VTM代码学习（1）CU划分jwgroot的博客-enctestmodetype

新人上路，请多多指教。  一直想写博客，今天才开始写第一篇。

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这次来讲一下VTM9.0中关于CU划分的部分，主要是两个函数xCompressCU和xCheckModeSplit。

xCompressCU主要针对当前CU可能进行的预测划分模式，完成相应的操作。主要分为以下几种模式（后面两种暂时还没学习，后面如果接触到会补充）

1划分模式：四叉树划分，水平二叉树划分，垂直二叉树划分，水平三叉树划分，垂直三叉树划分。通过调用函数xCompressCU完成。

2帧内预测：调用函数xCheckRDCostIntra完成。

3帧间预测：。。。。

4屏幕内容编码：。。。。

xCompressCU函数流程:初始化，调用函数initCULevel()，获取当前CU可能的预测和编码模式，并且按照顺序推入栈中。然后进入一循环，改循环会不断调取栈顶模式，将CU按照相应模式进行编码或划分，直至栈内不储存模式为止。具体代码如下：

 void EncCu::xCompressCU( CodingStructure*& tempCS, CodingStructure*& bestCS, Partitioner& partitioner, double maxCostAllowed ) {  /*************************************** 初始化 ****************************************/   CHECK(maxCostAllowed < 0, "Wrong value of maxCostAllowed!"); #if ENABLE_SPLIT_PARALLELISM   CHECK( m_dataId != tempCS->picture->scheduler.getDataId(), "Working in the wrong dataId!" );    if( m_pcEncCfg->getNumSplitThreads() != 1 && tempCS->picture->scheduler.getSplitJobId() == 0 )   {     if( m_modeCtrl->isParallelSplit( *tempCS, partitioner ) )     {       m_modeCtrl->setParallelSplit( true );       xCompressCUParallel( tempCS, bestCS, partitioner );       return;     }   }  #endif   uint32_t compBegin;   uint32_t numComp;   bool jointPLT = false;   if (partitioner.isSepTree( *tempCS ))   { #if JVET_Q0504_PLT_NON444     if( !CS::isDualITree(*tempCS) && partitioner.treeType != TREE_D )     {       compBegin = COMPONENT_Y;       numComp = (tempCS->area.chromaFormat != CHROMA_400)?3: 1;       jointPLT = true;     }     else     { #endif     if (isLuma(partitioner.chType))     {       compBegin = COMPONENT_Y;       numComp = 1;     }     else     {       compBegin = COMPONENT_Cb;       numComp = 2;     } #if JVET_Q0504_PLT_NON444     } #endif   }   else   {     compBegin = COMPONENT_Y; #if JVET_Q0504_PLT_NON444     numComp = (tempCS->area.chromaFormat != CHROMA_400) ? 3 : 1; #else     numComp = 3; #endif     jointPLT = true;   }   SplitSeries splitmode = -1;   uint8_t   bestLastPLTSize[MAX_NUM_CHANNEL_TYPE];   Pel       bestLastPLT[MAX_NUM_COMPONENT][MAXPLTPREDSIZE]; // store LastPLT for    uint8_t   curLastPLTSize[MAX_NUM_CHANNEL_TYPE];   Pel       curLastPLT[MAX_NUM_COMPONENT][MAXPLTPREDSIZE]; // store LastPLT if no partition   for (int i = compBegin; i < (compBegin + numComp); i++)   {     ComponentID comID = jointPLT ? (ComponentID)compBegin : ((i > 0) ? COMPONENT_Cb : COMPONENT_Y);     bestLastPLTSize[comID] = 0;     curLastPLTSize[comID] = tempCS->prevPLT.curPLTSize[comID];     memcpy(curLastPLT[i], tempCS->prevPLT.curPLT[i], tempCS->prevPLT.curPLTSize[comID] * sizeof(Pel));   }    Slice&   slice      = *tempCS->slice;   const PPS &pps      = *tempCS->pps;   const SPS &sps      = *tempCS->sps;   const uint32_t uiLPelX  = tempCS->area.Y().lumaPos().x;   const uint32_t uiTPelY  = tempCS->area.Y().lumaPos().y;    const ModeType modeTypeParent  = partitioner.modeType;   const TreeType treeTypeParent  = partitioner.treeType;   const ChannelType chTypeParent = partitioner.chType;   const UnitArea currCsArea = clipArea( CS::getArea( *bestCS, bestCS->area, partitioner.chType ), *tempCS->picture );    m_modeCtrl->initCULevel( partitioner, *tempCS );//初始化所有编码划分模式，为CU设置可能的编码划分模式   if( partitioner.currQtDepth == 0 && partitioner.currMtDepth == 0 && !tempCS->slice->isIntra() && ( sps.getUseSBT() || sps.getUseInterMTS() ) )   {     auto slsSbt = dynamic_cast<SaveLoadEncInfoSbt*>( m_modeCtrl );     int maxSLSize = sps.getUseSBT() ? tempCS->slice->getSPS()->getMaxTbSize() : MTS_INTER_MAX_CU_SIZE;     slsSbt->resetSaveloadSbt( maxSLSize ); #if ENABLE_SPLIT_PARALLELISM     CHECK( tempCS->picture->scheduler.getSplitJobId() != 0, "The SBT search reset need to happen in sequential region." );     if (m_pcEncCfg->getNumSplitThreads() > 1)     {       for (int jId = 1; jId < NUM_RESERVERD_SPLIT_JOBS; jId++)       {         auto slsSbt = dynamic_cast<SaveLoadEncInfoSbt *>(m_pcEncLib->getCuEncoder(jId)->m_modeCtrl);         slsSbt->resetSaveloadSbt(maxSLSize);       }     } #endif   }   m_sbtCostSave[0] = m_sbtCostSave[1] = MAX_DOUBLE;    m_CurrCtx->start = m_CABACEstimator->getCtx();    /************************* 处理色度QP ***************************/    m_cuChromaQpOffsetIdxPlus1 = 0;    if( slice.getUseChromaQpAdj() )   {     // TODO M0133 : double check encoder decisions with respect to chroma QG detection and actual encode     int lgMinCuSize = sps.getLog2MinCodingBlockSize() + #if