How to split a A*A std::array into chunks of B*B?

Question

if I have a std::array<std::array<int, 4>, 4> mydata, how would I split this into smaller chunks or std::array<std::array<int, 2>, 2>, so it would look like this (visually):

where each color is one std::array<std::array<int, 2>, 2>?

I have read some questions but they don't always ask the same or are incomplete:

Split array into chunks in C/C++ - asks how to split one continous stream of data into smaller continous bits, one dimensional

Split an image into 64x64 chunks - no source or explaination provided for ProcessChunk?

Answer 1

The way I would do it is by not splitting the image at all.
let me elaborate:

if you create new arrays, you will have to copy the arrays over some new structure, probably std::vectors, since you don't know the different sizes at compile time.

What you can do instead, is keeping the original structure, and have a vector of Areas, where an Area is described by the 4 vertices that describe your inner square.

struct Area{
  std::pair<int,int> topleft;
  std::pair<int,int> topright;
  std::pair<int,int> bottomleft;
  std::pair<int,int> bottomright;
};

vector<Area> areas;
areas.emplace_back({0,0},{0,2},{2,0},{2,2});

If you need to use less information, you could store only two corners and compute the other two, you actually only need 4 ints to know the area.