OpenSubdiv: Re-work C-API integration

Main goal is to make API simpler to follow (at least ion terms what
is defined/declared where, as opposite of handful big headers which
includes all the declarations), and also avoid a big set of long and
obscure functions.

Now C-API files are split into smaller ones, following OpenSubdiv
behavior more closely, and also function pointers in structures
used a lot more, which shortens functions names,

UV integration part in GL Mesh is mainly stripped away, it needs
to be done differently. On a related topic, UV coordinates API in
converter needs to be removed as well, we do not need coordinates,
only island connectivity information there.

Additional changes:

- Varying interpolation in evaluator API are temporarily disabled,
  need to extend API somewhere (probably, evaluator's API) to inform
  layout information of vertex data (whether it contains varying
  data, width, stride and such).

- Evaluator now can interpolate face-varying data.
  Only works for adaptive refiner, since some issues in OpenSubdiv
  itself.

Planned changes:

- Remove uv coordinates from TopologyConverter.
- Support evaluation of patches (as opposite to individual coordinates
  as it happens currently).
- Support more flexible layout of varying and face-varying data.
  It is stupid to assume varying is 3 floats and face-varying 2 floats.
- Support of second order derivatives.
- Everything else what i'm missing in this list.

1 files changed, 734 insertions, 0 deletions

diff --git a/intern/opensubdiv/internal/opensubdiv_evaluator_internal.cc b/intern/opensubdiv/internal/opensubdiv_evaluator_internal.cc
new file mode 100644
index 00000000000..595df3eaa75
--- /dev/null
+++ b/intern/opensubdiv/internal/opensubdiv_evaluator_internal.cc
@@ -0,0 +1,734 @@
+// 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 "internal/opensubdiv_evaluator_internal.h"
+
+#include <cassert>
+#include <cstdio>
+#include <vector>
+
+#ifdef _MSC_VER
+#  include <iso646.h>
+#endif
+
+#include <opensubdiv/far/patchMap.h>
+#include <opensubdiv/far/patchTable.h>
+#include <opensubdiv/far/patchTableFactory.h>
+#include <opensubdiv/osd/cpuEvaluator.h>
+#include <opensubdiv/osd/cpuPatchTable.h>
+#include <opensubdiv/osd/cpuVertexBuffer.h>
+#include <opensubdiv/osd/mesh.h>
+#include <opensubdiv/osd/types.h>
+
+#include "MEM_guardedalloc.h"
+
+#include "internal/opensubdiv_topology_refiner_internal.h"
+#include "opensubdiv_topology_refiner_capi.h"
+
+using OpenSubdiv::Osd::BufferDescriptor;
+using OpenSubdiv::Osd::CpuEvaluator;
+using OpenSubdiv::Osd::CpuPatchTable;
+using OpenSubdiv::Osd::CpuVertexBuffer;
+using OpenSubdiv::Osd::PatchCoord;
+using OpenSubdiv::Far::PatchMap;
+using OpenSubdiv::Far::PatchTable;
+using OpenSubdiv::Far::PatchTableFactory;
+using OpenSubdiv::Far::StencilTable;
+using OpenSubdiv::Far::StencilTableFactory;
+using OpenSubdiv::Far::TopologyRefiner;
+
+namespace opensubdiv_capi {
+
+namespace {
+
+// Helper class to wrap numerous of patch coordinates into a buffer.
+// Used to pass coordinates to the CPU evaluator. Other evaluators are not
+// supported.
+class PatchCoordBuffer : public std::vector<PatchCoord> {
+ public:
+  static PatchCoordBuffer* Create(int size) {
+    PatchCoordBuffer* buffer = new PatchCoordBuffer();
+    buffer->resize(size);
+    return buffer;
+  }
+
+  PatchCoord* BindCpuBuffer() {
+    return reinterpret_cast<PatchCoord*>(&(*this)[0]);
+  }
+
+  int GetNumVertices() {
+    return size();
+  }
+
+  void UpdateData(const PatchCoord* patch_coords, int num_patch_coords) {
+    memcpy(&(*this)[0],
+           reinterpret_cast<const void*>(patch_coords),
+           sizeof(PatchCoord) * num_patch_coords);
+  }
+};
+
+// Helper class to wrap single of patch coord into a buffer. Used to pass
+// coordinates to the CPU evaluator. Other evaluators are not supported.
+class SinglePatchCoordBuffer {
+ public:
+  static SinglePatchCoordBuffer* Create() {
+    return new SinglePatchCoordBuffer();
+  }
+
+  SinglePatchCoordBuffer() {
+  }
+
+  explicit SinglePatchCoordBuffer(const PatchCoord &patch_coord)
+      : patch_coord_(patch_coord) {
+  }
+
+  PatchCoord* BindCpuBuffer() {
+    return &patch_coord_;
+  }
+
+  int GetNumVertices() {
+    return 1;
+  }
+
+  void UpdateData(const PatchCoord &patch_coord) {
+    patch_coord_ = patch_coord;
+  }
+
+ protected:
+  PatchCoord patch_coord_;
+};
+
+// Helper class which is aimed to be used in cases when buffer is small enough
+// and better to be allocated in stack rather than in heap.
+//
+// TODO(sergey): Check if bare arrays could be used by CPU evaluator.
+template <int element_size, int num_vertices>
+class StackAllocatedBuffer {
+ public:
+  static PatchCoordBuffer* Create(int /*size*/) {
+    // TODO(sergey): Validate that requested dize is smaller than static
+    // stack memory size.
+    return new StackAllocatedBuffer<element_size, num_vertices>();
+  }
+
+  float* BindCpuBuffer() {
+    return &data_[0];
+  }
+
+  int GetNumVertices() {
+    return num_vertices;
+  }
+
+  // TODO(sergey): Support UpdateData().
+ protected:
+  float data_[element_size * num_vertices];
+};
+
+// Volatile evaluator which can be used from threads.
+//
+// TODO(sergey): Make it possible to evaluate coordinates in chunks.
+// TODO(sergey): Make it possible to evaluate multiple face varying layers.
+//               (or maybe, it's cheap to create new evaluator for existing
+//               topology to evaluate all needed face varying layers?)
+template <typename SRC_VERTEX_BUFFER,
+          typename EVAL_VERTEX_BUFFER,
+          typename STENCIL_TABLE,
+          typename PATCH_TABLE,
+          typename EVALUATOR,
+          typename DEVICE_CONTEXT = void>
+class VolatileEvalOutput {
+ public:
+  typedef OpenSubdiv::Osd::EvaluatorCacheT<EVALUATOR> EvaluatorCache;
+
+  VolatileEvalOutput(const StencilTable* vertex_stencils,
+                     const StencilTable* varying_stencils,
+                     const StencilTable* face_varying_stencils,
+                     const int face_varying_channel,
+                     const int face_varying_width,
+                     const PatchTable* patch_table,
+                     EvaluatorCache* evaluator_cache = NULL,
+                     DEVICE_CONTEXT* device_context = NULL)
+      : src_desc_(0, 3, 3),
+        src_varying_desc_(0, 3, 3),
+        src_face_varying_desc_(0, face_varying_width, face_varying_width),
+        face_varying_channel_(face_varying_channel),
+        face_varying_width_(face_varying_width),
+        evaluator_cache_(evaluator_cache),
+        device_context_(device_context) {
+    // Total number of vertices = coarse points + refined points + local points.
