matplotlib · mishanilkazreen · Jun 22, 2026
diff --git a/lib/matplotlib/backends/backend_qt.py b/lib/matplotlib/backends/backend_qt.py
@@ -331,17 +331,21 @@ def leaveEvent(self, event):
     def mousePressEvent(self, event):
         button = self.buttond.get(event.button())
         if button is not None and self.figure is not None:
+            mods = self._mpl_modifiers()
             MouseEvent("button_press_event", self,
-                       *self.mouseEventCoords(event), button,
-                       modifiers=self._mpl_modifiers(),
+                       *self.mouseEventCoords(event),
+                       self._remap_darwin_button(button, mods),
+                       modifiers=mods,
                        guiEvent=event)._process()
 
     def mouseDoubleClickEvent(self, event):
         button = self.buttond.get(event.button())
         if button is not None and self.figure is not None:
+            mods = self._mpl_modifiers()
             MouseEvent("button_press_event", self,
-                       *self.mouseEventCoords(event), button, dblclick=True,
-                       modifiers=self._mpl_modifiers(),
+                       *self.mouseEventCoords(event),
+                       self._remap_darwin_button(button, mods), dblclick=True,
+                       modifiers=mods,
                        guiEvent=event)._process()
 
     def mouseMoveEvent(self, event):
@@ -356,9 +360,11 @@ def mouseMoveEvent(self, event):
     def mouseReleaseEvent(self, event):
         button = self.buttond.get(event.button())
         if button is not None and self.figure is not None:
+            mods = self._mpl_modifiers()
             MouseEvent("button_release_event", self,
-                       *self.mouseEventCoords(event), button,
-                       modifiers=self._mpl_modifiers(),
+                       *self.mouseEventCoords(event),
+                       self._remap_darwin_button(button, mods),
+                       modifiers=mods,
                        guiEvent=event)._process()
 
     def wheelEvent(self, event):
@@ -424,6 +430,13 @@ def _mpl_buttons(buttons):
         return {button for mask, button in FigureCanvasQT.buttond.items()
                 if _to_int(mask) & buttons}
 
+    @staticmethod
+    def _remap_darwin_button(button, mods):
+        # On macOS, Option+left-click emulates middle-click (mirrors _macosx.m).
+        if sys.platform == "darwin" and button == MouseButton.LEFT and 'alt' in mods:
+            return MouseButton.MIDDLE
+        return button
+
     @staticmethod
     def _mpl_modifiers(modifiers=None, *, exclude=None):
         if modifiers is None:

diff --git a/lib/matplotlib/tests/test_backend_qt.py b/lib/matplotlib/tests/test_backend_qt.py
@@ -131,6 +131,43 @@ def on_key_press(event):
     assert result == answer
 
 
+@pytest.mark.parametrize('backend', [
+    # Note: the value is irrelevant; the important part is the marker.
+    pytest.param(
+        'Qt5Agg',
+        marks=pytest.mark.backend('Qt5Agg', skip_on_importerror=True)),
+    pytest.param(
+        'QtAgg',
+        marks=pytest.mark.backend('QtAgg', skip_on_importerror=True)),
+])
+def test_macos_option_click_emulates_middle_button(backend, monkeypatch):
+    """
+    Make a figure.
+    Send a mouse press and release event with the Alt/Option modifier held.
+    Catch the events.
+    Assert the button is remapped to middle on macOS, unchanged elsewhere.
+    """
+    from matplotlib.backend_bases import MouseButton
+    from matplotlib.backends.qt_compat import QtCore, QtWidgets
+
+    monkeypatch.setattr(QtWidgets.QApplication, "keyboardModifiers",
+                        lambda self: QtCore.Qt.KeyboardModifier.AltModifier)
+
+    class _MouseEvent:
+        def button(self): return QtCore.Qt.MouseButton.LeftButton
+        def position(self): return QtCore.QPointF(0, 0)  # Qt6
+        def pos(self): return QtCore.QPoint(0, 0)        # Qt5
+
+    expected = MouseButton.MIDDLE if sys.platform == "darwin" else MouseButton.LEFT
+    results = []
+    fig = plt.figure()
+    fig.canvas.mpl_connect('button_press_event', lambda e: results.append(e.button))
+    fig.canvas.mpl_connect('button_release_event', lambda e: results.append(e.button))
+    fig.canvas.mousePressEvent(_MouseEvent())
+    fig.canvas.mouseReleaseEvent(_MouseEvent())
+    assert results == [expected, expected]
+
+
 @pytest.mark.backend('QtAgg', skip_on_importerror=True)
 def test_device_pixel_ratio_change():
     """

diff --git a/src/_macosx.m b/src/_macosx.m
@@ -71,6 +71,8 @@
 static bool keyChangeCapsLock = false;
 /* Keep track of the current mouse up/down state for open/closed cursor hand */
 static bool leftMouseGrabbing = false;
+/* Mouse button number set on press, Option/Ctrl remap effective left to 2/3 */
+static int effectiveLeftButton = 1;
 // Global variable to store the original SIGINT handler
 static PyOS_sighandler_t originalSigintAction = NULL;
 
@@ -1597,6 +1599,7 @@ - (void)mouseDown:(NSEvent *)event
                      [[NSCursor closedHandCursor] set];
                  }
              }
+             effectiveLeftButton = button;
              break;
          }
          case NSEventTypeOtherMouseDown: button = 2; break;
@@ -1622,8 +1625,8 @@ - (void)mouseUp:(NSEvent *)event
     y = location.y * device_scale;
     switch ([event type])
     {    case NSEventTypeLeftMouseUp:
+             button = effectiveLeftButton;
              leftMouseGrabbing = false;
-             button = 1;
              if ([NSCursor currentCursor]==[NSCursor closedHandCursor])
                  [[NSCursor openHandCursor] set];
              break;