be exact due to screen integer resolution