class_docstr: Class to support multiple render passes for a renderer.
  
  Notes
  -----
  Passes are organized here as "primary" (vtkOpenGLRenderPass) that act
  within the renderer and "post-processing" (vtkImageProcessingPass) passes,
  which act on the image generated from the renderer.
  
  The primary passes are added as part of a vtk.vtkRenderPassCollection or
  are "stacked", while the post-processing passes are added as a final pass
  to the rendered image.
  
  Parameters
  ----------
  renderer : vtk.vtkRenderer
      Renderer to initialize render passes for.
docstr: Add a render pass.
docstr_tok: ["Add","a","render","pass","."]
code: def _add_pass(self, render_pass):
      """Add a render pass."""
      class_name = render_pass.GetClassName()
  
      if class_name in PRE_PASS and render_pass in self._passes:
          return
  
      if class_name not in self._passes:
          self._passes[class_name] = [render_pass]
      else:
          self._passes[class_name].append(render_pass)
  
      self._update_passes()
  
imports: import weakref
  from .None import _vtk
label_desc: Use image node_id 21 for calling the RenderPasses obj's underlying member method code with example usage: obj._add_pass(render_pass) without return types