draco/compression/mesh/mesh_edgebreaker_decoder_impl.cc

// Copyright 2016 The Draco Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
#include "compression/mesh/mesh_edgebreaker_decoder_impl.h"

#include <algorithm>

#include "compression/attributes/mesh_attribute_indices_encoding_observer.h"
#include "compression/attributes/mesh_traversal_sequencer.h"
#include "compression/attributes/sequential_attribute_decoders_controller.h"
#include "compression/mesh/mesh_edgebreaker_decoder.h"
#include "compression/mesh/mesh_edgebreaker_traversal_predictive_decoder.h"
#include "mesh/corner_table_traversal_processor.h"
#include "mesh/edgebreaker_traverser.h"

namespace draco {

// Types of "free" edges that are used during topology decoding.
// A free edge is an edge that is connected to one face only.
// All edge types are stored in the opposite_corner_id_ array, where each
// edge "e" is uniquely identified by the the opposite corner "C" in its parent
// triangle:
//          *
//         /C\
//        /   \
//       /  e  \
//      *-------*
// For more description about how the edges are used, see comment inside
// ZipConnectivity() method.

// The initial status of all edges.
static constexpr CornerIndex EDGEBREAKER_FREE_EDGE_DEFAULT(kInvalidCornerIndex);

// A mark assigned to free edge that was part of a face encoded as
// with TOPOLOGY_C (or the init face).
static constexpr CornerIndex EDGEBREAKER_FREE_EDGE_A(kInvalidCornerIndex + 1);

// A mark assigned to free edge that was created when processing faces
// with other topologies.
static constexpr CornerIndex EDGEBREAKER_FREE_EDGE_B(kInvalidCornerIndex + 2);

template <class TraversalDecoder>
MeshEdgeBreakerDecoderImpl<TraversalDecoder>::MeshEdgeBreakerDecoderImpl()
    : decoder_(nullptr),
      num_processed_hole_events_(0),
      last_symbol_id_(-1),
      last_vert_id_(-1),
      last_face_id_(-1),
      num_new_vertices_(0),
      num_encoded_vertices_(0) {}

template <class TraversalDecoder>
bool MeshEdgeBreakerDecoderImpl<TraversalDecoder>::Init(
    MeshEdgeBreakerDecoder *decoder) {
  decoder_ = decoder;
  return true;
}

template <class TraversalDecoder>
const MeshAttributeCornerTable *
MeshEdgeBreakerDecoderImpl<TraversalDecoder>::GetAttributeCornerTable(
    int att_id) const {
  for (int i = 0; i < attribute_data_.size(); ++i) {
    const AttributesDecoder *const dec =
        decoder_->attributes_decoder(attribute_data_[i].decoder_id);
    for (int j = 0; j < dec->num_attributes(); ++j) {
      if (dec->GetAttributeId(j) == att_id) {
        if (attribute_data_[i].is_connectivity_used)
          return &attribute_data_[i].connectivity_data;
        return nullptr;
      }
    }
  }
  return nullptr;
}

template <class TraversalDecoder>
const MeshAttributeIndicesEncodingData *
MeshEdgeBreakerDecoderImpl<TraversalDecoder>::GetAttributeEncodingData(
    int att_id) const {
  for (int i = 0; i < attribute_data_.size(); ++i) {
    const AttributesDecoder *const dec =
        decoder_->attributes_decoder(attribute_data_[i].decoder_id);
    for (int j = 0; j < dec->num_attributes(); ++j) {
      if (dec->GetAttributeId(j) == att_id)
        return &attribute_data_[i].encoding_data;
    }
  }
  return &pos_encoding_data_;
}

template <class TraversalDecoder>
bool MeshEdgeBreakerDecoderImpl<TraversalDecoder>::CreateAttributesDecoder(
    int32_t att_decoder_id) {
  int8_t att_data_id;
  if (!decoder_->buffer()->Decode(&att_data_id))
    return false;
  uint8_t decoder_type;
  if (!decoder_->buffer()->Decode(&decoder_type))
    return false;

  if (att_data_id >= 0) {
    attribute_data_[att_data_id].decoder_id = att_decoder_id;
  }

  const Mesh *mesh = decoder_->mesh();
  std::unique_ptr<PointsSequencer> sequencer;

  if (decoder_type == MESH_VERTEX_ATTRIBUTE) {
    // Per-vertex attribute decoder.
    typedef CornerTableTraversalProcessor<CornerTable> AttProcessor;
    typedef MeshAttributeIndicesEncodingObserver<CornerTable> AttObserver;
    // Traverser that is used to generate the encoding order of each attribute.
    typedef EdgeBreakerTraverser<AttProcessor, AttObserver> AttTraverser;

    MeshAttributeIndicesEncodingData *encoding_data = nullptr;
    if (att_data_id < 0) {
      encoding_data = &pos_encoding_data_;
    } else {
      encoding_data = &attribute_data_[att_data_id].encoding_data;
      // Mark the attribute connectivity data invalid to ensure it's not used
      // later on.
      attribute_data_[att_data_id].is_connectivity_used = false;
    }

    std::unique_ptr<MeshTraversalSequencer<AttTraverser>> traversal_sequencer(
        new MeshTraversalSequencer<AttTraverser>(mesh, encoding_data));

    AttTraverser att_traverser;
    AttObserver att_observer(corner_table_.get(), mesh,
                             traversal_sequencer.get(), encoding_data);
    AttProcessor att_processor;

    att_processor.ResetProcessor(corner_table_.get());
    att_traverser.Init(att_processor, att_observer);

    traversal_sequencer->SetTraverser(att_traverser);
    sequencer = std::move(traversal_sequencer);

  } else {
    // Per-corner attribute decoder.
    typedef CornerTableTraversalProcessor<MeshAttributeCornerTable>
        AttProcessor;
    typedef MeshAttributeIndicesEncodingObserver<MeshAttributeCornerTable>
        AttObserver;
    // Traverser that is used to generate the encoding order of each attribute.
    typedef EdgeBreakerTraverser<AttProcessor, AttObserver> AttTraverser;

    std::unique_ptr<MeshTraversalSequencer<AttTraverser>> traversal_sequencer(
        new MeshTraversalSequencer<AttTraverser>(
            mesh, &attribute_data_[att_data_id].encoding_data));

    AttTraverser att_traverser;
    AttObserver att_observer(&attribute_data_[att_data_id].connectivity_data,
                             mesh, traversal_sequencer.get(),
                             &attribute_data_[att_data_id].encoding_data);
    AttProcessor att_processor;

    att_processor.ResetProcessor(
        &attribute_data_[att_data_id].connectivity_data);
    att_traverser.Init(att_processor, att_observer);

    traversal_sequencer->SetTraverser(att_traverser);
    sequencer = std::move(traversal_sequencer);
  }

  if (!sequencer)
    return false;

  std::unique_ptr<SequentialAttributeDecodersController> att_controller(
      new SequentialAttributeDecodersController(std::move(sequencer)));

  decoder_->SetAttributesDecoder(att_decoder_id, std::move(att_controller));
  return true;
}

template <class TraversalDecoder>
bool MeshEdgeBreakerDecoderImpl<TraversalDecoder>::DecodeConnectivity() {
  num_new_vertices_ = 0;
  new_to_parent_vertex_map_.clear();
  uint32_t num_new_verts;
  if (!decoder_->buffer()->Decode(&num_new_verts))
    return false;
  num_new_vertices_ = num_new_verts;

  uint32_t num_encoded_vertices;
  if (!decoder_->buffer()->Decode(&num_encoded_vertices))
    return false;
  num_encoded_vertices_ = num_encoded_vertices;

  uint32_t num_faces;
  if (!decoder_->buffer()->Decode(&num_faces))
    return false;