JVET_Q0468_Q0469_MIN_LUMA_CB_AND_MIN_QT_FIX       std::max<int>(0, floorLog2(sps.getCTUSize()) - sps.getLog2MinCodingBlockSize() - int(slice.getCuChromaQpOffsetSubdiv() / 2)); #else       std::max<int>( 0, sps.getLog2DiffMaxMinCodingBlockSize() - int( slice.getCuChromaQpOffsetSubdiv()/2 ) ); #endif #if JVET_Q0267_RESET_CHROMA_QP_OFFSET     if( partitioner.currQgChromaEnable() )      {       m_cuChromaQpOffsetIdxPlus1 = ( ( uiLPelX >> lgMinCuSize ) + ( uiTPelY >> lgMinCuSize ) ) % ( pps.getChromaQpOffsetListLen() + 1 );     } #else     m_cuChromaQpOffsetIdxPlus1 = ( ( uiLPelX >> lgMinCuSize ) + ( uiTPelY >> lgMinCuSize ) ) % ( pps.getChromaQpOffsetListLen() + 1 ); #endif   }    if( !m_modeCtrl->anyMode() )   {     m_modeCtrl->finishCULevel( partitioner );     return;   }    DTRACE_UPDATE( g_trace_ctx, std::make_pair( "cux", uiLPelX ) );   DTRACE_UPDATE( g_trace_ctx, std::make_pair( "cuy", uiTPelY ) );   DTRACE_UPDATE( g_trace_ctx, std::make_pair( "cuw", tempCS->area.lwidth() ) );   DTRACE_UPDATE( g_trace_ctx, std::make_pair( "cuh", tempCS->area.lheight() ) );   DTRACE( g_trace_ctx, D_COMMON, "@(%4d,%4d) [%2dx%2d]n", tempCS->area.lx(), tempCS->area.ly(), tempCS->area.lwidth(), tempCS->area.lheight() );     m_pcInterSearch->resetSavedAffineMotion();    double bestIntPelCost = MAX_DOUBLE;    if (tempCS->slice->getSPS()->getUseColorTrans())   {     tempCS->tmpColorSpaceCost = MAX_DOUBLE;     bestCS->tmpColorSpaceCost = MAX_DOUBLE;     tempCS->firstColorSpaceSelected = true;     bestCS->firstColorSpaceSelected = true;   }    if (tempCS->slice->getSPS()->getUseColorTrans() && !CS::isDualITree(*tempCS))   {     tempCS->firstColorSpaceTestOnly = false;     bestCS->firstColorSpaceTestOnly = false;     tempCS->tmpColorSpaceIntraCost[0] = MAX_DOUBLE;     tempCS->tmpColorSpaceIntraCost[1] = MAX_DOUBLE;     bestCS->tmpColorSpaceIntraCost[0] = MAX_DOUBLE;     bestCS->tmpColorSpaceIntraCost[1] = MAX_DOUBLE;      if (tempCS->bestParent && tempCS->bestParent->firstColorSpaceTestOnly)     {       tempCS->firstColorSpaceTestOnly = bestCS->firstColorSpaceTestOnly = true;     }   }   /***************************按照堆栈中的模式进行循环预测编码或划分，当循环结束时当前CU已选择最小的RDcost进行划分与编码****************************/   do//尝试当前编码器各种可用的模式：如skip，帧间，帧内，PCM等，进行预测及划分。   {     for (int i = compBegin; i < (compBegin + numComp); i++)     {       ComponentID comID = jointPLT ? (ComponentID)compBegin : ((i > 0) ? COMPONENT_Cb : COMPONENT_Y);       tempCS->prevPLT.curPLTSize[comID] = curLastPLTSize[comID];       memcpy(tempCS->prevPLT.curPLT[i], curLastPLT[i], curLastPLTSize[comID] * sizeof(Pel));     }     EncTestMode currTestMode = m_modeCtrl->currTestMode();//获得本次循环的编码或划分模式     currTestMode.maxCostAllowed = maxCostAllowed;      if (pps.getUseDQP() && partitioner.isSepTree(*tempCS) && isChroma( partitioner.chType ))     {       const Position chromaCentral(tempCS->area.Cb().chromaPos().offset(tempCS->area.Cb().chromaSize().width >> 1, tempCS->area.Cb().chromaSize().height >> 1));       const Position lumaRefPos(chromaCentral.x << getComponentScaleX(COMPONENT_Cb, tempCS->area.chromaFormat), chromaCentral.y << getComponentScaleY(COMPONENT_Cb, tempCS->area.chromaFormat));       const CodingStructure* baseCS = bestCS->picture->cs;       const CodingUnit* colLumaCu = baseCS->getCU(lumaRefPos, CHANNEL_TYPE_LUMA);        if (colLumaCu)       {         currTestMode.qp = colLumaCu->qp;       }     }  #if SHARP_LUMA_DELTA_QP || ENABLE_QPA_SUB_CTU     if (partitioner.currQgEnable() && ( #if SHARP_LUMA_DELTA_QP         (m_pcEncCfg->getLumaLevelToDeltaQPMapping().isEnabled()) || #endif #if ENABLE_QPA_SUB_CTU         (m_pcEncCfg->getUsePerceptQPA() && !m_pcEncCfg->getUseRateCtrl() && pps.getUseDQP()) #else         false #endif       ))     { #if ENABLE_SPLIT_PARALLELISM       CHECK( tempCS->picture->scheduler.getSplitJobId() > 0, "Changing lambda is only allowed in the master thread!" ); #endif       if (currTestMode.qp >= 0)       {         updateLambda (&slice, currTestMode.qp,  #if WCG_EXT && ER_CHROMA_QP_WCG_PPS                       m_pcEncCfg->getWCGChromaQPControl().isEnabled(),  #endif                       CS::isDualITree (*tempCS) || (partitioner.currDepth == 0));       }     } #endif      if( currTestMode.type == ETM_INTER_ME )//帧间运动估计-运动搜索（wan）     {       if( ( currTestMode.opts & ETO_IMV ) != 0 )       {         const bool skipAltHpelIF = ( int( ( currTestMode.opts & ETO_IMV ) >> ETO_IMV_SHIFT ) == 4 ) && ( bestIntPelCost > 1.25 * bestCS->cost );         if (!skipAltHpelIF)         {           tempCS->bestCS = bestCS;           xCheckRDCostInterIMV(tempCS, bestCS, partitioner, currTestMode, bestIntPelCost);           tempCS->bestCS = nullptr;         }       }       else       {         tempCS->bestCS = bestCS;         xCheckRDCostInter( tempCS, bestCS, partitioner, currTestMode );         tempCS->bestCS = nullptr;       }      }     else if (currTestMode.type == ETM_HASH_INTER)// IBC？     {       xCheckRDCostHashInter( tempCS, bestCS, partitioner, currTestMode );     }     else if( currTestMode.type == ETM_AFFINE )// 仿射，旋转（266）     {       xCheckRDCostAffineMerge2Nx2N( tempCS, bestCS, partitioner, currTestMode );     } #if REUSE_CU_RESULTS     else if( currTestMode.type == ETM_RECO_CACHED )//快速算法，内存级别     {       xReuseCachedResult( tempCS, bestCS, partitioner );     } #endif     else if( currTestMode.type == ETM_MERGE_SKIP )//MERGE，SKIP（wan）     {       xCheckRDCostMerge2Nx2N( tempCS, bestCS, partitioner, currTestMode );       CodingUnit* cu = bestCS->getCU(partitioner.chType);       if (cu)       cu->mmvdSkip = cu->skip == false ? false : cu->mmvdSkip;     } #if !JVET_Q0806     else if( currTestMode.type == ETM_MERGE_TRIANGLE )     {       xCheckRDCostMergeTriangle2Nx2N( tempCS, bestCS, partitioner, currTestMode );     } #else     else if( currTestMode.type == ETM_MERGE_GEO )//一个CU划分成两个，分别找     {       xCheckRDCostMergeGeo2Nx2N( tempCS, bestCS, partitioner, currTestMode );     } #endif     else if( currTestMode.type == ETM_INTRA )//帧内     { #if SPLIT_TEST   printf("intra: (%2d,%2d) %2d %2d : mode:%2d chan:%dn", tempCS->area.blocks[0].x, tempCS->area.blocks[0].y, tempCS->area.blocks[0].width, tempCS->area.blocks[0].height, currTestMode.type, partitioner.chType); #endif       if (slice.getSPS()->getUseColorTrans() && !CS::isDualITree(*tempCS))       {         bool skipSecColorSpace = false;         skipSecColorSpace = xCheckRDCostIntra(tempCS, bestCS, partitioner, currTestMode, (m_pcEncCfg->getRGBFormatFlag() ? true : false));//帧内预测编码 #if JVET_Q0820_ACT         if ((m_pcEncCfg->getCostMode() == COST_LOSSLESS_CODING) && !m_pcEncCfg->getRGBFormatFlag())         {           skipSecColorSpace = true;         } #endif          if (!skipSecColorSpace && !tempCS->firstColorSpaceTestOnly)         {           xCheckRDCostIntra(tempCS, bestCS, partitioner, currTestMode, (m_pcEncCfg->getRGBFormatFlag() ? false : true));         }          if (!tempCS->firstColorSpaceTestOnly)         {           if (tempCS->tmpColorSpaceIntraCost[0] != MAX_DOUBLE && tempCS->tmpColorSpaceIntraCost[1] != MAX_DOUBLE)           {             double skipCostRatio = m_pcEncCfg->getRGBFormatFlag() ? 1.1 : 1.0;             if (tempCS->tmpColorSpaceIntraCost[1] > (skipCostRatio*tempCS->tmpColorSpaceIntraCost[0]))             {               tempCS->firstColorSpaceTestOnly = bestCS->firstColorSpaceTestOnly = true;             }           }         }         else         {           CHECK(tempCS->tmpColorSpaceIntraCost[1] != MAX_DOUBLE, "the RD test of the second color space should be skipped");         }       }       else       {         xCheckRDCostIntra(tempCS, bestCS, partitioner, currTestMode, false);       }     }     else if (currTestMode.type == ETM_PALETTE)//调色板     {       xCheckPLT( tempCS, bestCS, partitioner, currTestMode );     }     else if (currTestMode.type == ETM_IBC)//IBC     {       xCheckRDCostIBCMode(tempCS, bestCS, partitioner, currTestMode);     }     else if (currTestMode.type == ETM_IBC_MERGE)     {       xCheckRDCostIBCModeMerge2Nx2N(tempCS, bestCS, partitioner, currTestMode);     }     else if( isModeSplit( currTestMode ) )//compresscu-先判断能否继续划分-xCheckModeSplit-compresscu        {//如果判断type是五种划分模式其中一种 #if SPLIT_TEST   printf("split: (%2d,%2d) %2d %2d : mode:%2d chan:%dn", tempCS->area.blocks[0].x, tempCS->area.blocks[0].y, tempCS->area.blocks[0].width, tempCS->area.blocks[0].height, currTestMode.type, partitioner.chType); #endif       if (bestCS->cus.size() != 0)       {         splitmode = bestCS->cus[0]->splitSeries;       }       assert( partitioner.modeType == tempCS->modeType );       int signalModeConsVal = tempCS->signalModeCons( getPartSplit( currTestMode ), partitioner, modeTypeParent );       int numRoundRdo = signalModeConsVal == LDT_MODE_TYPE_SIGNAL ? 