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

francisayyad03 · francisayyad03 · commit 3f42ea84018b · 2026-03-15T00:11:16.000-04:00
diff --git a/lib/matplotlib/lines.py b/lib/matplotlib/lines.py
@@ -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)
 
@@ -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()
 
diff --git a/lib/matplotlib/patches.py b/lib/matplotlib/patches.py
@@ -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)
@@ -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)
 
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -8084,6 +8084,14 @@ def test_twinning_default_axes_class():
 def test_zero_linewidth():
     # Check that setting a zero linewidth doesn't error
     plt.plot([0, 1], [0, 1], ls='--', lw=0)
+    plt.gcf().canvas.draw()
+
+
+@mpl.style.context('mpl20')
+def test_stairs_fill_zero_linewidth():
+    fig, ax = plt.subplots()
+    ax.stairs([1, 2, 3, 4], [1, 2, 3, 4, 5], fill=True, ls='--')
+    fig.canvas.draw()
 
 
 def test_empty_errorbar_legend():
diff --git a/lib/matplotlib/tests/test_patches.py b/lib/matplotlib/tests/test_patches.py
@@ -907,6 +907,12 @@ def test_default_linestyle():
     assert patch.get_linestyle() == 'solid'
 
 
+def test_patch_zero_linewidth_dashed_draw():
+    fig, ax = plt.subplots()
+    ax.add_patch(Rectangle((0, 0), 1, 1, fill=False, linewidth=0, linestyle='--'))
+    fig.canvas.draw()
+
+
 def test_default_capstyle():
     patch = Patch()
     assert patch.get_capstyle() == 'butt'
