ddee5cca85
# Objective Certain classes of games, usually those with enormous worlds, require some amount of support for double-precision. Libraries like `big_space` exist to allow for large worlds while integrating cleanly with Bevy's primarily single-precision ecosystem, but even then, games will often still work directly in double-precision throughout the part of the pipeline that feeds into the Bevy interface. Currently, working with double-precision types in Bevy is a pain. `glam` provides types like `DVec3`, but Bevy doesn't provide double-precision analogs for `glam` wrappers like `Dir3`. This is mostly because doing so involves one of: - code duplication - generics - templates (like `glam` uses) - macros Each of these has issues that are enough to be deal-breakers as far as maintainability, usability or readability. To work around this, I'm putting together `bevy_dmath`, a crate that duplicates `bevy_math` types and functionality to allow downstream users to enjoy the ergonomics and power of `bevy_math` in double-precision. For the most part, it's a smooth process, but in order to fully integrate, there are some necessary changes that can only be made in `bevy_math`. ## Solution This PR addresses the first and easiest issue with downstream double-precision math support: `VectorSpace` currently can only represent vector spaces over `f32`. This automatically closes the door to double-precision curves, among other things. This restriction can be easily lifted by allowing vector spaces to specify the underlying scalar field. This PR adds a new trait `ScalarField` that satisfies the properties of a scalar field (the ones that can be upheld statically) and adds a new associated type `type Scalar: ScalarField` to `VectorSpace`. It's mostly an unintrusive change. The biggest annoyances are: - it touches a lot of curve code - `bevy_math::ops` doesn't support `f64`, so there are some annoying workarounds As far as curves code, I wanted to make this change unintrusive and bite-sized, so I'm trying to touch as little code as possible. To prove to myself it can be done, I went ahead and (*not* in this PR) migrated most of the curves API to support different `ScalarField`s and it went really smoothly! The ugliest thing was adding `P::Scalar: From<usize>` in several places. There's an argument to be made here that we should be using `num-traits`, but that's not immediately relevant. The point is that for now, the smallest change I could make was to go into every curve impl and make them generic over `VectorSpace<Scalar = f32>`. Curves work exactly like before and don't change the user API at all. # Follow-up - **Extend `bevy_math::ops` to work with `f64`.** `bevy_math::ops` is used all over, and if curves are ever going to support different `ScalarField` types, we'll need to be able to use the correct `std` or `libm` ops for `f64` types as well. Adding an `ops64` mod turned out to be really ugly, but I'll point out the maintenance burden is low because we're not going to be adding new floating-point ops anytime soon. Another solution is to build a floating-point trait that calls the right op variant and impl it for `f32` and `f64`. This reduces maintenance burden because on the off chance we ever *do* want to go modify it, it's all tied together: you can't change the interface on one without changing the trait, which forces you to update the other. A third option is to use `num-traits`, which is basically option 2 but someone else did the work for us. They already support `no_std` using `libm`, so it would be more or less a drop-in replacement. They're missing a couple floating-point ops like `floor` and `ceil`, but we could make our own floating-point traits for those (there's even the potential for upstreaming them into `num-traits`). - **Tweak curves to accept vector spaces over any `ScalarField`.** Curves are ready to support custom scalar types as soon as the bullet above is addressed. I will admit that the code is not as fun to look at: `P::Scalar` instead of `f32` everywhere. We could consider an alternate design where we use `f32` even to interpolate something like a `DVec3`, but personally I think that's a worse solution than parameterizing curves over the vector space's scalar type. At the end of the day, it's not really bad to deal with in my opinion... `ScalarType` supports enough operations that working with them is almost like working with raw float types, and it unlocks a whole ecosystem for games that want to use double-precision. |
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Release Content
This directory contains drafts of documentation for the current development cycle, which will be published to the website during the next release. You can find more information in the release notes and migration guides files.