Display cursor coordinates for all axes twinned with the current one.

anntzer · anntzer · commit c8072b26aa1a · 2023-03-26T23:45:00.000+02:00
diff --git a/lib/matplotlib/axes/_base.py b/lib/matplotlib/axes/_base.py
@@ -3906,10 +3906,33 @@ def format_ydata(self, y):
 
     def format_coord(self, x, y):
         """Return a format string formatting the *x*, *y* coordinates."""
-        return "x={} y={}".format(
-            "???" if x is None else self.format_xdata(x),
-            "???" if y is None else self.format_ydata(y),
-        )
+        x_twins = []
+        y_twins = []
+        twins = self._twinned_axes.get_siblings(self)
+        # Retrieve twins in the order of self.figure.axes to sort tied zorders (which is
+        # the common case) by the order in which they are added to the figure.
+        for ax in self.figure.axes:
+            if ax in twins:
+                if ax is self or ax._sharex is self or self._sharex is ax:
+                    x_twins.append(ax)
+                if ax is self or ax._sharey is self or self._sharey is ax:
+                    y_twins.append(ax)
+        if len(x_twins) == len(y_twins) == 1:
+            return "x={} y={}".format(
+                "???" if x is None else self.format_xdata(x),
+                "???" if y is None else self.format_ydata(y))
+        else:
+            get_zorder = attrgetter("zorder")
+            x_twins.sort(key=get_zorder)
+            y_twins.sort(key=get_zorder)
+            screen_xy = self.transData.transform((x, y))
+            return "x={} y={}".format(
+                " / ".join(
+                    ax.format_xdata(ax.transData.inverted().transform(screen_xy)[0])
+                    for ax in y_twins),
+                " / ".join(
+                    ax.format_xdata(ax.transData.inverted().transform(screen_xy)[1])
+                    for ax in x_twins))
 
     def minorticks_on(self):
         """
diff --git a/lib/matplotlib/tests/test_backend_bases.py b/lib/matplotlib/tests/test_backend_bases.py
@@ -130,6 +130,16 @@ def test_location_event_position(x, y):
         assert re.match("x=foo +y=foo", ax.format_coord(x, y))
 
 
+def test_location_event_position_twin():
+    fig, ax = plt.subplots()
+    ax.set(xlim=(0, 10), ylim=(0, 20))
+    assert ax.format_coord(5., 5.) == "x=5.00 y=5.00"
+    ax.twinx().set(ylim=(0, 40))
+    assert ax.format_coord(5., 5.) == "x=5.00 y=5.00 / 10.00"
+    ax.twiny().set(xlim=(0, 5))
+    assert ax.format_coord(5., 5.) == "x=5.00 / 2.50 y=5.00 / 10.00"
+
+
 def test_pick():
     fig = plt.figure()
     fig.text(.5, .5, "hello", ha="center", va="center", picker=True)
