Combine disjoint line collection subpaths using None separators

Author: robertoffmoura

plotly/matplotlylib/renderer.py

@@ -563,8 +563,8 @@ def per_path(colors, i, default):
             edgecolor = per_path(edgecolors, i, "rgba(0,0,0,0)")
             linewidth = per_path(linewidths, i, 0)
             # a path may contain several disjoint lines (e.g. contour lines
-            # of the same level); drawing them in one trace would connect
-            # them, so draw each subpath separately.
+            # of the same level); separate disjoint subpaths with None so
+            # plotly does not connect them.
             # In SVG paths, codes carry different numbers of vertices:
             # M/L: 1, C: 3 (cubic curve), S: 2 (smooth/quad curve), Z: 0.
             code_steps = {"M": 1, "L": 1, "C": 3, "S": 2, "Z": 0}
@@ -587,17 +587,27 @@ def per_path(colors, i, default):
                     vi += step
             if current:
                 subpaths.append((current, closed))
+            x_combined = []
+            y_combined = []
             for sub, closed in subpaths:
                 if len(sub) < 2:
                     continue
                 # a closed subpath (Z code) must be closed explicitly since
                 # plotly's lines mode does not close the loop
                 if closed:
                     sub = sub + [sub[0]]
+                sub_x = self._convert_x_dates([v[0] for v in sub])
+                sub_y = [v[1] for v in sub]
+                if x_combined:
+                    x_combined.append(None)
+                    y_combined.append(None)
+                x_combined.extend(sub_x)
+                y_combined.extend(sub_y)
+            if x_combined:
                 self.plotly_fig.add_trace(
                     go.Scatter(
-                        x=self._convert_x_dates([v[0] for v in sub]),
-                        y=[v[1] for v in sub],
+                        x=x_combined,
+                        y=y_combined,
                         mode="lines",
                         line=go.scatter.Line(
                             color=_export_color(edgecolor), width=linewidth

plotly/matplotlylib/tests/test_renderer.py

@@ -358,17 +358,17 @@ def test_custom_date_xtickvals_given_as_numbers_are_converted():
 
 def test_contour_rings_are_closed():
     """Closed contour loops (Z codes) must close in plotly, not leave a gap."""
-    x = np.linspace(-3, 3, 30)
+    x = np.linspace(-3, 3, 50)
     X, Y = np.meshgrid(x, x)
     fig, ax = plt.subplots()
-    ax.contour(X, Y, np.sin(X) * np.cos(Y), 10)
+    ax.contour(X, Y, X**2 + Y**2, levels=[1, 4])
     plotly_fig = tls.mpl_to_plotly(fig)
-    rings = [
-        t
-        for t in plotly_fig.data
-        if len(t.x) > 30 and t.x[0] == t.x[-1] and t.y[0] == t.y[-1]
-    ]
-    assert len(rings) >= 2
+
+    assert len(plotly_fig.data) == 2
+    assert plotly_fig.data[0].x[0] == plotly_fig.data[0].x[-1]
+    assert plotly_fig.data[0].y[0] == plotly_fig.data[0].y[-1]
+    assert plotly_fig.data[1].x[0] == plotly_fig.data[1].x[-1]
+    assert plotly_fig.data[1].y[0] == plotly_fig.data[1].y[-1]
 
 
 def test_line_collection_date_xaxis():
@@ -385,5 +385,5 @@ def test_line_collection_date_xaxis():
     plotly_fig = tls.mpl_to_plotly(fig)
     lines = [t for t in plotly_fig.data if t.mode == "lines"]
     assert len(lines) >= 1
-    assert all(isinstance(x, str) for t in lines for x in t.x)
-
+    assert any(isinstance(x, str) for t in lines for x in t.x)
+    assert all(x is None or isinstance(x, str) for t in lines for x in t.x)