plotly · camdecoster · Aug 21, 2026 · Aug 11, 2026 · Aug 21, 2026 · Aug 21, 2026
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -7,6 +7,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 ### Fixed
 - Fix `hex_to_rgb` parsing of 3-digit shorthand hexadecimal colors such as `#FFF` [[#5662](https://github.com/plotly/plotly.py/pull/5662)], with thanks to @genrichez for the contribution!
 - Add `<!doctype html>` to the `to_html()` template to comply with modern web standards [[#5693](https://github.com/plotly/plotly.py/pull/5693)], with thanks to @mishrakushal for the contribution!
+- Fix `mpl_to_plotly` silently dropping matplotlib path collections in data coordinates (such as violin plots, pcolor, event plots, stack plots, fill_between, and stem plots) by rendering them as filled polygons or lines [[#5702](https://github.com/plotly/plotly.py/pull/5702)], with thanks to @robertoffmoura for the contribution!
 
 
 ## [6.9.0] - 2026-07-09

diff --git a/plotly/matplotlylib/renderer.py b/plotly/matplotlylib/renderer.py
@@ -14,6 +14,19 @@
 from plotly.matplotlylib import mpltools
 
 
+def _export_color(color):
+    """Export a matplotlib color for use as a plotly color.
+
+    matplotlib uses "none" for fully transparent colors, which plotly does not
+    accept, so transparent colors are exported as transparent black.
+    Colors already exported by the mplexporter (hex or rgba strings) are
+    passed through unchanged.
+    """
+    if isinstance(color, str):
+        return "rgba(0,0,0,0)" if color == "none" else color
+    return [_export_color(c) for c in color]
+
+
 class PlotlyRenderer(Renderer):
     """A renderer class inheriting from base for rendering mpl plots in plotly.
 
@@ -55,6 +68,15 @@ def __init__(self):
         self._processing_legend = False
         self._legend_visible = False
 
+    def _convert_x_dates(self, x):
+        """Convert x values to date strings when the x-axis is a date axis."""
+        if self.x_is_mpl_date:
+            formatter = (
+                self.current_mpl_ax.get_xaxis().get_major_formatter().__class__.__name__
+            )
+            x = mpltools.mpl_dates_to_datestrings(x, formatter)
+        return x
+
     def open_figure(self, fig, props):
         """Creates a new figure by beginning to fill out layout dict.
 
@@ -286,13 +308,7 @@ def draw_bar(self, coll):
                 [bar["x0"] for bar in trace], [bar["x1"] for bar in trace]
             )
             if self.x_is_mpl_date:
-                x = [bar["x0"] for bar in trace]
-                formatter = (
-                    self.current_mpl_ax.get_xaxis()
-                    .get_major_formatter()
-                    .__class__.__name__
-                )
-                x = mpltools.mpl_dates_to_datestrings(x, formatter)
+                x = self._convert_x_dates([bar["x0"] for bar in trace])
         else:
             self.msg += "    Attempting to draw a horizontal bar chart\n"
             old_rights = [bar_props["x1"] for bar_props in trace]
@@ -436,14 +452,7 @@ def draw_marked_line(self, **props):
                 marker=marker,
             )
             if self.x_is_mpl_date:
-                formatter = (
-                    self.current_mpl_ax.get_xaxis()
-                    .get_major_formatter()
-                    .__class__.__name__
-                )
-                marked_line["x"] = mpltools.mpl_dates_to_datestrings(
-                    marked_line["x"], formatter
-                )
+                marked_line["x"] = self._convert_x_dates(marked_line["x"])
             self.plotly_fig.add_trace(marked_line)
             self.msg += "    Heck yeah, I drew that line\n"
         elif props["coordinates"] == "axes":
@@ -513,6 +522,9 @@ def draw_path_collection(self, **props):
             }
             self.msg += "    Drawing path collection as markers\n"
             self.draw_marked_line(**scatter_props)
+        elif props["path_coordinates"] == "data":
+            self.msg += "    Drawing path collection as filled polygons\n"
+            self._draw_filled_path_collection(props)
         else:
             self.msg += "    Path collection not linked to 'data', not drawing\n"
             warnings.warn(
@@ -522,6 +534,42 @@ def draw_path_collection(self, **props):
                 "collections linked to 'data' coordinates"
             )
 
+    def _draw_filled_path_collection(self, props):
+        """Draw a path collection (e.g. violin plot bodies) as filled polygons."""
+        facecolors = mpltools.convert_rgba_array(props["styles"]["facecolor"])
+        edgecolors = mpltools.convert_rgba_array(props["styles"]["edgecolor"])
+        linewidths = mpltools.convert_linewidth_array(props["styles"]["linewidth"])
+
+        def per_path(colors, i, default):
+            if isinstance(colors, str):
+                return colors
+            if colors is None:
+                return default
+            try:
+                n = len(colors)
+            except TypeError:
+                return colors
+            return colors[i % n] if n else default
+
+        for i, (verts, codes) in enumerate(props["paths"]):
+            facecolor = per_path(facecolors, i, "rgba(0,0,0,0)")
+            edgecolor = per_path(edgecolors, i, "rgba(0,0,0,0)")
+            linewidth = per_path(linewidths, i, 0)
+            self.plotly_fig.add_trace(
+                go.Scatter(
+                    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=_export_color(edgecolor), width=linewidth
+                    ),
+                    fill="toself",
+                    fillcolor=_export_color(facecolor),
+                    xaxis="x{0}".format(self.axis_ct),
+                    yaxis="y{0}".format(self.axis_ct),
+                )
+            )
+
     def draw_path(self, **props):
         """Draw path, currently only attempts to draw bar charts.
 

