Fix ternary tri* delegation and add example

docs/examples/plot_types/08_ternary.py

@@ -0,0 +1,40 @@
+"""
+Ternary Plots
+=============
+Ternary plots are a type of plot that displays the proportions of three variables that sum to a constant. They are commonly used in fields such as geology, chemistry, and materials science to represent the composition of mixtures. UltraPlot makes it easy to create publication-quality ternary plots using the `mpltern` library as a backend.
+
+Why UltraPlot here?
+-------------------
+UltraPlot offers seamless integration with `mpltern`, allowing users to create and customize ternary plots with minimal effort. UltraPlot's high-level API simplifies the process of setting up ternary plots, adding data, and formatting the axes and labels.
+
+See also
+--------
+* :ref:`External axes containers <ug_external_axes>`
+"""
+
+# %%
+import mpltern
+
+
+from mpltern.datasets import get_shanon_entropies, get_spiral
+import ultraplot as uplt, numpy as np
+
+t, l, r, v = get_shanon_entropies()
+
+fig, ax = uplt.subplots(projection="ternary")
+vmin = 0.0
+vmax = 1.0
+levels = np.linspace(vmin, vmax, 7)
+
+cs = ax.tripcolor(t, l, r, v, cmap="lapaz_r", shading="flat", vmin=vmin, vmax=vmax)
+ax.set_title("Ternary Plot of Shannon Entropies")
+ax.plot(*get_spiral(), color="white", lw=1.25)
+colorbar = ax.colorbar(
+    cs,
+    loc="b",
+    align="c",
+    title="Entropy",
+    length=0.33,
+)
+
+fig.show()

docs/usage.rst

@@ -158,6 +158,8 @@ plotting packages.
 Since these features are optional,
 UltraPlot can be used without installing any of these packages.
 
+.. _ug_external_axes:
+
 External axes containers (mpltern, others)
 ------------------------------------------
 

ultraplot/axes/container.py

@@ -610,6 +610,34 @@ def pcolormesh(self, *args, **kwargs):
             return self._external_axes.pcolormesh(*args, **kwargs)
         return super().pcolormesh(*args, **kwargs)
 
+    def tripcolor(self, *args, **kwargs):
+        """Delegate tripcolor to external axes."""
+        if self._external_axes is not None:
+            self._external_stale = True  # Mark for redraw
+            return self._external_axes.tripcolor(*args, **kwargs)
+        return super().tripcolor(*args, **kwargs)
+
+    def tricontour(self, *args, **kwargs):
+        """Delegate tricontour to external axes."""
+        if self._external_axes is not None:
+            self._external_stale = True  # Mark for redraw
+            return self._external_axes.tricontour(*args, **kwargs)
+        return super().tricontour(*args, **kwargs)
+
+    def tricontourf(self, *args, **kwargs):
+        """Delegate tricontourf to external axes."""
+        if self._external_axes is not None:
+            self._external_stale = True  # Mark for redraw
+            return self._external_axes.tricontourf(*args, **kwargs)
+        return super().tricontourf(*args, **kwargs)
+
+    def triplot(self, *args, **kwargs):
+        """Delegate triplot to external axes."""
+        if self._external_axes is not None:
+            self._external_stale = True  # Mark for redraw
+            return self._external_axes.triplot(*args, **kwargs)
+        return super().triplot(*args, **kwargs)
+
     def imshow(self, *args, **kwargs):
         """Delegate imshow to external axes."""
         if self._external_axes is not None: