code: def add_post_processing(self, klass, *args, **kwargs):
          '''Add a post processing effect to the current scene.
          
          The usage is as following::
          
              from chemlab.graphics.qt import QtViewer
              from chemlab.graphics.postprocessing import SSAOEffect
              
              v = QtViewer()
              effect = v.add_post_processing(SSAOEffect)
          
          .. seealso:: :doc:`/api/chemlab.graphics.postprocessing`
          
          **Return**
          
          an instance of :py:class:`~chemlab.graphics.postprocessing.base.AbstractEffect`
          
          .. versionadded:: 0.3
          '''
          pp = klass(self.widget, *args, **kwargs)
          self.widget.post_processing.append(pp)
          return pf add_post_processing(self, klass, *args, **kwargs):
          '''Add a post processing effect to the current scene.
          
          The usage is as following::
          
              from chemlab.graphics.qt import QtViewer
              from chemlab.graphics.postprocessing import SSAOEffect
              
              v = QtViewer()
              effect = v.add_post_processing(SSAOEffect)
          
          .. seealso:: :doc:`/api/chemlab.graphics.postprocessing`
          
          **Return**
          
          an instance of :py:class:`~chemlab.graphics.postprocessing.base.AbstractEffect`
          
          .. versionadded:: 0.3
          '''
          pp = klass(self.widget, *args, **kwargs)
          self.widget.post_processing.append(pp)
          return pp
docs: Add a post processing effect to the current scene.
          
          The usage is as following::
          
              from chemlab.graphics.qt import QtViewer
              from chemlab.graphics.postprocessing import SSAOEffect
              
              v = QtViewer()
              effect = v.add_post_processing(SSAOEffect)
          
          .. seealso:: :doc:`/api/chemlab.graphics.postprocessing`
          
          **Return**
          
          an instance of :py:class:`~chemlab.graphics.postprocessing.base.AbstractEffect`
          
          .. versionadded:: 0.3