  // Decode topology (connectivity).
  vertex_traversal_length_.clear();
  corner_table_ = std::unique_ptr<CornerTable>(new CornerTable());
  if (corner_table_ == nullptr)
    return false;
  corner_table_->Reset(num_faces);
  processed_corner_ids_.clear();
  processed_corner_ids_.reserve(num_faces);
  processed_connectivity_corners_.clear();
  processed_connectivity_corners_.reserve(num_faces);
  topology_split_data_.clear();
  hole_event_data_.clear();
  init_face_configurations_.clear();
  init_corners_.clear();

  num_processed_hole_events_ = 0;
  last_symbol_id_ = -1;

  last_face_id_ = -1;
  last_vert_id_ = -1;

  int8_t num_attribute_data;
  if (!decoder_->buffer()->Decode(&num_attribute_data))
    return false;

  attribute_data_.clear();
  // Add one attribute data for each attribute decoder.
  attribute_data_.resize(num_attribute_data);

  uint32_t num_encoded_symbols;
  if (!decoder_->buffer()->Decode(&num_encoded_symbols))
    return false;

  uint32_t num_encoded_split_symbols;
  if (!decoder_->buffer()->Decode(&num_encoded_split_symbols))
    return false;

  // Start with all vertices marked as holes (boundaries).
  // Only vertices decoded with TOPOLOGY_C symbol (and the initial face) will
  // be marked as non hole vertices. We need to allocate the array larger
  // because split symbols can create extra vertices during the decoding
  // process (these extra vertices are then eliminated during deduplication).
  is_vert_hole_.assign(num_encoded_vertices_ + num_encoded_split_symbols, true);

  uint32_t encoded_connectivity_size;
  decoder_->buffer()->Decode(&encoded_connectivity_size);
  DecoderBuffer event_buffer;
  event_buffer.Init(
      decoder_->buffer()->data_head() + encoded_connectivity_size,
      decoder_->buffer()->remaining_size() - encoded_connectivity_size);
  // Decode hole and topology split events.
  int32_t topology_split_decoded_bytes =
      DecodeHoleAndTopologySplitEvents(&event_buffer);
  if (topology_split_decoded_bytes == -1)
    return false;

  traversal_decoder_.Init(this);
  traversal_decoder_.SetNumEncodedVertices(num_encoded_vertices_);
  traversal_decoder_.SetNumAttributeData(num_attribute_data);

  const DecoderBuffer traversal_end_buffer = traversal_decoder_.Start();

  const int num_connectivity_verts = DecodeConnectivity(num_encoded_symbols);
  if (num_connectivity_verts == -1)
    return false;

  // Set the main buffer to the end of the traversal.
  decoder_->buffer()->Init(traversal_end_buffer.data_head(),
                           traversal_end_buffer.remaining_size());

  // Skip topology split data that was already decoded earlier.
  decoder_->buffer()->Advance(topology_split_decoded_bytes);

  // Decode connectivity of non-position attributes.
  if (attribute_data_.size() > 0) {
    for (CornerIndex ci(0); ci < corner_table_->num_corners(); ci += 3) {
      if (!DecodeAttributeConnectivitiesOnFace(ci))
        return false;
    }
  }
  traversal_decoder_.Done();

  // Update vertex to corner mapping on boundary vertices as it was not set
  // correctly in the previous steps.
  for (int i = 0; i < corner_table_->num_vertices(); ++i) {
    if (is_vert_hole_[i]) {
      corner_table_->UpdateVertexToCornerMap(VertexIndex(i));
    }
  }

  // Decode attribute connectivity.
  // Prepare data structure for decoding non-position attribute connectivites.
  for (int i = 0; i < attribute_data_.size(); ++i) {
    attribute_data_[i].connectivity_data.InitEmpty(corner_table_.get());
    // Add all seams.
    for (int32_t c : attribute_data_[i].attribute_seam_corners) {
      attribute_data_[i].connectivity_data.AddSeamEdge(CornerIndex(c));
    }
    // Recompute vertices from the newly added seam edges.
    attribute_data_[i].connectivity_data.RecomputeVertices(nullptr, nullptr);
  }

