MeshAlgo::MeshSplitter : Preserve vertex order

src/IECoreScene/MeshAlgoSplit.cpp

@@ -490,7 +490,8 @@ class Reindexer
 		m_newIndices( m_newIndicesData->writable() ),
 		m_blockSize( blockSize ),
 		m_fromOldIds( ( numOriginalIds - 1 ) / blockSize + 1 ),
-		m_numIdsUsed( 0 )
+		m_numIdsUsed( 0 ),
+		m_indicesComputed( false )
 	{
 		m_newIndices.reserve( numIndices );
 	}
@@ -510,19 +511,53 @@ class Reindexer
 			block = std::make_unique< std::vector<int> >( m_blockSize, -1 );
 		}
 
-		int &r = (*block)[ subIndex ];
-		if( r == -1 )
+		// We initially record that this index is used just by marking it with a 0, against the background of -1.
+		// Once computeIndices is called, the 0 will be replaced with a new index, only counting indices that are
+		// used.
+		(*block)[ subIndex ] = 0;
+
+		m_newIndices.push_back( id );
+	}
+
+	void computeIndices()
+	{
+		if( m_indicesComputed )
+		{
+			return;
+		}
+
+		m_indicesComputed = true;
+
+		for( unsigned int blockId = 0; blockId < m_fromOldIds.size(); blockId++ )
 		{
-			// Id isn't used yet, we need to set this location in the block, and use it
-			r = m_numIdsUsed;
-			m_numIdsUsed++;
+			auto &block = m_fromOldIds[ blockId ];
+			if( !block )
+			{
+				continue;
+			}
+
+			for( int i = 0; i < m_blockSize; i++ )
+			{
+				if( (*block)[i] != -1 )
+				{
+					(*block)[i] = m_numIdsUsed;
+					m_numIdsUsed++;
+				}
+			}
 		}
 
-		m_newIndices.push_back( r );
+		for( int &id : m_newIndices )
+		{
+			int blockId = id / m_blockSize;
+			int subIndex = id % m_blockSize;
+
+			id = (*m_fromOldIds[ blockId ])[subIndex];
+		}
 	}
 
 	// Don't add the index, but just test if it is a part of the reindex. If it is an
 	// id which has already been added, return the new id, otherwise return -1
+	// You must call computeIndices() after calling addIndex and before calling this function.
 	inline int testIndex( int id )
 	{
 		int blockId = id / m_blockSize;
@@ -541,6 +576,7 @@ class Reindexer
 	// Get the new indices. Call after calling addIndex for every original index
 	IntVectorDataPtr getNewIndices()
 	{
+		computeIndices();
 		return m_newIndicesData;
 	}
 
@@ -550,6 +586,7 @@ class Reindexer
 	template <typename T >
 	void remapData( const std::vector<T> &in, std::vector<T> &out )
 	{
+		computeIndices();
 		out.resize( m_numIdsUsed );
 		for( unsigned int i = 0; i < m_fromOldIds.size(); i++ )
 		{
@@ -574,6 +611,7 @@ class Reindexer
 	// original id corresponding to each id of the output
 	void getDataRemapping( std::vector<int> &dataRemap )
 	{
+		computeIndices();
 		dataRemap.resize( m_numIdsUsed );
 		for( unsigned int i = 0; i < m_fromOldIds.size(); i++ )
 		{
@@ -605,13 +643,16 @@ class Reindexer
 	// Store the mapping from old ids to new ids. The outer vector holds a unique_ptr for each
 	// block of m_blockSize ids in the original id range. These pointers are null if no ids from
 	// that block have been used. Once a block is used, it is allocated with a vector that is set
-	// to -1 for ids which have not been used, and the new corresponding id for ids which have been
-	// used
+	// to -1 for ids which have not been used, and zeros for ids which have been used.  When computeIndices()
+	// is called, all used elements get a new id assigned, relative to just the used ids.
 	std::vector< std::unique_ptr< std::vector< int > > > m_fromOldIds;
 
 	// How many unique ids have appeared in the indices added so far
 	int m_numIdsUsed;
 