+    int num_total_vertices = vertex_stencils->GetNumControlVertices() +
+                             vertex_stencils->GetNumStencils();
+    num_coarse_vertices_ = vertex_stencils->GetNumControlVertices();
+    using OpenSubdiv::Osd::convertToCompatibleStencilTable;
+    src_data_ =
+        SRC_VERTEX_BUFFER::Create(3, num_total_vertices, device_context_);
+    src_varying_data_ =
+        SRC_VERTEX_BUFFER::Create(3, num_total_vertices, device_context_);
+    patch_table_ = PATCH_TABLE::Create(patch_table, device_context_);
+    patch_coords_ = NULL;
+    vertex_stencils_ = convertToCompatibleStencilTable<STENCIL_TABLE>(
+        vertex_stencils, device_context_);
+    varying_stencils_ = convertToCompatibleStencilTable<STENCIL_TABLE>(
+        varying_stencils, device_context_);
+    if (face_varying_stencils != NULL) {
+      num_coarse_face_varying_vertices_ =
+          face_varying_stencils->GetNumControlVertices();
+      const int num_total_face_varying_vertices =
+          face_varying_stencils->GetNumControlVertices() +
+          face_varying_stencils->GetNumStencils();
+      src_face_varying_data_ =
+          EVAL_VERTEX_BUFFER::Create(2,
+                                     num_total_face_varying_vertices,
+                                     device_context_);
+        face_varying_stencils_ = convertToCompatibleStencilTable<STENCIL_TABLE>(
+            face_varying_stencils, device_context_);
+    } else {
+      num_coarse_face_varying_vertices_ = 0;
+      src_face_varying_data_ = NULL;
+      face_varying_stencils_ = NULL;
+    }
+  }
+
+  ~VolatileEvalOutput() {
+    delete src_data_;
+    delete src_varying_data_;
+    delete src_face_varying_data_;
+    delete patch_table_;
+    delete vertex_stencils_;
+    delete varying_stencils_;
+    delete face_varying_stencils_;
+  }
+
+  // TODO(sergey): Implement binding API.
+
+  void updateData(const float* src, int start_vertex, int num_vertices) {
+    src_data_->UpdateData(src, start_vertex, num_vertices, device_context_);
+  }
+
+  void updateVaryingData(const float* src, int start_vertex, int num_vertices) {
+    src_varying_data_->UpdateData(src,
+                                  start_vertex,
+                                  num_vertices,
+                                  device_context_);
+  }
+
+  void updateFaceVaryingData(const float* src,
+                             int start_vertex,
+                             int num_vertices) {
+    src_face_varying_data_->UpdateData(src,
+                                       start_vertex,
+                                       num_vertices,
+                                       device_context_);
+  }
+
+  bool hasVaryingData() const {
+    // return varying_stencils_ != NULL;
+    // TODO(sergey): Check this based on actual topology.
+    return false;
+  }
+
+  bool hasFaceVaryingData() const {
+    return face_varying_stencils_ != NULL;
+  }
+
+  void refine() {
+    // Evaluate vertex positions.
+    BufferDescriptor dst_desc = src_desc_;
+    dst_desc.offset += num_coarse_vertices_ * src_desc_.stride;
+    const EVALUATOR* eval_instance =
+        OpenSubdiv::Osd::GetEvaluator<EVALUATOR>(evaluator_cache_,
+                                                 src_desc_,
+                                                 dst_desc,
+                                                 device_context_);
+    EVALUATOR::EvalStencils(src_data_, src_desc_,
+                            src_data_, dst_desc,
+                            vertex_stencils_,
+                            eval_instance,
+                            device_context_);
+    // Evaluate varying data.
+    if (hasVaryingData()) {
+      BufferDescriptor dst_varying_desc = src_varying_desc_;
+      dst_varying_desc.offset +=
+          num_coarse_vertices_ * src_varying_desc_.stride;
+      eval_instance = OpenSubdiv::Osd::GetEvaluator<EVALUATOR>(
+          evaluator_cache_,
+          src_varying_desc_,
+          dst_varying_desc,
+          device_context_);
+      EVALUATOR::EvalStencils(src_varying_data_, src_varying_desc_,
+                              src_varying_data_, dst_varying_desc,
+                              varying_stencils_,
+                              eval_instance, device_context_);
+    }
+    // Evaluate face-varying data.
