Convert only axis-aligned rectangles to span shapes

Author: robertoffmoura

plotly/matplotlylib/renderer.py

@@ -78,6 +78,27 @@ def _has_blended_transform(transform):
     return _find_blended_transform(transform) is not None
 
 
+def _is_axis_aligned_rectangle(points):
+    """Check whether polygon vertices trace an axis-aligned rectangle: every
+    vertex is a corner of the bounding box and all four corners appear."""
+    xs = [float(x) for x, _ in points]
+    ys = [float(y) for _, y in points]
+    if not xs:
+        return False
+    x_min, x_max = min(xs), max(xs)
+    y_min, y_max = min(ys), max(ys)
+    corners = set()
+    for x, y in zip(xs, ys):
+        at_x_min = math.isclose(x, x_min, abs_tol=1e-9)
+        at_x_max = math.isclose(x, x_max, abs_tol=1e-9)
+        at_y_min = math.isclose(y, y_min, abs_tol=1e-9)
+        at_y_max = math.isclose(y, y_max, abs_tol=1e-9)
+        if not (at_x_min or at_x_max) or not (at_y_min or at_y_max):
+            return False
+        corners.add((at_x_max, at_y_max))
+    return len(corners) == 4
+
+
 class PlotlyRenderer(Renderer):
     """A renderer class inheriting from base for rendering mpl plots in plotly.
 
@@ -705,6 +726,19 @@ def _draw_axes_line(self, props):
         self.msg += "    Heck yeah, I drew that reference line\n"
         return True
 
+    def _is_axes_span(self, props):
+        """Check whether a path qualifies as a reference span (e.g. axhspan,
+        axvspan): an axis-aligned rectangle in a blended axes/data
+        transform."""
+        if not isinstance(props["mplobj"], (mpatches.Rectangle, mpatches.Polygon)):
+            return False
+        if not (
+            props["coordinates"] == "display"
+            and _has_blended_transform(props["mplobj"].get_transform())
+        ):
+            return False
+        return _is_axis_aligned_rectangle(props["data"])
+
     def _draw_axes_span(self, props):
         """Draw a reference span (axhspan/axvspan) as a layout shape.
 
@@ -977,11 +1011,7 @@ def draw_path(self, **props):
         elif isinstance(props["mplobj"], mpatches.StepPatch):
             self.msg += "    Drawing a step path\n"
             self._draw_step_path(props)
-        elif (
-            isinstance(props["mplobj"], (mpatches.Rectangle, mpatches.Polygon))
-            and props["coordinates"] == "display"
-            and _has_blended_transform(props["mplobj"].get_transform())
-        ):
+        elif self._is_axes_span(props):
             if self._processing_legend:
                 self.msg += "    Using native legend\n"
             else:

plotly/matplotlylib/tests/test_renderer.py

@@ -5,6 +5,7 @@
 import matplotlib
 import matplotlib.pyplot as plt
 import matplotlib.dates as mdates
+import matplotlib.patches as mpatches
 from packaging.version import Version
 from matplotlib import transforms
 import plotly.tools as tls
@@ -1482,3 +1483,27 @@ def test_axhspan_with_custom_style_converts():
     assert shape.line.color == "rgba(0, 0, 255, 0.5)"
     assert shape.line.dash == "dash"
     assert shape.line.width == 1.0
+
+
+def test_blended_unaligned_shapes_do_not_convert_to_spans():
+    """A triangle and a rotated rectangle in a blended axes/data transform
+    warn and leave the layout shapes empty."""
+    fig, ax = plt.subplots()
+    ax.plot([0, 10], [0, 10])
+    ax.add_patch(
+        mpatches.Polygon(
+            [[5, 0.1], [9, 0.1], [7, 0.5]],
+            transform=ax.get_xaxis_transform(),
+            color="b",
+        )
+    )
+    ax.add_patch(
+        mpatches.Rectangle(
+            (6, 0.6), 2, 0.2, angle=30, transform=ax.get_xaxis_transform(), color="g"
+        )
+    )
+
+    with pytest.warns(UserWarning, match="path object"):
+        plotly_fig = tls.mpl_to_plotly(fig)
+
+    assert len(plotly_fig.layout.shapes) == 0