freecs

freecs is a zero-abstraction ECS library for Rust, designed for high performance and simplicity. 🚀

It provides an archetypal table-based storage system for components, allowing for fast queries, fast system iteration, and parallel processing.

A macro is used to define the world and its components, and generates the entity component system as part of your source code at compile time. The generated code contains only plain data structures (no methods) and free functions that transform them, achieving static dispatch.

The internal implementation is ~500 loc, and does not use object orientation, generics, traits, or dynamic dispatch.

Quick Start

Add this to your Cargo.toml:

[dependencies]
freecs = "0.1.8"
serde = { version = "1.0.214", features = ["derive"] } # or higher

# (optional) add rayon if you want to parallize systems
rayon = "1.10.0" # or higher

And in main.rs:

use freecs::{has_components, world};
use rayon::prelude::*;

world! {
  World {
      components {
        position: Position => POSITION,
        velocity: Velocity => VELOCITY,
        health: Health => HEALTH,
      },
      Resources {
          delta_time: f32
      }
  }
}

pub fn main() {
    let mut world = World::default();

    // Inject resources for systems to use
    world.resources.delta_time = 0.016;

    // Spawn entities with components
    let entity = spawn_entities(&mut world, POSITION | VELOCITY, 1)[0];
    println!(
        "Spawned {} with position and velocity",
        total_entities(&world)
    );

    // Read a component
    let position = get_component::<Position>(&world, entity, POSITION);
    println!("Position: {:?}", position);

    // Mutate a component
    if let Some(position) = get_component_mut::<Position>(&mut world, entity, POSITION) {
        position.x += 1.0;
    }

    // Get an entity's component mask
    println!(
        "Component mask before adding health component: {:b}",
        component_mask(&world, entity).unwrap()
    );

    // Add a new component to an entity
    add_components(&mut world, entity, HEALTH);

    println!(
        "Component mask after adding health component: {:b}",
        component_mask(&world, entity).unwrap()
    );

    // Query all entities with a specific component
    let players = query_entities(&world, POSITION | VELOCITY | HEALTH);
    println!("Player entities: {players:?}");

    // Query the first entity with a specific component,
    // returning early instead of checking remaining entities
    let first_player_entity = query_first_entity(&world, POSITION | VELOCITY | HEALTH);
    println!("First player entity : {first_player_entity:?}");

    // Remove a component from an entity
    remove_components(&mut world, entity, HEALTH);

    // This runs the systems once in parallel
    // Not part of the library's public API, but a demonstration of how to run systems
    systems::run_systems(&mut world, 0.01);

    // Call this manually to compact tables, ideally periodically (such as every 60 frames).
    // This is a performance benefit and is optional.
    merge_tables(&mut world);

    // Despawn entities, freeing their table slots for reuse
    despawn_entities(&mut world, &[entity]);
}

use components::*;
mod components {
    #[derive(Default, Debug, Clone, serde::Serialize, serde::Deserialize)]
    pub struct Position {
        pub x: f32,
        pub y: f32,
    }

    #[derive(Default, Debug, Clone, serde::Serialize, serde::Deserialize)]
    pub struct Velocity {
        pub x: f32,
        pub y: f32,
    }

    #[derive(Default, Debug, Clone, serde::Serialize, serde::Deserialize)]
    pub struct Health {
        pub value: f32,
    }
}

mod systems {
    use super::*;

    // Systems are functions that iterate over
    // the component tables and transform component data.
    // This function invokes two systems in parallel
    // for each table in the world filtered by component mask.
    pub fn run_systems(world: &mut World) {
        let delta_time = world.resources.delta_time;
        world.tables.par_iter_mut().for_each(|table| {
            if has_components!(table, POSITION | VELOCITY | HEALTH) {
                update_positions_system(&mut table.position, &table.velocity, delta_time);
            }
            if has_components!(table, HEALTH) {
                health_system(&mut table.health);
            }
        });
    }

    // The system itself can also access components in parallel
    #[inline]
    pub fn update_positions_system(positions: &mut [Position], velocities: &[Velocity], dt: f32) {
        positions
            .par_iter_mut()
            .zip(velocities.par_iter())
            .for_each(|(pos, vel)| {
                pos.x += vel.x * dt;
                pos.y += vel.y * dt;
            });
    }

    #[inline]
    pub fn health_system(health: &mut [Health]) {
        health.par_iter_mut().for_each(|health| {
            health.value *= 0.98; // gradually decline health value
        });
    }
}

License

This project is licensed under the MIT License - see the LICENSE file for details.