apecs

apecs is an Entity Component System inspired by specs and Entitas. It provides a collection of mutable component stores, and an expressive DSL for operating on those stores, both easily extended.

Links

• documentation
• introductory tutorial
• performance guide
• apecs-physics

Performance

ecs-bench shows that apecs is competitive with the fastest Rust ECS frameworks.

Example

{-# LANGUAGE DataKinds, ScopedTypeVariables, TypeFamilies, MultiParamTypeClasses, TemplateHaskell #-}

import Apecs
import Apecs.Stores
import Apecs.Core
import Linear

newtype Position = Position (V2 Double) deriving Show
-- To declare a component, we need to specify how to store it
instance Component Position where
  type Storage Position = Map Position -- The simplest store is a Map

newtype Velocity = Velocity (V2 Double) deriving Show
instance Component Velocity where
  type Storage Velocity = Cache 100 (Map Velocity) -- Caching adds fast reads/writes

data Flying = Flying
instance Component Flying where
  type Storage Flying = Map Flying

makeWorld "World" [''Position, ''Velocity, ''Flying] -- Generate World and instances

game :: System World ()
game = do
  newEntity (Position 0, Velocity 1)
  newEntity (Position 2, Velocity 1)
  newEntity (Position 1, Velocity 2, Flying)

  -- Add velocity to position
  cmap $ \(Position p, Velocity v) -> Position (v+p)
  -- Apply gravity to non-flying entities
  cmap $ \(Velocity v, _ :: Not Flying) -> Velocity (v - (V2 0 1))
  -- Print a list of entities and their positions
  cmapM_ $ \(Position p, Entity e) -> liftIO . print $ (e, p)

main :: IO ()
main = initWorld >>= runSystem game