Merge pull request matplotlib#18575 from ShawnChen1996/colorbarGridPosition

Colorbar grid position

Author: QuLogic

examples/color/colorbar_basics.py

@@ -32,8 +32,9 @@
 fig.colorbar(pos, ax=ax1)
 
 # repeat everything above for the negative data
+# you can specify location, anchor and shrink the colorbar
 neg = ax2.imshow(Zneg, cmap='Reds_r', interpolation='none')
-fig.colorbar(neg, ax=ax2)
+fig.colorbar(neg, ax=ax2, location='right', anchor=(0, 0.3), shrink=0.7)
 
 # Plot both positive and negative values between +/- 1.2
 pos_neg_clipped = ax3.imshow(Z, cmap='RdBu', vmin=-1.2, vmax=1.2,

lib/matplotlib/colorbar.py

@@ -1493,35 +1493,51 @@ def make_axes_gridspec(parent, *, location=None, orientation=None,
     kw['orientation'] = loc_settings['orientation']
     location = kw['ticklocation'] = loc_settings['location']
 
-    pad = loc_settings["pad"]
+    anchor = kw.pop('anchor', loc_settings['anchor'])
+    panchor = kw.pop('panchor', loc_settings['panchor'])
+    pad = kw.pop('pad', loc_settings["pad"])
     wh_space = 2 * pad / (1 - pad)
 
-    # for shrinking
-    pad_s = (1 - shrink) * 0.5
-    wh_ratios = [pad_s, shrink, pad_s]
-
-    if location == "left":
-        gs = parent.get_subplotspec().subgridspec(
-            1, 2, wspace=wh_space, width_ratios=[fraction, 1-fraction-pad])
-        ss_main = gs[1]
-        ss_cb = gs[0].subgridspec(3, 1, hspace=0, height_ratios=wh_ratios)[1]
-    elif location == "right":
-        gs = parent.get_subplotspec().subgridspec(
-            1, 2, wspace=wh_space, width_ratios=[1-fraction-pad, fraction])
-        ss_main = gs[0]
-        ss_cb = gs[1].subgridspec(3, 1, hspace=0, height_ratios=wh_ratios)[1]
-    elif location == "top":
-        gs = parent.get_subplotspec().subgridspec(
-            2, 1, hspace=wh_space, height_ratios=[fraction, 1-fraction-pad])
-        ss_main = gs[1]
-        ss_cb = gs[0].subgridspec(1, 3, wspace=0, width_ratios=wh_ratios)[1]
-        aspect = 1 / aspect
-    else:  # "bottom"
-        gs = parent.get_subplotspec().subgridspec(
-            2, 1, hspace=wh_space, height_ratios=[1-fraction-pad, fraction])
-        ss_main = gs[0]
-        ss_cb = gs[1].subgridspec(1, 3, wspace=0, width_ratios=wh_ratios)[1]
-        aspect = 1 / aspect
+    if location in ('left', 'right'):
+        # for shrinking
+        height_ratios = [
+                (1-anchor[1])*(1-shrink), shrink, anchor[1]*(1-shrink)]
+
+        if location == 'left':
+            gs = parent.get_subplotspec().subgridspec(
+                    1, 2, wspace=wh_space,
+                    width_ratios=[fraction, 1-fraction-pad])
+            ss_main = gs[1]
+            ss_cb = gs[0].subgridspec(
+                    3, 1, hspace=0, height_ratios=height_ratios)[1]
+        else:
+            gs = parent.get_subplotspec().subgridspec(
+                    1, 2, wspace=wh_space,
+                    width_ratios=[1-fraction-pad, fraction])
+            ss_main = gs[0]
+            ss_cb = gs[1].subgridspec(
+                    3, 1, hspace=0, height_ratios=height_ratios)[1]
+    else:
+        # for shrinking
+        width_ratios = [
+                anchor[0]*(1-shrink), shrink, (1-anchor[0])*(1-shrink)]
+
+        if location == 'bottom':
+            gs = parent.get_subplotspec().subgridspec(
+                    2, 1, hspace=wh_space,
+                    height_ratios=[1-fraction-pad, fraction])
+            ss_main = gs[0]
+            ss_cb = gs[1].subgridspec(
+                    1, 3, wspace=0, width_ratios=width_ratios)[1]
+            aspect = 1 / aspect
+        else:
+            gs = parent.get_subplotspec().subgridspec(
+                    2, 1, hspace=wh_space,
+                    height_ratios=[fraction, 1-fraction-pad])
+            ss_main = gs[1]
+            ss_cb = gs[0].subgridspec(
+                    1, 3, wspace=0, width_ratios=width_ratios)[1]
+            aspect = 1 / aspect
 
