HEVC帧间预测之三——TEncCu::xCheckRDCostMerge2Nx2N函数分析

本文将对实现merge模式的主函数xCheckRDCostMerge2Nx2N进行分析，方便理清merge模式的整个过程。之前的一篇分析了getInterMergeCandidates的具体实现，还有两个比较重要的函数motionCompensation和encodeResAndCalcRdInterCU，将留在后面陆续进行分析，但是根据它们的命名就不难猜出它们的作用，而且事实也是这样，因此对理解merge模式的整个过程没有影响，可以暂时不用去细究具体实现。下面仍然以贴代码及注释的方式来进行分析：

Void TEncCu::xCheckRDCostMerge2Nx2N( TComDataCU*& rpcBestCU, TComDataCU*& rpcTempCU, Bool *earlyDetectionSkipMode )
{
  assert( rpcTempCU->getSlice()->getSliceType() != I_SLICE );
  TComMvField  cMvFieldNeighbours[MRG_MAX_NUM_CANDS << 1]; // double length for mv of both lists
  UChar uhInterDirNeighbours[MRG_MAX_NUM_CANDS];
  Int numValidMergeCand = 0;
  for( UInt ui = 0; ui < rpcTempCU->getSlice()->getMaxNumMergeCand(); ++ui )
  {
    uhInterDirNeighbours[ui] = 0;
  }
  UChar uhDepth = rpcTempCU->getDepth( 0 );
  rpcTempCU->setPartSizeSubParts( SIZE_2Nx2N, 0, uhDepth ); // interprets depth relative to LCU level
  rpcTempCU->setCUTransquantBypassSubParts( m_pcEncCfg->getCUTransquantBypassFlagValue(), 0, uhDepth );
  rpcTempCU->getInterMergeCandidates( 0, 0, cMvFieldNeighbours,uhInterDirNeighbours, numValidMergeCand );
  //! 创建一个merging candidates的列表
  Int mergeCandBuffer[MRG_MAX_NUM_CANDS];
  for( UInt ui = 0; ui < rpcTempCU->getSlice()->getMaxNumMergeCand(); ++ui )
  {
    mergeCandBuffer[ui] = 0;
  }
  Bool bestIsSkip = false;
  UInt iteration;
  if ( rpcTempCU->isLosslessCoded(0)) //!< 默认为false
  {
    iteration = 1;
  }
  else 
  {
    iteration = 2;
  }
  for( UInt uiNoResidual = 0; uiNoResidual < iteration; ++uiNoResidual )
  {
    for( UInt uiMergeCand = 0; uiMergeCand < numValidMergeCand; ++uiMergeCand ) //!< 遍历所有merging candidates
    {
      {
        if(!(uiNoResidual==1 && mergeCandBuffer[uiMergeCand]==1)) //!< uiNoResidual等于0或者mergeCandBuffer[uiMergeCand]等于0时条件成立
        {
        if( !(bestIsSkip && uiNoResidual == 0) ) //!< bestIsSkip等于false或者uiNoResidual等于1时条件成立
        {
          // set MC parameters
          rpcTempCU->setPredModeSubParts( MODE_INTER, 0, uhDepth ); // interprets depth relative to LCU level
          rpcTempCU->setCUTransquantBypassSubParts( m_pcEncCfg->getCUTransquantBypassFlagValue(),     0, uhDepth );
          rpcTempCU->setPartSizeSubParts( SIZE_2Nx2N, 0, uhDepth ); // interprets depth relative to LCU level
          rpcTempCU->setMergeFlagSubParts( true, 0, 0, uhDepth ); // interprets depth relative to LCU level
          rpcTempCU->setMergeIndexSubParts( uiMergeCand, 0, 0, uhDepth ); // interprets depth relative to LCU level
          rpcTempCU->setInterDirSubParts( uhInterDirNeighbours[uiMergeCand], 0, 0, uhDepth ); // interprets depth relative to LCU level
          rpcTempCU->getCUMvField( REF_PIC_LIST_0 )->setAllMvField( cMvFieldNeighbours[0 + 2*uiMergeCand], SIZE_2Nx2N, 0, 0 ); // interprets depth relative to rpcTempCU level
          rpcTempCU->getCUMvField( REF_PIC_LIST_1 )->setAllMvField( cMvFieldNeighbours[1 + 2*uiMergeCand], SIZE_2Nx2N, 0, 0 ); // interprets depth relative to rpcTempCU level
       // do MC
       m_pcPredSearch->motionCompensation ( rpcTempCU, m_ppcPredYuvTemp[uhDepth] ); //!< 运动补偿
       // estimate residual and encode everything
       m_pcPredSearch->encodeResAndCalcRdInterCU( rpcTempCU,
         m_ppcOrigYuv    [uhDepth],
         m_ppcPredYuvTemp[uhDepth],
         m_ppcResiYuvTemp[uhDepth],
         m_ppcResiYuvBest[uhDepth],
         m_ppcRecoYuvTemp[uhDepth],
         (uiNoResidual? true:false)); //!< 对残差进行编码并计算RDCost