  pos_encoding_data_.vertex_to_encoded_attribute_value_index_map.resize(
      corner_table_->num_vertices());
  for (int i = 0; i < attribute_data_.size(); ++i) {
    // For non-position attributes, preallocate the vertex to value mapping
    // using the maximum number of vertices from the base corner table and the
    // attribute corner table (since the attribute decoder may use either of
    // it).
    int32_t att_connectivity_verts =
        attribute_data_[i].connectivity_data.num_vertices();
    if (att_connectivity_verts < corner_table_->num_vertices())
      att_connectivity_verts = corner_table_->num_vertices();
    attribute_data_[i]
        .encoding_data.vertex_to_encoded_attribute_value_index_map.resize(
            att_connectivity_verts);
  }
  if (!AssignPointsToCorners())
    return false;
  return true;
}

template <class TraversalDecoder>
bool MeshEdgeBreakerDecoderImpl<TraversalDecoder>::OnAttributesDecoded() {
  return true;
}

template <class TraversalDecoder>
int MeshEdgeBreakerDecoderImpl<TraversalDecoder>::DecodeConnectivity(
    int num_symbols) {
  // Algorithm does the reverse decoding of the symbols encoded with the
  // edgebreaker method. The reverse decoding always keeps track of the active
  // edge identified by its opposite corner (active corner). New faces are
  // always added to this active edge. There may be multiple active corners at
  // one time that either correspond to separate mesh components or to
  // sub-components of one mesh that are going to be merged together using the
  // TOPOLOGY_S symbol. We can store these active edges on a stack, because the
  // decoder always processes only the latest active edge. TOPOLOGY_S then
  // removes the top edge from the stack and TOPOLOGY_E adds a new edge to the
  // stack.
  std::vector<CornerIndex> active_corner_stack;

  // Additional active edges may be added as a result of topology split events.
  // They can be added in arbitrary order, but we always know the split symbol
  // id they belong to, so we can address them using this symbol id.
  std::unordered_map<int, CornerIndex> topology_split_active_corners;

  int num_vertices = 0;
  int num_faces = 0;
  for (int symbol_id = 0; symbol_id < num_symbols; ++symbol_id) {
    const FaceIndex face(num_faces++);
    // Used to flag cases where we need to look for topology split events.
    bool check_topology_split = false;
    const uint32_t symbol = traversal_decoder_.DecodeSymbol();
    if (symbol == TOPOLOGY_C) {
      // Create a new face between two edges on the open boundary.
      // The first edge is opposite to the corner "a" from the image below.
      // The other edge is opposite to the corner "b" that can be reached
      // through a CCW traversal around the vertex "v".
      // One new active boundary edge is created, opposite to the new corner
      // "x".
      //
      //     *-------*
      //    / \     / \
      //   /   \   /   \
      //  /     \ /     \
      // *-------v-------*
      //  \b    /x\    a/
      //   \   /   \   /
      //    \ /  C  \ /
      //     *.......*

      // Find the corner "b" from the corner "a" which is the corner on the
      // top of the active stack.
      const CornerIndex corner_a = active_corner_stack.back();
      CornerIndex corner_b = corner_table_->Previous(corner_a);
      while (corner_table_->Opposite(corner_b) >= 0) {
        corner_b = corner_table_->Previous(corner_table_->Opposite(corner_b));
      }
      // New tip corner.
      const CornerIndex corner(3 * face.value());
      // Update opposite corner mappings.
      SetOppositeCorners(corner_a, corner + 1);
      SetOppositeCorners(corner_b, corner + 2);
      const VertexIndex vertex_x =
          corner_table_->Vertex(corner_table_->Next(corner_a));
      // Update vertex mapping.
      corner_table_->MapCornerToVertex(corner, vertex_x);
      corner_table_->MapCornerToVertex(
          corner + 1, corner_table_->Vertex(corner_table_->Next(corner_b)));
      corner_table_->MapCornerToVertex(
          corner + 2, corner_table_->Vertex(corner_table_->Previous(corner_a)));
      // Mark the vertex |x| as interior.
      is_vert_hole_[vertex_x.value()] = false;
      // Update the corner on the active stack.
      active_corner_stack.back() = corner;
    } else if (symbol == TOPOLOGY_R || symbol == TOPOLOGY_L) {
      // Create a new face extending from the open boundary edge opposite to the
      // corner "a" from the image below. Two new boundary edges are created
      // opposite to corners "r" and "l". New active corner is set to either "r"
      // or "l" depending on the decoded symbol. One new vertex is created
      // at the opposite corner to corner "a".
      //     *-------*
      //    /a\     / \
      //   /   \   /   \
      //  /     \ /     \
      // *-------v-------*
      //  .l   r.
      //   .   .
      //    . .
      //     *
      const CornerIndex corner_a = active_corner_stack.back();

