Affine Sprites

[jembishop]

Hi, I made a PR #363 , which was understandably not merged because it is desirable to track the affine matrix resources automatically rather than the user keeping track.

I know you said that you were going to implement this in a later release, I was wondering if you might let me have a stab at it if possible!

So looking at what's needed, I was imagining that affine matrices are created in the standard way then passed to the object controller, which inserts it into shadow OAM, and returns a handle which is a smart pointer which will deallocate the affine matrix when it leaves scope. You can then set this matrix on a sprite, which will consume it and would require an extra field on the sprite to store this optional ref.

let affine_matrix_ref = ObjectController.create_affine_matrix(AffineMatrixObject::identity());
sprite.set_affine_matrix(affine_matrix_ref);

Internally, the shadow OAM would have an arena style allocation method for allocating the affine sprites:
The matrix entry type would be a union:

union MatrixEntry {
    entry: Num<i32, 8>,
    next_free: *mut MatrixEntry
}

This scheme would not allow duplicate affine matrices, so if you wanted to share an affine matrix between 2 sprites say, you would use an Rc.

Does this sound like a good/feasible idea?

Thanks

[corwinkuiper]

My plan would be to allocate using a list of free indices into Rcs which objects hold if they're using the matrix.

[jembishop]

OK I think that is similar, however in my proposal the linked list of free indices is embedded into the shadow oam itself in the unused entries. Also I wonder if you need the Rc? If you aren't sharing the matrix with multiple sprites then rusts borrow system should handle this I think, and the user can wrap with Rc if needed. I will try doing a rough implementation to see if this is feasible.