"""
Demonstrate SVG filtering effects which might be used with mpl.

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

import matplotlib

matplotlib.use("Svg")

import matplotlib.pyplot as plt
import matplotlib.transforms as mtransforms

fig1 = plt.figure()
ax = fig1.add_axes([0.1, 0.1, 0.8, 0.8])

# draw lines
l1, = ax.plot([0.1, 0.5, 0.9], [0.1, 0.9, 0.5], "bo-",
              mec="b", lw=5, ms=10, label="Line 1")
l2, = ax.plot([0.1, 0.5, 0.9], [0.5, 0.2, 0.7], "rs-",
              mec="r", lw=5, ms=10, color="r", label="Line 2")


for l in [l1, l2]:

    # draw shadows with same lines with slight offset and gray colors.

    xx = l.get_xdata()
    yy = l.get_ydata()
    shadow, = ax.plot(xx, yy)
    shadow.update_from(l)

    # adjust color
    shadow.set_color("0.2")
    # adjust zorder of the shadow lines so that it is drawn below the
    # original lines
    shadow.set_zorder(l.get_zorder()-0.5)

    # offset transform
    ot = mtransforms.offset_copy(l.get_transform(), fig1,
                                 x=4.0, y=-6.0, units='points')

    shadow.set_transform(ot)

    # set the id for a later use
    shadow.set_gid(l.get_label()+"_shadow")


ax.set_xlim(0., 1.)
ax.set_ylim(0., 1.)

# save the figure as a string in the svg format.
from StringIO import StringIO
f = StringIO()
plt.savefig(f, format="svg")


import xml.etree.cElementTree as ET

# filter definition for a gaussian blur
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='3'/>
    </filter>
  </defs>
"""


# read in the saved svg 
tree, xmlid = ET.XMLID(f.getvalue())

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

for l in [l1, l2]:
    # pick up the svg element with given id
    shadow = xmlid[l.get_label()+"_shadow"]
    # apply shdow filter
    shadow.set("filter",'url(#dropshadow)')

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