ncnn Mat矩阵类

ncnn-mat.h

class NCNN_EXPORT Mat

构造函数

    // empty
    Mat();
    // vec
    Mat(int w, size_t elemsize = 4u, Allocator* allocator = 0);
    // image
    Mat(int w, int h, size_t elemsize = 4u, Allocator* allocator = 0);
    // dim
    Mat(int w, int h, int c, size_t elemsize = 4u, Allocator* allocator = 0);
    // cube
    Mat(int w, int h, int d, int c, size_t elemsize = 4u, Allocator* allocator = 0);
    // packed vec
    Mat(int w, size_t elemsize, int elempack, Allocator* allocator = 0);
    // packed image
    Mat(int w, int h, size_t elemsize, int elempack, Allocator* allocator = 0);
    // packed dim
    Mat(int w, int h, int c, size_t elemsize, int elempack, Allocator* allocator = 0);
    // packed cube
    Mat(int w, int h, int d, int c, size_t elemsize, int elempack, Allocator* allocator = 0);
    // copy
    Mat(const Mat& m);
    // external vec
    Mat(int w, void* data, size_t elemsize = 4u, Allocator* allocator = 0);
    // external image
    Mat(int w, int h, void* data, size_t elemsize = 4u, Allocator* allocator = 0);
    // external dim
    Mat(int w, int h, int c, void* data, size_t elemsize = 4u, Allocator* allocator = 0);
    // external cube
    Mat(int w, int h, int d, int c, void* data, size_t elemsize = 4u, Allocator* allocator = 0);
    // external packed vec
    Mat(int w, void* data, size_t elemsize, int elempack, Allocator* allocator = 0);
    // external packed image
    Mat(int w, int h, void* data, size_t elemsize, int elempack, Allocator* allocator = 0);
    // external packed dim
    Mat(int w, int h, int c, void* data, size_t elemsize, int elempack, Allocator* allocator = 0);
    // external packed cube
    Mat(int w, int h, int d, int c, void* data, size_t elemsize, int elempack, Allocator* allocator = 0);
    // release
    ~Mat();
    // assign
    Mat& operator=(const Mat& m);

    。。。
    。。。
    。。。

参数：

w:图像宽

h:图像高

c:通道数

elemsize：元素字节数  // 4 = float32/int32， // 2 = float16， // 1 = int8/uint8， // 0 = empty

elempack

构造函数实现内部调用create重载函数

NCNN_FORCEINLINE Mat::Mat()
    : data(0), refcount(0), elemsize(0), elempack(0), allocator(0), dims(0), w(0), h(0), d(0), c(0), cstep(0)
{
}

NCNN_FORCEINLINE Mat::Mat(int _w, size_t _elemsize, Allocator* _allocator)
    : data(0), refcount(0), elemsize(0), elempack(0), allocator(0), dims(0), w(0), h(0), d(0), c(0), cstep(0)
{
    create(_w, _elemsize, _allocator);
}

NCNN_FORCEINLINE Mat::Mat(int _w, int _h, size_t _elemsize, Allocator* _allocator)
    : data(0), refcount(0), elemsize(0), elempack(0), allocator(0), dims(0), w(0), h(0), d(0), c(0), cstep(0)
{
    create(_w, _h, _elemsize, _allocator);
}

NCNN_FORCEINLINE Mat::Mat(int _w, int _h, int _c, size_t _elemsize, Allocator* _allocator)
    : data(0), refcount(0), elemsize(0), elempack(0), allocator(0), dims(0), w(0), h(0), d(0), c(0), cstep(0)
{
    create(_w, _h, _c, _elemsize, _allocator);
}

NCNN_FORCEINLINE Mat::Mat(int _w, int _h, int _d, int _c, size_t _elemsize, Allocator* _allocator)
    : data(0), refcount(0), elemsize(0), elempack(0), allocator(0), dims(0), w(0), h(0), d(0), c(0), cstep(0)
{
    create(_w, _h, _d, _c, _elemsize, _allocator);
}
...
...
...

创建Mat对象后，根据构造函数重载对应调用create重载函数，实现数据内存空间申请，字节对齐等操作，没有赋值，默认值是？

void Mat::create(int _w, int _h, int _d, int _c, size_t _elemsize, int _elempack, Allocator* _allocator)
{
    if (dims == 4 && w == _w && h == _h && d == _d && c == _c && elemsize == _elemsize && elempack == _elempack && allocator == _allocator)
        return;

    release();

    elemsize = _elemsize;
    elempack = _elempack;
    allocator = _allocator;

    dims = 4;
    w = _w;
    h = _h;
    d = _d;
    c = _c;

    cstep = alignSize((size_t)w * h * d * elemsize, 16) / elemsize;

    if (total() > 0)
    {
        size_t totalsize = alignSize(total() * elemsize, 4);
        if (allocator)
            data = allocator->fastMalloc(totalsize + (int)sizeof(*refcount));
        else
            data = fastMalloc(totalsize + (int)sizeof(*refcount));
        refcount = (int*)(((unsigned char*)data) + totalsize);
        *refcount = 1;
    }
}

详细参考：ncnn初探二: 图解ncnn::Mat的内存排布 - 知乎