BUG: fix orientation of colorbar in multiplanel plot

yt/visualization/base_plot_types.py

@@ -341,7 +341,20 @@ def _set_axes(self) -> None:
         self.image.axes.set_facecolor(self.colorbar_handler.background_color)
 
         self.cax.tick_params(which="both", direction="in")
-        self.cb = self.figure.colorbar(self.image, self.cax)
+
+        # For creating a multipanel plot by ImageGrid
+        # we may need the location keyword, which requires Matplotlib >= 3.7.0
+        cb_location = getattr(self.cax, "orientation", None)
+        if matplotlib.__version_info__ >= (3, 7):
+            self.cb = self.figure.colorbar(self.image, self.cax, location=cb_location)
+        else:
+            if cb_location in ["top", "bottom"]:
+                warnings.warn(
+                    "Cannot properly set the orientation of colorbar. "
+                    "Consider upgrading matplotlib to version 3.7 or newer",
+                    stacklevel=6,
+                )
+            self.cb = self.figure.colorbar(self.image, self.cax)
 
         cb_axis: Axis
         if self.cb.orientation == "vertical":
@@ -526,9 +539,12 @@ def _toggle_colorbar(self, choice: bool):
 
     def _get_labels(self):
         labels = super()._get_labels()
-        cbax = self.cb.ax
-        labels += cbax.yaxis.get_ticklabels()
-        labels += [cbax.yaxis.label, cbax.yaxis.get_offset_text()]
+        if getattr(self.cb, "orientation", "vertical") == "horizontal":
+            cbaxis = self.cb.ax.xaxis
+        else:
+            cbaxis = self.cb.ax.yaxis
+        labels += cbaxis.get_ticklabels()
+        labels += [cbaxis.label, cbaxis.get_offset_text()]
         return labels
 
     def hide_axes(self, *, draw_frame=None):

yt/visualization/tests/test_image_comp_2D_plots.py

@@ -147,6 +147,40 @@ def test_particleprojectionplot_set_colorbar_properties():
     return p.plots[field].figure
 
 
+class TestMultipanelPlot:
+    @classmethod
+    def setup_class(cls):
+        cls.fields = [
+            ("gas", "density"),
+            ("gas", "velocity_x"),
+            ("gas", "velocity_y"),
+            ("gas", "velocity_magnitude"),
+        ]
+        cls.ds = fake_random_ds(16)
+
+    @pytest.mark.skipif(
+        mpl.__version_info__ < (3, 7),
+        reason="colorbar cannot currently be set horizontal in multi-panel plot with matplotlib older than 3.7.0",
+    )
+    @pytest.mark.parametrize("cbar_location", ["top", "bottom", "left", "right"])
+    @pytest.mark.mpl_image_compare
+    def test_multipanelplot_colorbar_orientation_simple(self, cbar_location):
+        p = SlicePlot(self.ds, "z", self.fields)
+        return p.export_to_mpl_figure((2, 2), cbar_location=cbar_location)
+
+    @pytest.mark.parametrize("cbar_location", ["top", "bottom"])
+    def test_multipanelplot_colorbar_orientation_warning(self, cbar_location):
+        p = SlicePlot(self.ds, "z", self.fields)
+        if mpl.__version_info__ < (3, 7):
+            with pytest.warns(
+                UserWarning,
+                match="Cannot properly set the orientation of colorbar.",
+            ):
+                p.export_to_mpl_figure((2, 2), cbar_location=cbar_location)
+        else:
+            p.export_to_mpl_figure((2, 2), cbar_location=cbar_location)
+
+
 class TestProfilePlot:
     @classmethod
     def setup_class(cls):