VVC系列（四）initCULevel代码解读

文章目录

函数流程
源码注释

函数流程

参考自 H.266/VVC-VTM代码学习19-CU层确定测试模式函数initCULevel， VVC中CTU的编码，块划分以及qp的决策 - 知乎 (zhihu.com)，本文主要讲解VTM18.0中的EncModeCtrlMTnoRQT::initCULevel的流程，该函数在EncCu::xCompressCU的开始被调用，将需要测试的划分模式和编码模式加入堆栈。主要步骤：

1、确定最大和最小搜索深度，如果开启Large CTU，会根据周围块的深度进行调整

2、根据baseQP设置附近的minQP和maxQP，并在添加后续模式时遍历可能的QP

3、添加划分模式，默认添加顺序是QT、TTV、TTH、BTV 、BTH和Non-split，因为是保存在堆栈中，测试顺序相反。值得注意的是，当current CU的 QtDepth 小于左侧和上侧相邻CU的 QtDepth 时，或者 current CU的决策深度较浅时，会将QT的测试顺序放在BT之前。此外，QT和TT共用一套QP range，BT单独使用一套QP range

4、添加测试模式，此时的QP range是Non-split的，包括 intra、inter、IBC 和 palette等模式

该函数进一步调用canSplit确定划分模式是否合法，

源码注释

// VTM18.0
void EncModeCtrlMTnoRQT::initCULevel( Partitioner &partitioner, const CodingStructure& cs )
{// 该函数主要完成编码端RD cost的模式筛选，并加入各种划分模式和inter intra模式等至RDO列表// Min/max depthunsigned minDepth = 0;unsigned maxDepth = floorLog2(cs.sps->getCTUSize()) - floorLog2(cs.sps->getMinQTSize( m_slice->getSliceType(), partitioner.chType ));// 最大搜索深度 = log(CTU_Size / minQTSize), by default log(128 / 4) = 5if( m_pcEncCfg->getUseFastLCTU() ){if( auto adPartitioner = dynamic_cast<AdaptiveDepthPartitioner*>( &partitioner ) ){// LARGE CTU// 根据当前块的临近块拓展maxDepth和minDepthadPartitioner->setMaxMinDepth( minDepth, maxDepth, cs );}}// 写入最大和最小深度m_ComprCUCtxList.push_back( ComprCUCtx( cs, minDepth, maxDepth, NUM_EXTRA_FEATURES ) ); const CodingUnit* cuLeft  = cs.getCU( cs.area.blocks[partitioner.chType].pos().offset( -1, 0 ), partitioner.chType );const CodingUnit* cuAbove = cs.getCU( cs.area.blocks[partitioner.chType].pos().offset( 0, -1 ), partitioner.chType );// 如果左侧CU和上方CU存在，而且存在CU的qtDepth大于当前CU的QT深度，则在BT之前尝试QT划分（默认顺序是non-split, BTH, BTV, TTH, QT）// 如果都不存在，Width >= 32 * 2^depth and Width > minQTSize * 2, 也将QT提前到BT之前const bool qtBeforeBt = ( (  cuLeft  &&  cuAbove  && cuLeft ->qtDepth > partitioner.currQtDepth && cuAbove->qtDepth > partitioner.currQtDepth )|| (  cuLeft  && !cuAbove  && cuLeft ->qtDepth > partitioner.currQtDepth )|| ( !cuLeft  &&  cuAbove  && cuAbove->qtDepth > partitioner.currQtDepth )|| ( !cuAbove && !cuLeft   && cs.area.lwidth() >= ( 32 << cs.slice->getDepth() ) ) )&& ( cs.area.lwidth() > ( cs.pcv->getMinQtSize( *cs.slice, partitioner.chType ) << 1 ) );// set featuresComprCUCtx &cuECtx  = m_ComprCUCtxList.back();cuECtx.set( BEST_NON_SPLIT_COST,  MAX_DOUBLE );cuECtx.set( BEST_VERT_SPLIT_COST, MAX_DOUBLE );cuECtx.set( BEST_HORZ_SPLIT_COST, MAX_DOUBLE );cuECtx.set( BEST_TRIH_SPLIT_COST, MAX_DOUBLE );cuECtx.set( BEST_TRIV_SPLIT_COST, MAX_DOUBLE );cuECtx.set( DO_TRIH_SPLIT,        1 );cuECtx.set( DO_TRIV_SPLIT,        1 );cuECtx.set( BEST_IMV_COST,        MAX_DOUBLE * .5 );cuECtx.set( BEST_NO_IMV_COST,     MAX_DOUBLE * .5 );cuECtx.set( QT_BEFORE_BT,         qtBeforeBt );cuECtx.set( DID_QUAD_SPLIT,       false );cuECtx.set( IS_BEST_NOSPLIT_SKIP, false );cuECtx.set( MAX_QT_SUB_DEPTH,     0 );// QPint baseQP = cs.baseQP;  // Slice级别的QP// SepTree 包括 帧内的Dual tree，以及帧间的local dual Treeif (!partitioner.isSepTree(cs) || isLuma(partitioner.chType))  // joint Tree 或者 luma 分量{if (m_pcEncCfg->getUseAdaptiveQP()){// baseQP 取 -(6 * (m_bitDepth[CHANNEL_TYPE_LUMA] - 8) 和 63 和 sliceQP + delta 中的中值baseQP = Clip3(-cs.sps->getQpBDOffset(CHANNEL_TYPE_LUMA), MAX_QP, baseQP + xComputeDQP(cs, partitioner));}
