Bevy is still in the _very_ stages of development. APIs can and will change. Important features are missing. Please don't build any serious projects in Bevy unless you are prepared to be broken by api changes constantly.
* Bevy can be built using stable rust with default configuration (ex: ```cargo build```), but for optimal build times we recommend using a nightly compiler with the following settings:
* LLD Linker: ```-Clink-arg=-fuse-ld=lld```
* LLD will significantly speed up compile times in Bevy, but it doesn't work out of the box on some platforms / os-es.
* See [this issue](https://github.com/rust-lang/rust/issues/39915) and [this issue](https://github.com/rust-gamedev/wg/issues/50) for more information.
* Most of the generics you will use in Bevy apps are also used by the Bevy engine code. Generic sharing is a nightly feature that lets your Bevy app re-use generics used in Bevy engine.
* Oddly in some cases compiling in release mode can actually reduce iterative compile times with the settings above. In our experience this is true for most of the examples in this project.
* [legion_transform](https://github.com/AThilenius/legion_transform): A hierarchical space transform system, implemented using Legion ECS
Additionally, we would like to thank the [Amethyst](https://github.com/amethyst/amethyst), [coffee](https://github.com/hecrj/coffee), [ggez](https://github.com/ggez/ggez), and [Piston](https://github.com/PistonDevelopers/piston) projects for providing solid examples of game engine development in Rust. If you are looking for a game engine to build Rust games in, it is worth considering all of your options. Each engine has different design goals and some will likely resonate with you more than others.
@cart (original creator of Bevy) speaking: I decided to build Bevy after years of contributing code to other engines (ex: Godot). I spent over four years building a game in Godot and I have experience with Unity, Unreal, Three.js, Armory, and Game Maker. I built multiple custom engines using Rust, Go, HTML5, and Java. I have also closely followed the other major players in the Rust gamedev ecosystem, namely [Amethyst](https://github.com/amethyst/amethyst), [coffee](https://github.com/hecrj/coffee), and [Piston](https://github.com/PistonDevelopers/piston). I am currently a senior software engineer at Microsoft which has also affected my opinions of software and what it should be.
* It needs to be free and open source with no strings attached. Games are a huge part of our culture and humanity is investing _millions_ of hours into the development of games. Why are we (as game developers / engine developers) continuing to build up the ecosystems of closed-source monopolies that take cuts of our sales and deny us visibilty into the tech we use daily? As a community I believe we can do so much better.
* It needs to have fast build/run/test loops, which translates to either scripting languages or fast compile times in native languages. But scripting languages introduce runtime overhead and cognitive load.
* Ideally the engine is written in the same lanugage as games are. I found myself loving engines where game code is written in the same language as engine code. Being able to run an IDE "go to definition" command on a symbol in your game and hop directly into the engine source is an extremely powerful concept. And you don't need to worry about translation layers or lossy abstractions. Also, if an engine's community builds games in the same language as the engine, they are more likely (and able) to contribute back to the engine.
* It needs to be easy to use for common tasks, but it also can't hide the details from you. Many engines are either "easy to use but too high level" or "very low level but difficult to do common tasks in".
* It needs to have an editor. Scene creation is a large part of game development and in many cases visual editors beat code. As a bonus, the editor should be built _in the engine_. Godot uses this approach and it is _so smart_. Doing so [dogfoods](https://en.wikipedia.org/wiki/Eating_your_own_dog_food) the engine's UI system. Improvements to the editor are also often improvements to the engine. And it makes sure your engine is flexible enough to build tooling (and not just games).
* It needs to be data-driven/data-oriented/data-first. ECS is a common way of doing this, but it definitely isn't the only way. These paradigms can make your game faster (cache friendly, easier to parallelize), but they also make common tasks like game state serialization and synchronization delightfully straightforward.
None of the engines on the market _quite_ meet my requirements. And the changes required to make them meet my requirements are either massive in scope, impossible (closed source), or unwelcome (the things I want aren't what the developers or customers want). On top of that, making new game engines is fun!
Bevy is not trying to out-compete other open-source game engines. As much as possible we should be collaborating and building common foundations. If you are an open source game engine developer and you think a Bevy component would make your engine better, one of your engine's components could make Bevy better, or both, please reach out! Bevy is already benefitting massively from the efforts of the Rust gamedev ecosystem and we would love to pay it forward in whatever way we can.
