HM16.0之帧间Merge模式——xCheckRDCostMerge2Nx2N

参考：https://blog.csdn.net/nb_vol_1/article/details/51163625

1、源代码：

/** check RD costs for a CU block encoded with merge
 * param rpcBestCU
 * param rpcTempCU
 * 
eturns Void
 */
Void TEncCu::xCheckRDCostMerge2Nx2N( TComDataCU*& rpcBestCU, TComDataCU*& rpcTempCU DEBUG_STRING_FN_DECLARE(sDebug), Bool *earlyDetectionSkipMode )
{
  assert( rpcTempCU->getSlice()->getSliceType() != I_SLICE ); // 确定该片是P Slice或者B Slice
  TComMvField  cMvFieldNeighbours[2 * MRG_MAX_NUM_CANDS]; // double length for mv of both lists
  UChar uhInterDirNeighbours[MRG_MAX_NUM_CANDS];
  Int numValidMergeCand = 0;
  const Bool bTransquantBypassFlag = rpcTempCU->getCUTransquantBypass(0);

  for( UInt ui = 0; ui < rpcTempCU->getSlice()->getMaxNumMergeCand(); ++ui )
  {
    uhInterDirNeighbours[ui] = 0;
  }
  UChar uhDepth = rpcTempCU->getDepth( 0 ); // 获取当前深度
  // 给PU中相应的partition写入分割模式
  rpcTempCU->setPartSizeSubParts( SIZE_2Nx2N, 0, uhDepth ); // interprets depth relative to LCU level
  // 取出Merge候选列表
  rpcTempCU->getInterMergeCandidates( 0, 0, cMvFieldNeighbours,uhInterDirNeighbours, numValidMergeCand );

  // 构造候选列表
  Int mergeCandBuffer[MRG_MAX_NUM_CANDS];
  for( UInt ui = 0; ui < numValidMergeCand; ++ui )
  {
    mergeCandBuffer[ui] = 0;
  }

  Bool bestIsSkip = false;

  UInt iteration;
  // 默认为false，iteration = 2
  if ( rpcTempCU->isLosslessCoded(0))
  {
    iteration = 1;
  }
  else
  {
    iteration = 2;
  }
  DEBUG_STRING_NEW(bestStr)

    //代码结构分析

    //第一次不理skip模式，bestIsSkip的初始值为false;

    //第二次不处理mergeCandBuffer[uiMergeCand]为1的情况.

  // 遍历两次：第一次无残差编码，第二次对残差编码
  for( UInt uiNoResidual = 0; uiNoResidual < iteration; ++uiNoResidual )
  {
    // 遍历所有Merge候选成员
    for( UInt uiMergeCand = 0; uiMergeCand < numValidMergeCand; ++uiMergeCand )
    {
      if(!(uiNoResidual==1 && mergeCandBuffer[uiMergeCand]==1))
      {
        if( !(bestIsSkip && uiNoResidual == 0) )
        {
          DEBUG_STRING_NEW(tmpStr)
          // set MC parameters 设置运动补偿参数
          rpcTempCU->setPredModeSubParts( MODE_INTER, 0, uhDepth ); // interprets depth relative to LCU level
          rpcTempCU->setCUTransquantBypassSubParts( bTransquantBypassFlag, 0, uhDepth );
          rpcTempCU->setChromaQpAdjSubParts( bTransquantBypassFlag ? 0 : m_ChromaQpAdjIdc, 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 进行运动补偿
          m_pcPredSearch->motionCompensation ( rpcTempCU, m_ppcPredYuvTemp[uhDepth] );
          // estimate residual and encode everything 计算残差和RDCost，并进行编码
          m_pcPredSearch->encodeResAndCalcRdInterCU( rpcTempCU,
                                                     m_ppcOrigYuv    [uhDepth],
                                                     m_ppcPredYuvTemp[uhDepth],
                                                     m_ppcResiYuvTemp[uhDepth],
                                                     m_ppcResiYuvBest[uhDepth],
                                                     m_ppcRecoYuvTemp[uhDepth],
                                                     (uiNoResidual != 0) DEBUG_STRING_PASS_INTO(tmpStr) );

#ifdef DEBUG_STRING
          DebugInterPredResiReco(tmpStr, *(m_ppcPredYuvTemp[uhDepth]), *(m_ppcResiYuvBest[uhDepth]), *(m_ppcRecoYuvTemp[uhDepth]), DebugStringGetPredModeMask(rpcTempCU->getPredictionMode(0)));
#endif
          // 第一次迭代时进行
          if ((uiNoResidual == 0) && (rpcTempCU->getQtRootCbf(0) == 0))
          {
            // If no residual when allowing for one, then set mark to not try case where residual is forced to 0
            mergeCandBuffer[uiMergeCand] = 1;
          }

          rpcTempCU->setSkipFlagSubParts( rpcTempCU->getQtRootCbf(0) == 0, 0, uhDepth );
          Int orgQP = rpcTempCU->getQP( 0 );
          xCheckDQP( rpcTempCU );
          // 更新最优模式
          xCheckBestMode(rpcBestCU, rpcTempCU, uhDepth DEBUG_STRING_PASS_INTO(bestStr) DEBUG_STRING_PASS_INTO(tmpStr));
          // 重新初始化预测参数，为下一次预测做准备
          rpcTempCU->initEstData( uhDepth, orgQP, bTransquantBypassFlag );

          if( m_pcEncCfg->getUseFastDecisionForMerge() && !bestIsSkip )
          {
            bestIsSkip = rpcBestCU->getQtRootCbf(0) == 0;
          }
        }
      }
    }

    // 如果开启earlyDetectionSkip时，第一次迭代执行
    if(uiNoResidual == 0 && m_pcEncCfg->getUseEarlySkipDetection())
    {
      if(rpcBestCU->getQtRootCbf( 0 ) == 0)
      {
        if( rpcBestCU->getMergeFlag( 0 ))
        {
          *earlyDetectionSkipMode = true;
        }
        else if(m_pcEncCfg->getFastSearch() != SELECTIVE)
        {
          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;
          }
        }
      }
    }
  }
  DEBUG_STRING_APPEND(sDebug, bestStr)
}