#if ENABLE_QPA_SUB_CTUelse if (m_pcEncCfg->getUsePerceptQPA() && !m_pcEncCfg->getUseRateCtrl() && cs.pps->getUseDQP() && cs.slice->getCuQpDeltaSubdiv() > 0){const PreCalcValues &pcv = *cs.pcv;if ((partitioner.currArea().lwidth() < pcv.maxCUWidth) && (partitioner.currArea().lheight() < pcv.maxCUHeight) && cs.picture){const Position    &pos = partitioner.currQgPos;const unsigned mtsLog2 = (unsigned)floorLog2(std::min (cs.sps->getMaxTbSize(), pcv.maxCUWidth));const unsigned  stride = pcv.maxCUWidth >> mtsLog2;baseQP = cs.picture->m_subCtuQP[((pos.x & pcv.maxCUWidthMask) >> mtsLog2) + stride * ((pos.y & pcv.maxCUHeightMask) >> mtsLog2)];}}
#endif
#if SHARP_LUMA_DELTA_QPif (m_pcEncCfg->getLumaLevelToDeltaQPMapping().isEnabled()){if (partitioner.currQgEnable()){m_lumaQPOffset = calculateLumaDQP (cs.getOrgBuf (clipArea (cs.area.Y(), cs.picture->Y())));}baseQP = Clip3 (-cs.sps->getQpBDOffset (CHANNEL_TYPE_LUMA), MAX_QP, baseQP - m_lumaQPOffset);}
#endifif (m_pcEncCfg->getSmoothQPReductionEnable()){int smoothQPoffset = 0;if (partitioner.currQgEnable()){// enable smooth QP reduction on selected framesbool checkSmoothQP = false;if (m_pcEncCfg->getSmoothQPReductionPeriodicity() != 0){checkSmoothQP = ((m_pcEncCfg->getSmoothQPReductionPeriodicity() == 0) && cs.slice->isIntra()) || (m_pcEncCfg->getSmoothQPReductionPeriodicity() == 1) || ((cs.slice->getPOC() % m_pcEncCfg->getSmoothQPReductionPeriodicity()) == 0);}else{checkSmoothQP = ((m_pcEncCfg->getSmoothQPReductionPeriodicity() == 0) && cs.slice->isIntra());}if (checkSmoothQP){bool isIntraSlice = cs.slice->isIntra();if (isIntraSlice){smoothQPoffset = calculateLumaDQPsmooth(cs.getOrgBuf(clipArea(cs.area.Y(), cs.picture->Y())), baseQP, m_pcEncCfg->getSmoothQPReductionThresholdIntra(), m_pcEncCfg->getSmoothQPReductionModelScaleIntra(), m_pcEncCfg->getSmoothQPReductionModelOffsetIntra(), m_pcEncCfg->getSmoothQPReductionLimitIntra());}else{smoothQPoffset = calculateLumaDQPsmooth(cs.getOrgBuf(clipArea(cs.area.Y(), cs.picture->Y())), baseQP, m_pcEncCfg->getSmoothQPReductionThresholdInter(), m_pcEncCfg->getSmoothQPReductionModelScaleInter(), m_pcEncCfg->getSmoothQPReductionModelOffsetInter(), m_pcEncCfg->getSmoothQPReductionLimitInter());}}}baseQP = Clip3(-cs.sps->getQpBDOffset(CHANNEL_TYPE_LUMA), MAX_QP, baseQP + smoothQPoffset);}}// 以下是在base QP附近设定minQP和maxQP，再RD 测试两者之间的所有取值，确定最佳的minQP和maxQPint minQP = baseQP;int maxQP = baseQP;xGetMinMaxQP( minQP, maxQP, cs, partitioner, baseQP, *cs.sps, *cs.pps, CU_QUAD_SPLIT );  // 针对四叉树和三叉树//色度分量不检查IBC模式bool checkIbc = true;if (partitioner.chType == CHANNEL_TYPE_CHROMA){checkIbc = false;}// Add coding modes here// NOTE: Working back to front, as a stack, which is more efficient with the container// NOTE: First added modes will be processed at the end.