H.266/VVC VTM阅读9-样点储存结构

  VTM中使用10位比特表示样点，也就是说样点值范围0-1023，因此可以用16位整型数表示一个样点值，VTM中定义了样点值类型Pel。

typedef short              int16_t;
typedef       int16_t           Pel;  

  VTM中建立了多种buffer灵活储存各种类型和用途的样点值，此处梳理下VTM中样点储存的部分buffer。

1、C++ Template简介

  模板Template用于将数据类型作为参数传入函数或者类中，例如常用的vector容器在使用中需要指定数据类型。模板可以用于分为函数模板和类\结构体模板，例如函数模板，

#include 
#include 
using namespace std;
 
template <typename T>
inline T const& Max (T const& a, T const& b) 
{ 
    return a < b ? b:a; 
} 
int main ()
{
 
    int i = 39;
    int j = 20;
    cout << "Max(i, j): " << Max(i, j) << endl; 
 
    double f1 = 13.5; 
    double f2 = 20.7; 
    cout << "Max(f1, f2): " << Max(f1, f2) << endl; 
 
    string s1 = "Hello"; 
    string s2 = "World"; 
    cout << "Max(s1, s2): " << Max(s1, s2) << endl; 
 
   return 0;
}

2、AreaBuf / PelBuf

  AreaBuf表示一个二维区域的某些元素组成的buffer，含有一个指向buffer第一个元素的指针buf，一组低维数据的元素个数stride，以及继承自Size表示区域宽和高的width和height。AreaBuf仅储存一个二维区域数据，不含该区域所在视频帧中位置的信息。

template<typename T>
struct AreaBuf : public Size
{
  T*        buf;
  int       stride;
  // the proper type causes awful lot of errors
  //ptrdiff_t stride;

  AreaBuf()                                                                               : Size(),                  buf( NULL ), stride( 0 )          { }
  AreaBuf( T *_buf, const Size &size )                                                    : Size( size ),            buf( _buf ), stride( size.width ) { }
  AreaBuf( T *_buf, const int &_stride, const Size &size )                                : Size( size ),            buf( _buf ), stride( _stride )    { }
  AreaBuf( T *_buf, const SizeType &_width, const SizeType &_height )                     : Size( _width, _height ), buf( _buf ), stride( _width )     { }
  AreaBuf( T *_buf, const int &_stride, const SizeType &_width, const SizeType &_height ) : Size( _width, _height ), buf( _buf ), stride( _stride )    { }
 
  ...
}

  AreaBuf使用了结构体模板，因此可以储存多种数据类型的数据，如果储存Pel类型数据，则定义为PelBuf。

typedef AreaBuf<      Pel>  PelBuf;
typedef AreaBuf<const Pel> CPelBuf;

typedef AreaBuf<      TCoeff>  CoeffBuf;
typedef AreaBuf<const TCoeff> CCoeffBuf;

typedef AreaBuf<      MotionInfo>  MotionBuf;
typedef AreaBuf<const MotionInfo> CMotionBuf;

typedef AreaBuf<      TCoeff>  PLTescapeBuf;
typedef AreaBuf<const TCoeff> CPLTescapeBuf;

typedef AreaBuf<      bool>  PLTtypeBuf;
typedef AreaBuf<const bool> CPLTtypeBuf;

3、UnitBuf / PelUnitBuf

  与CompArea和UnitArea的关系类似，可以用三个AreaBuf分别储存三个分量的元素来形成更高维度的区域UnitBuf。UnitBuf中含有表示视频格式的chromaFormat，以及用于储存元素的buf，buf由三个AreaBuf组成。

template<typename T>
struct UnitBuf
{
  typedef static_vector<AreaBuf<T>,       MAX_NUM_COMPONENT> UnitBufBuffers;
  typedef static_vector<AreaBuf<const T>, MAX_NUM_COMPONENT> ConstUnitBufBuffers;

  ChromaFormat chromaFormat;
  UnitBufBuffers bufs;

