polar-engine / hs-polar

Polar Game Engine is a modern, safe game engine written in Haskell.

Polar Game Engine

Polar Game Engine is a general-purpose, modern, safe game engine written in the functional programming language Haskell.

Architecture

The engine is comprised of three main abstraction layers.

The top layer is called Logic and represents the application logic of the engine. Logic should be used by default for most application code unless there is a strong reason to use Sys. Logic cannot perform or propagate IO and instead can only propogate a subset of actions down to the Sys layer for them to be handled appropriately.

The middle layer is called Sys and represents the operations systems of the engine, such as graphics renderer, audio mixer, physics integrator, and more. Sys is intended to be used by low-level application code that must operate across a subset of engine objects every tick. Sys can only perform IO through actions propagated down to Core, which Core may schedule and execute as needed.

The bottom layer is called Core and represents the inner workings of the engine. Core is not intended to be used by application developers as it has the full ability to perform any IO at any time.

Actions

LogicAction	Description
LogicExitAction	shutdown and exit
LogicLogWriteAction Priority Message	write to log if Priority is higher than Log.Level config option

SysAction	Description
SysExitAction	shutdown and exit
SysLogWriteAction Priority Message	write to log if Priority is higher than Log.Level config option
SysCoreAction Core	directly execute Core action (unsafe, backdoor)

Writing a System

Hello World

Hello.hs

module Hello (hello) where

import Polar.Types
import Polar.Log

hello :: System
hello = defaultSystem "Hello"
    & startup  .~ startupF
    & shutdown .~ shutdownF
    & tick     .~ tickF

startupF :: Sys ()
startupF = logWrite WARNING "let's make some noise"

shutdownF :: Sys ()
shutdownF = logWrite WARNING "i don't hate you"

tickF :: Sys ()
tickF = do
    logWrite INFO "hello"
    exit

Main.hs

import Polar.Run
import Hello

main :: IO ()
main = run $ defaultEngine
    & systems .~ [hello]

Text Renderer

TextRenderer.hs

module TextRenderer (textRenderer) where

import Data.Foldable (traverse_)

textRenderer :: System
textRenderer = defaultSystem "Text Renderer"
    & tick .~ tickF

tickF :: Sys ()
tickF = traverse_ f =<< retrieveAll
  where f s = logWrite INFO ("Saw " ++ s)

Main.hs

import Polar.Run
import TextRenderer

main :: IO ()
main = run $ defaultEngine
    & systems .~ [textRenderer]