refactor: hashing, offsetNeighbors

[andretchen0]

This adds a few useful functions to const.ts: hashOffsetCoords and offsetNeighbors. It also puts the hashing function to use in pointFacade.

Hash details

I had previously implemented a private hashing function in pointFacade. But I thought it could be useful elsewhere, so I moved it to const.ts.

An example useful case: sets. Sets are fast and practical. But they don't work with our Hex representation out of the box:

s.add({x:1, y:1})
s.has({x:1, y:1}) // false 

That's because objects in sets are compared by reference. However, if we hash the Hex to a value, it can be compared to other hashed values in the set:

s.add(hash({x:1, y:1}))
s.has(hash({x:1, y:1})) // true 

I also refactored the hash function. Previously, it was {x:number, y:number} => string. Now it's {x:number, y:number} => number.

Note

The hashing function uses 16 bits for x, 16 bits for y. (Bitwise operations in JS are limited to 32 bits.) That gives us a max hex x of 65535, and a max hex y of 65535. That should be more than enough – the current maps have a max x of 15 and max y of 8 – but I thought it was worth pointing out, as it's a hard limit.

Fwiw, this happens to be the same hashing scheme that Wesnoth uses for locations.

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[DreadKnight]

Good to know the info in the note 👍🏻