matplotlib/tutorials/advanced/path_tutorial.py at master · Nodd/matplotlib · GitHub

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"""

=============

Path Tutorial

=============

Defining paths in your Matplotlib visualization.

The object underlying all of the :mod:`matplotlib.patch` 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 a 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 matplotlib.pyplot as plt

from matplotlib.path import Path

import matplotlib.patches as patches

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.CLOSEPOLY,

]

path = Path(verts, codes)

fig = plt.figure()

ax = fig.add_subplot(111)

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 (1 control point, 1 endpoint) Draw a quadratic Bézier curve from the current position, with the given control point, to the given end point.

# ``CURVE4`` 3 (2 control points, 1 endpoint) Draw a cubic Bézier curve from the current position, with the given control points, to the given end point.

# ``CLOSEPOLY`` 1 (point itself 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 = Path(verts, codes)

fig = plt.figure()

ax = fig.add_subplot(111)

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 1 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 5 vertices: 1 for the ``MOVETO``, 3 for

# the ``LINETO``, and 1 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.patch.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)

import numpy as np

import matplotlib.patches as patches

import matplotlib.path as path

fig = plt.figure()

ax = fig.add_subplot(111)

# 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.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

barpath = path.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()

matplotlib/tutorials/advanced/path_tutorial.py at master · Nodd/matplotlib · GitHub

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