      // First corner on the new face is either corner "l" or "r".
      const CornerIndex corner(3 * face.value());
      CornerIndex opp_corner;
      if (symbol == TOPOLOGY_R) {
        // "r" is the new first corner.
        opp_corner = corner + 2;
      } else {
        // "l" is the new first corner.
        opp_corner = corner + 1;
      }
      SetOppositeCorners(opp_corner, corner_a);
      // Update vertex mapping.
      corner_table_->MapCornerToVertex(opp_corner, VertexIndex(num_vertices++));
      corner_table_->MapCornerToVertex(
          corner_table_->Next(opp_corner),
          corner_table_->Vertex(corner_table_->Previous(corner_a)));
      corner_table_->MapCornerToVertex(
          corner_table_->Previous(opp_corner),
          corner_table_->Vertex(corner_table_->Next(corner_a)));
      active_corner_stack.back() = corner;
      check_topology_split = true;
    } else if (symbol == TOPOLOGY_S) {
      // Create a new face that merges two last active edges from the active
      // stack. No new vertex is created, but two vertices at corners "p" and
      // "n" need to be merged into a single vertex.
      //
      // *-------v-------*
      //  \a   p/x\n   b/
      //   \   /   \   /
      //    \ /  S  \ /
      //     *.......*
      //
      const CornerIndex corner_b = active_corner_stack.back();
      active_corner_stack.pop_back();

      // Corner "a" can correspond either to a normal active edge, or to an edge
      // created from the topology split event.
      const auto it = topology_split_active_corners.find(symbol_id);
      if (it != topology_split_active_corners.end()) {
        // Topology split event. Move the retrieved edge to the stack.
        active_corner_stack.push_back(it->second);
      }
      const CornerIndex corner_a = active_corner_stack.back();
      // First corner on the new face is corner "x" from the image above.
      const CornerIndex corner(3 * face.value());
      // Update the opposite corner mapping.
      SetOppositeCorners(corner_a, corner + 2);
      SetOppositeCorners(corner_b, corner + 1);
      // Update vertices. For the vertex at corner "x", use the vertex id from
      // the corner "p".
      const VertexIndex vertex_p =
          corner_table_->Vertex(corner_table_->Previous(corner_a));
      corner_table_->MapCornerToVertex(corner, vertex_p);
      corner_table_->MapCornerToVertex(
          corner + 1, corner_table_->Vertex(corner_table_->Next(corner_a)));
      corner_table_->MapCornerToVertex(
          corner + 2, corner_table_->Vertex(corner_table_->Previous(corner_b)));
      // Also update the vertex id at corner "n" and all corners that are
      // connected to it in the CCW direction.
      CornerIndex corner_n = corner_table_->Next(corner_b);
      const VertexIndex vertex_n = corner_table_->Vertex(corner_n);
      traversal_decoder_.MergeVertices(vertex_p, vertex_n);
      while (corner_n >= 0) {
        corner_table_->MapCornerToVertex(corner_n, vertex_p);
        corner_n = corner_table_->SwingLeft(corner_n);
      }
      // Make sure the old vertex n is now mapped to an invalid corner (make it
      // isolated).
      corner_table_->MakeVertexIsolated(vertex_n);
      active_corner_stack.back() = corner;
    } else if (symbol == TOPOLOGY_E) {
      const CornerIndex corner(3 * face.value());
      // Create three new vertices at the corners of the new face.
      corner_table_->MapCornerToVertex(corner, VertexIndex(num_vertices++));
      corner_table_->MapCornerToVertex(corner + 1, VertexIndex(num_vertices++));
      corner_table_->MapCornerToVertex(corner + 2, VertexIndex(num_vertices++));
      // Add the tip corner to the active stack.
      active_corner_stack.push_back(corner);
      check_topology_split = true;
    }
    // Inform the traversal decoder that a new corner has been reached.
    traversal_decoder_.NewActiveCornerReached(active_corner_stack.back());

    if (check_topology_split) {
      // Check for topology splits happens only for TOPOLOGY_L, TOPOLOGY_R and
      // TOPOLOGY_E symbols because those are the symbols that correspond to
      // faces that can be directly connected a TOPOLOGY_S face through the
      // topology split event.
      // If a topology split is detected, we need to add a new active edge
      // onto the active_corner_stack because it will be used later when the
      // corresponding TOPOLOGY_S event is decoded.

