purescript-game

Documentation

This is a package for running a game loop in a browser in purescript using window.requestAnimationFrame.

It has a type alias called Game which is a record containing various functions needed to run your game loop.

It looks like this:

type Game state return =
  { gameWindow :: Window
  , init       :: Effect state
  , update     :: Seconds -> state -> Effect state
  , display    :: state -> Effect Unit
  , end        :: state -> Maybe (Either Error return)
  , events     :: List (GameEvent state)
  }

state is the type of the state used in your game. This will most likely be a record type containing all the different values your game needs.

return is the type of the value that will be returned by the Aff your game is run in, if and when it terminates.

gameWindow :: Window is the browser window your game runs in. To get the current window your code is running in, use window from Web.HTML.

init :: Effect state is the initial state of your game. It is wrapped in Effect so that it is possible for the initial state to depend on random number generation, database queries and other things.

update :: Seconds -> state -> Effect state is the state update function that will be run every frame. It takes a value of type Seconds, which is the time since the last frame, and a value of type state, which is the state of the game before the current frame started. It needs to return a value of type Effect state, where the containted state will be the state of the game after the frame.

display :: state -> Effect Unit is the function that is used to render your game. Given the state of the game, it needs to return an Effect Unit, which should display the game in some way. This is usually drawing on a HTML5 canvas, manipulating the DOM, or logging to the console. This function is run right after update.

end :: state -> Maybe (Either Error return) is the function that is used to determine whether to terminate the game loop. It is run after every frame. Given the current state, if it returns Nothing, the game loop will keep running for another frame. If it returns a Just, the game loop will end. If the inner value is an Error, the Aff will error, and if the inner value is of type return, it will resolve the Aff with that value.

events :: List (GameEvent state) is a list of events watched by the game. The type alias GameEvent is used to represent these events. It looks like this:

type GameEvent state =
  { eventType  :: EventType
  , target     :: EventTarget
  , update     :: Event -> state -> Effect state
  , useCapture :: Boolean
  }

eventType :: EventType is the type of the event, see EventType.

target :: EventTarget is the event target, see EventTarget.

update :: Event -> state -> Effect state is the function that gets run when the event occurs. It takes the Event object and the current state, and returns a new state, wrapped in Effect.

useCapture :: Boolean specifies whether to use capture, see EventTarget.addEventListener.

Use game to create an Aff from a Game value. From there, you can use launchAff_ from Effect.Aff to run the Aff in an Effect. Other ways to run an Aff and more info can be found here.

Reference

Module reference is published on Pursuit.