Improve autoscaling for high order Bezier curves

dstansby · dstansby · commit f71d7cd453d6 · 2021-12-28T18:57:27.000Z
diff --git a/doc/api/next_api_changes/behavior/19214-DS.rst b/doc/api/next_api_changes/behavior/19214-DS.rst
@@ -0,0 +1,5 @@
+Improved autoscaling for bezier curves
+--------------------------------------
+Bezier curves are now autoscaled to their extents - previously they were
+autoscaled to their ends and control points, which in some cases led to
+unnecessarily large limits.
diff --git a/lib/matplotlib/axes/_base.py b/lib/matplotlib/axes/_base.py
@@ -22,7 +22,6 @@
 import matplotlib.image as mimage
 import matplotlib.lines as mlines
 import matplotlib.patches as mpatches
-import matplotlib.path as mpath
 from matplotlib.rcsetup import cycler, validate_axisbelow
 import matplotlib.spines as mspines
 import matplotlib.table as mtable
@@ -2375,10 +2374,18 @@ def _update_patch_limits(self, patch):
                 ((not patch.get_width()) and (not patch.get_height()))):
             return
         p = patch.get_path()
-        vertices = p.vertices if p.codes is None else p.vertices[np.isin(
-            p.codes, (mpath.Path.CLOSEPOLY, mpath.Path.STOP), invert=True)]
-        if not vertices.size:
-            return
+        # Get all vertices on the path
+        # Loop through each sement to get extrema for Bezier curve sections
+        vertices = []
+        for curve, code in p.iter_bezier():
+            # Get distance along the curve of any extrema
+            _, dzeros = curve.axis_aligned_extrema()
+            # Calculate vertcies of start, end and any extrema in between
+            vertices.append(curve([0, *dzeros, 1]))
+
+        if len(vertices):
+            vertices = np.row_stack(vertices)
+
         patch_trf = patch.get_transform()
         updatex, updatey = patch_trf.contains_branch_seperately(self.transData)
         if not (updatex or updatey):
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -24,6 +24,7 @@
 import matplotlib.font_manager as mfont_manager
 import matplotlib.markers as mmarkers
 import matplotlib.patches as mpatches
+import matplotlib.path as mpath
 import matplotlib.pyplot as plt
 import matplotlib.ticker as mticker
 import matplotlib.transforms as mtransforms
@@ -7340,3 +7341,24 @@ def test_clim():
         clim = (7, 8)
         norm = plot_method(clim=clim).norm
         assert (norm.vmin, norm.vmax) == clim
+
+
+def test_bezier_autoscale():
+    # Check that bezier curves autoscale to their curves, and not their
+    # control points
+    verts = [[-1, 0],
+             [0, -1],
+             [1, 0],
+             [1, 0]]
+    codes = [mpath.Path.MOVETO,
+             mpath.Path.CURVE3,
+             mpath.Path.CURVE3,
+             mpath.Path.CLOSEPOLY]
+    p = mpath.Path(verts, codes)
+
+    fig, ax = plt.subplots()
+    ax.add_patch(mpatches.PathPatch(p))
+    ax.autoscale()
+    # Bottom ylim should be at the edge of the curve (-0.5), and not include
+    # the control point (at -1)
+    assert ax.get_ylim()[0] == -0.5
