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Merge pull request #3874 from ianthomas23/contour
New C++ contour code with corner_mask kwarg
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‎CHANGELOG

+10-6
Original file line numberDiff line numberDiff line change
@@ -1,14 +1,18 @@
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2015-02-19 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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15
2015-01-23 Text bounding boxes are now computed with advance width rather than
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ink area. This may result in slightly different placement of text.
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ink area. This may result in slightly different placement of text.
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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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@@ -64,7 +68,7 @@
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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/2015-02-19-IMT.rst

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@@ -0,0 +1,25 @@
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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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http://matplotlib.org/examples/pylab_examples/contour_corner_mask.py
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demonstrates the difference. Use of the old contouring algorithm, which is
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obtained with `corner_mask='legacy'`, is now deprecated.
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Contour labels may now appear in different places than in earlier versions of
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matplotlib.
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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.
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The C/C++ object that performs contour calculations used to be stored in the
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public attribute QuadContourSet.Cntr, but is now stored in a private attribute
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and should not be accessed by end users.

‎doc/users/whats_new/plotting.rst

+16
Original file line numberDiff line numberDiff line change
@@ -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
14+
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
19+
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

+35
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@@ -0,0 +1,35 @@
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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)
21+
22+
corner_masks = [False, True]
23+
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))
28+
29+
# 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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35+
plt.show()

‎lib/matplotlib/contour.py

+71-24
Original file line numberDiff line numberDiff line change
@@ -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
@@ -989,9 +990,10 @@ def get_transform(self):
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990991
def __getstate__(self):
991992
state = self.__dict__.copy()
992-
# the C object Cntr cannot currently be pickled. This isn't a big issue
993-
# as it is not actually used once the contour has been calculated
994-
state['Cntr'] = None
993+
# the C object _contour_generator cannot currently be pickled. This
994+
# isn't a big issue as it is not actually used once the contour has
995+
# been calculated.
996+
state['_contour_generator'] = None
995997
return state
996998

997999
def legend_elements(self, variable_name='x', str_format=str):
@@ -1433,18 +1435,34 @@ def _process_args(self, *args, **kwargs):
14331435
Process args and kwargs.
14341436
"""
14351437
if isinstance(args[0], QuadContourSet):
1436-
C = args[0].Cntr
14371438
if self.levels is None:
14381439
self.levels = args[0].levels
14391440
self.zmin = args[0].zmin
14401441
self.zmax = args[0].zmax
1442+
self._corner_mask = args[0]._corner_mask
1443+
if self._corner_mask == 'legacy':
1444+
contour_generator = args[0].Cntr
1445+
else:
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contour_generator = args[0]._contour_generator
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else:
14421448
x, y, z = self._contour_args(args, kwargs)
14431449

14441450
_mask = ma.getmask(z)
1445-
if _mask is ma.nomask:
1451+
if _mask is ma.nomask or not _mask.any():
14461452
_mask = None
1447-
C = _cntr.Cntr(x, y, z.filled(), _mask)
1453+
1454+
self._corner_mask = kwargs.get('corner_mask', None)
1455+
if self._corner_mask is None:
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self._corner_mask = mpl.rcParams['contour.corner_mask']
1457+
1458+
if self._corner_mask == 'legacy':
1459+
cbook.warn_deprecated('1.5',
1460+
name="corner_mask='legacy'",
1461+
alternative='corner_mask=False or True')
1462+
contour_generator = _cntr.Cntr(x, y, z.filled(), _mask)
1463+
else:
1464+
contour_generator = _contour.QuadContourGenerator(
1465+
x, y, z.filled(), _mask, self._corner_mask, self.nchunk)
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14491467
t = self.get_transform()
14501468

@@ -1465,7 +1483,10 @@ def _process_args(self, *args, **kwargs):
14651483
self.ax.update_datalim([(x0, y0), (x1, y1)])
14661484
self.ax.autoscale_view(tight=True)
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1468-
self.Cntr = C
1486+
if self._corner_mask == 'legacy':
1487+
self.Cntr = contour_generator
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else:
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self._contour_generator = contour_generator
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14701491
def _get_allsegs_and_allkinds(self):
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"""
@@ -1476,20 +1497,28 @@ def _get_allsegs_and_allkinds(self):
14761497
lowers, uppers = self._get_lowers_and_uppers()
14771498
allkinds = []
14781499
for level, level_upper in zip(lowers, uppers):
1479-
nlist = self.Cntr.trace(level, level_upper,
1480-
nchunk=self.nchunk)
1481-
nseg = len(nlist) // 2
1482-
segs = nlist[:nseg]
1483-
kinds = nlist[nseg:]
1484-
allsegs.append(segs)
1500+
if self._corner_mask == 'legacy':
1501+
nlist = self.Cntr.trace(level, level_upper,
1502+
nchunk=self.nchunk)
1503+
nseg = len(nlist) // 2
1504+
vertices = nlist[:nseg]
1505+
kinds = nlist[nseg:]
1506+
else:
1507+
vertices, kinds = \
1508+
self._contour_generator.create_filled_contour(
1509+
level, level_upper)
1510+
allsegs.append(vertices)
14851511
allkinds.append(kinds)
14861512
else:
14871513
allkinds = None
14881514
for level in self.levels:
1489-
nlist = self.Cntr.trace(level)
1490-
nseg = len(nlist) // 2
1491-
segs = nlist[:nseg]
1492-
allsegs.append(segs)
1515+
if self._corner_mask == 'legacy':
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nlist = self.Cntr.trace(level)
1517+
nseg = len(nlist) // 2
1518+
vertices = nlist[:nseg]
1519+
else:
1520+
vertices = self._contour_generator.create_contour(level)
1521+
allsegs.append(vertices)
14931522
return allsegs, allkinds
14941523

