Flax is a performant and ergonomic Entity Component System.
The world is organized by simple identifiers known as an Entity
, which can have any number of components attached to them.
Systems operate on the world's entities and provide the application logic.
Consider reading the User Guide
- Declarative component macro
- Expressive query system
- Change detection
- Query filtering
- System execution
- Multithreaded system execution
- Many to many entity relation and graphs
- Reflection through component metadata
- Ergonomic entity builder
- Serialization and deserialization
- (async) event subscription
- Runtime components
- ...and more
See a live demo of asteroids using wasm here.
// Declare static components
use flax::*;
component! {
health: f32,
regen: f32,
pos: (f32, f32),
player: (),
items: Vec<String>,
}
let mut world = World::new();
// Spawn an entity
let p = EntityBuilder::new()
.set(health(), 50.0)
.tag(player())
.set(pos(), (0.0, 0.0))
.set(regen(), 1.0)
.set_default(items())
.spawn(&mut world);
let mut query = Query::new((health().as_mut(), regen()));
// Apply health regeneration for all matched entites
for (health, regen) in &mut query.borrow(&world) {
*health = (*health regen).min(100.0);
}
Queries with logic can be abstracted into a system, and multiple systems can be collected into a schedule.
let regen_system = System::builder()
.with_query(Query::new((health().as_mut(), regen())))
.for_each(|(health, regen)| {
*health = (*health regen).min(100.0);
})
.boxed();
let despawn_system = System::builder()
.with_query(Query::new(entity_ids()).filter(health().le(0.0)))
.with_cmd_mut()
.build(|mut q: QueryBorrow<EntityIds, _>, cmd: &mut CommandBuffer| {
for id in &mut q {
cmd.despawn(id);
}
})
.boxed();
let mut schedule = Schedule::from([regen_system, despawn_system]);
schedule.execute_par(&mut world)?;
Flax provides first class many-many relations between entities, which is useful for tree scene hierarchies, graphs, and physics joints between entities.
Relations can be both state-less or have associated data, like spring or joint strengths.
Relations are cache friendly and querying children of does not require random access. In addition, relations are cleaned up on despawns and are stable during serialization, even if the entity ids migrate due to collisions.
See the guide for more details.
component! {
child_of(parent): () => [ Debuggable ],
}
let mut world = World::new();
let parent = Entity::builder()
.set(name(), "Parent".into())
.spawn(&mut world);
let child1 = Entity::builder()
.set(name(), "Child1".into())
.set_default(child_of(parent))
.spawn(&mut world);
Compared to other ECS implementations, a component is simply another Entity
identifier to which data is attached. This means the same "type" can be added to
an entity multiple times.
A limitation of existing implementations such as specs, planck, or hecs is that newtype wrappers need to be created to allow components of the same inner type to coexist.
This leads to having to forward all trait implementations trough e.g
derive-more
or dereferencing the newtypes during usage.
By making components separate from the type the components can work together without deref
or
newtype construction.
component! {
velocity: Vec3,
position: Vec3,
}
let vel = world.get(entity, velocity())?;
let mut pos = world.get_mut(entity, position())?;
let dt = 0.1;
*pos = *vel * dt;
On a further note, since the components have to be declared beforehand, it limits the amount of types which can be
inserted as components. This fixes subtle bugs which come by having the type
dictate the component, such as using an Arc<Type>
instead of just Type
,
which leads to subsequent systems not finding the Type
on the entity.
Using statically declared components makes the rust type system disallow these cases and catches these bugs earlier.
During development of a game in school I used the hecs
ECS. It is an awesome
library, and the author Ralith has been wonderful in accepting
contributions and inquiries.
Despite this, I often made subtle bugs with similar types. The game engine was
cluttered with gigantic newtypes for Velocity
, Position
with many deref
coercions in order to coexist.
This library makes use of unsafe for type erasure and the allocation in storage
of ComponentBuffer
s and Archetype
s.
License: MIT