Fix world DSL hash primitive to depend on seed
#1989
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Adds a new primitive `imap`, aka index map, primitive to the world DSL. `imap` has type `World int -> World int -> World a -> World a`. Think of it like `(Coords -> Coords) -> World a -> World a`, i.e. given a coordinate mapping, it creates a new world by looking up the cell at the transformed coordinates in the given base world. However, since there are no lambdas we cannot directly give it that type; instead, the first `World int` represents a function `Coords -> int` which gives an x coordinate, and the second gives the y coordinate. All told, `imap wx wy wa` is like `\c -> wa (wx c, wy c)`. For example, `imap (-x) y w` is a reflection of `w` across the y-axis. Adds a description of `imap` to the language reference, as well as adding a few examples. Also removes the `rot` and `reflect` primitives, since they can now be simply implemented in terms of `imap`. Depends on merging #1989 first. Closes #1584.
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It turns out that the
hashprimitive was always computing the same deterministic hash of the coordinates regardless of the seed. This meant that e.g. any world features placed in a way that depended on the hash were always in the same locations, and if you created a world that only relied onhashand not on, say, Perlin noise, it would always look the same regardless of the seed. This does not seem desirable.This PR fixes the DSL interpreter by passing the seed to the
murmur3hash function (we used to always pass the constant seed 0). In theory, this does mean that all the "classic" worlds are now slightly different than what they used to be (except for seed 0). However, there's no way to tell the difference between one random placement and another. The only scenario where we really depend on the particular locations of entities for a particular seed is theworld101tutorial, but that used seed 0 anyway, which did not change.Depends on merging #1988 first.