Backport PR #13563: FIX: inverted colorbar ticks

dstansby · MeeseeksDev[bot] · commit 5d2d419afc13 · 2019-03-02T17:49:17.000Z
diff --git a/lib/matplotlib/colorbar.py b/lib/matplotlib/colorbar.py
@@ -238,6 +238,9 @@ def __init__(self, colorbar):
         super().__init__(nbins=nbins, steps=steps)
 
     def tick_values(self, vmin, vmax):
+        # flip if needed:
+        if vmin > vmax:
+            vmin, vmax = vmax, vmin
         vmin = max(vmin, self._colorbar.norm.vmin)
         vmax = min(vmax, self._colorbar.norm.vmax)
         ticks = super().tick_values(vmin, vmax)
@@ -295,8 +298,10 @@ def __init__(self, colorbar, *args, **kwargs):
         super().__init__(*args, **kwargs)
 
     def tick_values(self, vmin, vmax):
-        vmin = self._colorbar.norm.vmin
-        vmax = self._colorbar.norm.vmax
+        if vmin > vmax:
+            vmin, vmax = vmax, vmin
+        vmin = max(vmin, self._colorbar.norm.vmin)
+        vmax = min(vmax, self._colorbar.norm.vmax)
         ticks = super().tick_values(vmin, vmax)
         rtol = (np.log10(vmax) - np.log10(vmin)) * 1e-10
         ticks = ticks[(np.log10(ticks) >= np.log10(vmin) - rtol) &
diff --git a/lib/matplotlib/tests/test_colorbar.py b/lib/matplotlib/tests/test_colorbar.py
@@ -514,8 +514,28 @@ def test_colorbar_scale_reset():
 def test_colorbar_get_ticks():
     with rc_context({'_internal.classic_mode': False}):
 
-        fig, ax = plt. subplots()
+        fig, ax = plt.subplots()
         np.random.seed(19680801)
         pc = ax.pcolormesh(np.random.rand(30, 30))
         cb = fig.colorbar(pc)
         np.testing.assert_allclose(cb.get_ticks(), [0.2, 0.4, 0.6, 0.8])
+
+
+def test_colorbar_inverted_ticks():
+    fig, axs = plt.subplots(2)
+    ax = axs[0]
+    pc = ax.pcolormesh(10**np.arange(1, 5).reshape(2, 2), norm=LogNorm())
+    cbar = fig.colorbar(pc, ax=ax, extend='both')
+    ticks = cbar.get_ticks()
+    cbar.ax.invert_yaxis()
+    np.testing.assert_allclose(ticks, cbar.get_ticks())
+
+    ax = axs[1]
+    pc = ax.pcolormesh(np.arange(1, 5).reshape(2, 2))
+    cbar = fig.colorbar(pc, ax=ax, extend='both')
+    cbar.minorticks_on()
+    ticks = cbar.get_ticks()
+    minorticks = cbar.get_ticks(minor=True)
+    cbar.ax.invert_yaxis()
+    np.testing.assert_allclose(ticks, cbar.get_ticks())
+    np.testing.assert_allclose(minorticks, cbar.get_ticks(minor=True))
