enh: Add Scalebar support for subcoordinate_y plots

holoviews/plotting/bokeh/element.py

@@ -72,6 +72,7 @@
     bokeh32,
     bokeh34,
     bokeh35,
+    bokeh36,
     cds_column_replace,
     compute_layout_properties,
     date_to_integer,
@@ -208,7 +209,7 @@ class ElementPlot(BokehPlot, GenericElementPlot):
         The scalebar_unit is only used if scalebar is True.""")
 
     scalebar_location = param.Selector(
-        default="bottom_right",
+        default=None,
         objects=[
             "top_left", "top_center", "top_right",
             "center_left", "center_center", "center_right",
@@ -218,6 +219,8 @@ class ElementPlot(BokehPlot, GenericElementPlot):
         doc="""
             Location anchor for positioning scale bar.
 
+            Default to 'bottom_right', except if subcoordinate_y is True then it will default to 'right'.
+
             The scalebar_location is only used if scalebar is True.""")
 
     scalebar_label = param.String(
@@ -2407,10 +2410,14 @@ def _draw_scalebar(self, plot):
         `scalebar_opts`, and `scalebar_unit` for more information.
 
         Requires Bokeh 3.4
+
+        For scalebar on a subcoordinate_y plot Bokeh 3.6 is needed.
         """
 
         if not bokeh34:
             raise RuntimeError("Scalebar requires Bokeh >= 3.4.0")
+        elif not bokeh36 and self._subcoord_overlaid:
+            raise RuntimeError("Scalebar with subcoordinate_y requires Bokeh >= 3.6.0")
 
         from bokeh.models import Metric, ScaleBar
 
@@ -2421,17 +2428,34 @@ def _draw_scalebar(self, plot):
         else:
             base_unit = unit
 
-        _default_scalebar_opts = {"background_fill_alpha": 0.8}
-        opts = dict(_default_scalebar_opts, **self.scalebar_opts)
+        if self._subcoord_overlaid:
+            srange = plot.renderers[-1].coordinates.y_source
+            orientation = "vertical"
+            # Integer is used for the location as `major_label_overrides` overrides the
+            # label with {0: labelA, 1: labelB}
+            location = (self.scalebar_location or "right", len(plot.renderers) - 1)
+            default_scalebar_opts = {
+                'bar_line_width': 3,
+                'label_location': 'left',
+                'background_fill_color': 'white',
+                'background_fill_alpha': 0.6,
+                'length_sizing': 'adaptive',
+                # Adding location so people can overwrite the default
+                'location': location,
+            }
+        else:
+            srange = plot.x_range if self.scalebar_range == "x" else plot.y_range
+            orientation = "horizontal" if self.scalebar_range == "x" else "vertical"
+            location = self.scalebar_location or "bottom_right"
+            default_scalebar_opts = {"background_fill_alpha": 0.8, "location": location}
 
         scale_bar = ScaleBar(
-            range=plot.x_range if self.scalebar_range == "x" else plot.y_range,
-            orientation="horizontal" if self.scalebar_range == "x" else "vertical",
+            range=srange,
+            orientation=orientation,
             unit=unit,
             dimensional=Metric(base_unit=base_unit),
-            location=self.scalebar_location,
             label=self.scalebar_label,
-            **opts,
+            **dict(default_scalebar_opts, **self.scalebar_opts),
         )
         self.handles['scalebar'] = scale_bar
         plot.add_layout(scale_bar)

holoviews/plotting/bokeh/util.py

@@ -67,6 +67,7 @@
 bokeh33 = bokeh_version >= Version("3.3")
 bokeh34 = bokeh_version >= Version("3.4")
 bokeh35 = bokeh_version >= Version("3.5")
+bokeh36 = bokeh_version >= Version("3.6")
 
 TOOL_TYPES = {
     'pan': tools.PanTool,

holoviews/tests/plotting/bokeh/test_elementplot.py

@@ -21,7 +21,7 @@
 from holoviews.core import Dimension, DynamicMap, HoloMap, NdOverlay, Overlay
 from holoviews.core.util import dt_to_int
 from holoviews.element import Curve, HeatMap, Image, Labels, Scatter
-from holoviews.plotting.bokeh.util import bokeh34
+from holoviews.plotting.bokeh.util import bokeh34, bokeh36
 from holoviews.plotting.util import process_cmap
 from holoviews.streams import PointDraw, Stream
 from holoviews.util import render
@@ -885,6 +885,31 @@ def test_scalebar_icon_multiple_overlay(self):
         scalebar_icon = [tool for tool in toolbar.tools if tool.description == "Toggle ScaleBar"]
         assert len(scalebar_icon) == 1
 
+    @pytest.mark.skipif(not bokeh36, reason="requires Bokeh >= 3.6")
+    @pytest.mark.parametrize("enabled1", [True, False])
+    @pytest.mark.parametrize("enabled2", [True, False])
+    @pytest.mark.parametrize("enabled3", [True, False])
+    def test_scalebar_with_subcoordinate_y(self, enabled1, enabled2, enabled3):
+        from bokeh.models import ScaleBar
+
+        enabled = [enabled1, enabled2, enabled3]
+        curve1 = Curve([1, 2, 3], label='c1').opts(scalebar=enabled1, subcoordinate_y=True)
+        curve2 = Curve([1, 2, 3], label='c2').opts(scalebar=enabled2, subcoordinate_y=True)
+        curve3 = Curve([1, 2, 3], label='c3').opts(scalebar=enabled3, subcoordinate_y=True)
+        curves = curve1 * curve2 * curve3
+
+        plot = bokeh_renderer.get_plot(curves).handles["plot"]
+        coordinates = [r.coordinates for r in plot.renderers][::-1]
+        sb = (c for c in plot.center if isinstance(c, ScaleBar))
+        scalebars = [next(sb) if e else None for e in enabled]
+        assert sum(map(bool, scalebars)) == sum(enabled)
+
+        for coordinate, scalebar, idx in zip(coordinates, scalebars, "123"):
+            assert coordinate.y_source.name == f"c{idx}"
+            if scalebar is None:
+                continue
+            assert coordinate.y_source is scalebar.range
+
 
 class TestColorbarPlot(LoggingComparisonTestCase, TestBokehPlot):