mesh_edgebreaker_traversal_decoder.h

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// 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.
//
#ifndef DRACO_COMPRESSION_MESH_MESH_EDGEBREAKER_TRAVERSAL_DECODER_H_
#define DRACO_COMPRESSION_MESH_MESH_EDGEBREAKER_TRAVERSAL_DECODER_H_
 
#include "draco/compression/bit_coders/rans_bit_decoder.h"
#include "draco/compression/mesh/mesh_edgebreaker_decoder.h"
#include "draco/compression/mesh/mesh_edgebreaker_decoder_impl_interface.h"
#include "draco/compression/mesh/mesh_edgebreaker_shared.h"
#include "draco/draco_features.h"
 
namespace draco {
 
typedef RAnsBitDecoder BinaryDecoder;
 
// Default implementation of the edgebreaker traversal decoder that reads the
// traversal data directly from a buffer.
class MeshEdgebreakerTraversalDecoder {
 public:
  MeshEdgebreakerTraversalDecoder()
      : attribute_connectivity_decoders_(nullptr),
        num_attribute_data_(0),
        decoder_impl_(nullptr) {}
  void Init(MeshEdgebreakerDecoderImplInterface *decoder) {
    decoder_impl_ = decoder;
    buffer_.Init(decoder->GetDecoder()->buffer()->data_head(),
                 decoder->GetDecoder()->buffer()->remaining_size(),
                 decoder->GetDecoder()->buffer()->bitstream_version());
  }
 
  // Returns the Draco bitstream version.
  uint16_t BitstreamVersion() const {
    return decoder_impl_->GetDecoder()->bitstream_version();
  }
 
  // Used to tell the decoder what is the number of expected decoded vertices.
  // Ignored by default.
  void SetNumEncodedVertices(int /* num_vertices */) {}
 
  // Set the number of non-position attribute data for which we need to decode
  // the connectivity.
  void SetNumAttributeData(int num_data) { num_attribute_data_ = num_data; }
 
  // Called before the traversal decoding is started.
  // Returns a buffer decoder that points to data that was encoded after the
  // traversal.
  bool Start(DecoderBuffer *out_buffer) {
    // Decode symbols from the main buffer decoder and face configurations from
    // the start_face_buffer decoder.
    if (!DecodeTraversalSymbols()) {
      return false;
    }
 
    if (!DecodeStartFaces()) {
      return false;
    }
 
    if (!DecodeAttributeSeams()) {
      return false;
    }
    *out_buffer = buffer_;
    return true;
  }
 
  // Returns the configuration of a new initial face.
  inline bool DecodeStartFaceConfiguration() {
    uint32_t face_configuration;
#ifdef DRACO_BACKWARDS_COMPATIBILITY_SUPPORTED
    if (buffer_.bitstream_version() < DRACO_BITSTREAM_VERSION(2, 2)) {
      start_face_buffer_.DecodeLeastSignificantBits32(1, &face_configuration);
 
    } else
#endif
    {
      face_configuration = start_face_decoder_.DecodeNextBit();
    }
    return face_configuration;
  }
 
  // Returns the next edgebreaker symbol that was reached during the traversal.
  inline uint32_t DecodeSymbol() {
    uint32_t symbol;
    symbol_buffer_.DecodeLeastSignificantBits32(1, &symbol);
    if (symbol == TOPOLOGY_C) {
      return symbol;
    }
    // Else decode two additional bits.
    uint32_t symbol_suffix;
    symbol_buffer_.DecodeLeastSignificantBits32(2, &symbol_suffix);
    symbol |= (symbol_suffix << 1);
    return symbol;
  }
 
  // Called whenever a new active corner is set in the decoder.
  inline void NewActiveCornerReached(CornerIndex /* corner */) {}
 
  // Called whenever |source| vertex is about to be merged into the |dest|
  // vertex.
  inline void MergeVertices(VertexIndex /* dest */, VertexIndex /* source */) {}
 
  // Returns true if there is an attribute seam for the next processed pair
  // of visited faces.
  // |attribute| is used to mark the id of the non-position attribute (in range
  // of <0, num_attributes - 1>).
  inline bool DecodeAttributeSeam(int attribute) {
    return attribute_connectivity_decoders_[attribute].DecodeNextBit();
  }
 
  // Called when the traversal is finished.
  void Done() {
    if (symbol_buffer_.bit_decoder_active()) {
      symbol_buffer_.EndBitDecoding();
    }
#ifdef DRACO_BACKWARDS_COMPATIBILITY_SUPPORTED
    if (buffer_.bitstream_version() < DRACO_BITSTREAM_VERSION(2, 2)) {
      start_face_buffer_.EndBitDecoding();
 
    } else
#endif
    {
      start_face_decoder_.EndDecoding();
    }
  }
 
 protected:
  DecoderBuffer *buffer() { return &buffer_; }
 
  bool DecodeTraversalSymbols() {
    uint64_t traversal_size;
    symbol_buffer_ = buffer_;
    if (!symbol_buffer_.StartBitDecoding(true, &traversal_size)) {
      return false;
    }
    buffer_ = symbol_buffer_;
    if (traversal_size > static_cast<uint64_t>(buffer_.remaining_size())) {
      return false;
    }
    buffer_.Advance(traversal_size);
    return true;
  }
 
  bool DecodeStartFaces() {
    // Create a decoder that is set to the end of the encoded traversal data.
#ifdef DRACO_BACKWARDS_COMPATIBILITY_SUPPORTED
    if (buffer_.bitstream_version() < DRACO_BITSTREAM_VERSION(2, 2)) {
      start_face_buffer_ = buffer_;
      uint64_t traversal_size;
      if (!start_face_buffer_.StartBitDecoding(true, &traversal_size)) {
        return false;
      }
      buffer_ = start_face_buffer_;
      if (traversal_size > static_cast<uint64_t>(buffer_.remaining_size())) {
        return false;
      }
      buffer_.Advance(traversal_size);
      return true;
    }
#endif
    return start_face_decoder_.StartDecoding(&buffer_);
  }
 
  bool DecodeAttributeSeams() {
    // Prepare attribute decoding.
    if (num_attribute_data_ > 0) {
      attribute_connectivity_decoders_ = std::unique_ptr<BinaryDecoder[]>(
          new BinaryDecoder[num_attribute_data_]);
      for (int i = 0; i < num_attribute_data_; ++i) {
        if (!attribute_connectivity_decoders_[i].StartDecoding(&buffer_)) {
          return false;
        }
      }
    }
    return true;
  }
 
 private:
  // Buffer that contains the encoded data.
  DecoderBuffer buffer_;
  DecoderBuffer symbol_buffer_;
  BinaryDecoder start_face_decoder_;
  DecoderBuffer start_face_buffer_;
  std::unique_ptr<BinaryDecoder[]> attribute_connectivity_decoders_;
  int num_attribute_data_;
  const MeshEdgebreakerDecoderImplInterface *decoder_impl_;
};
 
}  // namespace draco
 
#endif  // DRACO_COMPRESSION_MESH_MESH_EDGEBREAKER_TRAVERSAL_DECODER_H_