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# big-brain
`big-brain` is a [Utility AI](https://en.wikipedia.org/wiki/Utility_system)
library for games, built for the [Bevy Game Engine](https://bevyengine.org/)
It lets you define complex, intricate AI behaviors for your entities based on
their perception of the world. Definitions are heavily data-driven, using
plain Rust, and you only need to program Scorers (entities that look at your
game world and come up with a Score), and Actions (entities that perform
actual behaviors upon the world). No other code is needed for actual AI
behavior.
See [the documentation](https://docs.rs/big-brain) for more details.
### Features
* Highly concurrent/parallelizable evaluation.
* Integrates smoothly with Bevy.
* Easy AI definition using idiomatic Rust builders. You don't have to be some genius to define behavior that _feels_ realistic to players.
* High performance--supports hundreds of thousands of concurrent AIs.
* Graceful degradation--can be configured such that the less frame time is available, the slower an AI might "seem", without dragging down framerates, by simply processing fewer events per tick.
* Proven game AI model.
* Low code overhead--you only define two types of application-dependent things, and everything else is building blocks!
* Highly composable and reusable.
* State machine-style continuous actions/behaviors.
* Action cancellation.
### Example
First, you define actions and considerations, which are just plain old Bevy
Components and Systems. As a developer, you write application-dependent code
to define [`Scorers`](#scorers) and [`Actions`](#actions), and then put it
all together like building blocks, using [`Thinkers`](#thinkers) that will
define the actual behavior.
#### Scorers
`Scorer`s are entities that look at the world and evaluate into [`Score`](scorers::Score) values. You can think of them as the "eyes" of the AI system. They're a highly-parallel way of being able to look at the `World` and use it to make some decisions later.
They are created by types that implement [`ScorerBuilder`](scorers::ScorerBuilder).
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```rust
use bevy::prelude::*;
use big_brain::prelude::*;
#[derive(Debug, Clone)]
pub struct Thirsty;
impl Thirsty {
fn build() -> ThirstyBuilder {
ThirstyBuilder
}
}
#[derive(Debug, Clone)]
pub struct ThirstyBuilder;
impl ScorerBuilder for ThirstyBuilder {
fn build(&self, cmd: &mut Commands, scorer: Entity, _actor: Entity) {
cmd.entity(scorer).insert(Thirsty);
}
}
pub fn thirsty_scorer_system(
thirsts: Query<&Thirst>,
mut query: Query<(&Actor, &mut Score), With<Thirsty>>,
) {
for (Actor(actor), mut score) in query.iter_mut() {
if let Ok(thirst) = thirsts.get(*actor) {
score.set(thirst.thirst);
}
}
}
```
#### Actions
`Action`s are the actual things your entities will _do_. They are connected to [`ActionState`](actions::ActionState)s, and are created by types implementing [`ActionBuilder`](actions::ActionBuilder).
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```rust
use bevy::prelude::*;
use big_brain::prelude::*;
#[derive(Debug, Clone)]
pub struct Drink;
impl Drink {
pub fn build() -> DrinkBuilder {
DrinkBuilder
}
}
#[derive(Debug, Clone)]
pub struct DrinkBuilder;
impl ActionBuilder for DrinkBuilder {
fn build(&self, cmd: &mut Commands, action: Entity, _actor: Entity) {
cmd.entity(action).insert(Drink);
}
}
fn drink_action_system(
mut thirsts: Query<&mut Thirst>,
mut query: Query<(&Actor, &mut ActionState), With<Drink>>,
) {
for (Actor(actor), mut state) in query.iter_mut() {
if let Ok(mut thirst) = thirsts.get_mut(*actor) {
match *state {
ActionState::Requested => {
thirst.thirst = 10.0;
*state = ActionState::Success;
}
ActionState::Cancelled => {
*state = ActionState::Failure;
}
_ => {}
}
}
}
}
```
#### Thinkers
Finally, you can use it when define the [`Thinker`](thinker::Thinker), which you can attach as a
regular Component:
```rust
cmd.spawn().insert(Thirst::new(70.0, 2.0)).insert(
Thinker::build()
.when(Thirsty::build(), Drink::build()),
);
```
### Contributing
1. Install the latest Rust toolchain (stable supported).
2. `cargo run --example thirst`
3. Happy hacking!
### License
This project is licensed under [the Apache-2.0 License](LICENSE.md).