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New C++ contour code with corner_mask
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‎CHANGELOG

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@@ -1,11 +1,15 @@
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2014-12-02 Rewrite of C++ code that calculates contours to add support for
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corner masking. This is controlled by the 'corner_mask' keyword
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in plotting commands 'contour' and 'contourf'. - IMT
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2014-10-27 Allowed selection of the backend using the `MPLBACKEND` environment
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variable. Added documentation on backend selection methods.
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2014-09-27 Overhauled `colors.LightSource`. Added `LightSource.hillshade` to
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allow the independent generation of illumination maps. Added new
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types of blending for creating more visually appealing shaded relief
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plots (e.g. `blend_mode="overlay"`, etc, in addition to the legacy
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"hsv" mode).
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allow the independent generation of illumination maps. Added new
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types of blending for creating more visually appealing shaded relief
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plots (e.g. `blend_mode="overlay"`, etc, in addition to the legacy
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"hsv" mode).
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2014-06-10 Added Colorbar.remove()
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@@ -61,7 +65,7 @@
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of a generator at line 263.
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2014-04-02 Added `clipon=False` to patch creation of wedges and shadows
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in `pie`.
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in `pie`.
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2014-02-25 In backend_qt4agg changed from using update -> repaint under
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windows. See comment in source near `self._priv_update` for

‎doc/api/api_changes/2014-12-02-IMT.rst

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Changed behaviour of contour plots
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``````````````````````````````````
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The default behaviour of :func:`~matplotlib.pyplot.contour` and
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:func:`~matplotlib.pyplot.contourf` when using a masked array is now determined
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by the new keyword argument `corner_mask`, or if this is not specified then
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the new rcParam `contour.corner_mask` instead. The new default behaviour is
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equivalent to using `corner_mask=True`; the previous behaviour can be obtained
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using `corner_mask=False` or by changing the rcParam. The example
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`contour_corner_mask.py` demonstrates the difference.
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In addition, the keyword argument `nchunk` now applies to
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:func:`~matplotlib.pyplot.contour` as well as
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:func:`~matplotlib.pyplot.contourf`, and it subdivides the domain into
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subdomains of exactly `nchunk` by `nchunk` quads, whereas previously it was
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only roughly `nchunk` by `nchunk` quads.

‎doc/users/whats_new/plotting.rst

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@@ -3,3 +3,19 @@ Added center and frame kwargs to pie
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These control where the center of the pie graph are and if
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the Axes frame is shown.
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Contour plot corner masking
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```````````````````````````
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Ian Thomas rewrote the C++ code that calculates contours to add support for
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corner masking. This is controlled by a new keyword argument
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``corner_mask`` in the functions :func:`~matplotlib.pyplot.contour` and
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:func:`~matplotlib.pyplot.contourf`. The previous behaviour, which is now
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obtained using ``corner_mask=False``, was for a single masked point to
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completely mask out all four quads touching that point. The new behaviour,
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obtained using ``corner_mask=True``, only masks the corners of those
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quads touching the point; any triangular corners comprising three unmasked
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points are contoured as usual. If the ``corner_mask`` keyword argument is not
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specified, the default value is taken from rcParams.
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.. plot:: mpl_examples/pylab_examples/contour_corner_mask.py

‎examples/pylab_examples/contour_corner_mask.py

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#!/usr/bin/env python
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"""
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Illustrate the difference between corner_mask=False and corner_mask=True
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for masked contour plots.
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"""
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import matplotlib.pyplot as plt
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import numpy as np
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# Data to plot.
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x, y = np.meshgrid(np.arange(7), np.arange(10))
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z = np.sin(0.5*x)*np.cos(0.52*y)
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# Mask various z values.
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mask = np.zeros_like(z, dtype=np.bool)
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mask[2, 3:5] = True
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mask[3:5, 4] = True
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mask[7, 2] = True
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mask[5, 0] = True
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mask[0, 6] = True
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z = np.ma.array(z, mask=mask)
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corner_masks = [False, True]
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for i, corner_mask in enumerate(corner_masks):
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plt.subplot(1, 2, i+1)
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cs = plt.contourf(x, y, z, corner_mask=corner_mask)
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plt.contour(cs, colors='k')
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plt.title('corner_mask = {}'.format(corner_mask))
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# Plot grid.
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plt.grid(c='k', ls='-', alpha=0.3)
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# Indicate masked points with red circles.
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plt.plot(np.ma.array(x, mask=~mask), y, 'ro')
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plt.show()

