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"""
.. redirect-from:: /tutorials/advanced/path_tutorial
.. _paths:
=============
Path Tutorial
=============
Defining paths in your Matplotlib visualization.
The object underlying all of the :mod:`matplotlib.patches` objects is
the :class:`~matplotlib.path.Path`, which supports the standard set of
moveto, lineto, curveto commands to draw simple and compound outlines
consisting of line segments and splines. The ``Path`` is instantiated
with a (N, 2) array of (x, y) vertices, and an N-length array of path
codes. For example to draw the unit rectangle from (0, 0) to (1, 1), we
could use this code:
"""
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.patches as patches
from matplotlib.path import Path
verts = [
(0., 0.), # left, bottom
(0., 1.), # left, top
(1., 1.), # right, top
(1., 0.), # right, bottom
(0., 0.), # ignored
]
codes = [
Path.MOVETO,
Path.LINETO,
Path.LINETO,
Path.LINETO,
Path.CLOSEPOLY,
]
path = Path(verts, codes)
fig, ax = plt.subplots()
patch = patches.PathPatch(path, facecolor='orange', lw=2)
ax.add_patch(patch)
ax.set_xlim(-2, 2)
ax.set_ylim(-2, 2)
plt.show()
# %%
# The following path codes are recognized
#
# ============= ======================== ======================================
# Code Vertices Description
# ============= ======================== ======================================
# ``STOP`` 1 (ignored) A marker for the end of the entire
# path (currently not required and
# ignored).
# ``MOVETO`` 1 Pick up the pen and move to the given
# vertex.
# ``LINETO`` 1 Draw a line from the current position
# to the given vertex.
# ``CURVE3`` 2: Draw a quadratic Bézier curve from the
# 1 control point, current position, with the given
# 1 end point control point, to the given end point.
# ``CURVE4`` 3: Draw a cubic Bézier curve from the
# 2 control points, current position, with the given
# 1 end point control points, to the given end
# point.
# ``CLOSEPOLY`` 1 (the point is ignored) Draw a line segment to the start point
# of the current polyline.
# ============= ======================== ======================================
#
#
# .. path-curves:
#
#
# Bézier example
# ==============
#
# Some of the path components require multiple vertices to specify them:
# for example CURVE 3 is a `Bézier
# <https://en.wikipedia.org/wiki/B%C3%A9zier_curve>`_ curve with one
# control point and one end point, and CURVE4 has three vertices for the
# two control points and the end point. The example below shows a
# CURVE4 Bézier spline -- the Bézier curve will be contained in the
# convex hull of the start point, the two control points, and the end
# point
verts = [
(0., 0.), # P0
(0.2, 1.), # P1
(1., 0.8), # P2
(0.8, 0.), # P3
]
codes = [
Path.MOVETO,
Path.CURVE4,
Path.CURVE4,
Path.CURVE4,
]
path = Path(verts, codes)
fig, ax = plt.subplots()
patch = patches.PathPatch(path, facecolor='none', lw=2)
ax.add_patch(patch)
xs, ys = zip(*verts)
ax.plot(xs, ys, 'x--', lw=2, color='black', ms=10)
ax.text(-0.05, -0.05, 'P0')
ax.text(0.15, 1.05, 'P1')
ax.text(1.05, 0.85, 'P2')
ax.text(0.85, -0.05, 'P3')
ax.set_xlim(-0.1, 1.1)
ax.set_ylim(-0.1, 1.1)
plt.show()
# %%
# .. compound_paths:
#
# Compound paths
# ==============
#
# All of the simple patch primitives in matplotlib, Rectangle, Circle,
# Polygon, etc, are implemented with simple path. Plotting functions
# like :meth:`~matplotlib.axes.Axes.hist` and
# :meth:`~matplotlib.axes.Axes.bar`, which create a number of
# primitives, e.g., a bunch of Rectangles, can usually be implemented more
# efficiently using a compound path. The reason ``bar`` creates a list
# of rectangles and not a compound path is largely historical: the
# :class:`~matplotlib.path.Path` code is comparatively new and ``bar``
# predates it. While we could change it now, it would break old code,
# so here we will cover how to create compound paths, replacing the
# functionality in bar, in case you need to do so in your own code for
# efficiency reasons, e.g., you are creating an animated bar plot.
#
# We will make the histogram chart by creating a series of rectangles
# for each histogram bar: the rectangle width is the bin width and the
# rectangle height is the number of datapoints in that bin. First we'll
# create some random normally distributed data and compute the
# histogram. Because NumPy returns the bin edges and not centers, the
# length of ``bins`` is one greater than the length of ``n`` in the
# example below::
#
# # histogram our data with numpy
# data = np.random.randn(1000)
# n, bins = np.histogram(data, 100)
#
# We'll now extract the corners of the rectangles. Each of the
# ``left``, ``bottom``, etc., arrays below is ``len(n)``, where ``n`` is
# the array of counts for each histogram bar::
#
# # get the corners of the rectangles for the histogram
# left = np.array(bins[:-1])
# right = np.array(bins[1:])
# bottom = np.zeros(len(left))
# top = bottom + n
#
# Now we have to construct our compound path, which will consist of a
# series of ``MOVETO``, ``LINETO`` and ``CLOSEPOLY`` for each rectangle.
# For each rectangle, we need five vertices: one for the ``MOVETO``,
# three for the ``LINETO``, and one for the ``CLOSEPOLY``. As indicated
# in the table above, the vertex for the closepoly is ignored, but we still
# need it to keep the codes aligned with the vertices::
#
# nverts = nrects*(1+3+1)
# verts = np.zeros((nverts, 2))
# codes = np.ones(nverts, int) * path.Path.LINETO
# codes[0::5] = path.Path.MOVETO
# codes[4::5] = path.Path.CLOSEPOLY
# verts[0::5, 0] = left
# verts[0::5, 1] = bottom
# verts[1::5, 0] = left
# verts[1::5, 1] = top
# verts[2::5, 0] = right
# verts[2::5, 1] = top
# verts[3::5, 0] = right
# verts[3::5, 1] = bottom
#
# All that remains is to create the path, attach it to a
# :class:`~matplotlib.patches.PathPatch`, and add it to our Axes::
#
# barpath = path.Path(verts, codes)
# patch = patches.PathPatch(barpath, facecolor='green',
# edgecolor='yellow', alpha=0.5)
# ax.add_patch(patch)
fig, ax = plt.subplots()
# Fixing random state for reproducibility
np.random.seed(19680801)
# histogram our data with numpy
data = np.random.randn(1000)
n, bins = np.histogram(data, 100)
# get the corners of the rectangles for the histogram
left = np.array(bins[:-1])
right = np.array(bins[1:])
bottom = np.zeros(len(left))
top = bottom + n
nrects = len(left)
nverts = nrects*(1+3+1)
verts = np.zeros((nverts, 2))
codes = np.full(nverts, Path.LINETO, dtype=int)
codes[0::5] = Path.MOVETO
codes[4::5] = Path.CLOSEPOLY
verts[0::5, 0] = left
verts[0::5, 1] = bottom
verts[1::5, 0] = left
verts[1::5, 1] = top
verts[2::5, 0] = right
verts[2::5, 1] = top
verts[3::5, 0] = right
verts[3::5, 1] = bottom
barpath = Path(verts, codes)
patch = patches.PathPatch(barpath, facecolor='green',
edgecolor='yellow', alpha=0.5)
ax.add_patch(patch)
ax.set_xlim(left[0], right[-1])
ax.set_ylim(bottom.min(), top.max())
plt.show()
|