+    if (hasFaceVaryingData()) {
+      BufferDescriptor dst_face_varying_desc = src_face_varying_desc_;
+      dst_face_varying_desc.offset += num_coarse_face_varying_vertices_ *
+                                      src_face_varying_desc_.stride;
+      eval_instance = OpenSubdiv::Osd::GetEvaluator<EVALUATOR>(
+          evaluator_cache_,
+          src_face_varying_desc_,
+          dst_face_varying_desc,
+          device_context_);
+      EVALUATOR::EvalStencils(src_face_varying_data_, src_face_varying_desc_,
+                              src_face_varying_data_, dst_face_varying_desc,
+                              face_varying_stencils_,
+                              eval_instance,
+                              device_context_);
+    }
+  }
+
+  void evalPatchCoord(const PatchCoord& patch_coord, float P[3]) {
+    StackAllocatedBuffer<6, 1> vertex_data;
+    // TODO(sergey): Varying data is interleaved in vertex array, so need to
+    // adjust stride if there is a varying data.
+    // BufferDescriptor vertex_desc(0, 3, 6);
+    BufferDescriptor vertex_desc(0, 3, 3);
+    SinglePatchCoordBuffer patch_coord_buffer(patch_coord);
+    const EVALUATOR* eval_instance =
+        OpenSubdiv::Osd::GetEvaluator<EVALUATOR>(evaluator_cache_,
+                                                 src_desc_,
+                                                 vertex_desc,
+                                                 device_context_);
+    EVALUATOR::EvalPatches(src_data_,
+                           src_desc_,
+                           &vertex_data,
+                           vertex_desc,
+                           patch_coord_buffer.GetNumVertices(),
+                           &patch_coord_buffer,
+                           patch_table_,
+                           eval_instance,
+                           device_context_);
+    const float* refined_vertices = vertex_data.BindCpuBuffer();
+    memcpy(P, refined_vertices, sizeof(float) * 3);
+  }
+
+  void evalPatchesWithDerivatives(const PatchCoord& patch_coord,
+                                  float P[3],
+                                  float dPdu[3], float dPdv[3]) {
+    StackAllocatedBuffer<6, 1> vertex_data, derivatives;
+    // TODO(sergey): Varying data is interleaved in vertex array, so need to
+    // adjust stride if there is a varying data.
+    // BufferDescriptor vertex_desc(0, 3, 6);
+    BufferDescriptor vertex_desc(0, 3, 3);
+    BufferDescriptor du_desc(0, 3, 6), dv_desc(3, 3, 6);
+    SinglePatchCoordBuffer patch_coord_buffer(patch_coord);
+    const EVALUATOR* eval_instance =
+        OpenSubdiv::Osd::GetEvaluator<EVALUATOR>(evaluator_cache_,
+                                                 src_desc_,
+                                                 vertex_desc,
+                                                 du_desc, dv_desc,
+                                                 device_context_);
+    EVALUATOR::EvalPatches(src_data_, src_desc_,
+                           &vertex_data, vertex_desc,
+                           &derivatives, du_desc,
+                           &derivatives, dv_desc,
+                           patch_coord_buffer.GetNumVertices(),
+                           &patch_coord_buffer,
+                           patch_table_,
+                           eval_instance,
+                           device_context_);
+    const float* refined_vertices = vertex_data.BindCpuBuffer();
+    memcpy(P, refined_vertices, sizeof(float) * 3);
+    if (dPdu != NULL || dPdv != NULL) {
+      const float* refined_derivatives = derivatives.BindCpuBuffer();
+      if (dPdu != NULL) {
+        memcpy(dPdu, refined_derivatives, sizeof(float) * 3);
+      }
+      if (dPdv != NULL) {
+        memcpy(dPdv, refined_derivatives + 3, sizeof(float) * 3);
+      }
+    }
+  }
+
+  void evalPatchVarying(const PatchCoord& patch_coord, float varying[3]) {
+    StackAllocatedBuffer<6, 1> varying_data;
+    BufferDescriptor varying_desc(3, 3, 6);
+    SinglePatchCoordBuffer patch_coord_buffer(patch_coord);
+    const EVALUATOR* eval_instance =