      // Symbol id used by the encoder (reverse).
      const int encoder_symbol_id = num_symbols - symbol_id - 1;
      EdgeFaceName split_edge;
      int encoder_split_symbol_id;
      while (IsTopologySplit(encoder_symbol_id, &split_edge,
                             &encoder_split_symbol_id)) {
        // Symbol was part of a topology split. Now we need to determine which
        // edge should be added to the active edges stack.
        const CornerIndex act_top_corner = active_corner_stack.back();
        // The current symbol has one active edge (stored in act_top_corner) and
        // two remaining inactive edges that are attached to it.
        //              *
        //             / \
        //  left_edge /   \ right_edge
        //           /     \
        //          *.......*
        //         active_edge

        CornerIndex new_active_corner;
        if (split_edge == RIGHT_FACE_EDGE) {
          new_active_corner = corner_table_->Next(act_top_corner);
        } else {
          new_active_corner = corner_table_->Previous(act_top_corner);
        }
        // Add the new active edge.
        // Convert the encoder split symbol id to decoder symbol id.
        const int decoder_split_symbol_id =
            num_symbols - encoder_split_symbol_id - 1;
        topology_split_active_corners[decoder_split_symbol_id] =
            new_active_corner;
      }
    }
  }

  // Decode start faces and connect them to the faces from the active stack.
  while (active_corner_stack.size() > 0) {
    const CornerIndex corner = active_corner_stack.back();
    active_corner_stack.pop_back();
    const bool interior_face =
        traversal_decoder_.DecodeStartFaceConfiguration();
    if (interior_face) {
      // The start face is interior, we need to find three corners that are
      // opposite to it. The first opposite corner "a" is the corner from the
      // top of the active corner stack and the remaining two corners "b" and
      // "c" can be obtained by circulating around vertices "n" and "p" in CW
      // and CCW directions respectively.
      //
      //           *-------*
      //          / \     / \
      //         /   \   /   \
      //        /     \ /     \
      //       *-------p-------*
      //      / \a    . .    c/ \
      //     /   \   .   .   /   \
      //    /     \ .  I  . /     \
      //   *-------n.......*------*
      //    \     / \     / \     /
      //     \   /   \   /   \   /
      //      \ /     \b/     \ /
      //       *-------*-------*
      //
      // TODO(ostava): The ciruclation below should be replaced by functions
      // that can be reused elsewhere.
      CornerIndex corner_b = corner_table_->Previous(corner);
      while (corner_table_->Opposite(corner_b) >= 0) {
        corner_b = corner_table_->Previous(corner_table_->Opposite(corner_b));
      }
      CornerIndex corner_c = corner_table_->Next(corner);
      while (corner_table_->Opposite(corner_c) >= 0) {
        corner_c = corner_table_->Next(corner_table_->Opposite(corner_c));
      }
      const FaceIndex face(num_faces++);
      // The first corner of the initial face is the corner opposite to "a".
      const CornerIndex new_corner(3 * face.value());
      SetOppositeCorners(new_corner, corner);
      SetOppositeCorners(new_corner + 1, corner_b);
      SetOppositeCorners(new_corner + 2, corner_c);

      // Map new corners to existing vertices.
      corner_table_->MapCornerToVertex(
          new_corner, corner_table_->Vertex(corner_table_->Next(corner_b)));
      corner_table_->MapCornerToVertex(
          new_corner + 1, corner_table_->Vertex(corner_table_->Next(corner_c)));
      corner_table_->MapCornerToVertex(
          new_corner + 2, corner_table_->Vertex(corner_table_->Next(corner)));