2 : 1;       bool skipInterPass = false;       for( int i = 0; i < numRoundRdo; i++ )       {         //change cons modes         if( signalModeConsVal == LDT_MODE_TYPE_SIGNAL )         {           CHECK( numRoundRdo != 2, "numRoundRdo shall be 2 - [LDT_MODE_TYPE_SIGNAL]" );           tempCS->modeType = partitioner.modeType = (i == 0) ? MODE_TYPE_INTER : MODE_TYPE_INTRA;         }         else if( signalModeConsVal == LDT_MODE_TYPE_INFER )         {           CHECK( numRoundRdo != 1, "numRoundRdo shall be 1 - [LDT_MODE_TYPE_INFER]" );           tempCS->modeType = partitioner.modeType = MODE_TYPE_INTRA;         }         else if( signalModeConsVal == LDT_MODE_TYPE_INHERIT )         {           CHECK( numRoundRdo != 1, "numRoundRdo shall be 1 - [LDT_MODE_TYPE_INHERIT]" );           tempCS->modeType = partitioner.modeType = modeTypeParent;         }          //for lite intra encoding fast algorithm, set the status to save inter coding info   //对于精简帧内编码快速算法，设置状态以保存帧间编码信息    if( modeTypeParent == MODE_TYPE_ALL && tempCS->modeType == MODE_TYPE_INTER )         {           m_pcIntraSearch->setSaveCuCostInSCIPU( true );           m_pcIntraSearch->setNumCuInSCIPU( 0 );         }         else if( modeTypeParent == MODE_TYPE_ALL && tempCS->modeType != MODE_TYPE_INTER )         {           m_pcIntraSearch->setSaveCuCostInSCIPU( false );           if( tempCS->modeType == MODE_TYPE_ALL )           {             m_pcIntraSearch->setNumCuInSCIPU( 0 );           }         }          xCheckModeSplit( tempCS, bestCS, partitioner, currTestMode, modeTypeParent, skipInterPass );//划分函数           //recover cons modes         tempCS->modeType = partitioner.modeType = modeTypeParent;         tempCS->treeType = partitioner.treeType = treeTypeParent;         partitioner.chType = chTypeParent;         if( modeTypeParent == MODE_TYPE_ALL )         {           m_pcIntraSearch->setSaveCuCostInSCIPU( false );           if( numRoundRdo == 2 && tempCS->modeType == MODE_TYPE_INTRA )           {             m_pcIntraSearch->initCuAreaCostInSCIPU();           }         }         if( skipInterPass )         {           break;         }       }       if (splitmode != bestCS->cus[0]->splitSeries)       {         splitmode = bestCS->cus[0]->splitSeries;         const CodingUnit&     cu = *bestCS->cus.front();         cu.cs->prevPLT = bestCS->prevPLT;         for (int i = compBegin; i < (compBegin + numComp); i++)         {           ComponentID comID = jointPLT ? (ComponentID)compBegin : ((i > 0) ? COMPONENT_Cb : COMPONENT_Y);           bestLastPLTSize[comID] = bestCS->cus[0]->cs->prevPLT.curPLTSize[comID];           memcpy(bestLastPLT[i], bestCS->cus[0]->cs->prevPLT.curPLT[i], bestCS->cus[0]->cs->prevPLT.curPLTSize[comID] * sizeof(Pel));         }       }     }     else     {       THROW( "Don't know how to handle mode: type = " << currTestMode.type << ", options = " << currTestMode.opts );     }   } while( m_modeCtrl->nextMode( *tempCS, partitioner ) );//开始删掉栈顶的模式与接下来栈内不会存在的模式，进入CU下一个编码/划分模式     //////////////////////////////////////////////////////////////////////////   // Finishing CU #if ENABLE_SPLIT_PARALLELISM   if( bestCS->cus.empty() )   {     CHECK( bestCS->cost != MAX_DOUBLE, "Cost should be maximal if no encoding found" );     CHECK( bestCS->picture->scheduler.getSplitJobId() == 0, "Should always get a result in serial case" );      m_modeCtrl->finishCULevel( partitioner );     return;   }  #endif   //如果划分失败，则删除m_ComprCUCtxList栈顶，结束划分   if( tempCS->cost == MAX_DOUBLE && bestCS->cost == MAX_DOUBLE )   {     //although some coding modes were planned to be tried in RDO, no coding mode actually finished encoding due to early termination     //thus tempCS->cost and bestCS->cost are both MAX_DOUBLE; in this case, skip the following process for normal case     m_modeCtrl->finishCULevel( partitioner );     return;   }    // set context states   m_CABACEstimator->getCtx() = m_CurrCtx->best;    // QP from last processed CU for further processing   //copy the qp of the last non-chroma CU   int numCUInThisNode = (int)bestCS->cus.size();   if( numCUInThisNode > 1 && bestCS->cus.back()->chType == CHANNEL_TYPE_CHROMA && !CS::isDualITree( *bestCS ) )   {     CHECK( bestCS->cus[numCUInThisNode-2]->chType != CHANNEL_TYPE_LUMA, "wrong chType" );     bestCS->prevQP[partitioner.chType] = bestCS->cus[numCUInThisNode-2]->qp;   }   else   {   bestCS->prevQP[partitioner.chType] = bestCS->cus.back()->qp;   }   if ((!slice.isIntra() || slice.getSPS()->getIBCFlag())     && partitioner.chType == CHANNEL_TYPE_LUMA     && bestCS->cus.size() == 1 && (bestCS->cus.back()->predMode == MODE_INTER || bestCS->cus.back()->predMode == MODE_IBC)     && bestCS->area.Y() == (*bestCS->cus.back()).Y()     )   {     const CodingUnit&     cu = *bestCS->cus.front();      bool isIbcSmallBlk = CU::isIBC(cu) && (cu.lwidth() * cu.lheight() <= 16);     CU::saveMotionInHMVP( cu, isIbcSmallBlk );   }   bestCS->picture->getPredBuf(currCsArea).copyFrom(bestCS->getPredBuf(currCsArea));   bestCS->picture->getRecoBuf( currCsArea ).copyFrom( bestCS->getRecoBuf( currCsArea ) );   m_modeCtrl->finishCULevel( partitioner );//删除m_ComprCUCtxList栈顶   if( m_pcIntraSearch->getSaveCuCostInSCIPU() && bestCS->cus.size() == 1 )   {     m_pcIntraSearch->saveCuAreaCostInSCIPU( Area( partitioner.currArea().lumaPos(), partitioner.currArea().lumaSize() ), bestCS->cost );   }  #if ENABLE_SPLIT_PARALLELISM   if( tempCS->picture->scheduler.getSplitJobId() == 0 && m_pcEncCfg->getNumSplitThreads() != 1 )   {     tempCS->picture->finishParallelPart( currCsArea );   }  #endif   if (bestCS->cus.size() == 1) // no partition   {     CHECK(bestCS->cus[0]->tileIdx != bestCS->pps->getTileIdx(bestCS->area.lumaPos()), "Wrong tile index!");     if (bestCS->cus[0]->predMode == MODE_PLT)     {       for (int i = compBegin; i < (compBegin + numComp); i++)       {         ComponentID comID = jointPLT ? (ComponentID)compBegin : ((i > 0) ? COMPONENT_Cb : COMPONENT_Y);         bestCS->prevPLT.curPLTSize[comID] = curLastPLTSize[comID];         memcpy(bestCS->prevPLT.curPLT[i], curLastPLT[i], curLastPLTSize[comID] * sizeof(Pel));       }       bestCS->reorderPrevPLT(bestCS->prevPLT, bestCS->cus[0]->curPLTSize, bestCS->cus[0]->curPLT, bestCS->cus[0]->reuseflag, compBegin, numComp, jointPLT);     }     else     {       for (int i = compBegin; i<(compBegin + numComp); i++)       {         ComponentID comID = jointPLT ? (ComponentID)compBegin : ((i > 0) ? COMPONENT_Cb : COMPONENT_Y);         bestCS->prevPLT.curPLTSize[comID] = curLastPLTSize[comID];         memcpy(bestCS->prevPLT.curPLT[i], curLastPLT[i], bestCS->prevPLT.curPLTSize[comID] * sizeof(Pel));       }     }   }   else   {     for (int i = compBegin; i<(compBegin + numComp); i++)     {       ComponentID comID = jointPLT ? (ComponentID)compBegin : ((i > 0) ? COMPONENT_Cb : COMPONENT_Y);       bestCS->prevPLT.curPLTSize[comID] = bestLastPLTSize[comID];       memcpy(bestCS->prevPLT.curPLT[i], bestLastPLT[i], bestCS->prevPLT.curPLTSize[comID] * sizeof(Pel));     }   }   const CodingUnit&     cu = *bestCS->cus.front();   cu.cs->prevPLT = bestCS->prevPLT;   // Assert if Best prediction mode is NONE   // Selected mode's RD-cost must be not MAX_DOUBLE.   CHECK( bestCS->cus.empty()                                   , "No possible encoding found" );   CHECK( bestCS->cus[0]->predMode == NUMBER_OF_PREDICTION_MODES, "No possible encoding found" );   CHECK( bestCS->cost             == MAX_DOUBLE                , "No possible encoding found" ); }

划分主要时调用函数xCheckModeSplit完成。函数xCheckModeSplit流程如下

1. 首先完成初始化操作，设置上下文，判断当前划分模式是否可用。
2. 调用splitCurrArea对子块进行划分，主要是计算划分后各个子块高宽与坐标。
3. 进入循环，该循环会遍历每一个子块，调用函数xCompressCU，完成对子块的划分与预测编码。获得该子块划分编码后的RDcost，划分结构等相关信息。
4. 结束循环后将划分前的RDcost与划分后进行对比，判断该CU是否进行划分

函数xCheckModeSplit具体代码如下：

 void EncCu::xCheckModeSplit(CodingStructure *&tempCS, CodingStructure *&bestCS, Partitioner &partitioner, const EncTestMode& encTestMode, const ModeType modeTypeParent, bool &skipInterPass ) {   const int qp                = encTestMode.qp;   const Slice &slice          = *tempCS->slice;   const int oldPrevQp         = tempCS->prevQP[partitioner.chType];   const auto oldMotionLut     = tempCS->motionLut; #if ENABLE_QPA_SUB_CTU   const PPS &pps              = *tempCS->pps;   const uint32_t currDepth    = partitioner.currDepth; #endif   const auto oldPLT           = tempCS->prevPLT;    const PartSplit split = getPartSplit( encTestMode );//获得cu划分方式   const ModeType modeTypeChild = partitioner.modeType;    CHECK( split == CU_DONT_SPLIT, "No proper split provided!" );    tempCS->initStructData( qp );//初始化tempCS    m_CABACEstimator->getCtx() = m_CurrCtx->start;    const TempCtx ctxStartSP( m_CtxCache, SubCtx( Ctx::SplitFlag,   m_CABACEstimator->getCtx() ) );   const TempCtx ctxStartQt( m_CtxCache, SubCtx( Ctx::SplitQtFlag, m_CABACEstimator->getCtx() ) );   const TempCtx ctxStartHv( m_CtxCache, SubCtx( Ctx::SplitHvFlag, m_CABACEstimator->getCtx() ) );   const TempCtx ctxStart12( m_CtxCache, SubCtx( Ctx::Split12Flag, m_CABACEstimator->getCtx() ) );   const TempCtx ctxStartMC( m_CtxCache, SubCtx( Ctx::ModeConsFlag, m_CABACEstimator->getCtx() ) );   m_CABACEstimator->resetBits();    m_CABACEstimator->split_cu_mode( split, *tempCS, partitioner );   m_CABACEstimator->mode_constraint( split, *tempCS, partitioner, modeTypeChild );    const double factor = ( tempCS->currQP[partitioner.chType] > 30 ? 