+        OpenSubdiv::Osd::GetEvaluator<EVALUATOR>(evaluator_cache_,
+                                                 src_varying_desc_,
+                                                 varying_desc,
+                                                 device_context_);
+    EVALUATOR::EvalPatchesVarying(src_varying_data_, src_varying_desc_,
+                                  &varying_data, varying_desc,
+                                  patch_coord_buffer.GetNumVertices(),
+                                  &patch_coord_buffer,
+                                  patch_table_,
+                                  eval_instance,
+                                  device_context_);
+    const float* refined_varying = varying_data.BindCpuBuffer();
+    memcpy(varying, refined_varying, sizeof(float) * 3);
+  }
+
+  void evalPatchFaceVarying(const PatchCoord& patch_coord,
+                            float face_varying[2]) {
+    StackAllocatedBuffer<2, 1> face_varying_data;
+    BufferDescriptor face_varying_desc(0, 2, 2);
+    SinglePatchCoordBuffer patch_coord_buffer(patch_coord);
+    const EVALUATOR* eval_instance =
+        OpenSubdiv::Osd::GetEvaluator<EVALUATOR>(evaluator_cache_,
+                                                 src_face_varying_desc_,
+                                                 face_varying_desc,
+                                                 device_context_);
+    EVALUATOR::EvalPatchesFaceVarying(
+        src_face_varying_data_, src_face_varying_desc_,
+        &face_varying_data, face_varying_desc,
+        patch_coord_buffer.GetNumVertices(),
+        &patch_coord_buffer,
+        patch_table_,
+        face_varying_channel_,
+        eval_instance,
+        device_context_);
+    const float* refined_face_varying = face_varying_data.BindCpuBuffer();
+    memcpy(face_varying, refined_face_varying, sizeof(float) * 2);
+  }
+
+ private:
+  SRC_VERTEX_BUFFER* src_data_;
+  SRC_VERTEX_BUFFER* src_varying_data_;
+  EVAL_VERTEX_BUFFER* src_face_varying_data_;
+  PatchCoordBuffer* patch_coords_;
+  PATCH_TABLE* patch_table_;
+  BufferDescriptor src_desc_;
+  BufferDescriptor src_varying_desc_;
+  BufferDescriptor src_face_varying_desc_;
+
+  int num_coarse_vertices_;
+  int face_varying_channel_;
+  int face_varying_width_;
+  int num_coarse_face_varying_vertices_;
+
+  const STENCIL_TABLE* vertex_stencils_;
+  const STENCIL_TABLE* varying_stencils_;
+  const STENCIL_TABLE* face_varying_stencils_;
+
+  EvaluatorCache* evaluator_cache_;
+  DEVICE_CONTEXT* device_context_;
+};
+
+}  // namespace
+
+// Note: Define as a class instead of typedcef to make it possible
+// to have anonymous class in opensubdiv_evaluator_internal.h
+class CpuEvalOutput : public VolatileEvalOutput<CpuVertexBuffer,
+                                                CpuVertexBuffer,
+                                                StencilTable,
+                                                CpuPatchTable,
+                                                CpuEvaluator> {
+ public:
+  CpuEvalOutput(const StencilTable* vertex_stencils,
+                const StencilTable* varying_stencils,
+                const StencilTable* face_varying_stencils,
+                const int face_varying_channel,
+                const int face_varying_width,
+                const PatchTable* patch_table,
+                EvaluatorCache* evaluator_cache = NULL)
+      : VolatileEvalOutput<CpuVertexBuffer,
+                           CpuVertexBuffer,
+                           StencilTable,
+                           CpuPatchTable,
+                           CpuEvaluator> (vertex_stencils,
+                                          varying_stencils,
+                                          face_varying_stencils,
+                                          face_varying_channel,
+                                          face_varying_width,
+                                          patch_table,
+                                          evaluator_cache) {
+  }
+};
+
+////////////////////////////////////////////////////////////////////////////////
+// Evaluator wrapper for anonymous API.
