Instead of allocating a separate bitmap per grid for the hide status, store
all the bits in a recently added C++ data structure that stores all bits in one
contiguous memory chunk. When nothing is hidden, nothing is allocated
(that saves 32 MB for a 16 million vertex multires sculpt). Intuitively it
could have better performance because of the cache benefits of
contiguous memory, but this is hard to measure. It also has a nicer
API than `BLI_bitmap`.
I discussed this with Sergey in person recently. Most of the changes are
just straightforward refactors. The part that isn't is a change to the "show/hide"
operator to structure it similarly to the mesh handling in 4e66769ec0.
Pull Request: https://projects.blender.org/blender/blender/pulls/115687
ccab01f97f