sillyecs

A silly little compile-time generated archetype ECS in Rust.

Installation

sillyecs is a build-time dependency. To use it, add this to your Cargo.toml:

[build-dependencies]
sillyecs = "0.0.2"

Usage

Use sillyecs in your build.rs:

use sillyecs::EcsCode;
use std::fs::File;
use std::io::BufReader;

fn main() -> eyre::Result<()> {
    println!("cargo:rerun-if-changed=ecs.yaml");

    let file = File::open("ecs.yaml").expect("Failed to open ecs.yaml");
    let reader = BufReader::new(file);
    EcsCode::generate(reader)?.write_files()?;
    Ok(())
}

Define your ECS components and systems in a YAML file:

# ecs.yaml
states:
  - name: Render
    description: The render state

components:
  - name: Position
  - name: Velocity
  - name: Health
  - name: Collider

archetypes:
  - name: Particle
    description: A particle system particle.
    components:
      - Position
      - Velocity

  - name: Player
    components:
      - Position
      - Velocity
      - Health

  - name: ForegroundObject
    components:
      - Position
      - Collider
    promotions:
      - BackgroundObject

  - name: BackgroundObject
    components:
      - Position
    promotions:
      - ForegroundObject

phases:
  - name: Startup
  - name: FixedUpdate
    fixed: 60 Hz  # or "0.01666 s"
  - name: Update
  - name: Render

systems:
  - name: Physics
    phase: FixedUpdate
    context: true
    run_after: []  # optional
    inputs:
      - Velocity
    outputs:
      - Position
  - name: Render
    phase: Render
    states:
      - use: Render
        write: false  # optional
    inputs:
      - Position

worlds:
  - name: Main
    archetypes:
      - Particle
      - Player
      - ForegroundObject
      - BackgroundObject

Include the compile-time generated files:

include!(concat!(env!("OUT_DIR"), "/components_gen.rs"));
include!(concat!(env!("OUT_DIR"), "/archetypes_gen.rs"));
include!(concat!(env!("OUT_DIR"), "/systems_gen.rs"));
include!(concat!(env!("OUT_DIR"), "/world_gen.rs"));

The compiler will tell you which traits and functions to implement.

Command Queue

You will have to implement a command queue. Below is an example for a queue based on crossbeam-channel:

struct CommandQueue {
    sender: crossbeam_channel::Sender<WorldCommand>,
    receiver: crossbeam_channel::Receiver<WorldCommand>,
}

impl CommandQueue {
    pub fn new() -> Self {
        let (sender, receiver) = crossbeam_channel::unbounded();
        Self {
            sender,
            receiver,
        }
    }
}

impl WorldCommandReceiver for CommandQueue {
    type Error = TryRecvError;

    fn recv(&self) -> Result<Option<WorldCommand>, Self::Error> {
        match self.receiver.try_recv() {
            Ok(cmd) => Ok(Some(cmd)),
            Err(TryRecvError::Empty) => Ok(None),
            Err(err) => Err(err),
        }
    }
}

impl WorldCommandSender for CommandQueue {
    type Error = crossbeam_channel::SendError<WorldCommand>;

    fn send(&self, command: WorldCommand) -> Result<(), Self::Error> {
        self.sender.send(command)
    }
}