+
+CpuEvalOutputAPI::CpuEvalOutputAPI(CpuEvalOutput* implementation,
+                                   OpenSubdiv::Far::PatchMap* patch_map)
+    : implementation_(implementation),
+      patch_map_(patch_map) {
+}
+
+CpuEvalOutputAPI::~CpuEvalOutputAPI() {
+  delete implementation_;
+}
+
+void CpuEvalOutputAPI::setCoarsePositions(const float* positions,
+                                          const int start_vertex_index,
+                                          const int num_vertices) {
+  // TODO(sergey): Add sanity check on indices.
+  implementation_->updateData(positions, start_vertex_index, num_vertices);
+}
+
+void CpuEvalOutputAPI::setVaryingData(const float* varying_data,
+                                      const int start_vertex_index,
+                                      const int num_vertices) {
+  // TODO(sergey): Add sanity check on indices.
+  implementation_->updateVaryingData(varying_data,
+                                     start_vertex_index,
+                                     num_vertices);
+}
+
+void CpuEvalOutputAPI::setFaceVaryingData(const float* face_varying_data,
+                                          const int start_vertex_index,
+                                          const int num_vertices) {
+  // TODO(sergey): Add sanity check on indices.
+  implementation_->updateFaceVaryingData(face_varying_data,
+                                         start_vertex_index,
+                                         num_vertices);
+}
+
+void CpuEvalOutputAPI::setCoarsePositionsFromBuffer(
+    const void* buffer,
+    const int start_offset,
+    const int stride,
+    const int start_vertex_index,
+    const int num_vertices) {
+  // TODO(sergey): Add sanity check on indices.
+  const unsigned char* current_buffer = (unsigned char *)buffer;
+  current_buffer += start_offset;
+  for (int i = 0; i < num_vertices; ++i) {
+    const int current_vertex_index = start_vertex_index + i;
+    implementation_->updateData(reinterpret_cast<const float*>(current_buffer),
+                                current_vertex_index, 1);
+    current_buffer += stride;
+  }
+}
+
+void CpuEvalOutputAPI::setVaryingDataFromBuffer(
+    const void* buffer,
+    const int start_offset,
+    const int stride,
+    const int start_vertex_index,
+    const int num_vertices) {
+  // TODO(sergey): Add sanity check on indices.
+  const unsigned char* current_buffer = (unsigned char *)buffer;
+  current_buffer += start_offset;
+  for (int i = 0; i < num_vertices; ++i) {
+    const int current_vertex_index = start_vertex_index + i;
+    implementation_->updateVaryingData(
+        reinterpret_cast<const float*>(current_buffer),
+        current_vertex_index, 1);
+    current_buffer += stride;
+  }
+}
+
+void CpuEvalOutputAPI::setFaceVaryingDataFromBuffer(
+    const void* buffer,
+    const int start_offset,
+    const int stride,
+    const int start_vertex_index,
+    const int num_vertices) {
+  // TODO(sergey): Add sanity check on indices.
+  const unsigned char* current_buffer = (unsigned char *)buffer;
+  current_buffer += start_offset;
+  for (int i = 0; i < num_vertices; ++i) {
+    const int current_vertex_index = start_vertex_index + i;
+    implementation_->updateFaceVaryingData(
+        reinterpret_cast<const float*>(current_buffer),
+        current_vertex_index, 1);
+    current_buffer += stride;
+  }
+}
+
+void CpuEvalOutputAPI::refine() {
+  implementation_->refine();
+}
+
+void CpuEvalOutputAPI::evaluateLimit(const int ptex_face_index,
+                                     float face_u, float face_v,
+                                     float P[3], float dPdu[3], float dPdv[3]) {
+  assert(face_u >= 0.0f);
+  assert(face_u <= 1.0f);
+  assert(face_v >= 0.0f);
+  assert(face_v <= 1.0f);
+  const PatchTable::PatchHandle* handle =
