Convert matplotlib fill polygons to plotly filled scatter traces

CHANGELOG.md

@@ -4,6 +4,9 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ## Unreleased
 
+### Added
+- Add support for converting matplotlib fill polygons (`plt.fill`) to filled scatter traces in `mpl_to_plotly` [[#5795](https://github.com/plotly/plotly.py/pull/5795)], with thanks to @robertoffmoura for the contribution!
+
 ### Fixed
 - Fix concurrent first access to lazily initialized graph object properties, which could raise `ValueError("Invalid value")` [[#5691](https://github.com/plotly/plotly.py/pull/5691)], with thanks to @hb1915 for the contribution!
 - Fix `mpl_to_plotly` crashing on touching bars (such as `plt.hist`) due to floating-point noise producing negative `bargap` values by clamping `bargap` to `[0, 1]` [[#5696](https://github.com/plotly/plotly.py/pull/5696)], with thanks to @robertoffmoura for the contribution!

plotly/matplotlylib/renderer.py

@@ -9,6 +9,7 @@
 
 import warnings
 
+import matplotlib.patches as mpatches
 import plotly.graph_objs as go
 from plotly.matplotlylib.mplexporter import Renderer
 from plotly.matplotlylib import mpltools
@@ -602,13 +603,47 @@ def draw_path(self, **props):
         is_bar = mpltools.is_bar(self.current_mpl_ax.containers, **props)
         if is_bar:
             self.current_bars += [props]
+        elif (
+            isinstance(props["mplobj"], mpatches.Polygon)
+            and props["coordinates"] == "data"
+        ):
+            self.msg += "    Drawing a filled polygon\n"
+            self._draw_filled_polygon(props)
         else:
             self.msg += "    This path isn't a bar, not drawing\n"
             warnings.warn(
                 "I found a path object that I don't think is part "
                 "of a bar chart. Ignoring."
             )
 
+    def _draw_filled_polygon(self, props):
+        """Draw a matplotlib Polygon patch as a filled scatter trace."""
+        style = props["style"]
+        verts = props["data"]
+        facecolor = _export_color(style["facecolor"])
+        edgecolor = _export_color(style["edgecolor"])
+        mplobj = props.get("mplobj")
+        label = mplobj.get_label() if mplobj is not None else None
+        if not label or (isinstance(label, str) and label.startswith("_")):
+            label = None
+            showlegend = False
+        else:
+            showlegend = None
+        self.plotly_fig.add_trace(
+            go.Scatter(
+                name=label,
+                showlegend=showlegend,
+                x=self._convert_x_dates([v[0] for v in verts]),
+                y=[v[1] for v in verts],
+                mode="lines",
+                line=go.scatter.Line(color=edgecolor, width=style["edgewidth"]),
+                fill="toself",
+                fillcolor=facecolor,
+                xaxis="x{0}".format(self.axis_ct),
+                yaxis="y{0}".format(self.axis_ct),
+            )
+        )
+
     def draw_text(self, **props):
         """Create an annotation dict for a text obj.
 

plotly/matplotlylib/tests/test_renderer.py

@@ -348,6 +348,48 @@ def test_uneven_custom_date_xtickvals_are_converted():
     )
 
 
+def test_fill_converts():
+    """plt.fill polygons convert to filled scatter traces."""
+    x = np.linspace(0, 2 * np.pi, 50)
+    fig, ax = plt.subplots()
+    ax.fill(x, np.sin(x), "g")
+
+    plotly_fig = tls.mpl_to_plotly(fig)
+
+    assert len(plotly_fig.data) == 1
+    trace = plotly_fig.data[0]
+    assert trace.type == "scatter"
+    assert trace.fill == "toself"
+    assert np.allclose(trace.x, x)
+    assert np.allclose(trace.y, np.sin(x))
+    assert trace.fillcolor == "#007F00"
+    assert trace.line.color == "rgba(0,0,0,0)"
+
+
+def test_fill_with_legend_label():
+    """plt.fill polygons with labels export their name and show in legend."""
+    fig, ax = plt.subplots()
+    ax.fill([0, 1, 2], [0, 2, 0], "b", label="Shaded Area")
+    ax.fill([0, 1, 2], [0, 1, 0], "g")
+    ax.plot([0, 1, 2], [1, 1, 1], "r-", label="Threshold")
+    ax.legend()
+
+    plotly_fig = tls.mpl_to_plotly(fig)
+
+    assert plotly_fig.layout.showlegend == True
+    assert len(plotly_fig.data) == 3
+
+    labeled_fill = next(
+        t for t in plotly_fig.data if t.fill == "toself" and t.name == "Shaded Area"
+    )
+    assert labeled_fill.showlegend is not False
+
+    unlabeled_fill = next(
+        t for t in plotly_fig.data if t.fill == "toself" and t.name is None
+    )
+    assert unlabeled_fill.showlegend is False
+
+
 def test_custom_date_xtickvals_given_as_numbers_are_converted():
     """Custom date ticks given as matplotlib date numbers must be converted
     to date strings."""