matplotlib · NelleV · Oct 26, 2017 · Oct 22, 2017 · Oct 22, 2017 · Oct 23, 2017
diff --git a/doc/users/whats_new.rst b/doc/users/whats_new.rst
@@ -246,6 +246,13 @@ volumetric model.
 Improvements
 ++++++++++++
 
+Add ``capstyle`` and ``joinstyle`` attributes to `Collection`
+-------------------------------------------------------------
+
+The `Collection` class now has customizable ``capstyle`` and ``joinstyle``
+attributes. This allows the user for example to set the ``capstyle`` of
+errorbars.
+
 CheckButtons widget ``get_status`` function
 -------------------------------------------
 

diff --git a/lib/matplotlib/collections.py b/lib/matplotlib/collections.py
@@ -52,11 +52,16 @@ class Collection(artist.Artist, cm.ScalarMappable):
 
       prop[i % len(props)]
 
+    Exceptions are *capstyle* and *joinstyle* properties, these can
+    only be set globally for the whole collection.
+
     Keyword arguments and default values:
 
         * *edgecolors*: None
         * *facecolors*: None
         * *linewidths*: None
+        * *capstyle*:   None
+        * *joinstyle*:  None
         * *antialiaseds*: None
         * *offsets*: None
         * *transOffset*: transforms.IdentityTransform()
@@ -104,6 +109,8 @@ def __init__(self,
                  facecolors=None,
                  linewidths=None,
                  linestyles='solid',
+                 capstyle=None,
+                 joinstyle=None,
                  antialiaseds=None,
                  offsets=None,
                  transOffset=None,
@@ -145,6 +152,16 @@ def __init__(self,
         self.set_offset_position(offset_position)
         self.set_zorder(zorder)
 
+        if capstyle:
+            self.set_capstyle(capstyle)
+        else:
+            self._capstyle = None
+
+        if joinstyle:
+            self.set_joinstyle(joinstyle)
+        else:
+            self._joinstyle = None
+
         self._offsets = np.zeros((1, 2))
         self._uniform_offsets = None
         if offsets is not None:
@@ -304,6 +321,12 @@ def draw(self, renderer):
                 extents.height < height):
                 do_single_path_optimization = True
 
+        if self._joinstyle:
+            gc.set_joinstyle(self._joinstyle)
+
+        if self._capstyle:
+            gc.set_capstyle(self._capstyle)
+
         if do_single_path_optimization:
             gc.set_foreground(tuple(edgecolors[0]))
             gc.set_linewidth(self._linewidths[0])
@@ -536,6 +559,42 @@ def set_linestyle(self, ls):
         self._linewidths, self._linestyles = self._bcast_lwls(
             self._us_lw, self._us_linestyles)
 
+    def set_capstyle(self, cs):
+        """
+        Set the capstyle for the collection. The capstyle can
+        only be set globally for all elements in the collection
+
+        Parameters
+        ----------
+        cs : ['butt' | 'round' | 'projecting']
+            The capstyle
+        """
+        if cs in ('butt', 'round', 'projecting'):
+            self._capstyle = cs
+        else:
+            raise ValueError('Unrecognized cap style.  Found %s' % cs)
+
+    def get_capstyle(self):
+        return self._capstyle
+
+    def set_joinstyle(self, js):
+        """
+        Set the joinstyle for the collection. The joinstyle can only be
+        set globally for all elements in the collection.
+
+        Parameters
+        ----------
+        js : ['miter' | 'round' | 'bevel']
+            The joinstyle
+        """
+        if js in ('miter', 'round', 'bevel'):
+            self._joinstyle = js
+        else:
+            raise ValueError('Unrecognized join style.  Found %s' % js)
+
+    def get_joinstyle(self):
+        return self._joinstyle
+
     @staticmethod
     def _bcast_lwls(linewidths, dashes):
         '''Internal helper function to broadcast + scale ls/lw

diff --git a/lib/matplotlib/tests/baseline_images/test_collections/cap_and_joinstyle.png b/lib/matplotlib/tests/baseline_images/test_collections/cap_and_joinstyle.png
diff --git a/lib/matplotlib/tests/test_collections.py b/lib/matplotlib/tests/test_collections.py
@@ -14,7 +14,7 @@
 import matplotlib.pyplot as plt
 import matplotlib.collections as mcollections
 import matplotlib.transforms as mtransforms
-from matplotlib.collections import Collection, EventCollection
+from matplotlib.collections import Collection, LineCollection, EventCollection
 from matplotlib.testing.decorators import image_comparison
 
 
@@ -626,6 +626,44 @@ def test_lslw_bcast():
     assert_equal(col.get_linewidths(), [1, 2, 3])
 
 
+@pytest.mark.style('default')
+def test_capstyle():
+    col = mcollections.PathCollection([], capstyle='round')
+    assert_equal(col.get_capstyle(), 'round')
+    col.set_capstyle('butt')
+    assert_equal(col.get_capstyle(), 'butt')
+
+
+@pytest.mark.style('default')
+def test_joinstyle():
+    col = mcollections.PathCollection([], joinstyle='round')
+    assert_equal(col.get_joinstyle(), 'round')
+    col.set_joinstyle('miter')
+    assert_equal(col.get_joinstyle(), 'miter')
+
+
+@image_comparison(baseline_images=['cap_and_joinstyle'],
+                  extensions=['png'])
+def test_cap_and_joinstyle_image():
+    fig = plt.figure()
+    ax = fig.add_subplot(1, 1, 1)
+    ax.set_xlim([-0.5, 1.5])
+    ax.set_ylim([-0.5, 2.5])
+
+    x = np.array([0.0, 1.0, 0.5])
+    ys = np.array([[0.0], [0.5], [1.0]]) + np.array([[0.0, 0.0, 1.0]])
+
+    segs = np.zeros((3, 3, 2))
+    segs[:, :, 0] = x
+    segs[:, :, 1] = ys
+    line_segments = LineCollection(segs, linewidth=[10, 15, 20])
+    line_segments.set_capstyle("round")
+    line_segments.set_joinstyle("miter")
+
+    ax.add_collection(line_segments)
+    ax.set_title('Line collection with customized caps and joinstyle')
+
+
 @image_comparison(baseline_images=['scatter_post_alpha'],
                   extensions=['png'], remove_text=True,
                   style='default')