      // Mark all three vertices as interior.
      for (int ci = 0; ci < 3; ++ci) {
        is_vert_hole_[corner_table_->Vertex(new_corner + ci).value()] = false;
      }

      init_face_configurations_.push_back(true);
      init_corners_.push_back(new_corner);
    } else {
      // The initial face wasn't interior and the traversal had to start from
      // an open boundary. In this case no new face is added, but we need to
      // keep record about the first opposite corner to this boundary.
      init_face_configurations_.push_back(false);
      init_corners_.push_back(corner);
    }
  }
  vertex_id_map_.resize(num_vertices);
  return num_vertices;
}

template <class TraversalDecoder>
int32_t
MeshEdgeBreakerDecoderImpl<TraversalDecoder>::DecodeHoleAndTopologySplitEvents(
    DecoderBuffer *decoder_buffer) {
  // Prepare a new decoder from the provided buffer offset.
  uint32_t num_topology_splits;
  if (!decoder_buffer->Decode(&num_topology_splits))
    return -1;
  for (int i = 0; i < num_topology_splits; ++i) {
    TopologySplitEventData event_data;
    if (!decoder_buffer->Decode(&event_data.split_symbol_id))
      return -1;
    if (!decoder_buffer->Decode(&event_data.source_symbol_id))
      return -1;
    uint8_t edge_data;
    if (!decoder_buffer->Decode(&edge_data))
      return -1;
    event_data.source_edge = edge_data & 1;
    event_data.split_edge = (edge_data >> 1) & 1;
    topology_split_data_.push_back(event_data);
  }
  uint32_t num_hole_events;
  if (!decoder_buffer->Decode(&num_hole_events))
    return -1;
  for (int i = 0; i < num_hole_events; ++i) {
    HoleEventData event_data;
    if (!decoder_buffer->Decode(&event_data))
      return -1;
    hole_event_data_.push_back(event_data);
  }
  return decoder_buffer->decoded_size();
}

template <class TraversalDecoder>
bool MeshEdgeBreakerDecoderImpl<
    TraversalDecoder>::DecodeAttributeConnectivitiesOnFace(CornerIndex corner) {
  // Three corners of the face.
  const CornerIndex corners[3] = {corner, corner_table_->Next(corner),
                                  corner_table_->Previous(corner)};

  for (int c = 0; c < 3; ++c) {
    const CornerIndex opp_corner = corner_table_->Opposite(corners[c]);
    if (opp_corner < 0) {
      // Don't decode attribute seams on boundary edges (every boundary edge
      // is automatically an attribute seam).
      for (int32_t i = 0; i < attribute_data_.size(); ++i) {
        attribute_data_[i].attribute_seam_corners.push_back(corners[c].value());
      }
      continue;
    }

    for (int32_t i = 0; i < attribute_data_.size(); ++i) {
      const bool is_seam = traversal_decoder_.DecodeAttributeSeam(i);
      if (is_seam)
        attribute_data_[i].attribute_seam_corners.push_back(corners[c].value());
    }
  }
  return true;
}

template <class TraversalDecoder>
bool MeshEdgeBreakerDecoderImpl<TraversalDecoder>::AssignPointsToCorners() {
  // Map between the existing and deduplicated point ids.
  // Note that at this point we have one point id for each corner of the
  // mesh so there is corner_table_->num_corners() point ids.
  decoder_->mesh()->SetNumFaces(corner_table_->num_faces());

  if (attribute_data_.size() == 0) {
    // We have position only. In this case we can simplify the deduplication
    // because the only thing we need to do is to remove isolated vertices that
    // were introduced during the decoding.

    int32_t num_points = 0;
    std::vector<int32_t> vertex_to_point_map(corner_table_->num_vertices(), -1);
    // Add faces.
    for (FaceIndex f(0); f < decoder_->mesh()->num_faces(); ++f) {
      Mesh::Face face;
      for (int c = 0; c < 3; ++c) {
        // Remap old points to the new ones.
        const int32_t vert_id =
            corner_table_->Vertex(CornerIndex(3 * f.value() + c)).value();
        int32_t &point_id = vertex_to_point_map[vert_id];
        if (point_id == -1)
          point_id = num_points++;
        face[c] = point_id;
      }
      decoder_->mesh()->SetFace(f, face);
    }
    decoder_->point_cloud()->set_num_points(num_points);
    return true;
  }
  // Else we need to deduplicate multiple attributes.

