D3DXMATRIXA16 structure (D3dx9math.h)

Article
04/28/2022

Note

The D3DX utility library is deprecated. We recommend that you use DirectXMath instead.

A 4x4, 16-byte-aligned matrix that contains methods and operator overloads.

Syntax

typedef struct D3DXMATRIXA16 {
  FLOAT _ij;
} D3DXMATRIXA16, *LPD3DXMATRIXA16;

Members

_ij: Type: FLOAT; The (i, j) component of the matrix, where i is the row number and j is the column number. For example, _34 means the same as [a₃₄], the component in the third row and fourth column.

Remarks

A 16-byte aligned matrix, when used by D3DX math functions, has been optimized for improved performance on Intel Pentium 4 processors. Matrices are aligned independent of where they are created: on the program stack, in the heap, or in global scope. Alignment is accomplished using __declspec(align(16)), which works with Visual C++ .NET and with Visual C++ 6.0 only when the processor pack is installed. Unfortunately, there is no way to detect the processor pack, so byte alignment is turned on by default only with Visual C++ .NET.

Vectors and quaternions are not byte aligned in D3DX. When using vectors and quaternions with D3DX math functions, use _declspec(align(16)) to generate byte aligned vectors and quaternions, because they will perform significantly better. The definition of _declspec is shown here.

#define D3DX_ALIGN16 __declspec(align(16))

Other compilers interpret D3DXMATRIXA16 as D3DXMATRIX. Using this structure on a compiler that does not actually align the matrix can be problematic because it will not expose bugs that ignore alignment. For example, if a D3DXMATRIXA16 object is inside a structure or class, a memcpy might be done with tight packing (ignoring 16-byte boundaries). This would cause build breaks if the compiler were to sometime add matrix aligning.

D3DXMATRIXA16

D3DXMATRIXA16 has the following C++ extensions.

typedef struct _D3DXMATRIXA16 : public D3DXMATRIX
{
    _D3DXMATRIXA16();
    _D3DXMATRIXA16( CONST FLOAT * f);
    _D3DXMATRIXA16( CONST D3DMATRIX& m);
    _D3DXMATRIXA16( FLOAT _11, FLOAT _12, FLOAT _13, FLOAT _14,
                    FLOAT _21, FLOAT _22, FLOAT _23, FLOAT _24,
                    FLOAT _31, FLOAT _32, FLOAT _33, FLOAT _34,
                    FLOAT _41, FLOAT _42, FLOAT _43, FLOAT _44 );
    void* operator new(size_t s);
    void* operator new[](size_t s);

    // The two operators below are not virtual operators. If you cast
    //   to D3DXMATRIX, do not delete using them
    void operator delete(void* p);
    void operator delete[](void* p);

    struct _D3DXMATRIXA16& operator=(CONST D3DXMATRIX& rhs);
} _D3DXMATRIXA16;

typedef D3DX_ALIGN16 _D3DXMATRIXA16 D3DXMATRIXA16, *LPD3DXMATRIXA16;

Requirements

Requirement	Value
Header	D3dx9math.h