1.1 : 1.075 );   tempCS->useDbCost = m_pcEncCfg->getUseEncDbOpt();   if (!tempCS->useDbCost)     CHECK(bestCS->costDbOffset != 0, "error");   const double cost   = m_pcRdCost->calcRdCost( uint64_t( m_CABACEstimator->getEstFracBits() + ( ( bestCS->fracBits ) / factor ) ), Distortion( bestCS->dist / factor ) ) + bestCS->costDbOffset / factor;    m_CABACEstimator->getCtx() = SubCtx( Ctx::SplitFlag,   ctxStartSP );   m_CABACEstimator->getCtx() = SubCtx( Ctx::SplitQtFlag, ctxStartQt );   m_CABACEstimator->getCtx() = SubCtx( Ctx::SplitHvFlag, ctxStartHv );   m_CABACEstimator->getCtx() = SubCtx( Ctx::Split12Flag, ctxStart12 );   m_CABACEstimator->getCtx() = SubCtx( Ctx::ModeConsFlag, ctxStartMC );     //停止划分，具体原因不清楚   if (cost > bestCS->cost + bestCS->costDbOffset #if ENABLE_QPA_SUB_CTU     || (m_pcEncCfg->getUsePerceptQPA() && !m_pcEncCfg->getUseRateCtrl() && pps.getUseDQP() && (slice.getCuQpDeltaSubdiv() > 0) && (split == CU_HORZ_SPLIT || split == CU_VERT_SPLIT) &&         (currDepth == 0)) // force quad-split or no split at CTU level在CTU级别强制四叉树分割或不分割 #endif     )   {     xCheckBestMode( tempCS, bestCS, partitioner, encTestMode );     return;   }    const bool chromaNotSplit = modeTypeParent == MODE_TYPE_ALL && modeTypeChild == MODE_TYPE_INTRA ? true : false;   if( partitioner.treeType != TREE_D )   {     tempCS->treeType = TREE_L;   }   else   {     if( chromaNotSplit )     {       CHECK( partitioner.chType != CHANNEL_TYPE_LUMA, "chType must be luma" );       tempCS->treeType = partitioner.treeType = TREE_L;     }     else     {       tempCS->treeType = partitioner.treeType = TREE_D;     }   }     partitioner.splitCurrArea( split, *tempCS );//进行划分，计算划分子块区域以及坐上坐标   bool qgEnableChildren = partitioner.currQgEnable(); // QG possible at children level    m_CurrCtx++;    tempCS->getRecoBuf().fill( 0 );    tempCS->getPredBuf().fill(0);   AffineMVInfo tmpMVInfo;   bool isAffMVInfoSaved;   m_pcInterSearch->savePrevAffMVInfo(0, tmpMVInfo, isAffMVInfoSaved);   BlkUniMvInfo tmpUniMvInfo;   bool         isUniMvInfoSaved = false;   if (!tempCS->slice->isIntra())   {     m_pcInterSearch->savePrevUniMvInfo(tempCS->area.Y(), tmpUniMvInfo, isUniMvInfoSaved);   }    do   {     const auto &subCUArea  = partitioner.currArea();//划分后的子块区域      if( tempCS->picture->Y().contains( subCUArea.lumaPos() ) )      {       const unsigned wIdx    = gp_sizeIdxInfo->idxFrom( subCUArea.lwidth () );       const unsigned hIdx    = gp_sizeIdxInfo->idxFrom( subCUArea.lheight() );        CodingStructure *tempSubCS = m_pTempCS[wIdx][hIdx];       CodingStructure *bestSubCS = m_pBestCS[wIdx][hIdx];        tempCS->initSubStructure( *tempSubCS, partitioner.chType, subCUArea, false );//子块cu初始化       tempCS->initSubStructure( *bestSubCS, partitioner.chType, subCUArea, false );       tempSubCS->bestParent = bestSubCS->bestParent = bestCS;       double newMaxCostAllowed = isLuma(partitioner.chType) ? std::min(encTestMode.maxCostAllowed, bestCS->cost - m_pcRdCost->calcRdCost(tempCS->fracBits, tempCS->dist)) : MAX_DOUBLE;       newMaxCostAllowed = std::max(0.0, newMaxCostAllowed);       xCompressCU(tempSubCS, bestSubCS, partitioner, newMaxCostAllowed);//递归调用       tempSubCS->bestParent = bestSubCS->bestParent = nullptr;        if( bestSubCS->cost == MAX_DOUBLE )       {         CHECK( split == CU_QUAD_SPLIT, "Split decision reusing cannot skip quad split" );         tempCS->cost = MAX_DOUBLE;         tempCS->costDbOffset = 0;         tempCS->useDbCost = m_pcEncCfg->getUseEncDbOpt();         m_CurrCtx--;         partitioner.exitCurrSplit();         xCheckBestMode( tempCS, bestCS, partitioner, encTestMode );         if( partitioner.chType == CHANNEL_TYPE_LUMA )         {           tempCS->motionLut = oldMotionLut;         }         return;       }        bool keepResi = KEEP_PRED_AND_RESI_SIGNALS;       tempCS->useSubStructure( *bestSubCS, partitioner.chType, CS::getArea( *tempCS, subCUArea, partitioner.chType ), KEEP_PRED_AND_RESI_SIGNALS, true, keepResi, keepResi );    //从子结构中复制编码数据，将bestSubCS的cu,pu,tu复制到tempCS中       if( partitioner.currQgEnable() )       {         