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FIX: avoid applying dashed patterns to zero-width lines and patches #31307

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Merged
ksunden merged 4 commits into from
Mar 20, 2026
Merged

FIX: avoid applying dashed patterns to zero-width lines and patches #31307

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3f42ea8
FIX: avoid applying dashed patterns to zero-width lines and patches
francisayyad03 Mar 15, 2026
0fe9994
use figure-equality tests for zero-width dashed rendering
francisayyad03 Mar 16, 2026
7b3f389
strengthen zero-width dash regression tests
francisayyad03 Mar 16, 2026
aafeacd
simplify zero-width dash regression tests
francisayyad03 Mar 17, 2026
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12 changes: 9 additions & 3 deletions lib/matplotlib/lines.py
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Original file line number Diff line number Diff line change
Expand Up @@ -798,8 +798,11 @@ def draw(self, renderer):
if self.get_sketch_params() is not None:
gc.set_sketch_params(*self.get_sketch_params())

# We first draw a path within the gaps if needed.
if self.is_dashed() and self._gapcolor is not None:
# We first draw a path within the gaps if needed, but only for
# visible dashed lines; zero-width lines would otherwise yield
# all-zero dashes.
if (self._linewidth > 0 and self.is_dashed()
and self._gapcolor is not None):
lc_rgba = mcolors.to_rgba(self._gapcolor, self._alpha)
gc.set_foreground(lc_rgba, isRGBA=True)

Expand All @@ -812,7 +815,10 @@ def draw(self, renderer):
lc_rgba = mcolors.to_rgba(self._color, self._alpha)
gc.set_foreground(lc_rgba, isRGBA=True)

gc.set_dashes(*self._dash_pattern)
if self._linewidth > 0:
gc.set_dashes(*self._dash_pattern)
else:
gc.set_dashes(0, None)
renderer.draw_path(gc, tpath, affine.frozen())
gc.restore()

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10 changes: 7 additions & 3 deletions lib/matplotlib/patches.py
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Expand Up @@ -709,8 +709,9 @@ def _draw_paths_with_artist_properties(
from matplotlib.patheffects import PathEffectRenderer
renderer = PathEffectRenderer(self.get_path_effects(), renderer)

# Draw the gaps first if gapcolor is set
if self._has_dashed_edge() and self._gapcolor is not None:
# We first draw a path within the gaps if needed, but only for visible
# dashed edges; zero-width edges would otherwise yield all-zero dashes.
if lw > 0 and self._has_dashed_edge() and self._gapcolor is not None:
gc.set_foreground(self._gapcolor, isRGBA=True)
offset_gaps, gaps = mlines._get_inverse_dash_pattern(
*self._dash_pattern)
Expand All @@ -720,7 +721,10 @@ def _draw_paths_with_artist_properties(

# Draw the main edge
gc.set_foreground(self._edgecolor, isRGBA=True)
gc.set_dashes(*self._dash_pattern)
if lw > 0:
gc.set_dashes(*self._dash_pattern)
else:
gc.set_dashes(0, None)
for draw_path_args in draw_path_args_list:
renderer.draw_path(gc, *draw_path_args)

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10 changes: 7 additions & 3 deletions lib/matplotlib/tests/test_axes.py
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Expand Up @@ -8081,9 +8081,13 @@ def test_twinning_default_axes_class():
assert type(twiny) is Axes


def test_zero_linewidth():
# Check that setting a zero linewidth doesn't error
plt.plot([0, 1], [0, 1], ls='--', lw=0)
@mpl.style.context('mpl20')
@check_figures_equal()
def test_stairs_fill_zero_linewidth(fig_test, fig_ref):
fig_test.subplots().stairs(
[1, 2, 3, 4], [1, 2, 3, 4, 5], fill=True, ls='--')
fig_ref.subplots().stairs(
[1, 2, 3, 4], [1, 2, 3, 4, 5], fill=True, ls='-')


def test_empty_errorbar_legend():
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7 changes: 7 additions & 0 deletions lib/matplotlib/tests/test_lines.py
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Original file line number Diff line number Diff line change
Expand Up @@ -92,6 +92,13 @@ def test_valid_linestyles():
line.set_linestyle('aardvark')


@mpl.style.context('mpl20')
def test_zero_linewidth_dashed_uses_solid_gc_dashes():
fig, ax = plt.subplots()
ax.plot([0, 1], [0, 1], ls='--', lw=0)
fig.draw_without_rendering()


@image_comparison(['drawstyle_variants.png'], remove_text=True,
tol=0 if platform.machine() == 'x86_64' else 0.03)
def test_drawstyle_variants():
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8 changes: 8 additions & 0 deletions lib/matplotlib/tests/test_patches.py
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Original file line number Diff line number Diff line change
Expand Up @@ -907,6 +907,14 @@ def test_default_linestyle():
assert patch.get_linestyle() == 'solid'


@mpl.style.context('mpl20')
def test_patch_zero_linewidth_dashed_uses_solid_gc_dashes():
fig, ax = plt.subplots()
ax.add_patch(Rectangle(
(0, 0), 1, 1, fill=False, linewidth=0, linestyle='--'))
fig.draw_without_rendering()


def test_default_capstyle():
patch = Patch()
assert patch.get_capstyle() == 'butt'
Expand Down
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