Expand description
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
§Features
- 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
§Live Demo
See a live demo of asteroids using wasm here.
§Example Usage
// 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);
}
§Systems
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)?;
§Relations
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);
§Comparison to other ECS
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.
§Motivation
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.
§Unsafe
This library makes use of unsafe for type erasure and the allocation in storage
of ComponentBuffer
s and Archetype
s.
Re-exports§
pub use archetype::BatchSpawn;
pub use archetype::RefMut;
pub use commands::CommandBuffer;
pub use component::Component;
pub use entity::entity_ids;
pub use entity::Entity;
pub use entity::EntityBuilder;
pub use error::Error;
pub use fetch::relations_like;
pub use fetch::EntityIds;
pub use fetch::Fetch;
pub use fetch::FetchExt;
pub use fetch::FetchItem;
pub use fetch::Mutable;
pub use fetch::Opt;
pub use fetch::OptOr;
pub use fetch::Relations;
pub use metadata::Debuggable;
pub use metadata::Exclusive;
pub use query::Children;
pub use query::Dfs;
pub use query::DfsBorrow;
pub use query::DfsIter;
pub use query::EntityBorrow;
pub use query::EntityQuery;
pub use query::Planar;
pub use query::Query;
pub use query::QueryBorrow;
pub use query::QueryIter;
pub use query::Topo;
pub use relation::RelationExt;
pub use schedule::Schedule;
pub use schedule::ScheduleBuilder;
pub use schedule::SystemInfo;
pub use system::BoxedSystem;
pub use system::System;
pub use system::SystemBuilder;
pub use world::World;
Modules§
- Structured component storage
- Provides a buffer for holding multiple types simultaneously
- Contains a commandbuffer
- Low level component construction
- This module contains standard components that different libraries can agree on, though they don’t have to.
- Provides entity identifiers
- Defines the single error type and result alias
- Subscribe to changes in the world
- Traits for fetching multiple component values simultaneously
- Filter items yielded queries
- Formatting utilities
- Component metadata used for reflection
- Query the world
- Low level relation construction
- System execution
- serialize
serde
Allows for efficient serialization and deserialization of the world and the entities therein - Provides a sink trait for sending events
- System execution
- vtable implementation for dynamic dispatching
- Contains the main ecs world
Macros§
- Declarative component generation
- Helper macro for creating a vtable for custom components
Structs§
- Borrow all the components of an entity at once.
- Borrow all the components of an entity at once.
- A view into an occupied component entry
- A view into a vacant component entry
Enums§
- Entry like api for an entity’s component
Derive Macros§
- Fetch
derive