OpenSubdiv: Refactor, move topology refiner to own folder

In the future factory will also be moved there.

3 files changed, 762 insertions, 0 deletions

diff --git a/intern/opensubdiv/internal/topology/topology_refiner_capi.cc b/intern/opensubdiv/internal/topology/topology_refiner_capi.cc
new file mode 100644
index 00000000000..ff58ac68866
--- /dev/null
+++ b/intern/opensubdiv/internal/topology/topology_refiner_capi.cc
@@ -0,0 +1,672 @@
+// Copyright 2018 Blender Foundation. All rights reserved.
+//
+// This program is free software; you can redistribute it and/or
+// modify it under the terms of the GNU General Public License
+// as published by the Free Software Foundation; either version 2
+// of the License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program; if not, write to the Free Software Foundation,
+// Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+//
+// Author: Sergey Sharybin
+
+#include "opensubdiv_topology_refiner_capi.h"
+
+#include "MEM_guardedalloc.h"
+#include "internal/opensubdiv_converter_factory.h"
+#include "internal/opensubdiv_converter_internal.h"
+#include "internal/opensubdiv_edge_map.h"
+#include "internal/opensubdiv_internal.h"
+#include "internal/opensubdiv_util.h"
+#include "internal/topology/topology_refiner_impl.h"
+
+using blender::opensubdiv::vector;
+
+namespace {
+
+const OpenSubdiv::Far::TopologyRefiner *getOSDTopologyRefiner(
+    const OpenSubdiv_TopologyRefiner *topology_refiner)
+{
+  return topology_refiner->impl->osd_topology_refiner;
+}
+
+const OpenSubdiv::Far::TopologyLevel *getOSDTopologyBaseLevel(
+    const OpenSubdiv_TopologyRefiner *topology_refiner)
+{
+  return &getOSDTopologyRefiner(topology_refiner)->GetLevel(0);
+}
+
+int getSubdivisionLevel(const OpenSubdiv_TopologyRefiner *topology_refiner)
+{
+  return topology_refiner->impl->settings.level;
+}
+
+bool getIsAdaptive(const OpenSubdiv_TopologyRefiner *topology_refiner)
+{
+  return topology_refiner->impl->settings.is_adaptive;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Query basic topology information from base level.
+
+int getNumVertices(const OpenSubdiv_TopologyRefiner *topology_refiner)
+{
+  return getOSDTopologyBaseLevel(topology_refiner)->GetNumVertices();
+}
+
+int getNumEdges(const OpenSubdiv_TopologyRefiner *topology_refiner)
+{
+  return getOSDTopologyBaseLevel(topology_refiner)->GetNumEdges();
+}
+
+int getNumFaces(const OpenSubdiv_TopologyRefiner *topology_refiner)
+{
+  return getOSDTopologyBaseLevel(topology_refiner)->GetNumFaces();
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// PTex face geometry queries.
+
+static void convertArrayToRaw(const OpenSubdiv::Far::ConstIndexArray &array, int *raw_array)
+{
+  for (int i = 0; i < array.size(); ++i) {
+    raw_array[i] = array[i];
+  }
+}
+
+int getNumFaceVertices(const OpenSubdiv_TopologyRefiner *topology_refiner, const int face_index)
+{
+  const OpenSubdiv::Far::TopologyLevel *base_level = getOSDTopologyBaseLevel(topology_refiner);
+  return base_level->GetFaceVertices(face_index).size();
+}
+
+void getFaceVertices(const OpenSubdiv_TopologyRefiner *topology_refiner,
+                     const int face_index,
+                     int *face_vertices_indices)
+{
+  const OpenSubdiv::Far::TopologyLevel *base_level = getOSDTopologyBaseLevel(topology_refiner);
+  OpenSubdiv::Far::ConstIndexArray array = base_level->GetFaceVertices(face_index);
+  convertArrayToRaw(array, face_vertices_indices);
+}
+
+int getNumFaceEdges(const OpenSubdiv_TopologyRefiner *topology_refiner, const int face_index)
+{
+  const OpenSubdiv::Far::TopologyLevel *base_level = getOSDTopologyBaseLevel(topology_refiner);
+  return base_level->GetFaceEdges(face_index).size();
+}
+
+void getFaceEdges(const OpenSubdiv_TopologyRefiner *topology_refiner,
+                  const int face_index,