+	// Whether we have yet computed the new indices for each used index
+	bool m_indicesComputed;
+
 };
 
 struct ResamplePrimitiveVariableFunctor

test/IECoreScene/MeshAlgoSplitTest.py

@@ -170,16 +170,29 @@ def accumulateInPython2( iterable ):
 			newVerticesPerFace = []
 			newVertIndices = []
 			mapFaceVert = []
-			reverseIndices = []
+
+			usedIndices = set()
 			for i in r:
 				vpf = mesh.verticesPerFace[i]
 				newVerticesPerFace.append( vpf )
 				for j in range( vpf ):
 					origFaceVert = faceIndices[i] + j
 					origVert = mesh.vertexIds[ origFaceVert ]
-					newIndex = reindex.setdefault( origVert, len( reindex ) )
-					if len( reindex ) > len( reverseIndices ):
-						reverseIndices.append( origVert )
+
+					usedIndices.add( origVert )
+
+			usedIndices = sorted( usedIndices )
+
+			for i in range( len( usedIndices ) ):
+				reindex[ usedIndices[i] ] = i
+
+			for i in r:
+				vpf = mesh.verticesPerFace[i]
+				for j in range( vpf ):
+					origFaceVert = faceIndices[i] + j
+					origVert = mesh.vertexIds[ origFaceVert ]
+
+					newIndex = usedIndices.index( origVert )
 					newVertIndices.append( newIndex )
 					mapFaceVert.append( origFaceVert )
 
@@ -226,7 +239,7 @@ def accumulateInPython2( iterable ):
 				if p.interpolation == interp.Constant:
 					d = p.data.copy()
 				elif p.interpolation in [ interp.Vertex, interp.Varying ]:
-					d = type( p.data )( [ pd[i] for i in reverseIndices] )
+					d = type( p.data )( [ pd[i] for i in usedIndices] )
 				elif p.interpolation == interp.FaceVarying:
 					d = type( p.data )( [ pd[i] for i in mapFaceVert ] )
 				elif p.interpolation == interp.Uniform:
@@ -269,8 +282,8 @@ def testCanSplitUsingIntegerPrimvar( self ) :
 		p12 = imath.V3f( 1, 2, 0 )
 		p22 = imath.V3f( 2, 2, 0 )
 
-		self.assertEqual( s0["P"].data, IECore.V3fVectorData( [p00, p10, p11, p01, p20, p21], IECore.GeometricData.Interpretation.Point ) )
-		self.assertEqual( s1["P"].data, IECore.V3fVectorData( [p01, p11, p12, p02, p21, p22], IECore.GeometricData.Interpretation.Point ) )
+		self.assertEqual( s0["P"].data, IECore.V3fVectorData( [p00, p10, p20, p01, p11, p21], IECore.GeometricData.Interpretation.Point ) )
+		self.assertEqual( s1["P"].data, IECore.V3fVectorData( [p01, p11, p21, p02, p12, p22], IECore.GeometricData.Interpretation.Point ) )
 
 	def testSplitsFully( self ) :
 		mesh = IECoreScene.MeshPrimitive.createPlane( imath.Box2f( imath.V2f( 0 ), imath.V2f( 2 ) ), imath.V2i( 2 ) )
@@ -303,8 +316,8 @@ def testSplitsFully( self ) :
 		if s0["s"].data[0] != 'a':
 			s0,s1 = s1,s0
 
-		self.assertEqual( s0["P"].data, IECore.V3fVectorData( [p00, p10, p11, p01, p21, p22, p12], IECore.GeometricData.Interpretation.Point ) )
-		self.assertEqual( s1["P"].data, IECore.V3fVectorData( [p10, p20, p21, p11, p01, p12, p02], IECore.GeometricData.Interpretation.Point ) )
+		self.assertEqual( s0["P"].data, IECore.V3fVectorData( [p00, p10, p01, p11, p21, p12, p22], IECore.GeometricData.Interpretation.Point ) )
+		self.assertEqual( s1["P"].data, IECore.V3fVectorData( [p10, p20, p01, p11, p21, p02, p12], IECore.GeometricData.Interpretation.Point ) )
 
 	def testSplitUsingIndexedPrimitiveVariable( self ) :