Added option for an offset for MultipleLocator

Co-authored-by: Ruth Comer 10599679+rcomer@users.noreply.github.com
QuLogic · QuLogic · Sep 24, 2021 · Mar 30, 2023 · Mar 30, 2023 · Mar 31, 2023
commit 8796a8cf56ff484c7f02c7236b60efbc2381758d
diff --git a/lib/matplotlib/tests/test_ticker.py b/lib/matplotlib/tests/test_ticker.py
@@ -63,6 +63,12 @@ def test_basic(self):
                                9.441, 12.588])
         assert_almost_equal(loc.tick_values(-7, 10), test_value)
 
+    def test_basic_with_offset(self):
+        loc = mticker.MultipleLocator(base=3.147, offset=1.2)
+        test_value = np.array([-8.241, -5.094, -1.947, 1.2, 4.347, 7.494,
+                               10.641])
+        assert_almost_equal(loc.tick_values(-7, 10), test_value)
+
     def test_view_limits(self):
         """
         Test basic behavior of view limits.
@@ -80,6 +86,15 @@ def test_view_limits_round_numbers(self):
             loc = mticker.MultipleLocator(base=3.147)
             assert_almost_equal(loc.view_limits(-4, 4), (-6.294, 6.294))
 
+    def test_view_limits_round_numbers_with_offset(self):
+        """
+        Test that everything works properly with 'round_numbers' for auto
+        limit.
+        """
+        with mpl.rc_context({'axes.autolimit_mode': 'round_numbers'}):
+            loc = mticker.MultipleLocator(base=3.147, offset=1.3)
+            assert_almost_equal(loc.view_limits(-4, 4), (-4.994, 4.447))
+
     def test_set_params(self):
         """
         Create multiple locator with 0.7 base, and change it to something else.
@@ -88,6 +103,8 @@ def test_set_params(self):
         mult = mticker.MultipleLocator(base=0.7)
         mult.set_params(base=1.7)
         assert mult._edge.step == 1.7
+        mult.set_params(offset=3)
+        assert mult._offset == 3
 
 
 class TestAutoMinorLocator:

diff --git a/lib/matplotlib/ticker.py b/lib/matplotlib/ticker.py
@@ -1825,17 +1825,20 @@ def view_limits(self, vmin, vmax):
 
 class MultipleLocator(Locator):
     """
-    Set a tick on each integer multiple of the *base* within the view
-    interval.
+    Set a tick on each integer multiple of the *base* plus an *offset* within
+    the view interval.
     """
 
-    def __init__(self, base=1.0):
+    def __init__(self, base=1.0, offset=0.0):
         self._edge = _Edge_integer(base, 0)
+        self._offset = offset
 
-    def set_params(self, base):
+    def set_params(self, base=None, offset=None):
         """Set parameters within this locator."""
         if base is not None:
             self._edge = _Edge_integer(base, 0)
+        if offset is not None:
+            self._offset = offset
 
     def __call__(self):
         """Return the locations of the ticks."""
@@ -1846,19 +1849,20 @@ def tick_values(self, vmin, vmax):
         if vmax < vmin:
             vmin, vmax = vmax, vmin
         step = self._edge.step
+        vmin -= self._offset
+        vmax -= self._offset
         vmin = self._edge.ge(vmin) * step
         n = (vmax - vmin + 0.001 * step) // step
-        locs = vmin - step + np.arange(n + 3) * step
+        locs = vmin - step + np.arange(n + 3) * step + self._offset
         return self.raise_if_exceeds(locs)
 
     def view_limits(self, dmin, dmax):
         """
-        Set the view limits to the nearest multiples of *base* that
-        contain the data.
+        Set the view limits to the nearest tick values that contain the data.
         """
         if mpl.rcParams['axes.autolimit_mode'] == 'round_numbers':
-            vmin = self._edge.le(dmin) * self._edge.step
-            vmax = self._edge.ge(dmax) * self._edge.step
+            vmin = self._edge.le(dmin - self._offset) * self._edge.step + self._offse
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+            vmax = self._edge.ge(dmax - self._offset) * self._edge.step + self._offset
             if vmin == vmax:
                 vmin -= 1
                 vmax += 1