'Parameters
offset : pair of floats
The offset of the shadow in points.
shadow_rgbFace : color
The shadow color.
alpha : float
The alpha transparency of the created shadow patch.
Default is 0.3.
http://matplotlib.1069221.n5.nabble.com/path-effects-question-td27630.html
rho : float
A scale factor to apply to the rgbFace color if `shadow_rgbFace`
is not specified. Default is 0.3.
**kwargs
Extra keywords are stored and passed through to
:meth:`AbstractPathEffect._update_gc`.'

def __init__(self, offset=(2, (-2)), shadow_rgbFace=None, alpha=None, rho=0.3, **kwargs):

    super(SimplePatchShadow, self).__init__(offset)
    if (shadow_rgbFace is None):
        self._shadow_rgbFace = shadow_rgbFace
    else:
        self._shadow_rgbFace = mcolors.to_rgba(shadow_rgbFace)
    if (alpha is None):
        alpha = 0.3
    self._alpha = alpha
    self._rho = rho
    self._gc = kwargs
    self._offset_tran = mtransforms.Affine2D()
