Method packetWrite

plugins/e57/libE57Format/src/CompressedVectorWriterImpl.cpp:423–619

   }

   uint64_t CompressedVectorWriterImpl::packetWrite()
   {
#ifdef E57_VERBOSE
      std::cout << "CompressedVectorWriterImpl::packetWrite() called" << std::endl; //???
#endif

      // Double check that we have work to do
      const size_t cTotalOutput = totalOutputAvailable();
      if ( cTotalOutput == 0 )
      {
         return ( 0 );
      }

      // const bytestreams_ so it's clear it isn't modified in this function
      const auto &cStreams = bytestreams_;
      const auto cNumByteStreams = cStreams.size();

      // Calc maximum number of bytestream values can put in data packet.
      const size_t cPacketMaxPayloadBytes =
         DATA_PACKET_MAX - sizeof( DataPacketHeader ) - cNumByteStreams * sizeof( uint16_t );

#ifdef E57_VERBOSE
      std::cout << "  totalOutput=" << cTotalOutput << std::endl;
      std::cout << "  cNumByteStreams=" << cNumByteStreams << std::endl;
      std::cout << "  packetMaxPayloadBytes=" << cPacketMaxPayloadBytes << std::endl;
#endif

      // Allocate vector for number of bytes that each bytestream will write to file.
      std::vector<size_t> count( cNumByteStreams );

      // See if we can fit into a single data packet
      if ( cTotalOutput < cPacketMaxPayloadBytes )
      {
         // We can fit everything in one packet
         for ( unsigned i = 0; i < cNumByteStreams; ++i )
         {
            count.at( i ) = cStreams.at( i )->outputAvailable();
         }
      }
      else
      {
         // We have too much data for one packet.  Send proportional amounts from
         // each bytestream. Adjust packetMaxPayloadBytes down by one so have a
         // little slack for floating point weirdness.
         const float cFractionToSend =
            ( cPacketMaxPayloadBytes - 1 ) / static_cast<float>( cTotalOutput );
         for ( unsigned i = 0; i < cNumByteStreams; ++i )
         {
            // Round down here so sum <= packetMaxPayloadBytes
            count.at( i ) = static_cast<unsigned>(
               std::floor( cFractionToSend * cStreams.at( i )->outputAvailable() ) );
         }
      }

#ifdef E57_VERBOSE
      for ( unsigned i = 0; i < cNumByteStreams; ++i )
      {
         std::cout << "  count[" << i << "]=" << count.at( i ) << std::endl;