text: ##########################################################################
  #
  #  Copyright (c) 2014, John Haddon. All rights reserved.
  #
  #  Redistribution and use in source and binary forms, with or without
  #  modification, are permitted provided that the following conditions are
  #  met:
  #
  #      * Redistributions of source code must retain the above
  #        copyright notice, this list of conditions and the following
  #        disclaimer.
  #
  #      * Redistributions in binary form must reproduce the above
  #        copyright notice, this list of conditions and the following
  #        disclaimer in the documentation and/or other materials provided with
  #        the distribution.
  #
  #      * Neither the name of John Haddon nor the names of
  #        any other contributors to this software may be used to endorse or
  #        promote products derived from this software without specific prior
  #        written permission.
  #
  #  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
  #  IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
  #  THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  #  PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
  #  CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  #  EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  #  PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  #  PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
  #  LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  #  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  #  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  #
  ##########################################################################
  
  import functools
  
  import IECore
  
  import Gaffer
  import GafferUI
  import GafferScene
  import GafferSceneUI
  
  # add plugs to the preferences node
  
  preferences = application.root()["preferences"]
  preferences["viewer"] = Gaffer.CompoundPlug()
  preferences["viewer"]["gridDimensions"] = Gaffer.V2fPlug( defaultValue = IECore.V2f( 10 ), minValue = IECore.V2f( 0 ) )
  
  # register a customised view for viewing scenes
  
  def __sceneView( plug ) :
  
  	view = GafferSceneUI.SceneView()
  	view["in"].setInput( plug )
  	view["grid"]["dimensions"].setInput( preferences["viewer"]["gridDimensions"] )
  
  	return view
  
  GafferUI.View.registerView( GafferScene.ScenePlug.staticTypeId(), __sceneView )
  
  # register shading modes
  
  def __createNode( nodeType, plugValues ) :
  
  	node = nodeType()
  	for name, value in plugValues.items() :
  		node.descendant( name ).setValue( value )
  
  	return node
  
  def __registerShadingModes( modes ) :
  
  	for name, nodeType, plugValues in modes :
  		GafferSceneUI.SceneView.registerShadingMode(
  			name,
  			functools.partial(
  				__createNode,
  				nodeType,
  				plugValues,
  			)
  		)
  
  with IECore.IgnoredExceptions( ImportError ) :
  
  	# If this import fails, then our "with" block will swallow the error
  	# and we'll not add any useless visualisation modes (because the code
  	# below won't be reached). We leave the actual error reporting to the
  	# startup/gui/menus.py config file.
  	import GafferRenderMan
  
  	__registerShadingModes( [
  
  		( "Diagnostic/RenderMan/Shader Assignment", GafferScene.AttributeVisualiser, { "attributeName" : "ri:surface", "mode" : GafferScene.AttributeVisualiser.Mode.ShaderNodeColor } ),
  		( "Diagnostic/RenderMan/Camera Visibility", GafferScene.AttributeVisualiser, { "attributeName" : "ri:visibility:camera" } ),
  		( "Diagnostic/RenderMan/Transmission Visibility", GafferScene.AttributeVisualiser, { "attributeName" : "ri:visibility:transmission" } ),
  		( "Diagnostic/RenderMan/Diffuse Visibility", GafferScene.AttributeVisualiser, { "attributeName" : "ri:visibility:diffuse" } ),
  		( "Diagnostic/RenderMan/Specular Visibility", GafferScene.AttributeVisualiser, { "attributeName" : "ri:visibility:specular" } ),
  		( "Diagnostic/RenderMan/Photon Visibility", GafferScene.AttributeVisualiser, { "attributeName" : "ri:visibility:photon" } ),
  		( "Diagnostic/RenderMan/Matte", GafferScene.AttributeVisualiser, { "attributeName" : "ri:visibility:matte" } ),
  
  	] )
  
  with IECore.IgnoredExceptions( ImportError ) :
  
  	import GafferArnold
  
  	__registerShadingModes( [
  
  		( "Diagnostic/Arnold/Shader Assignment", GafferScene.AttributeVisualiser, { "attributeName" : "ai:surface", "mode" : GafferScene.AttributeVisualiser.Mode.ShaderNodeColor } ),
  		( "Diagnostic/Arnold/Camera Visibility", GafferScene.AttributeVisualiser, { "attributeName" : "ai:visibility:camera" } ),
  		( "Diagnostic/Arnold/Shadow Visibility", GafferScene.AttributeVisualiser, { "attributeName" : "ai:visibility:shadow" } ),
  		( "Diagnostic/Arnold/Reflection Visibility", GafferScene.AttributeVisualiser, { "attributeName" : "ai:visibility:reflected" } ),
  		( "Diagnostic/Arnold/Refraction Visibility", GafferScene.AttributeVisualiser, { "attributeName" : "ai:visibility:refracted" } ),
  		( "Diagnostic/Arnold/Diffuse Visibility", GafferScene.AttributeVisualiser, { "attributeName" : "ai:visibility:diffuse" } ),
  		( "Diagnostic/Arnold/Glossy Visibility", GafferScene.AttributeVisualiser, { "attributeName" : "ai:visibility:glossy" } ),
  
  	] )
  
  with IECore.IgnoredExceptions( ImportError ) :
  
  	import GafferAppleseed
  
  	__registerShadingModes( [
  
  		( "Diagnostic/Appleseed/Shader Assignment", GafferScene.AttributeVisualiser, { "attributeName" : "osl:surface", "mode" : GafferScene.AttributeVisualiser.Mode.ShaderNodeColor } ),
  		( "Diagnostic/Appleseed/Camera Visibility", GafferScene.AttributeVisualiser, { "attributeName" : "as:visibility:camera" } ),
  		( "Diagnostic/Appleseed/Shadow Visibility", GafferScene.AttributeVisualiser, { "attributeName" : "as:visibility:shadow" } ),
  		( "Diagnostic/Appleseed/Diffuse Visibility", GafferScene.AttributeVisualiser, { "attributeName" : "as:visibility:diffuse" } ),
  		( "Diagnostic/Appleseed/Specular Visibility", GafferScene.AttributeVisualiser, { "attributeName" : "as:visibility:specular" } ),
  		( "Diagnostic/Appleseed/Glossy Visibility", GafferScene.AttributeVisualiser, { "attributeName" : "as:visibility:glossy" } ),
  		( "Diagnostic/Appleseed/Photon Visibility", GafferScene.AttributeVisualiser, { "attributeName" : "as:visibility:light" } ),
  
  	] )
  