+                  int *face_edges_indices)
+{
+  const OpenSubdiv::Far::TopologyLevel *base_level = getOSDTopologyBaseLevel(topology_refiner);
+  OpenSubdiv::Far::ConstIndexArray array = base_level->GetFaceEdges(face_index);
+  convertArrayToRaw(array, face_edges_indices);
+}
+
+void getEdgeVertices(const OpenSubdiv_TopologyRefiner *topology_refiner,
+                     const int edge_index,
+                     int edge_vertices_indices[2])
+{
+  const OpenSubdiv::Far::TopologyLevel *base_level = getOSDTopologyBaseLevel(topology_refiner);
+  OpenSubdiv::Far::ConstIndexArray array = base_level->GetEdgeVertices(edge_index);
+  assert(array.size() == 2);
+  edge_vertices_indices[0] = array[0];
+  edge_vertices_indices[1] = array[1];
+}
+
+int getNumVertexEdges(const OpenSubdiv_TopologyRefiner *topology_refiner, const int vertex_index)
+{
+  const OpenSubdiv::Far::TopologyLevel *base_level = getOSDTopologyBaseLevel(topology_refiner);
+  return base_level->GetVertexEdges(vertex_index).size();
+}
+
+void getVertexEdges(const OpenSubdiv_TopologyRefiner *topology_refiner,
+                    const int vertex_index,
+                    int *vertex_edges_indices)
+{
+  const OpenSubdiv::Far::TopologyLevel *base_level = getOSDTopologyBaseLevel(topology_refiner);
+  OpenSubdiv::Far::ConstIndexArray array = base_level->GetVertexEdges(vertex_index);
+  convertArrayToRaw(array, vertex_edges_indices);
+}
+
+int getNumFacePtexFaces(const OpenSubdiv_TopologyRefiner *topology_refiner, const int face_index)
+{
+  const int num_face_vertices = topology_refiner->getNumFaceVertices(topology_refiner, face_index);
+  if (num_face_vertices == 4) {
+    return 1;
+  }
+  else {
+    return num_face_vertices;
+  }
+}
+
+int getNumPtexFaces(const OpenSubdiv_TopologyRefiner *topology_refiner)
+{
+  const int num_faces = topology_refiner->getNumFaces(topology_refiner);
+  int num_ptex_faces = 0;
+  for (int face_index = 0; face_index < num_faces; ++face_index) {
+    num_ptex_faces += topology_refiner->getNumFacePtexFaces(topology_refiner, face_index);
+  }
+  return num_ptex_faces;
+}
+
+void fillFacePtexIndexOffset(const OpenSubdiv_TopologyRefiner *topology_refiner,
+                             int *face_ptex_index_offset)
+{
+  const int num_faces = topology_refiner->getNumFaces(topology_refiner);
+  int num_ptex_faces = 0;
+  for (int face_index = 0; face_index < num_faces; ++face_index) {
+    face_ptex_index_offset[face_index] = num_ptex_faces;
+    num_ptex_faces += topology_refiner->getNumFacePtexFaces(topology_refiner, face_index);
+  }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Face-varying data.
+
+int getNumFVarChannels(const struct OpenSubdiv_TopologyRefiner *topology_refiner)
+{
+  const OpenSubdiv::Far::TopologyLevel *base_level = getOSDTopologyBaseLevel(topology_refiner);
+  return base_level->GetNumFVarChannels();
+}
+
+OpenSubdiv_FVarLinearInterpolation getFVarLinearInterpolation(
+    const struct OpenSubdiv_TopologyRefiner *topology_refiner)
+{
+  return blender::opensubdiv::getCAPIFVarLinearInterpolationFromOSD(
+      getOSDTopologyRefiner(topology_refiner)->GetFVarLinearInterpolation());
+}
+
+int getNumFVarValues(const struct OpenSubdiv_TopologyRefiner *topology_refiner, const int channel)
+{
+  const OpenSubdiv::Far::TopologyLevel *base_level = getOSDTopologyBaseLevel(topology_refiner);
+  return base_level->GetNumFVarValues(channel);
+}
+
+const int *getFaceFVarValueIndices(const struct OpenSubdiv_TopologyRefiner *topology_refiner,
+                                   const int face_index,
+                                   const int channel)
+{
+  const OpenSubdiv::Far::TopologyLevel *base_level = getOSDTopologyBaseLevel(topology_refiner);
+  return &base_level->GetFaceFVarValues(face_index, channel)[0];
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Internal helpers.
