Clipping for OffsetBoxes

- Child `Artists` of `DrawingArea` can now get clipped to the
  bounds of the parent

Author: has2k1

doc/api/api_changes/2015-04-18-drawingarea.rst

@@ -0,0 +1,8 @@
+'OffsetBox.DrawingArea' respects the 'clip' keyword argument
+````````````````````````````````````````````````````````````
+
+The call signature was `OffsetBox.DrawingArea(..., clip=True)` but nothing
+was done with the `clip` argument. The object did not do any clipping
+regardless of that parameter. Now the object can and does clip the child `Artists` if they are set to be clipped.
+
+You can turn off the clipping on a per-child basis using `child.set_clip_on(False)`.

doc/users/whats_new/offsetbox.rst

@@ -0,0 +1,11 @@
+OffsetBoxes now support clipping
+````````````````````````````````
+
+`Artists` draw onto objects of type :class:`~OffsetBox`
+through :class:`~OffsetBox.DrawingArea` and :class:`~OffsetBox.TextArea`.
+The `TextArea` calculates the required space for the text and so the
+text is always within the bounds, for this nothing has changed.
+
+However, `DrawingArea` acts as a parent for zero or more `Artists` that
+draw on it and may do so beyond the bounds. Now child `Artists` can be
+clipped to the bounds of the `DrawingArea`.

examples/pylab_examples/anchored_artists.py

@@ -63,7 +63,7 @@ class AnchoredDrawingArea(AnchoredOffsetbox):
     def __init__(self, width, height, xdescent, ydescent,
                  loc, pad=0.4, borderpad=0.5, prop=None, frameon=True):
 
-        self.da = DrawingArea(width, height, xdescent, ydescent, clip=True)
+        self.da = DrawingArea(width, height, xdescent, ydescent)
 
         super(AnchoredDrawingArea, self).__init__(loc, pad=pad, borderpad=borderpad,
                                                   child=self.da,

lib/matplotlib/__init__.py

@@ -1416,6 +1416,7 @@ def tk_window_focus():
     'matplotlib.tests.test_lines',
     'matplotlib.tests.test_mathtext',
     'matplotlib.tests.test_mlab',
+    'matplotlib.tests.test_offsetbox',
     'matplotlib.tests.test_patches',
     'matplotlib.tests.test_path',
     'matplotlib.tests.test_patheffects',

lib/matplotlib/offsetbox.py

@@ -24,6 +24,7 @@
 import matplotlib.transforms as mtransforms
 import matplotlib.artist as martist
 import matplotlib.text as mtext
+import matplotlib.path as mpath
 import numpy as np
 from matplotlib.transforms import Bbox, BboxBase, TransformedBbox
 
@@ -569,14 +570,16 @@ class DrawingArea(OffsetBox):
     """
     The DrawingArea can contain any Artist as a child. The DrawingArea
     has a fixed width and height. The position of children relative to
-    the parent is fixed.
+    the parent is fixed. The children can be  clipped at the
+    boundaries of the parent.
     """
 
     def __init__(self, width, height, xdescent=0.,
-                 ydescent=0., clip=True):
+                 ydescent=0., clip=False):
         """
         *width*, *height* : width and height of the container box.
         *xdescent*, *ydescent* : descent of the box in x- and y-direction.
+        *clip* : Whether to clip the children
         """
 
         super(DrawingArea, self).__init__()
@@ -585,6 +588,7 @@ def __init__(self, width, height, xdescent=0.,
         self.height = height
         self.xdescent = xdescent
         self.ydescent = ydescent
+        self._clip_children = clip
 
         self.offset_transform = mtransforms.Affine2D()
         self.offset_transform.clear()
@@ -656,7 +660,17 @@ def draw(self, renderer):
         self.dpi_transform.clear()
         self.dpi_transform.scale(dpi_cor, dpi_cor)
 
+        # At this point the DrawingArea has a transform
+        # to the display space so the path created is
+        # good for clipping children
+        tpath = mtransforms.TransformedPath(
+            mpath.Path([[0, 0], [0, self.height],
+                        [self.width, self.height],
+                        [self.width, 0]]),
+            self.get_transform())
         for c in self._children:
+            if self._clip_children and not (c.clipbox or c._clippath):
+                c.set_clip_path(tpath)
             c.draw(renderer)
 
         bbox_artist(self, renderer, fill=False, props=dict(pad=0.))

lib/matplotlib/tests/baseline_images/test_offsetbox/offsetbox_clipping.pdf

@@ -0,0 +1,49 @@
+from __future__ import (absolute_import, division, print_function,
+                        unicode_literals)
+
+import nose
+
+from matplotlib.testing.decorators import image_comparison
+import matplotlib.pyplot as plt
+import matplotlib.patches as mpatches
+import matplotlib.lines as mlines
+from matplotlib.offsetbox import AnchoredOffsetbox, DrawingArea
+
+
+@image_comparison(baseline_images=['offsetbox_clipping'], remove_text=True)
+def test_offsetbox_clipping():
+    # - create a plot
+    # - put an AnchoredOffsetbox with a child DrawingArea
+    #   at the center of the axes
+    # - give the DrawingArea a gray background
+    # - put a black line across the bounds of the DrawingArea
+    # - see that the black line is clipped to the edges of
+    #   the DrawingArea.
+    fig, ax = plt.subplots()
+    size = 100
+    da = DrawingArea(size, size, clip=True)
+    bg = mpatches.Rectangle((0, 0), size, size,
+                            facecolor='#CCCCCC',
+                            edgecolor='None',
+                            linewidth=0)
+    line = mlines.Line2D([-size*.5, size*1.5], [size/2, size/2],
+                         color='black',
+                         linewidth=10)
+    anchored_box = AnchoredOffsetbox(
+        loc=10,
+        child=da,
+        pad=0.,
+        frameon=False,
+        bbox_to_anchor=(.5, .5),
+        bbox_transform=ax.transAxes,
+        borderpad=0.)
+
+    da.add_artist(bg)
+    da.add_artist(line)
+    ax.add_artist(anchored_box)
+    ax.set_xlim((0, 1))
+    ax.set_ylim((0, 1))
+
+
+if __name__ == '__main__':
+    nose.runmodule(argv=['-s', '--with-doctest'], exit=False)

lib/matplotlib/tests/baseline_images/test_offsetbox/offsetbox_clipping.png

@@ -24,7 +24,7 @@ def __init__(self, width, height, xdescent, ydescent,
         *prop* : font property. This is only used for scaling the paddings.
         """
 
-        self.da = DrawingArea(width, height, xdescent, ydescent, clip=True)
+        self.da = DrawingArea(width, height, xdescent, ydescent)
         self.drawing_area = self.da
 
         super(AnchoredDrawingArea, self).__init__(loc, pad=pad, borderpad=borderpad,