// 注意：划分模式是先入后出//// Add unit split modes// 添加划分模式进入测试列表if( !cuECtx.get<bool>( QT_BEFORE_BT ) ){for( int qp = maxQP; qp >= minQP; qp-- )  // 遍历可能的QP参数{m_ComprCUCtxList.back().testModes.push_back( { ETM_SPLIT_QT, ETO_STANDARD, qp } );  // if not qt_before_bt, then push back QT_mode}}if( partitioner.canSplit( CU_TRIV_SPLIT, cs ) ){// add split modesfor( int qp = maxQP; qp >= minQP; qp-- ){m_ComprCUCtxList.back().testModes.push_back( { ETM_SPLIT_TT_V, ETO_STANDARD, qp } );    // 三叉树竖直划分}}if( partitioner.canSplit( CU_TRIH_SPLIT, cs ) ){// add split modesfor( int qp = maxQP; qp >= minQP; qp-- ){m_ComprCUCtxList.back().testModes.push_back( { ETM_SPLIT_TT_H, ETO_STANDARD, qp } );    // 三叉树水平划分}}int minQPq = minQP;int maxQPq = maxQP;xGetMinMaxQP( minQP, maxQP, cs, partitioner, baseQP, *cs.sps, *cs.pps, CU_BT_SPLIT );  // 针对二叉树if( partitioner.canSplit( CU_VERT_SPLIT, cs ) ){// add split modesfor( int qp = maxQP; qp >= minQP; qp-- ){m_ComprCUCtxList.back().testModes.push_back( { ETM_SPLIT_BT_V, ETO_STANDARD, qp } );  // 二叉树竖直划分}m_ComprCUCtxList.back().set( DID_VERT_SPLIT, true );}else{m_ComprCUCtxList.back().set( DID_VERT_SPLIT, false );}if( partitioner.canSplit( CU_HORZ_SPLIT, cs ) ){// add split modesfor( int qp = maxQP; qp >= minQP; qp-- ){m_ComprCUCtxList.back().testModes.push_back( { ETM_SPLIT_BT_H, ETO_STANDARD, qp } );  // 二叉树水平划分}m_ComprCUCtxList.back().set( DID_HORZ_SPLIT, true );}else{m_ComprCUCtxList.back().set( DID_HORZ_SPLIT, false );}if( cuECtx.get<bool>( QT_BEFORE_BT ) ){for( int qp = maxQPq; qp >= minQPq; qp-- ){m_ComprCUCtxList.back().testModes.push_back( { ETM_SPLIT_QT, ETO_STANDARD, qp } );   // QT优先于BT划分}}m_ComprCUCtxList.back().testModes.push_back( { ETM_POST_DONT_SPLIT } );  // 不划分xGetMinMaxQP( minQP, maxQP, cs, partitioner, baseQP, *cs.sps, *cs.pps, CU_DONT_SPLIT );  // 设置不划分的QP，即当前块的intra inter IBC等模式需要test的QP rangeint  lowestQP = minQP;//// Add unit coding modes: Intra, InterME, InterMerge ...// 添加单元编码模式bool tryIntraRdo = true;  // 是否尝试Intra mode RDObool tryInterRdo = true;  // 是否尝试Inter mode RDObool tryIBCRdo   = true;if( partitioner.isConsIntra() ){tryInterRdo = false;  }else if( partitioner.isConsInter() ){tryIntraRdo = tryIBCRdo = false;}checkIbc &= tryIBCRdo;for( int qpLoop = maxQP; qpLoop >= minQP; qpLoop-- ){const int  qp       = std::max( qpLoop, lowestQP );
#if REUSE_CU_RESULTSconst bool isReusingCu = isValid( cs, partitioner, qp );cuECtx.set( IS_REUSING_CU, isReusingCu );if( isReusingCu ){m_ComprCUCtxList.back().testModes.push_back( {ETM_RECO_CACHED, ETO_STANDARD, qp} );}