‎lib/matplotlib/contour.py

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@@ -13,6 +13,7 @@
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import numpy as np
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from numpy import ma
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import matplotlib._cntr as _cntr
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import matplotlib._contour as _contour
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import matplotlib.path as mpath
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import matplotlib.ticker as ticker
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import matplotlib.cm as cm
@@ -1438,13 +1439,23 @@ def _process_args(self, *args, **kwargs):
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self.levels = args[0].levels
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self.zmin = args[0].zmin
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self.zmax = args[0].zmax
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self._corner_mask = args[0]._corner_mask
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else:
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x, y, z = self._contour_args(args, kwargs)
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_mask = ma.getmask(z)
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if _mask is ma.nomask:
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if _mask is ma.nomask or not _mask.any():
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_mask = None
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C = _cntr.Cntr(x, y, z.filled(), _mask)
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self._corner_mask = kwargs.get('corner_mask', None)
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if self._corner_mask is None:
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self._corner_mask = mpl.rcParams['contour.corner_mask']
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if self._corner_mask == 'legacy':
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C = _cntr.Cntr(x, y, z.filled(), _mask)
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else:
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C = _contour.QuadContourGenerator(
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x, y, z.filled(), _mask, self._corner_mask, self.nchunk)
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t = self.get_transform()
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@@ -1476,19 +1487,27 @@ def _get_allsegs_and_allkinds(self):
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lowers, uppers = self._get_lowers_and_uppers()
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allkinds = []
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for level, level_upper in zip(lowers, uppers):
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nlist = self.Cntr.trace(level, level_upper,
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nchunk=self.nchunk)
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nseg = len(nlist) // 2
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segs = nlist[:nseg]
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kinds = nlist[nseg:]
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if self._corner_mask == 'legacy':
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nlist = self.Cntr.trace(level, level_upper,
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nchunk=self.nchunk)
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nseg = len(nlist) // 2
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segs = nlist[:nseg]
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kinds = nlist[nseg:]
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else:
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nlist = self.Cntr.create_filled_contour(level, level_upper)
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segs = nlist[::2]
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kinds = nlist[1::2]
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allsegs.append(segs)
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allkinds.append(kinds)
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else:
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allkinds = None
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for level in self.levels:
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nlist = self.Cntr.trace(level)
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nseg = len(nlist) // 2
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segs = nlist[:nseg]
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if self._corner_mask == 'legacy':
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nlist = self.Cntr.trace(level)
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nseg = len(nlist) // 2
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segs = nlist[:nseg]
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else:
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segs = self.Cntr.create_contour(level)
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allsegs.append(segs)
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return allsegs, allkinds
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@@ -1672,6 +1691,20 @@ def _initialize_x_y(self, z):
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Optional keyword arguments:
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*corner_mask*: [ *True* | *False* | 'legacy' ]
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Enable/disable corner masking, which only has an effect if *Z* is
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a masked array. If *False*, any quad touching a masked point is
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masked out. If *True*, only the triangular corners of quads
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nearest those points are always masked out, other triangular
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corners comprising three unmasked points are contoured as usual.
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If 'legacy', the old contouring algorithm is used, which is
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equivalent to *False* and is deprecated, only remaining whilst the
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new algorithm is tested fully.
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If not specified, the default is taken from
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rcParams['contour.corner_mask'], which is True unless it has
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been modified.
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*colors*: [ *None* | string | (mpl_colors) ]
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If *None*, the colormap specified by cmap will be used.
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filled contours, the default is *True*. For line contours,
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it is taken from rcParams['lines.antialiased'].
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*nchunk*: [ 0 | integer ]
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If 0, no subdivision of the domain. Specify a positive integer to
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divide the domain into subdomains of *nchunk* by *nchunk* quads.
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Chunking reduces the maximum length of polygons generated by the
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contouring algorithm which reduces the rendering workload passed
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on to the backend and also requires slightly less RAM. It can
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however introduce rendering artifacts at chunk boundaries depending
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on the backend, the *antialiased* flag and value of *alpha*.
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contour-only keyword arguments:
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*linewidths*: [ *None* | number | tuple of numbers ]
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contourf-only keyword arguments:
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*nchunk*: [ 0 | integer ]
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If 0, no subdivision of the domain. Specify a positive integer to
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divide the domain into subdomains of roughly *nchunk* by *nchunk*
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points. This may never actually be advantageous, so this option may
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be removed. Chunking introduces artifacts at the chunk boundaries
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unless *antialiased* is *False*.
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*hatches*:
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A list of cross hatch patterns to use on the filled areas.
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If None, no hatching will be added to the contour.
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.. plot:: mpl_examples/pylab_examples/contour_demo.py
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.. plot:: mpl_examples/pylab_examples/contourf_demo.py
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.. plot:: mpl_examples/pylab_examples/contour_corner_mask.py
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"""

‎lib/matplotlib/rcsetup.py

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@@ -379,6 +379,13 @@ def validate_negative_linestyle_legacy(s):
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return (0, dashes) # (offset, (solid, blank))
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382+
def validate_corner_mask(s):
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if s == 'legacy':
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return s
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else:
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return validate_bool(s)
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def validate_tkpythoninspect(s):
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# Introduced 2010/07/05
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warnings.warn("tk.pythoninspect is obsolete, and has no effect")
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'image.origin': ['upper', six.text_type], # lookup table
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'image.resample': [False, validate_bool],
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# contour props
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'contour.negative_linestyle': ['dashed',
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validate_negative_linestyle_legacy],
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'contour.corner_mask': [True, validate_corner_mask],
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# axes props
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'axes.axisbelow': [False, validate_bool],

‎lib/matplotlib/tests/baseline_images/test_contour/contour_corner_mask_False.png

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‎lib/matplotlib/tests/baseline_images/test_contour/contour_corner_mask_True.png

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‎lib/matplotlib/tests/baseline_images/test_patheffects/collection.pdf

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‎lib/matplotlib/tests/baseline_images/test_patheffects/collection.png

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