.. DO NOT EDIT.
.. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY.
.. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE:
.. "gallery/lines_bars_and_markers/gradient_bar.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_gallery_lines_bars_and_markers_gradient_bar.py>`
        to download the full example code

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

.. _sphx_glr_gallery_lines_bars_and_markers_gradient_bar.py:


========================
Bar chart with gradients
========================

Matplotlib does not natively support gradients. However, we can emulate a
gradient-filled rectangle by an `.AxesImage` of the right size and coloring.

In particular, we use a colormap to generate the actual colors. It is then
sufficient to define the underlying values on the corners of the image and
let bicubic interpolation fill out the area. We define the gradient direction
by a unit vector *v*. The values at the corners are then obtained by the
lengths of the projections of the corner vectors on *v*.

A similar approach can be used to create a gradient background for an Axes.
In that case, it is helpful to use Axes coordinates (``extent=(0, 1, 0, 1),
transform=ax.transAxes``) to be independent of the data coordinates.

.. GENERATED FROM PYTHON SOURCE LINES 19-74



.. image-sg:: /gallery/lines_bars_and_markers/images/sphx_glr_gradient_bar_001.png
   :alt: gradient bar
   :srcset: /gallery/lines_bars_and_markers/images/sphx_glr_gradient_bar_001.png, /gallery/lines_bars_and_markers/images/sphx_glr_gradient_bar_001_2_00x.png 2.00x
   :class: sphx-glr-single-img





.. code-block:: Python


    import matplotlib.pyplot as plt
    import numpy as np

    np.random.seed(19680801)


    def gradient_image(ax, direction=0.3, cmap_range=(0, 1), **kwargs):
        """
        Draw a gradient image based on a colormap.

        Parameters
        ----------
        ax : Axes
            The axes to draw on.
        direction : float
            The direction of the gradient. This is a number in
            range 0 (=vertical) to 1 (=horizontal).
        cmap_range : float, float
            The fraction (cmin, cmax) of the colormap that should be
            used for the gradient, where the complete colormap is (0, 1).
        **kwargs
            Other parameters are passed on to `.Axes.imshow()`.
            In particular, *cmap*, *extent*, and *transform* may be useful.
        """
        phi = direction * np.pi / 2
        v = np.array([np.cos(phi), np.sin(phi)])
        X = np.array([[v @ [1, 0], v @ [1, 1]],
                      [v @ [0, 0], v @ [0, 1]]])
        a, b = cmap_range
        X = a + (b - a) / X.max() * X
        im = ax.imshow(X, interpolation='bicubic', clim=(0, 1),
                       aspect='auto', **kwargs)
        return im


    def gradient_bar(ax, x, y, width=0.5, bottom=0):
        for left, top in zip(x, y):
            right = left + width
            gradient_image(ax, extent=(left, right, bottom, top),
                           cmap=plt.cm.Blues_r, cmap_range=(0, 0.8))


    fig, ax = plt.subplots()
    ax.set(xlim=(0, 10), ylim=(0, 1))

    # background image
    gradient_image(ax, direction=1, extent=(0, 1, 0, 1), transform=ax.transAxes,
                   cmap=plt.cm.RdYlGn, cmap_range=(0.2, 0.8), alpha=0.5)

    N = 10
    x = np.arange(N) + 0.15
    y = np.random.rand(N)
    gradient_bar(ax, x, y, width=0.7)
    plt.show()


.. _sphx_glr_download_gallery_lines_bars_and_markers_gradient_bar.py:

.. only:: html

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

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

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

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

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


.. only:: html

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

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