14951524
def _contour_args(self, args, kwargs):
@@ -1672,6 +1701,20 @@ def _initialize_x_y(self, z):
16721701
16731702
Optional keyword arguments:
16741703
1704+
*corner_mask*: [ *True* | *False* | 'legacy' ]
1705+
Enable/disable corner masking, which only has an effect if *Z* is
1706+
a masked array. If *False*, any quad touching a masked point is
1707+
masked out. If *True*, only the triangular corners of quads
1708+
nearest those points are always masked out, other triangular
1709+
corners comprising three unmasked points are contoured as usual.
1710+
If 'legacy', the old contouring algorithm is used, which is
1711+
equivalent to *False* and is deprecated, only remaining whilst the
1712+
new algorithm is tested fully.
1713+
1714+
If not specified, the default is taken from
1715+
rcParams['contour.corner_mask'], which is True unless it has
1716+
been modified.
1717+
16751718
*colors*: [ *None* | string | (mpl_colors) ]
16761719
If *None*, the colormap specified by cmap will be used.
16771720
@@ -1750,6 +1793,15 @@ def _initialize_x_y(self, z):
17501793
filled contours, the default is *True*. For line contours,
17511794
it is taken from rcParams['lines.antialiased'].
17521795
1796+
*nchunk*: [ 0 | integer ]
1797+
If 0, no subdivision of the domain. Specify a positive integer to
1798+
divide the domain into subdomains of *nchunk* by *nchunk* quads.
1799+
Chunking reduces the maximum length of polygons generated by the
1800+
contouring algorithm which reduces the rendering workload passed
1801+
on to the backend and also requires slightly less RAM. It can
1802+
however introduce rendering artifacts at chunk boundaries depending
1803+
on the backend, the *antialiased* flag and value of *alpha*.
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17531805
contour-only keyword arguments:
17541806
17551807
*linewidths*: [ *None* | number | tuple of numbers ]
@@ -1774,13 +1826,6 @@ def _initialize_x_y(self, z):
17741826
17751827
contourf-only keyword arguments:
17761828
1777-
*nchunk*: [ 0 | integer ]
1778-
If 0, no subdivision of the domain. Specify a positive integer to
1779-
divide the domain into subdomains of roughly *nchunk* by *nchunk*
1780-
points. This may never actually be advantageous, so this option may
1781-
be removed. Chunking introduces artifacts at the chunk boundaries
1782-
unless *antialiased* is *False*.
1783-
17841829
*hatches*:
17851830
A list of cross hatch patterns to use on the filled areas.
17861831
If None, no hatching will be added to the contour.
@@ -1802,4 +1847,6 @@ def _initialize_x_y(self, z):
18021847
.. plot:: mpl_examples/pylab_examples/contour_demo.py
18031848
18041849
.. plot:: mpl_examples/pylab_examples/contourf_demo.py
1850+
1851+
.. plot:: mpl_examples/pylab_examples/contour_corner_mask.py
18051852
"""

‎lib/matplotlib/rcsetup.py

+9
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@@ -389,6 +389,13 @@ def validate_negative_linestyle_legacy(s):
389389
return (0, dashes) # (offset, (solid, blank))
390390

391391

392+
def validate_corner_mask(s):
393+
if s == 'legacy':
394+
return s
395+
else:
396+
return validate_bool(s)
397+
398+
392399
def validate_tkpythoninspect(s):
393400
# Introduced 2010/07/05
394401
warnings.warn("tk.pythoninspect is obsolete, and has no effect")
@@ -589,8 +596,10 @@ def __call__(self, s):
589596
'image.origin': ['upper', six.text_type], # lookup table
590597
'image.resample': [False, validate_bool],
591598

599+
# contour props
592600
'contour.negative_linestyle': ['dashed',
593601
validate_negative_linestyle_legacy],
602+
'contour.corner_mask': [True, validate_corner_mask],
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595604
# axes props
596605
'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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