class_docstr: Base class for all filters that use fragment and/or vertex shaders.
  
  Parameters
  ----------
  vcode : str | Function | None
      Vertex shader code. If None, ``vhook`` and ``vpos`` will
      be ignored.
  vhook : {'pre', 'post'}
      Hook name to attach the vertex shader to.
  vpos : int
      Position in the hook to attach the vertex shader.
  fcode : str | Function | None
      Fragment shader code. If None, ``fhook`` and ``fpos`` will
      be ignored.
  fhook : {'pre', 'post'}
      Hook name to attach the fragment shader to.
  fpos : int
      Position in the hook to attach the fragment shader.
  
  Attributes
  ----------
  vshader : Function | None
      Vertex shader.
  fshader : Function | None
      Fragment shader.
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code: def attached(self):
      return self._attached
  
imports: from abc import ABCMeta, abstractmethod
  import numpy
  from vispy.gloo import VertexBuffer
  from ..shaders import Function
label_desc: Use image node_id 2 for calling the Filter obj's underlying member method code with example usage: obj.attached() and returns: self