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Use native legends when converting from matplotlib #5312

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Merged
emilykl merged 3 commits into plotly:main from robertoffmoura:rm/use-native-legend
Oct 1, 2025
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127 changes: 46 additions & 81 deletions plotly/matplotlylib/renderer.py
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -60,6 +60,8 @@ def __init__(self):
self.mpl_x_bounds = (0, 1)
self.mpl_y_bounds = (0, 1)
self.msg = "Initialized PlotlyRenderer\n"
self._processing_legend = False
self._legend_visible = False

def open_figure(self, fig, props):
"""Creates a new figure by beginning to fill out layout dict.
Expand Down Expand Up @@ -108,7 +110,6 @@ def close_figure(self, fig):
fig -- a matplotlib.figure.Figure object.

"""
self.plotly_fig["layout"]["showlegend"] = False
self.msg += "Closing figure\n"

def open_axes(self, ax, props):
Expand Down Expand Up @@ -198,6 +199,37 @@ def close_axes(self, ax):
self.msg += " Closing axes\n"
self.x_is_mpl_date = False

def open_legend(self, legend, props):
"""Enable Plotly's native legend when matplotlib legend is detected.

This method is called when a matplotlib legend is found. It enables
Plotly's showlegend only if the matplotlib legend is visible.

Positional arguments:
legend -- matplotlib.legend.Legend object
props -- legend properties dictionary
"""
self.msg += " Opening legend\n"
self._processing_legend = True
self._legend_visible = props.get("visible", True)
if self._legend_visible:
self.msg += (
" Enabling native plotly legend (matplotlib legend is visible)\n"
)
self.plotly_fig["layout"]["showlegend"] = True
else:
self.msg += " Not enabling legend (matplotlib legend is not visible)\n"

def close_legend(self, legend):
"""Finalize legend processing.

Positional arguments:
legend -- matplotlib.legend.Legend object
"""
self.msg += " Closing legend\n"
self._processing_legend = False
self._legend_visible = False

def draw_bars(self, bars):
# sort bars according to bar containers
mpl_traces = []
Expand Down Expand Up @@ -299,7 +331,7 @@ def draw_bar(self, coll):
) # TODO ditto
if len(bar["x"]) > 1:
self.msg += " Heck yeah, I drew that bar chart\n"
(self.plotly_fig.add_trace(bar),)
self.plotly_fig.add_trace(bar)
if bar_gap is not None:
self.plotly_fig["layout"]["bargap"] = bar_gap
else:
Expand All @@ -309,83 +341,6 @@ def draw_bar(self, coll):
"assuming data redundancy, not plotting."
)

def draw_legend_shapes(self, mode, shape, **props):
"""Create a shape that matches lines or markers in legends.

Main issue is that path for circles do not render, so we have to use 'circle'
instead of 'path'.
"""
for single_mode in mode.split("+"):
x = props["data"][0][0]
y = props["data"][0][1]
if single_mode == "markers" and props.get("markerstyle"):
size = shape.pop("size", 6)
symbol = shape.pop("symbol")
# aligning to "center"
x0 = 0
y0 = 0
x1 = size
y1 = size
markerpath = props["markerstyle"].get("markerpath")
if markerpath is None and symbol != "circle":
self.msg += (
"not sure how to handle this marker without a valid path\n"
)
return
# marker path to SVG path conversion
path = " ".join(
[f"{a} {t[0]},{t[1]}" for a, t in zip(markerpath[1], markerpath[0])]
)

if symbol == "circle":
# symbols like . and o in matplotlib, use circle
# plotly also maps many other markers to circle, such as 1,8 and p
path = None
shape_type = "circle"
x0 = -size / 2
y0 = size / 2
x1 = size / 2
y1 = size + size / 2
else:
# triangles, star etc
shape_type = "path"
legend_shape = go.layout.Shape(
type=shape_type,
xref="paper",
yref="paper",
x0=x0,
y0=y0,
x1=x1,
y1=y1,
xsizemode="pixel",
ysizemode="pixel",
xanchor=x,
yanchor=y,
path=path,
**shape,
)

elif single_mode == "lines":
mode = "line"
x1 = props["data"][1][0]
y1 = props["data"][1][1]

legend_shape = go.layout.Shape(
type=mode,
xref="paper",
yref="paper",
x0=x,
y0=y + 0.02,
x1=x1,
y1=y1 + 0.02,
**shape,
)
else:
self.msg += "not sure how to handle this element\n"
return
self.plotly_fig.add_shape(legend_shape)
self.msg += " Heck yeah, I drew that shape\n"

def draw_marked_line(self, **props):
"""Create a data dict for a line obj.

