BSD3 licensed by Jonas Carpay

apecs

apecs is an Entity Component System (ECS) framework inspired by specs and Entitas. ECS presents a data-driven approach to game development, that elegantly tackles many of the unique issues of game programming. apecs aims to be

  • Fast - apecs is designed for high-performance applications. Its performance is competitive with Rust ECS libraries.
  • Simple - Game logic is expressed using a small number of combinators, and minimal boilerplate.
  • Safe - The cmap/cfold-DSL hides all the dangers of the low-level API.
  • Extensible - apecs can be used with anything that implements the low-level API. See apecs-physics or apecs-stm for examples.

Links

Performance

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

Benchmarks

Example

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

import Apecs
import Control.Monad
import Apecs.Util
import Linear (V2 (..))

newtype Position = Position (V2 Double) deriving Show
newtype Velocity = Velocity (V2 Double) deriving Show
data Flying = Flying

makeWorldAndComponents "World" [''Position, ''Velocity, ''Flying]

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

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

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

Changes

[0.6.1]

Added

  • The Reactive store and module is a redesign of the Register store, and provides a more general solution for ‘stores that perform additional actions when written to’.
  • The Apecs.Stores.Extra submodule, which contains the Pushdown and ReadOnly stores. Pushdown adds pushdown semantics to stores, and ReadOnly hides the ExplSet instances of whatever it wraps.
  • The EntityCounter and associated functions have all been specified to IO, since Global EntityCounter only works in IO. Furthermore, EntityCounter now uses a ReadOnly store, to prevent users from accidentally changing its value.
  • Redirect component that writes to another entity in cmap.

Changed

  • Default stores have MonadIO m => m instances, rather than IO. This makes it easier to nest SystemT.
  • All apecs packages have been consolidated into a single git repo.
  • Apecs.Components contains the components (and corresponding stores) from Apecs.Core.

[0.6.0.0]

Changed

  • Nothing, but since 0.5.1 was API-breaking I’ve decided to bump to 0.6

[0.5.1.1]

Changed

  • Register needs UndecidableInstances in GHC 8.6.2, I’m looking for a way around this. I’ve removed it for now.

[0.5.1.0]

Added

  • The Register store, which allows reverse lookups for bounded enums. For example, if Bool has storage Register (Map Bool), regLookup True will yield a list of all entities with a True component. Can also be used to emulate a hash table, where fromEnum is the hashing function. This allows us to make simple spatial hashes. I’m open to suggestions for better names than Register.
  • cmapIf, cmap with a conditional test

Changed

  • ExplInit now too takes a monad argument.
  • Started rewrite of the test suite
  • Caches now internally use -2 to denote absence, to avoid possible conflict with -1 as a global entity

Removed

  • The STM instances have been removed, to be moved to their own package

[0.5.0.0]

Changed

  • System w a is now a synonym for SystemT w IO a. A variable monad argument allows apecs to be run in monads like ST or STM. Most of the library has been rewritten to be as permissive as possible in its monad argument.

Added

  • STM stores. These will be moved to a separate package soon.

[0.4.1.2]

Changed

  • Either can now be deleted, deleting Either a b is the same as deleting (a,b).
  • Some were missing their inline pragma’s, now they don’t

[0.4.1.1]

Changed

  • Export Get, Set, Destroy, Members by default
  • Export cfold, cfoldM, cfoldM_ by default
  • Fix () instance

[0.4.1.0]

Added

  • cfold, cfoldM, cfoldM_
  • Either instances and EitherStore

Changed

  • Changed MaybeStore implementation to no longer use -1 for missing entities.
  • Fixed some outdated documentation.
  • Change the global void entity to -2, just to be sure it won’t conflict if accidentally used in a cache.

[0.4.0.0]

Added

  • A changelog

Changed

  • Store is now split into 5 separate type classes; ExplInit, ExplGet, ExplSet, ExplDestroy, and ExplMembers. This makes it illegal to e.g. iterate over a Not.
  • phantom arguments are now given as Proxy values, re-exported from Data.Proxy. This makes phantom arguments explicit and avoids undefined values.
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