+
+void assignFunctionPointers(OpenSubdiv_TopologyRefiner *topology_refiner)
+{
+  topology_refiner->getSubdivisionLevel = getSubdivisionLevel;
+  topology_refiner->getIsAdaptive = getIsAdaptive;
+  // Basic topology information.
+  topology_refiner->getNumVertices = getNumVertices;
+  topology_refiner->getNumEdges = getNumEdges;
+  topology_refiner->getNumFaces = getNumFaces;
+  topology_refiner->getNumFaceVertices = getNumFaceVertices;
+  topology_refiner->getFaceVertices = getFaceVertices;
+  topology_refiner->getNumFaceEdges = getNumFaceEdges;
+  topology_refiner->getFaceEdges = getFaceEdges;
+  topology_refiner->getEdgeVertices = getEdgeVertices;
+  topology_refiner->getNumVertexEdges = getNumVertexEdges;
+  topology_refiner->getVertexEdges = getVertexEdges;
+  // PTex face geometry.
+  topology_refiner->getNumFacePtexFaces = getNumFacePtexFaces;
+  topology_refiner->getNumPtexFaces = getNumPtexFaces;
+  topology_refiner->fillFacePtexIndexOffset = fillFacePtexIndexOffset;
+  // Face-varying data.
+  topology_refiner->getNumFVarChannels = getNumFVarChannels;
+  topology_refiner->getFVarLinearInterpolation = getFVarLinearInterpolation;
+  topology_refiner->getNumFVarValues = getNumFVarValues;
+  topology_refiner->getFaceFVarValueIndices = getFaceFVarValueIndices;
+}
+
+OpenSubdiv_TopologyRefiner *allocateTopologyRefiner()
+{
+  OpenSubdiv_TopologyRefiner *topology_refiner = OBJECT_GUARDED_NEW(OpenSubdiv_TopologyRefiner);
+  topology_refiner->impl = OBJECT_GUARDED_NEW(OpenSubdiv_TopologyRefinerImpl);
+  assignFunctionPointers(topology_refiner);
+  return topology_refiner;
+}
+
+}  // namespace
+
+OpenSubdiv_TopologyRefiner *openSubdiv_createTopologyRefinerFromConverter(
+    OpenSubdiv_Converter *converter, const OpenSubdiv_TopologyRefinerSettings *settings)
+{
+  OpenSubdiv::Far::TopologyRefiner *osd_topology_refiner =
+      blender::opensubdiv::createOSDTopologyRefinerFromConverter(converter);
+  if (osd_topology_refiner == NULL) {
+    // Happens on empty or bad topology.
+    return NULL;
+  }
+  OpenSubdiv_TopologyRefiner *topology_refiner = allocateTopologyRefiner();
+  topology_refiner->impl->osd_topology_refiner = osd_topology_refiner;
+  // Store setting which we want to keep track of and which can not be stored
+  // in OpenSubdiv's descriptor yet.
+  topology_refiner->impl->settings = *settings;
+  return topology_refiner;
+}
+
+void openSubdiv_deleteTopologyRefiner(OpenSubdiv_TopologyRefiner *topology_refiner)
+{
+  OBJECT_GUARDED_DELETE(topology_refiner->impl, OpenSubdiv_TopologyRefinerImpl);
+  OBJECT_GUARDED_DELETE(topology_refiner, OpenSubdiv_TopologyRefiner);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+// Comparison with converter.
+
+namespace blender {
+namespace opensubdiv {
+namespace {
+
+///////////////////////////////////////////////////////////
+// Quick preliminary checks.
