text: //////////////////////////////////////////////////////////////////////////
  //
  //  Copyright (c) 2020, 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.
  //
  //////////////////////////////////////////////////////////////////////////
  
  #include "GafferScene/ClosestPointSampler.h"
  
  using namespace Imath;
  using namespace IECore;
  using namespace IECoreScene;
  using namespace Gaffer;
  using namespace GafferScene;
  
  GAFFER_NODE_DEFINE_TYPE( ClosestPointSampler );
  
  size_t ClosestPointSampler::g_firstPlugIndex = 0;
  
  ClosestPointSampler::ClosestPointSampler( const std::string &name )
  	:	PrimitiveSampler( name )
  {
  	storeIndexOfNextChild( g_firstPlugIndex );
  
  	addChild( new StringPlug( "position", Plug::In, "P" ) );
  }
  
  ClosestPointSampler::~ClosestPointSampler()
  {
  }
  
  Gaffer::StringPlug *ClosestPointSampler::positionPlug()
  {
  	return getChild<StringPlug>( g_firstPlugIndex );
  }
  
  const Gaffer::StringPlug *ClosestPointSampler::positionPlug() const
  {
  	return getChild<StringPlug>( g_firstPlugIndex );
  }
  
  bool ClosestPointSampler::affectsSamplingFunction( const Gaffer::Plug *input ) const
  {
  	return PrimitiveSampler::affectsSamplingFunction( input ) || input == positionPlug();
  }
  
  void ClosestPointSampler::hashSamplingFunction( IECore::MurmurHash &h ) const
  {
  	PrimitiveSampler::hashSamplingFunction( h );
  	positionPlug()->hash( h );
  }
  
  PrimitiveSampler::SamplingFunction ClosestPointSampler::computeSamplingFunction( const IECoreScene::Primitive *destinationPrimitive, IECoreScene::PrimitiveVariable::Interpolation &interpolation ) const
  {
  	const std::string position = positionPlug()->getValue();
  	if( position.empty() )
  	{
  		return SamplingFunction();
  	}
  
  	auto it = destinationPrimitive->variables.find( position );
  	if( it == destinationPrimitive->variables.end() )
  	{
  		throw IECore::Exception( "No primitive variable named \"" + position + "\"" );
  	}
  
  	interpolation = it->second.interpolation;
  	PrimitiveVariable::IndexedView<V3f> positionView( it->second );
  
  	return [positionView] ( const PrimitiveEvaluator &evaluator, size_t index, const M44f &transform, PrimitiveEvaluator::Result &result ) {
  		return evaluator.closestPoint( positionView[index] * transform, &result );
  	};
  }
  
  