+      patch_map_->FindPatch(ptex_face_index, face_u, face_v);
+  PatchCoord patch_coord(*handle, face_u, face_v);
+  if (dPdu != NULL || dPdv != NULL) {
+    implementation_->evalPatchesWithDerivatives(patch_coord, P, dPdu, dPdv);
+  } else {
+    implementation_->evalPatchCoord(patch_coord, P);
+  }}
+
+void CpuEvalOutputAPI::evaluateVarying(const int ptex_face_index,
+                                       float face_u, float face_v,
+                                       float varying[3]) {
+  assert(face_u >= 0.0f);
+  assert(face_u <= 1.0f);
+  assert(face_v >= 0.0f);
+  assert(face_v <= 1.0f);
+  const PatchTable::PatchHandle* handle =
+      patch_map_->FindPatch(ptex_face_index, face_u, face_v);
+  PatchCoord patch_coord(*handle, face_u, face_v);
+  implementation_->evalPatchVarying(patch_coord, varying);
+}
+
+void CpuEvalOutputAPI::evaluateFaceVarying(const int ptex_face_index,
+                                           float face_u, float face_v,
+                                           float face_varying[2]) {
+  assert(face_u >= 0.0f);
+  assert(face_u <= 1.0f);
+  assert(face_v >= 0.0f);
+  assert(face_v <= 1.0f);
+  const PatchTable::PatchHandle* handle =
+      patch_map_->FindPatch(ptex_face_index, face_u, face_v);
+  PatchCoord patch_coord(*handle, face_u, face_v);
+  implementation_->evalPatchFaceVarying(patch_coord, face_varying);
+}
+
+}  // namespace opensubdiv_capi
+
+OpenSubdiv_EvaluatorInternal::OpenSubdiv_EvaluatorInternal()
+    : eval_output(NULL),
+      patch_map(NULL),
+      patch_table(NULL) {
+}
+
+OpenSubdiv_EvaluatorInternal::~OpenSubdiv_EvaluatorInternal() {
+  delete eval_output;
+  delete patch_map;
+  delete patch_table;
+}
+
+OpenSubdiv_EvaluatorInternal* openSubdiv_createEvaluatorInternal(
+    OpenSubdiv_TopologyRefiner* topology_refiner) {
+  TopologyRefiner* refiner = topology_refiner->internal->osd_topology_refiner;
+  if (refiner == NULL) {
+    // Happens on bad topology.
+    return NULL;
+  }
+  // TODO(sergey): Base this on actual topology.
+  // const bool bas_varying_data = false;
+  const bool has_face_varying_data =
+      (refiner->GetNumFVarChannels() != 0);
+  const int level = topology_refiner->getSubdivisionLevel(topology_refiner);
+  // TODO(sergey): Query from topology refiner.
+  const bool is_adaptive = topology_refiner->getIsAdaptive(topology_refiner);
+  // Refine the topology with given settings.
+  // TODO(sergey): What if topology is already refined?
+  if (is_adaptive) {
+    TopologyRefiner::AdaptiveOptions options(level);
+    options.considerFVarChannels = has_face_varying_data;
+    options.useInfSharpPatch = false;
+    refiner->RefineAdaptive(options);
+  } else {
+    TopologyRefiner::UniformOptions options(level);
+    refiner->RefineUniform(options);
+  }
+  // Generate stencil table to update the bi-cubic patches control vertices
+  // after they have been re-posed (both for vertex & varying interpolation).
+  //
+  // Vertex stencils.
+  StencilTableFactory::Options vertex_stencil_options;
+  vertex_stencil_options.generateOffsets = true;
+  vertex_stencil_options.generateIntermediateLevels = is_adaptive;
+  const StencilTable* vertex_stencils =
+      StencilTableFactory::Create(*refiner, vertex_stencil_options);
+  // Varying stencils.
+  //
+  // TODO(sergey): Seems currently varying stencils are always required in
+  // OpenSubdiv itself.
+  const StencilTable* varying_stencils = NULL;
+  StencilTableFactory::Options varying_stencil_options;
+  varying_stencil_options.generateOffsets = true;
+  varying_stencil_options.generateIntermediateLevels = is_adaptive;
+  varying_stencil_options.interpolationMode =
+      StencilTableFactory::INTERPOLATE_VARYING;
+  varying_stencils =
+      StencilTableFactory::Create(*refiner, varying_stencil_options);
+  // Face warying stencil.
