Backport PR #21293: Fix snap argument to pcolormesh

anntzer · meeseeksmachine · commit aa2822398370 · 2021-10-06T07:56:00.000Z
diff --git a/lib/matplotlib/axes/_axes.py b/lib/matplotlib/axes/_axes.py
@@ -6016,9 +6016,10 @@ def pcolormesh(self, *args, alpha=None, norm=None, cmap=None, vmin=None,
         # convert to one dimensional array
         C = C.ravel()
 
-        snap = kwargs.get('snap', rcParams['pcolormesh.snap'])
+        kwargs.setdefault('snap', rcParams['pcolormesh.snap'])
+
         collection = mcoll.QuadMesh(
-            coords, antialiased=antialiased, shading=shading, snap=snap,
+            coords, antialiased=antialiased, shading=shading,
             array=C, cmap=cmap, norm=norm, alpha=alpha, **kwargs)
         collection._scale_norm(norm, vmin, vmax)
         self._pcolor_grid_deprecation_helper()
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -1249,22 +1249,23 @@ def test_pcolorflaterror():
         ax.pcolormesh(x, y, Z, shading='flat')
 
 
+@pytest.mark.parametrize('snap', [False, True])
 @check_figures_equal(extensions=["png"])
-def test_pcolorauto(fig_test, fig_ref):
+def test_pcolorauto(fig_test, fig_ref, snap):
     ax = fig_test.subplots()
     x = np.arange(0, 10)
     y = np.arange(0, 4)
     np.random.seed(19680801)
     Z = np.random.randn(3, 9)
     # this is the same as flat; note that auto is default
-    ax.pcolormesh(x, y, Z)
+    ax.pcolormesh(x, y, Z, snap=snap)
 
     ax = fig_ref.subplots()
     # specify the centers
     x2 = x[:-1] + np.diff(x) / 2
     y2 = y[:-1] + np.diff(y) / 2
     # this is same as nearest:
-    ax.pcolormesh(x2, y2, Z)
+    ax.pcolormesh(x2, y2, Z, snap=snap)
 
 
 @image_comparison(['canonical'])