Expand Down Expand Up @@ -497,11 +452,11 @@ def draw_marked_line(self, **props):
marked_line["x"] = mpltools.mpl_dates_to_datestrings(
marked_line["x"], formatter
)
(self.plotly_fig.add_trace(marked_line),)
self.plotly_fig.add_trace(marked_line)
self.msg += " Heck yeah, I drew that line\n"
elif props["coordinates"] == "axes":
# dealing with legend graphical elements
self.draw_legend_shapes(mode=mode, shape=shape, **props)
self.msg += " Using native legend\n"
else:
self.msg += " Line didn't have 'data' coordinates, not drawing\n"
warnings.warn(
Expand Down Expand Up @@ -667,6 +622,16 @@ def draw_text(self, **props):
self.draw_title(**props)
else: # just a regular text annotation...
self.msg += " Text object is a normal annotation\n"
# Skip creating annotations for legend text when using native legend
if (
self._processing_legend
and self._legend_visible
and props["coordinates"] == "axes"
):
self.msg += (
" Skipping legend text annotation (using native legend)\n"
)
return
if props["coordinates"] != "data":
self.msg += " Text object isn't linked to 'data' coordinates\n"
x_px, y_px = (
Expand Down
4 changes: 4 additions & 0 deletions plotly/matplotlylib/tests/__init__.py
View file Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
import matplotlib

matplotlib.use("Agg")
import matplotlib.pyplot as plt
87 changes: 87 additions & 0 deletions plotly/matplotlylib/tests/test_renderer.py
View file Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,87 @@
import plotly.tools as tls

from . import plt


def test_native_legend_enabled_when_matplotlib_legend_present():
"""Test that when matplotlib legend is present, Plotly uses native legend."""
fig, ax = plt.subplots()
ax.plot([0, 1], [0, 1], label="Line 1")
ax.plot([0, 1], [1, 0], label="Line 2")
ax.legend()

plotly_fig = tls.mpl_to_plotly(fig)

# Should enable native legend
assert plotly_fig.layout.showlegend == True
# Should have 2 traces with names
assert len(plotly_fig.data) == 2
assert plotly_fig.data[0].name == "Line 1"
assert plotly_fig.data[1].name == "Line 2"


def test_no_fake_legend_shapes_with_native_legend():
"""Test that fake legend shapes are not created when using native legend."""
fig, ax = plt.subplots()
ax.plot([0, 1], [0, 1], "o-", label="Data with markers")
ax.legend()

plotly_fig = tls.mpl_to_plotly(fig)

# Should use native legend
assert plotly_fig.layout.showlegend == True
# Should not create fake legend elements
assert len(plotly_fig.layout.shapes) == 0
assert len(plotly_fig.layout.annotations) == 0


def test_legend_disabled_when_no_matplotlib_legend():
"""Test that legend is not enabled when no matplotlib legend is present."""
fig, ax = plt.subplots()
ax.plot([0, 1], [0, 1], label="Line 1") # Has label but no legend() call

plotly_fig = tls.mpl_to_plotly(fig)

# Should not have showlegend explicitly set to True
# (Plotly's default behavior when no legend elements exist)
assert (
not hasattr(plotly_fig.layout, "showlegend")
or plotly_fig.layout.showlegend != True
)


def test_legend_disabled_when_matplotlib_legend_not_visible():
"""Test that legend is not enabled when no matplotlib legend is not visible."""
fig, ax = plt.subplots()
ax.plot([0, 1], [0, 1], label="Line 1")
legend = ax.legend()
legend.set_visible(False) # Hide the legend

plotly_fig = tls.mpl_to_plotly(fig)

# Should not enable legend when matplotlib legend is hidden
assert (
not hasattr(plotly_fig.layout, "showlegend")
or plotly_fig.layout.showlegend != True
)


def test_multiple_traces_native_legend():
"""Test native legend works with multiple traces of different types."""
fig, ax = plt.subplots()
ax.plot([0, 1, 2], [0, 1, 0], "-", label="Line")
ax.plot([0, 1, 2], [1, 0, 1], "o", label="Markers")
ax.plot([0, 1, 2], [0.5, 0.5, 0.5], "s-", label="Line+Markers")
ax.legend()

plotly_fig = tls.mpl_to_plotly(fig)

assert plotly_fig.layout.showlegend == True
assert len(plotly_fig.data) == 3
assert plotly_fig.data[0].name == "Line"
assert plotly_fig.data[1].name == "Markers"
assert plotly_fig.data[2].name == "Line+Markers"
# Verify modes are correct
assert plotly_fig.data[0].mode == "lines"
assert plotly_fig.data[1].mode == "markers"
assert plotly_fig.data[2].mode == "lines+markers"

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