关于HEVC HM中的xPredIntraAng帧内预测的方向性预测代码说明

此函数是针对HEVC draft中的8.4.4.2.6部分的解释

/** Function for deriving the simplified angular intra predictions.
 * \param pSrc pointer to reconstructed sample array
 * \param srcStride the stride of the reconstructed sample array
 * \param rpDst reference to pointer for the prediction sample array
 * \param dstStride the stride of the prediction sample array
 * \param width the width of the block
 * \param height the height of the block
 * \param dirMode the intra prediction mode index
 * \param blkAboveAvailable boolean indication if the block above is available
 * \param blkLeftAvailable boolean indication if the block to the left is available
 *
 * This function derives the prediction samples for the angular mode based on the prediction direction indicated by
 * the prediction mode index. The prediction direction is given by the displacement of the bottom row of the block and
 * the reference row above the block in the case of vertical prediction or displacement of the rightmost column
 * of the block and reference column left from the block in the case of the horizontal prediction. The displacement
 * is signalled at 1/32 pixel accuracy. When projection of the predicted pixel falls inbetween reference samples,
 * the predicted value for the pixel is linearly interpolated from the reference samples. All reference samples are taken
 * from the extended main reference.
 */
//NOTE: Bit-Limit - 25-bit source
//这个函数对应了8.4.4.2.6
Void TComPrediction::xPredIntraAng(       Int bitDepth,
                                    const Pel* pSrc,     Int srcStride,
                                          Pel* pTrueDst, Int dstStrideTrue,
                                          UInt uiWidth, UInt uiHeight, ChannelType channelType, ChromaFormat format,
                                          UInt dirMode, Bool blkAboveAvailable, Bool blkLeftAvailable
                                  , const Bool bEnableEdgeFilters
                                  )
{
  Int width=Int(uiWidth);
  Int height=Int(uiHeight);


  // Map the mode index to main prediction direction and angle
  assert( dirMode != PLANAR_IDX ); //no planar
  const Bool modeDC        = dirMode==DC_IDX;


  // Do the DC prediction
  if (modeDC)
  {
    const Pel dcval = predIntraGetPredValDC(pSrc, srcStride, width, height, channelType, format, blkAboveAvailable, blkLeftAvailable);
    for (Int y=height;y>0;y--, pTrueDst+=dstStrideTrue)
    {
      for (Int x=0; x<width;) // width is always a multiple of 4.
      {
        pTrueDst[x++] = dcval;
      }
    }
  }


  else // Do angular predictions
  {
    const Bool       bIsModeVer         = (dirMode >= 18);
    const Int        intraPredAngleMode = (bIsModeVer) ? (Int)dirMode - VER_IDX :  -((Int)dirMode - HOR_IDX);
    const Int        absAngMode         = abs(intraPredAngleMode);
    const Int        signAng            = intraPredAngleMode < 0 ? -1 : 1;
    const Bool       edgeFilter         = bEnableEdgeFilters && isLuma(channelType) && (width <= MAXIMUM_INTRA_FILTERED_WIDTH) && (height <= MAXIMUM_INTRA_FILTERED_HEIGHT);


    // Set bitshifts and scale the angle parameter to block size
    static const Int angTable[9]    = {0,    2,    5,   9,  13,  17,  21,  26,  32};
    static const Int invAngTable[9] = {0, 4096, 1638, 910, 630, 482, 390, 315, 256}; // (256 * 32) / Angle
    Int invAngle                    = invAngTable[absAngMode];
    Int absAng                      = angTable[absAngMode];
    Int intraPredAngle              = signAng * absAng;//从模式2~35获得角度方向（30~-30）,也就是从predModeIntra到intraPredAngle的转换




    Pel* refMain;
    Pel* refSide;


    Pel  refAbove[2*MAX_CU_SIZE+1];
    Pel  refLeft[2*MAX_CU_SIZE+1];


    // Initialise the Main and Left reference array.
    if (intraPredAngle < 0)
    {
      const Int refMainOffsetPreScale = (bIsModeVer ? height : width ) - 1;
      const Int refMainOffset         = height - 1;
      for (Int x=0;x<width+1;x++)
      {
        refAbove[x+refMainOffset] = pSrc[x-srcStride-1];
      }
      for (Int y=0;y<height+1;y++)
      {
        refLeft[y+refMainOffset] = pSrc[(y-1)*srcStride-1];
      }
      refMain = (bIsModeVer ? refAbove : refLeft)  + refMainOffset;
      refSide = (bIsModeVer ? refLeft  : refAbove) + refMainOffset;


      // Extend the Main reference to the left.
      Int invAngleSum    = 128;       // rounding for (shift by 8)
      for (Int k=-1; k>(refMainOffsetPreScale+1)*intraPredAngle>>5; k--)
      {
        invAngleSum += invAngle;
        refMain[k] = refSide[invAngleSum>>8];
      }
    }
    else
    {
      for (Int x=0;x<2*width+1;x++)
      {
        refAbove[x] = pSrc[x-srcStride-1];
      }
      for (Int y=0;y<2*height+1;y++)
      {
        refLeft[y] = pSrc[(y-1)*srcStride-1];
      }
      refMain = bIsModeVer ? refAbove : refLeft ;
      refSide = bIsModeVer ? refLeft  : refAbove;
    }


    // swap width/height if we are doing a horizontal mode:
    Pel tempArray[MAX_CU_SIZE*MAX_CU_SIZE];
    const Int dstStride = bIsModeVer ? dstStrideTrue : MAX_CU_SIZE;
    Pel *pDst = bIsModeVer ? pTrueDst : tempArray;
    if (!bIsModeVer)
    {
      std::swap(width, height);
    }


    if (intraPredAngle == 0)  // pure vertical or pure horizontal
    {
      for (Int y=0;y<height;y++)
      {
        for (Int x=0;x<width;x++)
        {
          pDst[y*dstStride+x] = refMain[x+1];
        }
      }


      if (edgeFilter)
      {
        for (Int y=0;y<height;y++)
        {
          pDst[y*dstStride] = Clip3 (0, ((1 << bitDepth) - 1), pDst[y*dstStride] + (( refSide[y+1] - refSide[0] ) >> 1) );
        }
      }
    }
    else
    {
      Pel *pDsty=pDst;


      for (Int y=0, deltaPos=intraPredAngle; y<height; y++, deltaPos+=intraPredAngle, pDsty+=dstStride)
      {
        const Int deltaInt   = deltaPos >> 5;//对应draft里的iIdx
        const Int deltaFract = deltaPos & (32 - 1);//对应draft里的iFact


        if (deltaFract)
        {
          // Do linear filtering
          const Pel *pRM=refMain+deltaInt+1;
          Int lastRefMainPel=*pRM++;
          for (Int x=0;x<width;pRM++,x++)
          {
            Int thisRefMainPel=*pRM;
            pDsty[x+0] = (Pel) ( ((32-deltaFract)*lastRefMainPel + deltaFract*thisRefMainPel +16) >> 5 );
            lastRefMainPel=thisRefMainPel;
          }
        }
        else
        {
          // Just copy the integer samples
          for (Int x=0;x<width; x++)
          {
            pDsty[x] = refMain[x+deltaInt+1];
          }
        }
      }
    }


    // Flip the block if this is the horizontal mode
    if (!bIsModeVer)
    {
      for (Int y=0; y<height; y++)
      {
        for (Int x=0; x<width; x++)
        {
          pTrueDst[x*dstStrideTrue] = pDst[x];
        }
        pTrueDst++;
        pDst+=dstStride;
      }
    }
  }

}

代码里已经解释的很清楚，希望大家可以相互交流。