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# SVG Filter Pie

Demonstrate SVG filtering effects which might be used with mpl. The pie chart drawing code is borrowed from pie_demo.py

Note that the filtering effects are only effective if your svg renderer support it.

Out:

    Saving 'svg_filter_pie.svg'

    import matplotlib
    matplotlib.use("Svg")

    import matplotlib.pyplot as plt
    from matplotlib.patches import Shadow

    # make a square figure and axes
    fig1 = plt.figure(1, figsize=(6, 6))
    ax = fig1.add_axes([0.1, 0.1, 0.8, 0.8])

    labels = 'Frogs', 'Hogs', 'Dogs', 'Logs'
    fracs = [15, 30, 45, 10]

    explode = (0, 0.05, 0, 0)

    # We want to draw the shadow for each pie but we will not use "shadow"
    # option as it does'n save the references to the shadow patches.
    pies = ax.pie(fracs, explode=explode, labels=labels, autopct='%1.1f%%')

    for w in pies[0]:
        # set the id with the label.
        w.set_gid(w.get_label())

        # we don't want to draw the edge of the pie
        w.set_ec("none")

    for w in pies[0]:
        # create shadow patch
        s = Shadow(w, -0.01, -0.01)
        s.set_gid(w.get_gid() + "_shadow")
        s.set_zorder(w.get_zorder() - 0.1)
        ax.add_patch(s)

    # save
    from io import BytesIO
    f = BytesIO()
    plt.savefig(f, format="svg")

    import xml.etree.cElementTree as ET

    # filter definition for shadow using a gaussian blur
    # and lightening effect.
    # The lightening filter is copied from http://www.w3.org/TR/SVG/filters.html

    # I tested it with Inkscape and Firefox3. "Gaussian blur" is supported
    # in both, but the lightening effect only in the Inkscape. Also note
    # that, Inkscape's exporting also may not support it.

    filter_def = """
      <defs  xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink'>
        <filter id='dropshadow' height='1.2' width='1.2'>
          <feGaussianBlur result='blur' stdDeviation='2'/>
        </filter>

        <filter id='MyFilter' filterUnits='objectBoundingBox' x='0' y='0' width='1' height='1'>
          <feGaussianBlur in='SourceAlpha' stdDeviation='4%' result='blur'/>
          <feOffset in='blur' dx='4%' dy='4%' result='offsetBlur'/>
          <feSpecularLighting in='blur' surfaceScale='5' specularConstant='.75'
               specularExponent='20' lighting-color='#bbbbbb' result='specOut'>
            <fePointLight x='-5000%' y='-10000%' z='20000%'/>
          </feSpecularLighting>
          <feComposite in='specOut' in2='SourceAlpha' operator='in' result='specOut'/>
          <feComposite in='SourceGraphic' in2='specOut' operator='arithmetic'
        k1='0' k2='1' k3='1' k4='0'/>
        </filter>
      </defs>
    """

    tree, xmlid = ET.XMLID(f.getvalue())

    # insert the filter definition in the svg dom tree.
    tree.insert(0, ET.XML(filter_def))

    for i, pie_name in enumerate(labels):
        pie = xmlid[pie_name]
        pie.set("filter", 'url(#MyFilter)')

        shadow = xmlid[pie_name + "_shadow"]
        shadow.set("filter", 'url(#dropshadow)')

    fn = "svg_filter_pie.svg"
    print("Saving '%s'" % fn)
    ET.ElementTree(tree).write(fn)

Total running time of the script: ( 0 minutes 0.067 seconds)

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