+  const StencilTable* face_varying_stencils = NULL;
+  if (has_face_varying_data) {
+    StencilTableFactory::Options face_varying_stencil_options;
+    face_varying_stencil_options.generateOffsets = true;
+    face_varying_stencil_options.generateIntermediateLevels = is_adaptive;
+    face_varying_stencil_options.interpolationMode =
+        StencilTableFactory::INTERPOLATE_FACE_VARYING;
+    // TODO(sergey): Make it configurable which face varying channel is being
+    // interpolated.
+    face_varying_stencil_options.fvarChannel = 0;
+    face_varying_stencils =
+        StencilTableFactory::Create(*refiner, face_varying_stencil_options);
+  }
+  // Generate bi-cubic patch table for the limit surface.
+  // TODO(sergey): Ideally we would want to expose end-cap settings via
+  // C-API to make it more generic. Currently it matches old Blender's
+  // subsurf code.
+  PatchTableFactory::Options patch_options(level);
+  patch_options.SetEndCapType(PatchTableFactory::Options::ENDCAP_BSPLINE_BASIS);
+  patch_options.useInfSharpPatch = false;
+  patch_options.generateFVarTables = has_face_varying_data;
+  patch_options.generateFVarLegacyLinearPatches = false;
+  const PatchTable* patch_table = PatchTableFactory::Create(
+      *refiner, patch_options);
+  // Append local points stencils.
+  const StencilTable* local_point_stencil_table =
+      patch_table->GetLocalPointStencilTable();
+  if (local_point_stencil_table != NULL) {
+    const StencilTable* table =
+        StencilTableFactory::AppendLocalPointStencilTable(
+            *refiner, vertex_stencils, local_point_stencil_table);
+    delete vertex_stencils;
+    vertex_stencils = table;
+  }
+  const StencilTable* local_point_varying_stencil_table =
+      patch_table->GetLocalPointVaryingStencilTable();
+  if (local_point_varying_stencil_table != NULL) {
+    const StencilTable* table =
+        StencilTableFactory::AppendLocalPointStencilTable(
+            *refiner, varying_stencils, local_point_varying_stencil_table);
+    delete varying_stencils;
+    varying_stencils = table;
+  }
+  const StencilTable* local_point_face_varying_stencil_table =
+      patch_table->GetLocalPointFaceVaryingStencilTable();
+  if (local_point_face_varying_stencil_table != NULL) {
+    const StencilTable* table =
+        StencilTableFactory::AppendLocalPointStencilTableFaceVarying(
+              *refiner,
+              face_varying_stencils,
+              local_point_face_varying_stencil_table);
+      delete face_varying_stencils;
+      face_varying_stencils = table;
+  }
+  // Create OpenSubdiv's CPU side evaluator.
+  // TODO(sergey): Make it possible to use different evaluators.
+  opensubdiv_capi::CpuEvalOutput* eval_output =
+      new opensubdiv_capi::CpuEvalOutput(vertex_stencils,
+                                         varying_stencils,
+                                         face_varying_stencils,
+                                         0, 2,
+                                         patch_table);
+  OpenSubdiv::Far::PatchMap* patch_map = new PatchMap(*patch_table);
+  // Wrap everything we need into an object which we control from our side.
+  OpenSubdiv_EvaluatorInternal* evaluator_descr;
+  evaluator_descr = OBJECT_GUARDED_NEW(OpenSubdiv_EvaluatorInternal);
+  evaluator_descr->eval_output =
+      new opensubdiv_capi::CpuEvalOutputAPI(eval_output, patch_map);
+  evaluator_descr->patch_map = patch_map;
+  evaluator_descr->patch_table = patch_table;
+  // TOOD(sergey): Look into whether we've got duplicated stencils arrays.
+  delete vertex_stencils;
+  delete varying_stencils;
+  delete face_varying_stencils;
+  return evaluator_descr;
+}
+
+void openSubdiv_deleteEvaluatorInternal(
+    OpenSubdiv_EvaluatorInternal* evaluator) {
+  OBJECT_GUARDED_DELETE(evaluator, OpenSubdiv_EvaluatorInternal);
+}