ENH: pad_inches='layout' for savefig

Author: rcomer

doc/users/next_whats_new/savefig_bbox_layout.rst

@@ -0,0 +1,10 @@
+pad_inches="layout" for savefig
+-------------------------------
+
+When using constrained or compressed layout,
+
+.. code-block:: python
+
+    savefig(filename, bbox_inches="tight", pad_inches="layout")
+
+will now use the padding sizes defined on the layout engine.

lib/matplotlib/backend_bases.py

@@ -48,6 +48,7 @@
 from matplotlib._pylab_helpers import Gcf
 from matplotlib.backend_managers import ToolManager
 from matplotlib.cbook import _setattr_cm
+from matplotlib.layout_engine import ConstrainedLayoutEngine
 from matplotlib.path import Path
 from matplotlib.texmanager import TexManager
 from matplotlib.transforms import Affine2D
@@ -2273,8 +2274,11 @@ def print_figure(
             Bounding box in inches: only the given portion of the figure is
             saved.  If 'tight', try to figure out the tight bbox of the figure.
 
-        pad_inches : float, default: :rc:`savefig.pad_inches`
-            Amount of padding around the figure when *bbox_inches* is 'tight'.
+        pad_inches : float or 'layout', default: :rc:`savefig.pad_inches`
+            Amount of padding in inches around the figure when bbox_inches is
+            'tight'. If 'layout' use the padding from the constrained or
+            compressed layout engine; ignored if one of those engines is not in
+            use.
 
         bbox_extra_artists : list of `~matplotlib.artist.Artist`, optional
             A list of extra artists that will be considered when the
@@ -2324,8 +2328,8 @@ def print_figure(
             if bbox_inches is None:
                 bbox_inches = rcParams['savefig.bbox']
 
-            if (self.figure.get_layout_engine() is not None or
-                    bbox_inches == "tight"):
+            layout_engine = self.figure.get_layout_engine()
+            if layout_engine is not None or bbox_inches == "tight":
                 # we need to trigger a draw before printing to make sure
                 # CL works.  "tight" also needs a draw to get the right
                 # locations:
@@ -2341,9 +2345,15 @@ def print_figure(
                 if bbox_inches == "tight":
                     bbox_inches = self.figure.get_tightbbox(
                         renderer, bbox_extra_artists=bbox_extra_artists)
-                    if pad_inches is None:
-                        pad_inches = rcParams['savefig.pad_inches']
-                    bbox_inches = bbox_inches.padded(pad_inches)
+                    if (isinstance(layout_engine, ConstrainedLayoutEngine) and
+                            pad_inches == "layout"):
+                        h_pad = layout_engine.get()["h_pad"]
+                        w_pad = layout_engine.get()["w_pad"]
+                    else:
+                        if pad_inches in [None, "layout"]:
+                            pad_inches = rcParams['savefig.pad_inches']
+                        h_pad = w_pad = pad_inches
+                    bbox_inches = bbox_inches.padded(w_pad, h_pad)
 
                 # call adjust_bbox to save only the given area
                 restore_bbox = _tight_bbox.adjust_bbox(

lib/matplotlib/figure.py

@@ -3257,8 +3257,11 @@ def savefig(self, fname, *, transparent=None, **kwargs):
             Bounding box in inches: only the given portion of the figure is
             saved.  If 'tight', try to figure out the tight bbox of the figure.
 
-        pad_inches : float, default: :rc:`savefig.pad_inches`
-            Amount of padding around the figure when bbox_inches is 'tight'.
+        pad_inches : float or 'layout', default: :rc:`savefig.pad_inches`
+            Amount of padding in inches around the figure when bbox_inches is
+            'tight'. If 'layout' use the padding from the constrained or
+            compressed layout engine; ignored if one of those engines is not in
+            use.
 
         facecolor : color or 'auto', default: :rc:`savefig.facecolor`
             The facecolor of the figure.  If 'auto', use the current figure

lib/matplotlib/layout_engine.py

@@ -203,7 +203,7 @@ def __init__(self, *, h_pad=None, w_pad=None,
         Parameters
         ----------
         h_pad, w_pad : float
-            Padding around the axes elements in figure-normalized units.
+            Padding around the axes elements in inches.
             Default to :rc:`figure.constrained_layout.h_pad` and
             :rc:`figure.constrained_layout.w_pad`.
         hspace, wspace : float
@@ -261,7 +261,7 @@ def set(self, *, h_pad=None, w_pad=None,
         Parameters
         ----------
         h_pad, w_pad : float
-            Padding around the axes elements in figure-normalized units.
+            Padding around the axes elements in inches.
             Default to :rc:`figure.constrained_layout.h_pad` and
             :rc:`figure.constrained_layout.w_pad`.
         hspace, wspace : float

lib/matplotlib/tests/baseline_images/test_bbox_tight/bbox_inches_tight_layout.png

@@ -69,6 +69,22 @@ def test_bbox_inches_tight_suptitle_non_default():
     fig.suptitle('Booo', x=0.5, y=1.1)
 
 
+@image_comparison(['bbox_inches_tight_layout.png'], remove_text=True,
+                  style='mpl20',
+                  savefig_kwarg=dict(bbox_inches='tight', pad_inches='layout'))
+def test_bbox_inches_tight_layout_constrained():
+    fig, ax = plt.subplots(layout='constrained')
+    fig.get_layout_engine().set(h_pad=0.5)
+    ax.set_aspect('equal')
+
+
+def test_bbox_inches_tight_layout_notconstrained(tmp_path):
+    # pad_inches='layout' should be ignored when not using constrained/
+    # compressed layout.  Smoke test that savefig doesn't error in this case.
+    fig, ax = plt.subplots()
+    fig.savefig(tmp_path / 'foo.png', bbox_inches='tight', pad_inches='layout')
+
+
 @image_comparison(['bbox_inches_tight_clipping'],
                   remove_text=True, savefig_kwarg={'bbox_inches': 'tight'})
 def test_bbox_inches_tight_clipping():

lib/matplotlib/tests/test_bbox_tight.py

@@ -616,10 +616,23 @@ def expanded(self, sw, sh):
         a = np.array([[-deltaw, -deltah], [deltaw, deltah]])
         return Bbox(self._points + a)
 
-    def padded(self, p):
-        """Construct a `Bbox` by padding this one on all four sides by *p*."""
+    @_api.rename_parameter("3.8", "p", "w_pad")
+    def padded(self, w_pad, h_pad=None):
+        """
+        Construct a `Bbox` by padding this one on all four sides.
+
+        Parameters
+        ----------
+        w_pad : float
+            Width pad
+        h_pad: float, optional
+            Height pad.  Defaults to *w_pad*.
+
+        """
         points = self.get_points()
-        return Bbox(points + [[-p, -p], [p, p]])
+        if h_pad is None:
+            h_pad = w_pad
+        return Bbox(points + [[-w_pad, -h_pad], [w_pad, h_pad]])
 
     def translated(self, tx, ty):
         """Construct a `Bbox` by translating this one by *tx* and *ty*."""