+
+bool checkSchemeTypeMatches(const OpenSubdiv::Far::TopologyRefiner *topology_refiner,
+                            const OpenSubdiv_Converter *converter)
+{
+  const OpenSubdiv::Sdc::SchemeType converter_scheme_type =
+      blender::opensubdiv::getSchemeTypeFromCAPI(converter->getSchemeType(converter));
+  return (converter_scheme_type == topology_refiner->GetSchemeType());
+}
+
+bool checkOptionsMatches(const OpenSubdiv::Far::TopologyRefiner *topology_refiner,
+                         const OpenSubdiv_Converter *converter)
+{
+  typedef OpenSubdiv::Sdc::Options Options;
+  const Options options = topology_refiner->GetSchemeOptions();
+  const Options::FVarLinearInterpolation fvar_interpolation = options.GetFVarLinearInterpolation();
+  const Options::FVarLinearInterpolation converter_fvar_interpolation =
+      blender::opensubdiv::getFVarLinearInterpolationFromCAPI(
+          converter->getFVarLinearInterpolation(converter));
+  if (fvar_interpolation != converter_fvar_interpolation) {
+    return false;
+  }
+  return true;
+}
+
+bool checkGeometryCountersMatches(const OpenSubdiv::Far::TopologyRefiner *topology_refiner,
+                                  const OpenSubdiv_Converter *converter)
+{
+  using OpenSubdiv::Far::TopologyLevel;
+  const TopologyLevel &base_level = topology_refiner->GetLevel(0);
+  return ((converter->getNumVertices(converter) == base_level.GetNumVertices()) &&
+          (converter->getNumEdges(converter) == base_level.GetNumEdges()) &&
+          (converter->getNumFaces(converter) == base_level.GetNumFaces()));
+}
+
+bool checkPreliminaryMatches(const OpenSubdiv::Far::TopologyRefiner *topology_refiner,
+                             const OpenSubdiv_Converter *converter)
+{
+  return checkSchemeTypeMatches(topology_refiner, converter) &&
+         checkOptionsMatches(topology_refiner, converter) &&
+         checkGeometryCountersMatches(topology_refiner, converter);
+}
+
+///////////////////////////////////////////////////////////
+// Geometry comparison.
+
+// A thin wrapper around index like array which does cyclic access. This means,
+// it basically does indices[requested_index % num_indices].
+//
+// NOTE: This array does not own the memory.
+//
+// TODO(sergey): Consider moving this to a more reusable place.
+class CyclicArray {
+ public:
+  typedef int value_type;
+  typedef int size_type;
+  static constexpr size_type npos = -1;
+
+  explicit CyclicArray(const std::vector<int> &data) : data_(data.data()), size_(data.size())
+  {
+  }
+
+  explicit CyclicArray(const OpenSubdiv::Far::ConstIndexArray &data)
+      : data_(&data[0]), size_(data.size())
+  {
+  }
+
+  inline value_type operator[](int index) const
+  {
+    assert(index >= 0);
+    // TODO(sergey): Check whether doing check for element index exceeding total
+    // number of indices prior to modulo helps performance.
+    return data_[index % size()];
+  }
+
+  inline size_type size() const
+  {
+    return size_;
+  }
+
+  // Find index of first occurrence of a given value.
+  inline size_type find(const value_type value) const
+  {
+    const int num_indices = size();
+    for (size_type i = 0; i < num_indices; ++i) {
+      if (value == (*this)[i]) {
+        return i;
+      }
+    }
+    return npos;
+  }
+
+ protected:
+  const value_type *data_;
+  const size_type size_;
+};
+
+bool compareCyclicForward(const CyclicArray &array_a,
+                          const int start_a,
+                          const CyclicArray &array_b,
+                          const int start_b)
+{
+  const int num_elements = array_a.size();
+  for (int i = 0; i < num_elements; ++i) {
+    if (array_a[start_a + i] != array_b[start_b + i]) {
+      return false;
+    }
+  }
+  return true;
+}
+
+bool compareCyclicBackward(const CyclicArray &array_a,
+                           const int start_a,
+                           const CyclicArray &array_b,
+                           const int start_b)
+{
+  const int num_elements = array_a.size();
+  // TODO(sergey): Some optimization might be possible with memcmp trickery.
