FIX: Artifacts in stackplot if height of input is zero

closes #22393

lib/matplotlib/pyplot.py

@@ -2860,11 +2860,12 @@ def spy(
 # Autogenerated by boilerplate.py.  Do not edit as changes will be lost.
 @_copy_docstring_and_deprecators(Axes.stackplot)
 def stackplot(
-        x, *args, labels=(), colors=None, baseline='zero', data=None,
-        **kwargs):
+        x, *args, labels=(), colors=None, baseline='zero',
+        where=None, data=None, **kwargs):
     return gca().stackplot(
         x, *args, labels=labels, colors=colors, baseline=baseline,
-        **({"data": data} if data is not None else {}), **kwargs)
+        where=where, **({"data": data} if data is not None else {}),
+        **kwargs)
 
 
 # Autogenerated by boilerplate.py.  Do not edit as changes will be lost.

lib/matplotlib/stackplot.py

@@ -14,7 +14,7 @@
 
 
 def stackplot(axes, x, *args,
-              labels=(), colors=None, baseline='zero',
+              labels=(), colors=None, baseline='zero', where=None,
               **kwargs):
     """
     Draw a stacked area plot.
@@ -56,6 +56,13 @@ def stackplot(axes, x, *args,
     data : indexable object, optional
         DATA_PARAMETER_PLACEHOLDER
 
+    where: bool or array of bool, optional
+        Passed to `.Axes.fill_between` and defines where to exclude horizontal
+        regions from being filled. The filled regions are defined by the
+        coordinates `x[where]`. Can be either a single bool, an array of shape
+        (N,) or an array of shape (M, N).
+        Should be used together with `interpolate=True`.
+
     **kwargs
         All other keyword arguments are passed to `.Axes.fill_between`.
 
@@ -68,6 +75,10 @@ def stackplot(axes, x, *args,
 
     y = np.row_stack(args)
 
+    if where is None:
+        where = True
+    where = np.broadcast_to(where, np.shape(y))
+
     labels = iter(labels)
     if colors is not None:
         axes.set_prop_cycle(color=colors)
@@ -111,6 +122,7 @@ def stackplot(axes, x, *args,
     color = axes._get_lines.get_next_color()
     coll = axes.fill_between(x, first_line, stack[0, :],
                              facecolor=color, label=next(labels, None),
+                             where=where[0, :],
                              **kwargs)
     coll.sticky_edges.y[:] = [0]
     r = [coll]
@@ -120,5 +132,6 @@ def stackplot(axes, x, *args,
         color = axes._get_lines.get_next_color()
         r.append(axes.fill_between(x, stack[i, :], stack[i + 1, :],
                                    facecolor=color, label=next(labels, None),
+                                   where=where[i+1, :],
                                    **kwargs))
     return r