#endif// add intra modesif( tryIntraRdo ){if (cs.slice->getSPS()->getPLTMode()&& (partitioner.treeType != TREE_D || cs.slice->isIntra()|| (cs.area.lwidth() == 4 && cs.area.lheight() == 4))&& getPltEnc()){m_ComprCUCtxList.back().testModes.push_back({ ETM_PALETTE, ETO_STANDARD, qp });  // paletee mode， 屏幕内容编码的一种模式}m_ComprCUCtxList.back().testModes.push_back({ ETM_INTRA, ETO_STANDARD, qp });if (cs.slice->getSPS()->getPLTMode() && partitioner.treeType == TREE_D && !cs.slice->isIntra()&& !(cs.area.lwidth() == 4 && cs.area.lheight() == 4) && getPltEnc()){m_ComprCUCtxList.back().testModes.push_back({ ETM_PALETTE, ETO_STANDARD, qp });}}// add ibc mode to intra pathif (cs.sps->getIBCFlag() && checkIbc){m_ComprCUCtxList.back().testModes.push_back({ ETM_IBC,         ETO_STANDARD,  qp });if (partitioner.chType == CHANNEL_TYPE_LUMA){m_ComprCUCtxList.back().testModes.push_back({ ETM_IBC_MERGE,   ETO_STANDARD,  qp });}}}// add first pass modesif ( !m_slice->isIntra() && !( cs.area.lwidth() == 4 && cs.area.lheight() == 4 ) && tryInterRdo ){for( int qpLoop = maxQP; qpLoop >= minQP; qpLoop-- ){const int  qp       = std::max( qpLoop, lowestQP );if (m_pcEncCfg->getIMV()){m_ComprCUCtxList.back().testModes.push_back({ ETM_INTER_ME,  EncTestModeOpts( 4 << ETO_IMV_SHIFT ), qp });  }if( m_pcEncCfg->getIMV() || m_pcEncCfg->getUseAffineAmvr() ){int imv = m_pcEncCfg->getIMV4PelFast() ? 3 : 2;m_ComprCUCtxList.back().testModes.push_back( { ETM_INTER_ME, EncTestModeOpts( imv << ETO_IMV_SHIFT ), qp } );m_ComprCUCtxList.back().testModes.push_back( { ETM_INTER_ME, EncTestModeOpts( 1 << ETO_IMV_SHIFT ), qp } );}// add inter modesif( m_pcEncCfg->getUseEarlySkipDetection() ){if( cs.sps->getUseGeo() && cs.slice->isInterB() ){m_ComprCUCtxList.back().testModes.push_back( { ETM_MERGE_GEO, ETO_STANDARD, qp } );}m_ComprCUCtxList.back().testModes.push_back( { ETM_MERGE_SKIP,  ETO_STANDARD, qp } );if (cs.sps->getUseAffine() || (cs.sps->getSbTMVPEnabledFlag() && cs.slice->getPicHeader()->getEnableTMVPFlag())){m_ComprCUCtxList.back().testModes.push_back( { ETM_AFFINE,    ETO_STANDARD, qp } );}m_ComprCUCtxList.back().testModes.push_back( { ETM_INTER_ME,    ETO_STANDARD, qp } );}else{m_ComprCUCtxList.back().testModes.push_back( { ETM_INTER_ME,    ETO_STANDARD, qp } );if( cs.sps->getUseGeo() && cs.slice->isInterB() ){m_ComprCUCtxList.back().testModes.push_back( { ETM_MERGE_GEO, ETO_STANDARD, qp } );}m_ComprCUCtxList.back().testModes.push_back( { ETM_MERGE_SKIP,  ETO_STANDARD, qp } );if (cs.sps->getUseAffine() || (cs.sps->getSbTMVPEnabledFlag() && cs.slice->getPicHeader()->getEnableTMVPFlag())){m_ComprCUCtxList.back().testModes.push_back( { ETM_AFFINE,    ETO_STANDARD, qp } );}}if (m_pcEncCfg->getUseHashME()){int minSize = min(cs.area.lwidth(), cs.area.lheight());if (minSize < 128 && minSize >= 4){m_ComprCUCtxList.back().testModes.push_back({ ETM_HASH_INTER, ETO_STANDARD, qp });}}}}