
.. DO NOT EDIT.
.. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY.
.. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE:
.. "users/explain/artists/paths.py"
.. LINE NUMBERS ARE GIVEN BELOW.

.. only:: html

    .. meta::
        :keywords: codex

    .. note::
        :class: sphx-glr-download-link-note

        :ref:`Go to the end <sphx_glr_download_users_explain_artists_paths.py>`
        to download the full example code.

.. rst-class:: sphx-glr-example-title

.. _sphx_glr_users_explain_artists_paths.py:


.. 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:

.. GENERATED FROM PYTHON SOURCE LINES 20-54

.. code-block:: Python


    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()





.. image-sg:: /users/explain/artists/images/sphx_glr_paths_001.png
   :alt: paths
   :srcset: /users/explain/artists/images/sphx_glr_paths_001.png, /users/explain/artists/images/sphx_glr_paths_001_2_00x.png 2.00x
   :class: sphx-glr-single-img





.. GENERATED FROM PYTHON SOURCE LINES 55-93

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

.. GENERATED FROM PYTHON SOURCE LINES 93-126

.. code-block:: Python


    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()




.. image-sg:: /users/explain/artists/images/sphx_glr_paths_002.png
   :alt: paths
   :srcset: /users/explain/artists/images/sphx_glr_paths_002.png, /users/explain/artists/images/sphx_glr_paths_002_2_00x.png 2.00x
   :class: sphx-glr-single-img





.. GENERATED FROM PYTHON SOURCE LINES 127-195

.. 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)

.. GENERATED FROM PYTHON SOURCE LINES 195-234

.. code-block:: Python


    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()



.. image-sg:: /users/explain/artists/images/sphx_glr_paths_003.png
   :alt: paths
   :srcset: /users/explain/artists/images/sphx_glr_paths_003.png, /users/explain/artists/images/sphx_glr_paths_003_2_00x.png 2.00x
   :class: sphx-glr-single-img






.. _sphx_glr_download_users_explain_artists_paths.py:

.. only:: html

  .. container:: sphx-glr-footer sphx-glr-footer-example

    .. container:: sphx-glr-download sphx-glr-download-jupyter

      :download:`Download Jupyter notebook: paths.ipynb <paths.ipynb>`

    .. container:: sphx-glr-download sphx-glr-download-python

      :download:`Download Python source code: paths.py <paths.py>`

    .. container:: sphx-glr-download sphx-glr-download-zip

      :download:`Download zipped: paths.zip <paths.zip>`


.. only:: html

 .. rst-class:: sphx-glr-signature

    `Gallery generated by Sphinx-Gallery <https://sphinx-gallery.github.io>`_