+  for (int i = 0; i < num_elements; ++i) {
+    if (array_a[start_a + (num_elements - i - 1)] != array_b[start_b + (num_elements - i - 1)]) {
+      return false;
+    }
+  }
+  return true;
+}
+
+// Utility function dedicated for checking whether whether vertices indices
+// used by two faces match.
+// The tricky part here is that we can't trust 1:1 array match here, since it's
+// possible that OpenSubdiv oriented edges of a face to make it compatible with
+// an internal representation of non-manifold meshes.
+//
+// TODO(sergey): Check whether this is needed, ot whether OpenSubdiv is only
+// creating edges in a proper orientation without modifying indices of face
+// vertices.
+bool checkVerticesOfFacesMatch(const CyclicArray &indices_a, const CyclicArray &indices_b)
+{
+  if (indices_a.size() != indices_b.size()) {
+    return false;
+  }
+  // "Align" the arrays so we know first matched element.
+  const int start_b = indices_b.find(indices_a[0]);
+  if (start_b == indices_b.npos) {
+    return false;
+  }
+  // Check match in both directions, for the case OpenSubdiv did orient face in
+  // a way which made normals more consistent internally.
+  if (compareCyclicForward(indices_a, 0, indices_b, start_b)) {
+    return true;
+  }
+  if (compareCyclicBackward(indices_a, 0, indices_b, start_b)) {
+    return true;
+  }
+  return false;
+}
+
+bool checkGeometryFacesMatch(const OpenSubdiv::Far::TopologyRefiner *topology_refiner,
+                             const OpenSubdiv_Converter *converter)
+{
+  using OpenSubdiv::Far::ConstIndexArray;
+  using OpenSubdiv::Far::TopologyLevel;
+  const TopologyLevel &base_level = topology_refiner->GetLevel(0);
+  const int num_faces = base_level.GetNumFaces();
+  // TODO(sergey): Consider using data structure which keeps handful of
+  // elements on stack before doing heep allocation.
+  vector<int> conv_face_vertices;
+  for (int face_index = 0; face_index < num_faces; ++face_index) {
+    const ConstIndexArray &face_vertices = base_level.GetFaceVertices(face_index);
+    const int num_face_vertices = face_vertices.size();
+    if (num_face_vertices != converter->getNumFaceVertices(converter, face_index)) {
+      return false;
+    }
+    conv_face_vertices.resize(num_face_vertices);
+    converter->getFaceVertices(converter, face_index, &conv_face_vertices[0]);
+    if (!checkVerticesOfFacesMatch(CyclicArray(conv_face_vertices), CyclicArray(face_vertices))) {
+      return false;
+    }
+  }
+  return true;
+}
+
+bool checkGeometryMatches(const OpenSubdiv::Far::TopologyRefiner *topology_refiner,
+                          const OpenSubdiv_Converter *converter)
+{
+  // NOTE: Since OpenSubdiv's topology refiner doesn't contain loose edges, we
+  // are only checking for faces to be matched. Changes in edges we don't care
+  // here too much (they'll be checked for creases changes later).
+  return checkGeometryFacesMatch(topology_refiner, converter);
+}
+
+///////////////////////////////////////////////////////////
+// Compare attributes which affects on topology
+
+inline bool checkSingleEdgeSharpnessMatch(const OpenSubdiv::Far::TopologyLevel &base_level,
+                                          int base_level_edge_index,
+                                          const OpenSubdiv_Converter *converter,
+                                          int converter_edge_index)
+{
+  // NOTE: Boundary and non-manifold edges are internally forced to an infinite
+  // sharpness. So we can not reliably compare those.
+  //
+  // TODO(sergey): Watch for NON_MANIFOLD_SHARP option.
