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# 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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What is Bevy?
Bevy is a refreshingly simple data-driven game engine built in Rust. It is free and open-source forever!
WARNING
Bevy is still in the early stages of development. Important features are missing. Documentation is sparse. A new version of Bevy containing breaking changes to the API is released approximately once every 3 months. We provide migration guides, but we can't guarantee migrations will always be easy. Use only if you are willing to work in this environment.
MSRV: Bevy relies heavily on improvements in the Rust language and compiler. As a result, the Minimum Supported Rust Version (MSRV) is generally close to "the latest stable release" of Rust.
Design Goals
- Capable: Offer a complete 2D and 3D feature set
- Simple: Easy for newbies to pick up, but infinitely flexible for power users
- Data Focused: Data-oriented architecture using the Entity Component System paradigm
- Modular: Use only what you need. Replace what you don't like
- Fast: App logic should run quickly, and when possible, in parallel
- Productive: Changes should compile quickly ... waiting isn't fun
About
- Features: A quick overview of Bevy's features.
- News: A development blog that covers our progress, plans and shiny new features.
Docs
- Quick Start Guide: Bevy's official Quick Start Guide. The best place to start learning Bevy.
- Bevy Rust API Docs: Bevy's Rust API docs, which are automatically generated from the doc comments in this repo.
- Official Examples: Bevy's dedicated, runnable examples, which are great for digging into specific concepts.
- Community-Made Learning Resources: More tutorials, documentation, and examples made by the Bevy community.
Community
Before contributing or participating in discussions with the community, you should familiarize yourself with our Code of Conduct.
- Discord: Bevy's official discord server.
- Reddit: Bevy's official subreddit.
- GitHub Discussions: The best place for questions about Bevy, answered right here!
- Bevy Assets: A collection of awesome Bevy projects, tools, plugins and learning materials.
Contributing
If you'd like to help build Bevy, check out the Contributor's Guide. For simple problems, feel free to open an issue or PR and tackle it yourself!
For more complex architecture decisions and experimental mad science, please open an RFC (Request For Comments) so we can brainstorm together effectively!
Getting Started
We recommend checking out the Quick Start Guide for a brief introduction.
Follow the Setup guide to ensure your development environment is set up correctly. Once set up, you can quickly try out the examples by cloning this repo and running the following commands:
# Switch to the correct version (latest release, default is main development branch)
git checkout latest
# Runs the "breakout" example
cargo run --example breakout
To draw a window with standard functionality enabled, use:
use bevy::prelude::*;
fn main() {
App::new()
.add_plugins(DefaultPlugins)
.run();
}
Fast Compiles
Bevy can be built just fine using default configuration on stable Rust. However for really fast iterative compiles, you should enable the "fast compiles" setup by following the instructions here.
Bevy Cargo Features
This list outlines the different cargo features supported by Bevy. These allow you to customize the Bevy feature set for your use-case.
Thanks
Bevy is the result of the hard work of many people. A huge thanks to all Bevy contributors, the many open source projects that have come before us, the Rust gamedev ecosystem, and the many libraries we build on.
A huge thanks to Bevy's generous sponsors. Bevy will always be free and open source, but it isn't free to make. Please consider sponsoring our work if you like what we're building.
This project is tested with BrowserStack.
License
Bevy is free, open source and permissively licensed! Except where noted (below and/or in individual files), all code in this repository is dual-licensed under either:
- MIT License (LICENSE-MIT or http://opensource.org/licenses/MIT)
- Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
at your option. This means you can select the license you prefer! This dual-licensing approach is the de-facto standard in the Rust ecosystem and there are very good reasons to include both.
Some of the engine's code carries additional copyright notices and license terms due to their external origins.
These are generally BSD-like, but exact details vary by crate:
If the README of a crate contains a 'License' header (or similar), the additional copyright notices and license terms applicable to that crate will be listed.
The above licensing requirement still applies to contributions to those crates, and sections of those crates will carry those license terms.
The license field of each crate will also reflect this.
For example, bevy_mikktspace has code under the Zlib license (as well as a copyright notice when choosing the MIT license).
The assets included in this repository (for our examples) typically fall under different open licenses. These will not be included in your game (unless copied in by you), and they are not distributed in the published bevy crates. See CREDITS.md for the details of the licenses of those files.
Your contributions
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.