Questions about openslide image processing operations

Question

I am now using C++ to study related operations on pathological images, which involves the openslide library. I try to use the openslide_read_region(openslide_t* osr, uint32_t* dest, int64_t x, int64_t y, int32_t level, int64_t w, int64_t h); function to get a part of the image, but I can't understand the usage of dest, how can I use this function to get a part of the image? Or is it possible to convert objects of type openslide_t* into objects that can be manipulated by opencv? Sincere thanks to everyone who helped me