apecs is an Entity Component System (ECS) library 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 - Performance is competitive with Rust ECS libraries (see benchmark results below).
Concise - Game logic is expressed using a small number of powerful combinators.
Safe - The cmap/cfold-DSL completely hides the dangers of the low-level API.
Extensible - At its heart apecs is just a data manipulation DSL that can be implemented with any number of backends. as a monad transformer it easily integrates into larger applications.
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeFamilies #-}
import Apecs
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
[0.7.3]
Changed
Added Data.Semigroup to Stores.Extra to build with GHC 8.2.2 in hackage matrix
[0.7.2]
Changed
Fixed bug in the Pushdown store
Apecs module no longer re-exports the entire Data.Proxy module, but instead just Proxy (..).
Added (approximate?) lower and upper version bounds to dependencies
[0.7.1]
Added
$= and $~ operators as synonyms for set and get respectively
Removed
getAll and count, which were made redundant by cfold.
[0.7.0]
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.