       if(uiNoResidual==0)
       {
         if(rpcTempCU->getQtRootCbf(0) == 0) //!< CBF为0，说明变换系数全为0
         {
           mergeCandBuffer[uiMergeCand] = 1;
         }
       }
       rpcTempCU->setSkipFlagSubParts( rpcTempCU->getQtRootCbf(0) == 0, 0, uhDepth );
          Int orgQP = rpcTempCU->getQP( 0 );
          xCheckDQP( rpcTempCU );
          xCheckBestMode(rpcBestCU, rpcTempCU, uhDepth); //!< 更新最佳模式
          rpcTempCU->initEstData( uhDepth, orgQP ); //!< 重新初始化预测参数，为下一次预测做准备

      if( m_pcEncCfg->getUseFastDecisionForMerge() && !bestIsSkip ) //!< m_useFastDecisionForMerge默认为true
      {
        bestIsSkip = rpcBestCU->getQtRootCbf(0) == 0;
      }
    }//!< if( !(bestIsSkip && uiNoResidual == 0) ) 
    }//!< if(!(uiNoResidual==1 && mergeCandBuffer[uiMergeCand]==1))
   }//!< 
  }//!< for( UInt uiMergeCand = 0; uiMergeCand < numValidMergeCand; ++uiMergeCand )
  if(uiNoResidual == 0 && m_pcEncCfg->getUseEarlySkipDetection()) //!< 第一次对merging candidates迭代后
  {
    if(rpcBestCU->getQtRootCbf( 0 ) == 0) //!< earlyDetectionSkip 算法
    {
      if( rpcBestCU->getMergeFlag( 0 ))
      {
        *earlyDetectionSkipMode = true;
      }
      else
      {
        Int absoulte_MV=0;
        for ( UInt uiRefListIdx = 0; uiRefListIdx < 2; uiRefListIdx++ )
        {
          if ( rpcBestCU->getSlice()->getNumRefIdx( RefPicList( uiRefListIdx ) ) > 0 )
          {
            TComCUMvField* pcCUMvField = rpcBestCU->getCUMvField(RefPicList( uiRefListIdx ));
            Int iHor = pcCUMvField->getMvd( 0 ).getAbsHor();
            Int iVer = pcCUMvField->getMvd( 0 ).getAbsVer();
            absoulte_MV+=iHor+iVer;
          }
        }
        if(absoulte_MV == 0)
        {
          *earlyDetectionSkipMode = true;
        }
      }//!< else
    }//!< if(rpcBestCU->getQtRootCbf( 0 ) == 0)
  }//!< if(uiNoResidual == 0 && m_pcEncCfg->getUseEarlySkipDetection())
 }//!< for( UInt uiNoResidual = 0; uiNoResidual < iteration; ++uiNoResidual ) 
}