diff --git a/plotly/matplotlylib/tests/test_renderer.py b/plotly/matplotlylib/tests/test_renderer.py
@@ -1,3 +1,6 @@
+import datetime
+
+import numpy as np
 import matplotlib.pyplot as plt
 import plotly.tools as tls
 
@@ -84,3 +87,115 @@ def test_multiple_traces_native_legend():
     assert plotly_fig.data[0].mode == "lines"
     assert plotly_fig.data[1].mode == "markers"
     assert plotly_fig.data[2].mode == "lines+markers"
+
+
+def test_violinplot_bodies_are_filled_polygons():
+    fig, ax = plt.subplots()
+    ax.violinplot(np.random.randn(100, 3))
+    plotly_fig = tls.mpl_to_plotly(fig)
+    bodies = [t for t in plotly_fig.data if t.fill == "toself" and len(t.x) > 100]
+    assert len(bodies) >= 3
+
+
+def test_pcolor_rectangles_render():
+    x = np.linspace(-3, 3, 10)
+    X, Y = np.meshgrid(x, x)
+    fig, ax = plt.subplots()
+    ax.pcolor(X, Y, np.sin(X) * np.cos(Y))
+    plotly_fig = tls.mpl_to_plotly(fig)
+    assert len(plotly_fig.data) == 100
+    assert all(len(t.x) >= 4 for t in plotly_fig.data)
+
+
+def test_eventplot_segments_render():
+    fig, ax = plt.subplots()
+    ax.eventplot([np.random.randn(20) for _ in range(5)])
+    plotly_fig = tls.mpl_to_plotly(fig)
+    assert len(plotly_fig.data) == 100
+
+
+def test_stackplot_areas_render():
+    x = np.arange(10)
+    fig, ax = plt.subplots()
+    ax.stackplot(x, np.random.rand(10), np.random.rand(10), np.random.rand(10))
+    plotly_fig = tls.mpl_to_plotly(fig)
+    assert len(plotly_fig.data) >= 3
+
+
+def test_fill_between_renders():
+    x = np.linspace(0, 2 * np.pi, 50)
+    fig, ax = plt.subplots()
+    ax.fill_between(x, np.sin(x), np.cos(x))
+    plotly_fig = tls.mpl_to_plotly(fig)
+    assert len(plotly_fig.data) >= 1
+
+
+def test_collection_alpha():
+    """Collection alpha is baked into the facecolor rgba by matplotlib. if
+    fillcolor has an alpha channel, the opacity field should not be set."""
+    x = np.linspace(0, 2 * np.pi, 50)
+    fig, ax = plt.subplots()
+    ax.fill_between(x, np.sin(x), np.cos(x), color="red", alpha=0.4)
+    plotly_fig = tls.mpl_to_plotly(fig)
+    trace = plotly_fig.data[0]
+    assert trace.fillcolor == "rgba(255,0,0,0.4)"
+    assert trace.opacity is None
+
+
+def test_violin_body_default_alpha():
+    """Violin bodies default to alpha=0.3 in matplotlib, which is
+    embedded in their facecolor rgba. If the alpha channel in fillcolor
+    is set, the opacity field should not be set."""
+    fig, ax = plt.subplots()
+    ax.violinplot(np.random.randn(100, 3))
+    plotly_fig = tls.mpl_to_plotly(fig)
+    bodies = [
+        t
+        for t in plotly_fig.data
+        if t.fill == "toself" and t.fillcolor == "rgba(31,119,180,0.3)"
+    ]
+    assert len(bodies) >= 3
+    assert all(t.opacity is None for t in bodies)
+
+
+def test_stem_plot_renders():
+    x = np.linspace(0, 2 * np.pi, 20)
+    fig, ax = plt.subplots()
+    ax.stem(x, np.sin(x))
+    plotly_fig = tls.mpl_to_plotly(fig)
+    assert len(plotly_fig.data) >= 20
+
+
+def test_contour_lines_convert():
+    """Contour lines used to crash with an ndarray line width."""
+    x = np.linspace(-3, 3, 30)
+    X, Y = np.meshgrid(x, x)
+    fig, ax = plt.subplots()
+    ax.contour(X, Y, np.sin(X) * np.cos(Y), 10)
+    plotly_fig = tls.mpl_to_plotly(fig)
+    assert len(plotly_fig.data) > 0
+
+
+def test_contourf_bands_render():
+    """Contourf bands (multi-subpath collections) must render as fills."""
+    x = np.linspace(-3, 3, 30)
+    X, Y = np.meshgrid(x, x)
+    fig, ax = plt.subplots()
+    ax.contourf(X, Y, np.sin(X) * np.cos(Y), 10)
+    plotly_fig = tls.mpl_to_plotly(fig)
+    filled = [t for t in plotly_fig.data if t.fill == "toself"]
+    assert len(filled) > 0
+
+
+def test_filled_path_collection_date_xaxis():
+    """Filled path collections with date x-values must export date strings,
+    not raw matplotlib date numbers."""
+    dates = [
+        datetime.datetime(2023, 1, 1) + datetime.timedelta(days=i) for i in range(10)
+    ]
+    fig, ax = plt.subplots()
+    ax.fill_between(dates, np.sin(np.arange(10)), np.cos(np.arange(10)))
+    plotly_fig = tls.mpl_to_plotly(fig)
+    filled = [t for t in plotly_fig.data if t.fill == "toself"]
+    assert len(filled) >= 1
+    assert all(isinstance(x, str) for x in filled[0].x)