+  if (base_level.IsEdgeBoundary(base_level_edge_index) ||
+      base_level.IsEdgeNonManifold(base_level_edge_index)) {
+    return true;
+  }
+  const float sharpness = base_level.GetEdgeSharpness(base_level_edge_index);
+  const float converter_sharpness = converter->getEdgeSharpness(converter, converter_edge_index);
+  if (sharpness != converter_sharpness) {
+    return false;
+  }
+  return true;
+}
+
+inline bool checkSingleEdgeTagMatch(const OpenSubdiv::Far::TopologyLevel &base_level,
+                                    int base_level_edge_index,
+                                    const OpenSubdiv_Converter *converter,
+                                    int converter_edge_index)
+{
+  return checkSingleEdgeSharpnessMatch(
+      base_level, base_level_edge_index, converter, converter_edge_index);
+}
+
+// Compares edge tags between topology refiner and converter in a case when
+// converter specifies a full topology.
+// This is simplest loop, since we know that order of edges matches.
+bool checkEdgeTagsMatchFullTopology(const OpenSubdiv::Far::TopologyRefiner *topology_refiner,
+                                    const OpenSubdiv_Converter *converter)
+{
+  using OpenSubdiv::Far::ConstIndexArray;
+  using OpenSubdiv::Far::TopologyLevel;
+  const TopologyLevel &base_level = topology_refiner->GetLevel(0);
+  const int num_edges = base_level.GetNumEdges();
+  for (int edge_index = 0; edge_index < num_edges; ++edge_index) {
+    if (!checkSingleEdgeTagMatch(base_level, edge_index, converter, edge_index)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+// Compares tags of edges in the case when orientation of edges is left up to
+// OpenSubdiv. In this case we do need to take care of mapping edges from the
+// converter to current topology refiner, since the order is not guaranteed.
+bool checkEdgeTagsMatchAutoOrient(const OpenSubdiv::Far::TopologyRefiner *topology_refiner,
+                                  const OpenSubdiv_Converter *converter)
+{
+  using OpenSubdiv::Far::ConstIndexArray;
+  using OpenSubdiv::Far::TopologyLevel;
+  const TopologyLevel &base_level = topology_refiner->GetLevel(0);
+  const int num_edges = base_level.GetNumEdges();
+  // Create mapping for quick lookup of edge index from its vertices indices.
+  //
+  // TODO(sergey): Consider caching it in some sort of wrapper around topology
+  // refiner.
+  EdgeTagMap<int> edge_map;
+  for (int edge_index = 0; edge_index < num_edges; ++edge_index) {
+    ConstIndexArray edge_vertices = base_level.GetEdgeVertices(edge_index);
+    edge_map.insert(edge_vertices[0], edge_vertices[1], edge_index);
+  }
+  // Compare all edges.
+  for (int converter_edge_index = 0; converter_edge_index < num_edges; ++converter_edge_index) {
+    // Get edge vertices indices, and lookup corresponding edge index in the
+    // base topology level.
+    int edge_vertices[2];
+    converter->getEdgeVertices(converter, converter_edge_index, edge_vertices);
+    const int base_level_edge_index = edge_map.at(edge_vertices[0], edge_vertices[1]);
+    // Perform actual test.
+    if (!checkSingleEdgeTagMatch(
+            base_level, base_level_edge_index, converter, converter_edge_index)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+bool checkEdgeTagsMatch(const OpenSubdiv::Far::TopologyRefiner *topology_refiner,
+                        const OpenSubdiv_Converter *converter)
+{
+  if (converter->specifiesFullTopology(converter)) {
+    return checkEdgeTagsMatchFullTopology(topology_refiner, converter);
+  }
+  else {
+    return checkEdgeTagsMatchAutoOrient(topology_refiner, converter);
+  }
+}
+
+bool checkvertexSharpnessMatch(const OpenSubdiv::Far::TopologyRefiner *topology_refiner,
+                               const OpenSubdiv_Converter *converter)
+{
+  using OpenSubdiv::Far::ConstIndexArray;
+  using OpenSubdiv::Far::TopologyLevel;
+  using OpenSubdiv::Sdc::Crease;
+  const TopologyLevel &base_level = topology_refiner->GetLevel(0);
+  // Create mapping for quick lookup of edge index from its vertices indices.
+  //
+  // TODO(sergey): Consider caching it in some sort of wrapper around topology
+  // refiner.
