Window does not expose setter for the size.

[nikita-leonov]

Currently to change the window size after the engine initialization develop needs to work directly with SDLEngine as shown in the following code. It is bad, as we want to ensure that engine replacement is non-breaking change.

module Main where

import Helm
import Helm.Engine.SDL.Engine
import Helm.Graphics2D

import qualified Helm.Cmd as Cmd
import qualified Helm.Window as Window
import qualified Helm.Engine.SDL as SDL

import Data.StateVar (($=))
import Linear.V2 (V2(V2))
import qualified SDL.Video as Video

data Action = Idle | FitWindow Video.Window (V2 Int)
data Model = Model

initial :: (Model, Cmd SDLEngine Action)
initial = (Model, Cmd.none)

fit :: (V2 Int) -> (V2 Int)
fit (V2 width height) = V2 dimension dimension
  where dimension = min width height

update :: Model -> Action -> (Model, Cmd SDLEngine Action)
update model Idle = (model, Cmd.none)
update model (FitWindow window size) = (model, resizeCommand)
  where resizeCommand = Cmd.execute (Video.windowSize window $= fromIntegral <$> fit size) $ const Idle

subscriptions :: Video.Window -> Sub SDLEngine Action
subscriptions window = Window.resizes $ FitWindow window

view :: Model -> Graphics SDLEngine
view _ = Graphics2D $ collage []

main :: IO ()
main = do
  engine@SDLEngine { window } <- SDL.startup
  run engine GameConfig
    { initialFn       = initial
    , updateFn        = update
    , subscriptionsFn = subscriptions window
    , viewFn          = view
    }

Engine should have its own setter for window size.