FIX: CenterNorm setting vmin/vmax should keep symmetry

greglucas · greglucas · commit 48272bfd49ab · 2022-11-14T19:51:42.000-07:00
This fixes the case where someone explicitly sets vmin or vmax by
keeping vcenter fixed and also updating vmax or vmin respectively,
ensuring that the halfrange is the same on each side of vcenter.
diff --git a/lib/matplotlib/colors.py b/lib/matplotlib/colors.py
@@ -1532,6 +1532,30 @@ def autoscale_None(self, A):
         if self.halfrange is None and A.size:
             self.autoscale(A)
 
+    @property
+    def vmin(self):
+        return self._vmin
+
+    @vmin.setter
+    def vmin(self, value):
+        value = _sanitize_extrema(value)
+        if value != self._vmin:
+            self._vmin = value
+            self._vmax = 2*self.vcenter - value
+            self._changed()
+
+    @property
+    def vmax(self):
+        return self._vmax
+
+    @vmax.setter
+    def vmax(self, value):
+        value = _sanitize_extrema(value)
+        if value != self._vmax:
+            self._vmax = value
+            self._vmin = 2*self.vcenter - value
+            self._changed()
+
     @property
     def vcenter(self):
         return self._vcenter
diff --git a/lib/matplotlib/tests/test_colors.py b/lib/matplotlib/tests/test_colors.py
@@ -492,6 +492,19 @@ def test_CenteredNorm():
     assert norm.vmax == 2
     assert norm.halfrange == 1
 
+    # Check setting vmin directly updates the halfrange and vmax, but
+    # leaves vcenter alone
+    norm.vmin = -1
+    assert norm.halfrange == 2
+    assert norm.vmax == 3
+    assert norm.vcenter == 1
+
+    # also check vmax updates
+    norm.vmax = 2
+    assert norm.halfrange == 1
+    assert norm.vmin == 0
+    assert norm.vcenter == 1
+
 
 @pytest.mark.parametrize("vmin,vmax", [[-1, 2], [3, 1]])
 def test_lognorm_invalid(vmin, vmax):