+  const int num_edges = base_level.GetNumEdges();
+  EdgeTagMap<int> edge_map;
+  for (int edge_index = 0; edge_index < num_edges; ++edge_index) {
+    int edge_vertices[2];
+    converter->getEdgeVertices(converter, edge_index, edge_vertices);
+    edge_map.insert(edge_vertices[0], edge_vertices[1], edge_index);
+  }
+  const int num_vertices = base_level.GetNumVertices();
+  for (int vertex_index = 0; vertex_index < num_vertices; ++vertex_index) {
+    const float current_sharpness = base_level.GetVertexSharpness(vertex_index);
+    if (converter->isInfiniteSharpVertex(converter, vertex_index)) {
+      if (current_sharpness != Crease::SHARPNESS_INFINITE) {
+        return false;
+      }
+    }
+    else {
+      ConstIndexArray vertex_edges = base_level.GetVertexEdges(vertex_index);
+      float sharpness = converter->getVertexSharpness(converter, vertex_index);
+      if (vertex_edges.size() == 2) {
+        const int edge0 = vertex_edges[0], edge1 = vertex_edges[1];
+        // Construct keys for lookup.
+        ConstIndexArray edge0_vertices = base_level.GetEdgeVertices(edge0);
+        ConstIndexArray edge1_vertices = base_level.GetEdgeVertices(edge1);
+        EdgeKey edge0_key(edge0_vertices[0], edge0_vertices[1]);
+        EdgeKey edge1_key(edge1_vertices[0], edge1_vertices[1]);
+        // Lookup edge indices in the converter.
+        const int edge0_converter_index = edge_map[edge0_key];
+        const int edge1_converter_index = edge_map[edge1_key];
+        // Lookup sharpness.
+        const float sharpness0 = converter->getEdgeSharpness(converter, edge0_converter_index);
+        const float sharpness1 = converter->getEdgeSharpness(converter, edge1_converter_index);
+        // TODO(sergey): Find a better mixing between edge and vertex sharpness.
+        sharpness += min(sharpness0, sharpness1);
+        sharpness = min(sharpness, 10.0f);
+      }
+      if (sharpness != current_sharpness) {
+        return false;
+      }
+    }
+  }
+  return true;
+}
+
+bool checkSingleUVLayerMatch(const OpenSubdiv::Far::TopologyLevel &base_level,
+                             const OpenSubdiv_Converter *converter,
+                             const int layer_index)
+{
+  converter->precalcUVLayer(converter, layer_index);
+  const int num_faces = base_level.GetNumFaces();
+  // TODO(sergey): Need to check whether converter changed the winding of
+  // face to match OpenSubdiv's expectations.
+  for (int face_index = 0; face_index < num_faces; ++face_index) {
+    OpenSubdiv::Far::ConstIndexArray base_level_face_uvs = base_level.GetFaceFVarValues(
+        face_index, layer_index);
+    for (int corner = 0; corner < base_level_face_uvs.size(); ++corner) {
+      const int uv_index = converter->getFaceCornerUVIndex(converter, face_index, corner);
+      if (base_level_face_uvs[corner] != uv_index) {
+        converter->finishUVLayer(converter);
+        return false;
+      }
+    }
+  }
+  converter->finishUVLayer(converter);
+  return true;
+}
+
+bool checkUVLayersMatch(const OpenSubdiv::Far::TopologyRefiner *topology_refiner,
+                        const OpenSubdiv_Converter *converter)
+{
+  using OpenSubdiv::Far::TopologyLevel;
+  const int num_layers = converter->getNumUVLayers(converter);
+  const TopologyLevel &base_level = topology_refiner->GetLevel(0);
+  // Number of UV layers should match.
