apecs

Asyncronous Parallel Entity Component System

Why

apecs is an entity-component system written in Rust that supports traditional syncronous systems as well as asyncronous systems that can evolve over time. This makes it great for general applications, quick game prototypes, DIY engines and any simulation that has discrete steps.

Goals

• productivity
• flexibility
• observability
• very well rounded performance, competitive with inspirational ECS libraries
  • like specs, bevy_ecs, hecs, legion, shipyard, planck_ecs

Features

• syncronous systems with early exit and failure

  use apecs::{anyhow, Write, world::*, system::*};
  let mut world = World::default();
  world
      .with_system("demo", |mut u32_number: Write<u32>| -> anyhow::Result<ShouldContinue> {
          *u32_number += 1;
          if *u32_number == 3 {
              end()
          } else {
              ok()
          }
      })
      .unwrap();
  world.run();
  assert_eq!(3, *world.resource::<u32>().unwrap());
  

• async systems, ie systems that end and/or change over time (for scenes, stories, etc)
  • fetch resources from the world asyncronously
  • resources are acquired without lifetimes

  use apecs::{anyhow, Write, world::*};
  async fn demo(mut facade: Facade) -> anyhow::Result<()> {
      loop {
          let mut u32_number: Write<u32> = facade.fetch().await?;
          *u32_number += 1;
          if *u32_number > 5 {
              break;
          }
      }
      Ok(())
  }
  let mut world = World::default();
  world
      .with_resource(0u32)
      .unwrap()
      .with_async_system("demo", demo);
  world.run();
  assert_eq!(6, *world.resource::<u32>().unwrap());
  

• support for async futures

  use apecs::world::World;
  let mut world = World::default();
  world
      .with_async(async {
          log::trace!("hello");
      });
  world.run();
  

• fetch data (system data) derive macros

  use apecs::{CanFetch, Read, Write, world::*};
  
  #[derive(CanFetch)]
  struct MyData {
      entities: Read<Entities>,
      u32_number: Write<u32>,
  }
  
  let mut world = World::default();
  world
      .with_resource(0u32)
      .unwrap();
  
  let mut my_data: MyData = world.fetch().unwrap();
  *my_data.u32_number = 1;
  

• system scheduling
  • compatible systems are placed in parallel batches (a batch is a group of systems that can run in parallel, ie they don't have conflicting borrows)
  • systems may depend on other systems running first
  • barriers

  use apecs::{Read, Write, system::*, world::*};
  
  fn one(mut u32_number: Write<u32>) -> anyhow::Result<ShouldContinue> {
      *u32_number += 1;
      end()
  }
  
  fn two(mut u32_number: Write<u32>) -> anyhow::Result<ShouldContinue> {
      *u32_number += 1;
      end()
  }
  
  fn thrice(mut f32_number: Write<f32>) -> anyhow::Result<ShouldContinue> {
      *f32_number += 1.0;
      if *f32_number == 3.0 {
          end()
      } else {
          ok()
      }
  }
  
  fn lastly((u32_number, f32_number): (Read<u32>, Read<f32>)) -> anyhow::Result<ShouldContinue> {
      if *u32_number == 2 && *f32_number == 3.0 {
          end()
      } else {
          ok()
      }
  }
  
  let mut world = World::default();
  world
      .with_system("one", one).unwrap()
      .with_system_with_dependencies("two", two, &["one"]).unwrap()
      .with_system("thrice", thrice).unwrap()
      .with_system_barrier()
      .with_system("lastly", lastly).unwrap();
  
  assert_eq!(
      vec![
          vec!["one", "thrice"],
          vec!["two"],
          vec!["lastly"],
      ],
      world.get_sync_schedule_names()
  );
  
  world.tick();
  assert_eq!(
      vec![
          vec!["thrice"],
          vec!["lastly"],
      ],
      world.get_sync_schedule_names()
  );
  
  world.tick();
  world.tick();
  assert!(world.get_sync_schedule_names().is_empty());
  

• component storage
  • optimized for space and iteration time as archetypes
  • queries with "maybe" and "without" semantics
  • queries can find a single entity without iteration or filtering
  • add and modified time tracking
  • parallel queries (inner parallelism)

  use apecs::{world::*, storage::*, system::*, Read, Write};
  
  // Make a type for tracking changes
  #[derive(Default)]
  struct MyTracker(u64);
  
  // Entities and ArchetypeSet (which stores components) are default
  // resources
  let mut world = World::default();
  world
      .with_system("create", |mut entities: Write<Entities>| {
          for mut entity in (0..100).map(|_| entities.create()) {
              entity.insert_bundle((0.0f32, 0u32, format!("{}:0", entity.id())));
          }
          end()
      }).unwrap()
      .with_system_with_dependencies("progress", |q_f32s: Query<&mut f32>| {
          for f32 in q_f32s.query().iter_mut() {
              **f32 += 1.0;
          }
          ok()
      }, &["create"]).unwrap()
      .with_system_with_dependencies(
          "sync",
          |(q_others, mut tracker): (Query<(&f32, &mut String, &mut u32)>, Write<MyTracker>)| {
              for (f32, string, u32) in q_others.query().iter_mut() {
                  if f32.was_modified_since(tracker.0) {
                      **u32 = **f32 as u32;
                      **string = format!("{}:{}", f32.id(), **u32);
                  }
              }
              tracker.0 = apecs::system::current_iteration();
              ok()
          },
          &["progress"]
      ).unwrap();
  
  assert_eq!(
      vec![
          vec!["create"],
          vec!["progress"],
          vec!["sync"],
      ],
      world.get_sync_schedule_names()
  );
  
  world.tick(); // entities are created
  world.tick(); // f32s are modified, u32s and strings are synced
  world.tick(); // f32s are modified, u32s and strings are synced
  
  let q_bundle: Query<(&f32, &u32, &String)> = world.fetch().unwrap();
  assert_eq!(
      (2.0, 2u32, "13:2.0".to_string()),
      q_bundle.query().find_one(13).map(|(f, u, s)| (**f, **u, s.to_string())).unwrap()
  );
  

• outer parallelism (running systems in parallel)
  • parallel system scheduling
  • parallel execution of async futures
• plugins (groups of systems, resources and sub-plugins)
• configurable parallelism (can be automatic or a requested number of threads, including 1)
• fully compatible with wasm

Roadmap

• your ideas go here

Tests

cargo test
wasm-pack test --firefox crates/apecs

I like firefox, but you can use different browsers for the wasm tests. For the most part they're there just to make sure apecs works on wasm.

Benchmarks

The apecs benchmarks measure itself against my favorite ECS libs: specs, bevy, hecs, legion, shipyard and planck_ecs.

cargo bench -p benchmarks

Caveats

apecs uses generic associated types. This means it can only be compiled with nightly.