BSD3 licensed by Jonas Carpay

apecs

Build Status Hackage Stackage

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. The apecs front-end DSL exposes a small number of combinators that allow game logic to be expressive and extremely fast.

Links

Performance

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

Benchmarks

Example

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

import Apecs
import Linear (V2 (..))

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

Changes

[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.
Depends on 5 packages:
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