     parent.set_subplotspec(ss_main)
     parent.set_anchor(loc_settings["panchor"])

lib/matplotlib/tests/test_colorbar.py

@@ -623,3 +623,85 @@ def test_colorbar_int(clim):
     im = ax.imshow([[*map(np.int16, clim)]])
     fig.colorbar(im)
     assert (im.norm.vmin, im.norm.vmax) == clim
+
+
+def test_anchored_cbar_position_using_specgrid():
+    data = np.arange(1200).reshape(30, 40)
+    levels = [0, 200, 400, 600, 800, 1000, 1200]
+    shrink = 0.5
+    anchor_y = 0.3
+    # right
+    fig, ax = plt.subplots()
+    cs = ax.contourf(data, levels=levels)
+    cbar = plt.colorbar(
+            cs, ax=ax, use_gridspec=True,
+            location='right', anchor=(1, anchor_y), shrink=shrink)
+
+    # the bottom left corner of one ax is (x0, y0)
+    # the top right corner of one ax is (x1, y1)
+    # p0: the vertical / horizontal position of anchor
+    x0, y0, x1, y1 = ax.get_position().extents
+    cx0, cy0, cx1, cy1 = cbar.ax.get_position().extents
+    p0 = (y1 - y0) * anchor_y + y0
+
+    np.testing.assert_allclose(
+            [cy1, cy0],
+            [y1 * shrink + (1 - shrink) * p0, p0 * (1 - shrink) + y0 * shrink])
+
+    # left
+    fig, ax = plt.subplots()
+    cs = ax.contourf(data, levels=levels)
+    cbar = plt.colorbar(
+            cs, ax=ax, use_gridspec=True,
+            location='left', anchor=(1, anchor_y), shrink=shrink)
+
+    # the bottom left corner of one ax is (x0, y0)
+    # the top right corner of one ax is (x1, y1)
+    # p0: the vertical / horizontal position of anchor
+    x0, y0, x1, y1 = ax.get_position().extents
+    cx0, cy0, cx1, cy1 = cbar.ax.get_position().extents
+    p0 = (y1 - y0) * anchor_y + y0
+
+    np.testing.assert_allclose(
+            [cy1, cy0],
+            [y1 * shrink + (1 - shrink) * p0, p0 * (1 - shrink) + y0 * shrink])
+
+    # top
+    shrink = 0.5
+    anchor_x = 0.3
+    fig, ax = plt.subplots()
+    cs = ax.contourf(data, levels=levels)
+    cbar = plt.colorbar(
+            cs, ax=ax, use_gridspec=True,
+            location='top', anchor=(anchor_x, 1), shrink=shrink)
+
+    # the bottom left corner of one ax is (x0, y0)
+    # the top right corner of one ax is (x1, y1)
+    # p0: the vertical / horizontal position of anchor
+    x0, y0, x1, y1 = ax.get_position().extents
+    cx0, cy0, cx1, cy1 = cbar.ax.get_position().extents
+    p0 = (x1 - x0) * anchor_x + x0
+
+    np.testing.assert_allclose(
+            [cx1, cx0],
+            [x1 * shrink + (1 - shrink) * p0, p0 * (1 - shrink) + x0 * shrink])
+
+    # bottom
+    shrink = 0.5
+    anchor_x = 0.3
+    fig, ax = plt.subplots()
+    cs = ax.contourf(data, levels=levels)
+    cbar = plt.colorbar(
+            cs, ax=ax, use_gridspec=True,
+            location='bottom', anchor=(anchor_x, 1), shrink=shrink)
+
+    # the bottom left corner of one ax is (x0, y0)
+    # the top right corner of one ax is (x1, y1)
+    # p0: the vertical / horizontal position of anchor
+    x0, y0, x1, y1 = ax.get_position().extents
+    cx0, cy0, cx1, cy1 = cbar.ax.get_position().extents
+    p0 = (x1 - x0) * anchor_x + x0
+
+    np.testing.assert_allclose(
+            [cx1, cx0],
+            [x1 * shrink + (1 - shrink) * p0, p0 * (1 - shrink) + x0 * shrink])