tempCS->prevQP[partitioner.chType] = bestSubCS->prevQP[partitioner.chType];       }       if( partitioner.isConsInter() )       {         for( int i = 0; i < bestSubCS->cus.size(); i++ )         {           CHECK( bestSubCS->cus[i]->predMode != MODE_INTER, "all CUs must be inter mode in an Inter coding region (SCIPU)" );         }       }       else if( partitioner.isConsIntra() )       {         for( int i = 0; i < bestSubCS->cus.size(); i++ )         {           CHECK( bestSubCS->cus[i]->predMode == MODE_INTER, "all CUs must not be inter mode in an Intra coding region (SCIPU)" );         }       }        tempSubCS->releaseIntermediateData();//清空子节点数据       bestSubCS->releaseIntermediateData();       if( !tempCS->slice->isIntra() && partitioner.isConsIntra() )       {         tempCS->cost = m_pcRdCost->calcRdCost( tempCS->fracBits, tempCS->dist );         if( tempCS->cost > bestCS->cost )         {           tempCS->cost = MAX_DOUBLE;           tempCS->costDbOffset = 0;           tempCS->useDbCost = m_pcEncCfg->getUseEncDbOpt();           m_CurrCtx--;           partitioner.exitCurrSplit();           if( partitioner.chType == CHANNEL_TYPE_LUMA )           {             tempCS->motionLut = oldMotionLut;           }           return;         }       }     }   } while( partitioner.nextPart( *tempCS ) );//进行下一个子块的划分    partitioner.exitCurrSplit();//清除m_partStack栈顶，将深度减一     m_CurrCtx--;    if( chromaNotSplit )   {     //Note: In local dual tree region, the chroma CU refers to the central luma CU's QP.     //If the luma CU QP shall be predQP (no residual in it and before it in the QG), it must be revised to predQP before encoding the chroma CU     //Otherwise, the chroma CU uses predQP+deltaQP in encoding but is decoded as using predQP, thus causing encoder-decoded mismatch on chroma qp.     if( tempCS->pps->getUseDQP() )     {       //find parent CS that including all coded CUs in the QG before this node       CodingStructure* qgCS = tempCS;       bool deltaQpCodedBeforeThisNode = false;       if( partitioner.currArea().lumaPos() != partitioner.currQgPos )       {         int numParentNodeToQgCS = 0;         while( qgCS->area.lumaPos() != partitioner.currQgPos )         {           CHECK( qgCS->parent == nullptr, "parent of qgCS shall exsit" );           qgCS = qgCS->parent;           numParentNodeToQgCS++;         }          //check whether deltaQP has been coded (in luma CU or luma&chroma CU) before this node         CodingStructure* parentCS = tempCS->parent;         for( int i = 0; i < numParentNodeToQgCS; i++ )         {           //checking each parent           CHECK( parentCS == nullptr, "parentCS shall exsit" );           for( const auto &cu : parentCS->cus )           {             if( cu->rootCbf && !isChroma( cu->chType ) )             {               deltaQpCodedBeforeThisNode = true;               break;             }           }           parentCS = parentCS->parent;         }       }        //revise luma CU qp before the first luma CU with residual in the SCIPU to predQP       if( !deltaQpCodedBeforeThisNode )       {         //get pred QP of the QG         const CodingUnit* cuFirst = qgCS->getCU( CHANNEL_TYPE_LUMA );         CHECK( cuFirst->lumaPos() != partitioner.currQgPos, "First cu of the Qg is wrong" );         int predQp = CU::predictQP( *cuFirst, qgCS->prevQP[CHANNEL_TYPE_LUMA] );          //revise to predQP         int firstCuHasResidual = (int)tempCS->cus.size();         for( int i = 0; i < tempCS->cus.size(); i++ )         {           if( tempCS->cus[i]->rootCbf )           {             firstCuHasResidual = i;             break;           }         }          for( int i = 0; i < firstCuHasResidual; i++ )         {           tempCS->cus[i]->qp = predQp;         }       }     }     assert( tempCS->treeType == TREE_L );     uint32_t numCuPuTu[6];     tempCS->picture->cs->getNumCuPuTuOffset( numCuPuTu );     tempCS->picture->cs->useSubStructure( *tempCS, partitioner.chType, CS::getArea( *tempCS, partitioner.currArea(), partitioner.chType ), false, true, false, false );  #if JVET_Q0438_MONOCHROME_BUGFIXES     if (isChromaEnabled(tempCS->pcv->chrFormat))     { #endif     partitioner.chType = CHANNEL_TYPE_CHROMA;     tempCS->treeType = partitioner.treeType = TREE_C;      m_CurrCtx++;      const unsigned wIdx = gp_sizeIdxInfo->idxFrom( partitioner.currArea().lwidth() );     const unsigned hIdx = gp_sizeIdxInfo->idxFrom( partitioner.currArea().lheight() );     CodingStructure *tempCSChroma = m_pTempCS2[wIdx][hIdx];     CodingStructure *bestCSChroma = m_pBestCS2[wIdx][hIdx];     tempCS->initSubStructure( *tempCSChroma, partitioner.chType, partitioner.currArea(), false );     tempCS->initSubStructure( *bestCSChroma, partitioner.chType, partitioner.currArea(), false );     tempCS->treeType = TREE_D;     xCompressCU( tempCSChroma, bestCSChroma, partitioner );      //attach chromaCS to luma CS and update cost     bool keepResi = KEEP_PRED_AND_RESI_SIGNALS;     //bestCSChroma->treeType = tempCSChroma->treeType = TREE_C;     CHECK( bestCSChroma->treeType != TREE_C || tempCSChroma->treeType != TREE_C, "wrong treeType for chroma CS" );     tempCS->useSubStructure( *bestCSChroma, partitioner.chType, CS::getArea( *bestCSChroma, partitioner.currArea(), partitioner.chType ), KEEP_PRED_AND_RESI_SIGNALS, true, keepResi, true );      //release tmp resource     tempCSChroma->releaseIntermediateData();     bestCSChroma->releaseIntermediateData();     //tempCS->picture->cs->releaseIntermediateData(); #if JVET_Q0438_MONOCHROME_BUGFIXES       m_CurrCtx--;     } #endif     tempCS->picture->cs->clearCuPuTuIdxMap( partitioner.currArea(), numCuPuTu[0], numCuPuTu[1], numCuPuTu[2], numCuPuTu + 3 );  #if !JVET_Q0438_MONOCHROME_BUGFIXES     m_CurrCtx--; #endif      //recover luma tree status     partitioner.chType = CHANNEL_TYPE_LUMA;     partitioner.treeType = TREE_D;     partitioner.modeType = MODE_TYPE_ALL;   }    // Finally, generate split-signaling bits for RD-cost check   const PartSplit implicitSplit = partitioner.getImplicitSplit( *tempCS );    {     bool enforceQT = implicitSplit == CU_QUAD_SPLIT;      // LARGE CTU bug     if( m_pcEncCfg->getUseFastLCTU() )     {       unsigned minDepth = 0;       unsigned maxDepth = floorLog2(tempCS->sps->getCTUSize()) - floorLog2(tempCS->sps->getMinQTSize(slice.getSliceType(), partitioner.chType));        if( auto ad = dynamic_cast<AdaptiveDepthPartitioner*>( &partitioner ) )       {         ad->setMaxMinDepth( minDepth, maxDepth, *tempCS );       }        if( minDepth > partitioner.currQtDepth )       {         // enforce QT         enforceQT = true;       }     }      if( !enforceQT )     {       m_CABACEstimator->resetBits();        m_CABACEstimator->split_cu_mode( split, *tempCS, partitioner );       partitioner.modeType = modeTypeParent;       m_CABACEstimator->mode_constraint( split, *tempCS, partitioner, modeTypeChild );       tempCS->fracBits += m_CABACEstimator->getEstFracBits(); // split bits加上划分的bit     }   }    tempCS->cost = m_pcRdCost->calcRdCost( tempCS->fracBits, tempCS->dist );//计算当前划分模式总的代价    // Check Delta QP bits for splitted structure   if( !qgEnableChildren ) // check at deepest QG level only   xCheckDQP( *tempCS, partitioner, true );    // If the configuration being tested exceeds the maximum number of bytes for a slice / slice-segment, then   // a proper RD evaluation cannot be performed. Therefore, termination of the   // slice/slice-segment must be made prior to this CTU.   // This can be achieved by forcing the decision to be that of the rpcTempCU.   // The exception is each slice / slice-segment must have at least one CTU.   if (bestCS->cost != MAX_DOUBLE)   {   }   else   {     bestCS->costDbOffset = 0;   }   tempCS->useDbCost = m_pcEncCfg->getUseEncDbOpt();   if( tempCS->cus.size() > 0 && modeTypeParent == MODE_TYPE_ALL && modeTypeChild == MODE_TYPE_INTER )   {     int areaSizeNoResiCu = 0;     for( int k = 0; k < tempCS->cus.size(); k++ )     {       areaSizeNoResiCu += (tempCS->cus[k]->rootCbf == false) ? tempCS->cus[k]->lumaSize().area() : 0;     }     if( areaSizeNoResiCu >= (tempCS->area.lumaSize().area() >> 1) )     {       skipInterPass = true;     }   }    // RD check for sub partitioned coding structure.   xCheckBestMode( tempCS, bestCS, partitioner, encTestMode );//比较当前划分方式与之前划分方式，然后选择代价较小的    if (isAffMVInfoSaved)     m_pcInterSearch->addAffMVInfo(tmpMVInfo);   if (!tempCS->slice->isIntra() && isUniMvInfoSaved)   {     m_pcInterSearch->addUniMvInfo(tmpUniMvInfo);   }    tempCS->motionLut = oldMotionLut;    tempCS->prevPLT   = oldPLT;    tempCS->releaseIntermediateData();    tempCS->prevQP[partitioner.chType] = oldPrevQp;  }

      这部分代码稍微看的有点绕，是由于xCompressCU函数中调用了函数xCheckModeSplit，在函数xCheckModeSplit又调用了xCompressCU。这样CU递归划分直到不能划分为止。对CU进行RDO的逻辑是先对当前CU进行编码，再对其划分，对划分完的各个子块进行编码，若（不划分的RDcost）> (划分的RDcost+划分需要多传输的bit数)，那么就进行划分，否则不划分。可以在xCompressCU函数开头打印log判断cu划分与编码的顺序。如下图所示，其中模式5为帧内预测模式，其余为划分模式。