  // Map between point id and an associated corner id. Only one corner for
  // each point is stored. The corners are used to sample the attribute values
  // in the last stage of the deduplication.
  std::vector<int32_t> point_to_corner_map;
  // Map between every corner and their new point ids.
  std::vector<int32_t> corner_to_point_map(corner_table_->num_corners());
  for (int v = 0; v < corner_table_->num_vertices(); ++v) {
    CornerIndex c = corner_table_->LeftMostCorner(VertexIndex(v));
    if (c < 0)
      continue;  // Isolated vertex.
    CornerIndex deduplication_first_corner = c;
    if (is_vert_hole_[v]) {
      // If the vertex is on a boundary, start deduplication from the left most
      // corner that is guaranteed to lie on the boundary.
      deduplication_first_corner = c;
    } else {
      // If we are not on the boundary we need to find the first seam (of any
      // attribute).
      for (int i = 0; i < attribute_data_.size(); ++i) {
        if (!attribute_data_[i].connectivity_data.IsCornerOnSeam(c))
          continue;  // No seam for this attribute, ignore it.
        // Else there needs to be at least one seam edge.

        // At this point, we use identity mapping between corners and point ids.
        const VertexIndex vert_id =
            attribute_data_[i].connectivity_data.Vertex(c);
        CornerIndex act_c = corner_table_->SwingRight(c);
        bool seam_found = false;
        while (act_c != c) {
          if (attribute_data_[i].connectivity_data.Vertex(act_c) != vert_id) {
            // Attribute seam found. Stop.
            deduplication_first_corner = act_c;
            seam_found = true;
            break;
          }
          act_c = corner_table_->SwingRight(act_c);
        }
        if (seam_found)
          break;  // No reason to process other attributes if we found a seam.
      }
    }

    // Do a deduplication pass over the corners on the processed vertex.
    // At this point each corner corresponds to one point id and our goal is to
    // merge similar points into a single point id.
    // We do one one pass in a clocwise direction over the corners and we add
    // a new point id whenever one of the attributes change.
    c = deduplication_first_corner;
    // Create a new point.
    corner_to_point_map[c.value()] = point_to_corner_map.size();
    point_to_corner_map.push_back(c.value());
    // Traverse in CW direction.
    CornerIndex prev_c = c;
    c = corner_table_->SwingRight(c);
    while (c >= 0 && c != deduplication_first_corner) {
      bool attribute_seam = false;
      for (int i = 0; i < attribute_data_.size(); ++i) {
        if (attribute_data_[i].connectivity_data.Vertex(c) !=
            attribute_data_[i].connectivity_data.Vertex(prev_c)) {
          // Attribute index changed from the previous corner. We need to add a
          // new point here.
          attribute_seam = true;
          break;
        }
      }
      if (attribute_seam) {
        corner_to_point_map[c.value()] = point_to_corner_map.size();
        point_to_corner_map.push_back(c.value());
      } else {
        corner_to_point_map[c.value()] = corner_to_point_map[prev_c.value()];
      }
      prev_c = c;
      c = corner_table_->SwingRight(c);
    }
  }
  // Add faces.
  for (FaceIndex f(0); f < decoder_->mesh()->num_faces(); ++f) {
    Mesh::Face face;
    for (int c = 0; c < 3; ++c) {
      // Remap old points to the new ones.
      face[c] = corner_to_point_map[3 * f.value() + c];
    }
    decoder_->mesh()->SetFace(f, face);
  }
  decoder_->point_cloud()->set_num_points(point_to_corner_map.size());
  return true;
}

template class MeshEdgeBreakerDecoderImpl<MeshEdgeBreakerTraversalDecoder>;
template class MeshEdgeBreakerDecoderImpl<
    MeshEdgeBreakerTraversalPredictiveDecoder>;

}  // namespace draco