+  if (base_level.GetNumFVarChannels() != num_layers) {
+    return false;
+  }
+  for (int layer_index = 0; layer_index < num_layers; ++layer_index) {
+    if (!checkSingleUVLayerMatch(base_level, converter, layer_index)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+bool checkTopologyAttributesMatch(const OpenSubdiv::Far::TopologyRefiner *topology_refiner,
+                                  const OpenSubdiv_Converter *converter)
+{
+  return checkEdgeTagsMatch(topology_refiner, converter) &&
+         checkvertexSharpnessMatch(topology_refiner, converter) &&
+         checkUVLayersMatch(topology_refiner, converter);
+}
+
+}  // namespace
+}  // namespace opensubdiv
+}  // namespace blender
+
+bool openSubdiv_topologyRefinerCompareWithConverter(
+    const OpenSubdiv_TopologyRefiner *topology_refiner, const OpenSubdiv_Converter *converter)
+{
+  const OpenSubdiv::Far::TopologyRefiner *refiner = getOSDTopologyRefiner(topology_refiner);
+  return (blender::opensubdiv::checkPreliminaryMatches(refiner, converter) &&
+          blender::opensubdiv::checkGeometryMatches(refiner, converter) &&
+          blender::opensubdiv::checkTopologyAttributesMatch(refiner, converter));
+}
diff --git a/intern/opensubdiv/internal/topology/topology_refiner_impl.cc b/intern/opensubdiv/internal/topology/topology_refiner_impl.cc
new file mode 100644
index 00000000000..7d2ae2a6304
--- /dev/null
+++ b/intern/opensubdiv/internal/topology/topology_refiner_impl.cc
@@ -0,0 +1,34 @@
+// Copyright 2016 Blender Foundation. All rights reserved.
+//
+// This program is free software; you can redistribute it and/or
+// modify it under the terms of the GNU General Public License
+// as published by the Free Software Foundation; either version 2
+// of the License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program; if not, write to the Free Software Foundation,
+// Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+//
+// Author: Sergey Sharybin
+
+#include "internal/topology/topology_refiner_impl.h"
+
+namespace blender {
+namespace opensubdiv {
+
+TopologyRefinerImpl::TopologyRefinerImpl() : osd_topology_refiner(nullptr)
+{
+}
+
+TopologyRefinerImpl::~TopologyRefinerImpl()
+{
+  delete osd_topology_refiner;
+}
+
+}  // namespace opensubdiv
+}  // namespace blender
diff --git a/intern/opensubdiv/internal/topology/topology_refiner_impl.h b/intern/opensubdiv/internal/topology/topology_refiner_impl.h
new file mode 100644
index 00000000000..507f3d0f869
--- /dev/null
+++ b/intern/opensubdiv/internal/topology/topology_refiner_impl.h
@@ -0,0 +1,56 @@
+// Copyright 2016 Blender Foundation. All rights reserved.
+//
+// This program is free software; you can redistribute it and/or
+// modify it under the terms of the GNU General Public License
+// as published by the Free Software Foundation; either version 2
+// of the License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program; if not, write to the Free Software Foundation,
+// Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+//
+// Author: Sergey Sharybin
+
+#ifndef OPENSUBDIV_TOPOLOGY_REFINER_IMPL_H_
+#define OPENSUBDIV_TOPOLOGY_REFINER_IMPL_H_
+
+#ifdef _MSC_VER
+#  include <iso646.h>
+#endif
+
+#include <opensubdiv/far/topologyRefiner.h>
+
+#include "opensubdiv_topology_refiner_capi.h"
+
+namespace blender {
+namespace opensubdiv {
+
+class TopologyRefinerImpl {
+ public:
+  TopologyRefinerImpl();
+  ~TopologyRefinerImpl();
+
+  OpenSubdiv::Far::TopologyRefiner *osd_topology_refiner;
+
+  // Subdivision settingsa this refiner is created for.
+  //
+  // We store it here since OpenSubdiv's refiner will only know about level and
+  // "adaptivity" after performing actual "refine" step.
+  //
+  // Ideally, we would also support refining topology without re-importing it
+  // from external world, but that is for later.
+  OpenSubdiv_TopologyRefinerSettings settings;
+};
+
+}  // namespace opensubdiv
+}  // namespace blender
+
+struct OpenSubdiv_TopologyRefinerImpl : public blender::opensubdiv::TopologyRefinerImpl {
+};
+
+#endif  // OPENSUBDIV_TOPOLOGY_REFINER_IMPL_H_