text: // 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 "draco/compression/mesh/mesh_sequential_decoder.h"
  
  #include "draco/compression/attributes/linear_sequencer.h"
  #include "draco/compression/attributes/sequential_attribute_decoders_controller.h"
  #include "draco/compression/entropy/symbol_decoding.h"
  #include "draco/core/varint_decoding.h"
  
  namespace draco {
  
  MeshSequentialDecoder::MeshSequentialDecoder() {}
  
  bool MeshSequentialDecoder::DecodeConnectivity() {
    uint32_t num_faces;
    uint32_t num_points;
  #ifdef DRACO_BACKWARDS_COMPATIBILITY_SUPPORTED
    if (bitstream_version() < DRACO_BITSTREAM_VERSION(2, 2)) {
      if (!buffer()->Decode(&num_faces)) {
        return false;
      }
      if (!buffer()->Decode(&num_points)) {
        return false;
      }
  
    } else
  #endif
    {
      if (!DecodeVarint(&num_faces, buffer())) {
        return false;
      }
      if (!DecodeVarint(&num_points, buffer())) {
        return false;
      }
    }
  
    // Check that num_faces and num_points are valid values.
    const uint64_t faces_64 = static_cast<uint64_t>(num_faces);
    const uint64_t points_64 = static_cast<uint64_t>(num_points);
    // Compressed sequential encoding can only handle (2^32 - 1) / 3 indices.
    if (faces_64 > 0xffffffff / 3) {
      return false;
    }
    if (faces_64 > buffer()->remaining_size() / 3) {
      // The number of faces is unreasonably high, because face indices do not
      // fit in the remaining size of the buffer.
      return false;
    }
    if (points_64 > faces_64 * 3) {
      return false;
    }
    uint8_t connectivity_method;
    if (!buffer()->Decode(&connectivity_method)) {
      return false;
    }
    if (connectivity_method == 0) {
      if (!DecodeAndDecompressIndices(num_faces)) {
        return false;
      }
    } else {
      if (num_points < 256) {
        // Decode indices as uint8_t.
        for (uint32_t i = 0; i < num_faces; ++i) {
          Mesh::Face face;
          for (int j = 0; j < 3; ++j) {
            uint8_t val;
            if (!buffer()->Decode(&val)) {
              return false;
            }
            face[j] = val;
          }
          mesh()->AddFace(face);
        }
      } else if (num_points < (1 << 16)) {
        // Decode indices as uint16_t.
        for (uint32_t i = 0; i < num_faces; ++i) {
          Mesh::Face face;
          for (int j = 0; j < 3; ++j) {
            uint16_t val;
            if (!buffer()->Decode(&val)) {
              return false;
            }
            face[j] = val;
          }
          mesh()->AddFace(face);
        }
      } else if (mesh()->num_points() < (1 << 21) &&
                 bitstream_version() >= DRACO_BITSTREAM_VERSION(2, 2)) {
        // Decode indices as uint32_t.
        for (uint32_t i = 0; i < num_faces; ++i) {
          Mesh::Face face;
          for (int j = 0; j < 3; ++j) {
            uint32_t val;
            if (!DecodeVarint(&val, buffer())) {
              return false;
            }
            face[j] = val;
          }
          mesh()->AddFace(face);
        }
      } else {
        // Decode faces as uint32_t (default).
        for (uint32_t i = 0; i < num_faces; ++i) {
          Mesh::Face face;
          for (int j = 0; j < 3; ++j) {
            uint32_t val;
            if (!buffer()->Decode(&val)) {
              return false;
            }
            face[j] = val;
          }
          mesh()->AddFace(face);
        }
      }
    }
    point_cloud()->set_num_points(num_points);
    return true;
  }
  
  bool MeshSequentialDecoder::CreateAttributesDecoder(int32_t att_decoder_id) {
    // Always create the basic attribute decoder.
    return SetAttributesDecoder(
        att_decoder_id,
        std::unique_ptr<AttributesDecoder>(
            new SequentialAttributeDecodersController(
                std::unique_ptr<PointsSequencer>(
                    new LinearSequencer(point_cloud()->num_points())))));
  }
  
  bool MeshSequentialDecoder::DecodeAndDecompressIndices(uint32_t num_faces) {
    // Get decoded indices differences that were encoded with an entropy code.
    std::vector<uint32_t> indices_buffer(num_faces * 3);
    if (!DecodeSymbols(num_faces * 3, 1, buffer(), indices_buffer.data())) {
      return false;
    }
    // Reconstruct the indices from the differences.
    // See MeshSequentialEncoder::CompressAndEncodeIndices() for more details.
    int32_t last_index_value = 0;
    int vertex_index = 0;
    for (uint32_t i = 0; i < num_faces; ++i) {
      Mesh::Face face;
      for (int j = 0; j < 3; ++j) {
        const uint32_t encoded_val = indices_buffer[vertex_index++];
        int32_t index_diff = (encoded_val >> 1);
        if (encoded_val & 1) {
          index_diff = -index_diff;
        }
        const int32_t index_value = index_diff + last_index_value;
        face[j] = index_value;
        last_index_value = index_value;
      }
      mesh()->AddFace(face);
    }
    return true;
  }
  
  }  // namespace draco
  