  UnitBuf() : chromaFormat( NUM_CHROMA_FORMAT ) { }
  UnitBuf( const ChromaFormat &_chromaFormat, const UnitBufBuffers&  _bufs ) : chromaFormat( _chromaFormat ), bufs( _bufs ) { }
  UnitBuf( const ChromaFormat &_chromaFormat,       UnitBufBuffers&& _bufs ) : chromaFormat( _chromaFormat ), bufs( std::forward<UnitBufBuffers>( _bufs ) ) { }
  UnitBuf( const ChromaFormat &_chromaFormat, const AreaBuf<T>  &blkY ) : chromaFormat( _chromaFormat ), bufs{ blkY } { }
  UnitBuf( const ChromaFormat &_chromaFormat,       AreaBuf<T> &&blkY ) : chromaFormat( _chromaFormat ), bufs{ std::forward<AreaBuf<T> >(blkY) } { }
  UnitBuf( const ChromaFormat &_chromaFormat, const AreaBuf<T>  &blkY, const AreaBuf<T>  &blkCb, const AreaBuf<T>  &blkCr ) : chromaFormat( _chromaFormat ), bufs{ blkY, blkCb, blkCr } { }
  UnitBuf( const ChromaFormat &_chromaFormat,       AreaBuf<T> &&blkY,       AreaBuf<T> &&blkCb,       AreaBuf<T> &&blkCr ) : chromaFormat( _chromaFormat ), bufs{ std::forward<AreaBuf<T> >(blkY), std::forward<AreaBuf<T> >(blkCb), std::forward<AreaBuf<T> >(blkCr) } { }
 
  ...
}

4、PelStorage

  PelStorage继承PelUnitBuf，区别是加了一个m_origin变量。m_origin储存了padding后的元素，具体操作参考以下代码。

void PelStorage::create( const ChromaFormat &_chromaFormat, const Area& _area, const unsigned _maxCUSize, const unsigned _margin, const unsigned _alignment, const bool _scaleChromaMargin )
{
  CHECK( !bufs.empty(), "Trying to re-create an already initialized buffer" );

  chromaFormat = _chromaFormat;

  const uint32_t numCh = getNumberValidComponents( _chromaFormat );

  unsigned extHeight = _area.height;
  unsigned extWidth  = _area.width;

  if( _maxCUSize )
  {
    extHeight = ( ( _area.height + _maxCUSize - 1 ) / _maxCUSize ) * _maxCUSize;
    extWidth  = ( ( _area.width  + _maxCUSize - 1 ) / _maxCUSize ) * _maxCUSize;
  }

  for( uint32_t i = 0; i < numCh; i++ )
  {
    const ComponentID compID = ComponentID( i );
    const unsigned scaleX = ::getComponentScaleX( compID, _chromaFormat );
    const unsigned scaleY = ::getComponentScaleY( compID, _chromaFormat );

    unsigned scaledHeight = extHeight >> scaleY;
    unsigned scaledWidth  = extWidth  >> scaleX;
    unsigned ymargin      = _margin >> (_scaleChromaMargin?scaleY:0);
    unsigned xmargin      = _margin >> (_scaleChromaMargin?scaleX:0);
    unsigned totalWidth   = scaledWidth + 2*xmargin;
    unsigned totalHeight  = scaledHeight +2*ymargin;

    if( _alignment )
    {
      // make sure buffer lines are align
      CHECK( _alignment != MEMORY_ALIGN_DEF_SIZE, "Unsupported alignment" );
      totalWidth = ( ( totalWidth + _alignment - 1 ) / _alignment ) * _alignment;
    }
    uint32_t area = totalWidth * totalHeight;
    CHECK( !area, "Trying to create a buffer with zero area" );

    m_origin[i] = ( Pel* ) xMalloc( Pel, area );
    Pel* topLeft = m_origin[i] + totalWidth * ymargin + xmargin;
    bufs.push_back( PelBuf( topLeft, totalWidth, _area.width >> scaleX, _area.height >> scaleY ) );
  }
}