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# Copyright Cartopy Contributors
#
# This file is part of Cartopy and is released under the LGPL license.
# See COPYING and COPYING.LESSER in the root of the repository for full
# licensing details.
"""
This module defines the :class:`FeatureArtist` class, for drawing
:class:`Feature` instances with matplotlib.
"""
from __future__ import (absolute_import, division, print_function)
from collections import OrderedDict
import warnings
import weakref
import numpy as np
import matplotlib.artist
import matplotlib.collections
import cartopy.mpl.patch as cpatch
from .style import merge as style_merge, finalize as style_finalize
class _GeomKey(object):
"""
Provide id() based equality and hashing for geometries.
Instances of this class must be treated as immutable for the caching
to operate correctly.
A workaround for Shapely polygons no longer being hashable as of 1.5.13.
"""
def __init__(self, geom):
self._id = id(geom)
def __eq__(self, other):
return self._id == other._id
def __hash__(self):
return hash(self._id)
def _freeze(obj):
"""
Recursively freeze the given object so that it might be suitable for
use as a hashable.
"""
if isinstance(obj, dict):
obj = frozenset(((k, _freeze(v)) for k, v in obj.items()))
elif isinstance(obj, list):
obj = tuple(_freeze(item) for item in obj)
elif isinstance(obj, np.ndarray):
obj = tuple(obj)
return obj
class FeatureArtist(matplotlib.artist.Artist):
"""
A subclass of :class:`~matplotlib.artist.Artist` capable of
drawing a :class:`cartopy.feature.Feature`.
"""
_geom_key_to_geometry_cache = weakref.WeakValueDictionary()
"""
A mapping from _GeomKey to geometry to assist with the caching of
transformed Matplotlib paths.
"""
_geom_key_to_path_cache = weakref.WeakKeyDictionary()
"""
A nested mapping from geometry (converted to a _GeomKey) and target
projection to the resulting transformed Matplotlib paths::
{geom: {target_projection: list_of_paths}}
This provides a significant boost when producing multiple maps of the
same projection.
"""
def __init__(self, feature, **kwargs):
"""
Parameters
----------
feature
An instance of :class:`cartopy.feature.Feature` to draw.
styler
A callable that given a gemometry, returns matplotlib styling
parameters.
Other Parameters
----------------
**kwargs
Keyword arguments to be used when drawing the feature. These
will override those shared with the feature.
"""
super(FeatureArtist, self).__init__()
if kwargs is None:
kwargs = {}
self._styler = kwargs.pop('styler', None)
self._kwargs = dict(kwargs)
if 'color' in self._kwargs:
# We want the user to be able to override both face and edge
# colours if the original feature already supplied it.
color = self._kwargs.pop('color')
self._kwargs['facecolor'] = self._kwargs['edgecolor'] = color
# Set default zorder so that features are drawn before
# lines e.g. contours but after images.
# Note that the zorder of Patch, PatchCollection and PathCollection
# are all 1 by default. Assuming equal zorder drawing takes place in
# the following order: collections, patches, lines (default zorder=2),
# text (default zorder=3), then other artists e.g. FeatureArtist.
if self._kwargs.get('zorder') is not None:
self.set_zorder(self._kwargs['zorder'])
elif feature.kwargs.get('zorder') is not None:
self.set_zorder(feature.kwargs['zorder'])
else:
# The class attribute matplotlib.collections.PathCollection.zorder
# was removed after mpl v1.2.0, so the hard-coded value of 1 is
# used instead.
self.set_zorder(1)
self._feature = feature
@matplotlib.artist.allow_rasterization
def draw(self, renderer, *args, **kwargs):
"""
Draw the geometries of the feature that intersect with the extent of
the :class:`cartopy.mpl.GeoAxes` instance to which this
object has been added.
"""
if not self.get_visible():
return
ax = self.axes
feature_crs = self._feature.crs
# Get geometries that we need to draw.
extent = None
try:
extent = ax.get_extent(feature_crs)
except ValueError:
warnings.warn('Unable to determine extent. Defaulting to global.')
geoms = self._feature.intersecting_geometries(extent)
# Combine all the keyword args in priority order.
prepared_kwargs = style_merge(self._feature.kwargs,
self._kwargs,
kwargs)
# Freeze the kwargs so that we can use them as a dict key. We will
# need to unfreeze this with dict(frozen) before passing to mpl.
prepared_kwargs = _freeze(prepared_kwargs)
# Project (if necessary) and convert geometries to matplotlib paths.
stylised_paths = OrderedDict()
key = ax.projection
for geom in geoms:
# As Shapely geometries cannot be relied upon to be
# hashable, we have to use a WeakValueDictionary to manage
# their weak references. The key can then be a simple,
# "disposable", hashable geom-key object that just uses the
# id() of a geometry to determine equality and hash value.
# The only persistent, strong reference to the geom-key is
# in the WeakValueDictionary, so when the geometry is
# garbage collected so is the geom-key.
# The geom-key is also used to access the WeakKeyDictionary
# cache of transformed geometries. So when the geom-key is
# garbage collected so are the transformed geometries.
geom_key = _GeomKey(geom)
FeatureArtist._geom_key_to_geometry_cache.setdefault(
geom_key, geom)
mapping = FeatureArtist._geom_key_to_path_cache.setdefault(
geom_key, {})
geom_paths = mapping.get(key)
if geom_paths is None:
if ax.projection != feature_crs:
projected_geom = ax.projection.project_geometry(
geom, feature_crs)
else:
projected_geom = geom
geom_paths = cpatch.geos_to_path(projected_geom)
mapping[key] = geom_paths
if not self._styler:
style = prepared_kwargs
else:
# Unfreeze, then add the computed style, and then re-freeze.
style = style_merge(dict(prepared_kwargs), self._styler(geom))
style = _freeze(style)
stylised_paths.setdefault(style, []).extend(geom_paths)
transform = ax.projection._as_mpl_transform(ax)
# Draw one PathCollection per style. We could instead pass an array
# of style items through to a single PathCollection, but that
# complexity does not yet justify the effort.
for style, paths in stylised_paths.items():
style = style_finalize(dict(style))
# Build path collection and draw it.
c = matplotlib.collections.PathCollection(paths,
transform=transform,
**style)
c.set_clip_path(ax.patch)
c.set_figure(ax.figure)
c.draw(renderer)
# n.b. matplotlib.collection.Collection.draw returns None
return None
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