affection/src/Affection/Particle.hs

{-# LANGUAGE RecordWildCards #-}

-- | This module introduces a simple particle system to Affection
module Affection.Particle
  ( updateParticle
  , drawParticles
  , updateParticleSystem
  ) where

import Affection.Types

import Data.Maybe (catMaybes)

import qualified GEGL as G

-- This function updates particles through a specified function. Particle ageing
-- and death is being handled by 'updateParticles' itself and does not need to
-- bother you.
updateParticle
  :: Double                           -- ^ Elapsed time in seconds
  -> (Double -> Particle -> Particle) -- ^ Update function for a single 'Particle'
                                      -- This Function should take the elapsed time
                                      -- in seconds and the initial particle as arguments.
  -> Particle                         -- ^ 'Particle' to be processed
  -> Maybe Particle                   -- ^ resulting 'Particle'
updateParticle time funct p@Particle{..} =
  if particleLife - time < 0
  then
    Nothing
  else
    Just $ funct time $ p { particleLife = particleLife - time }

drawParticles
  :: (Particle -> Affection us ())
  -> [Particle]
  -> Affection us ()
drawParticles = mapM_

updateParticleSystem
  :: ParticleSystem
  -> Double
  -> (Double -> Particle -> Particle)
  -> (G.GeglBuffer -> G.GeglNode -> Particle -> Affection us ())
  -> Affection us ParticleSystem
updateParticleSystem sys sec upd draw = do
  let x = catMaybes $ map (updateParticle sec upd) (psParts sys)
  mapM_ (draw (psBuffer sys) (psNode sys)) x
  return $ sys
    { psParts = x }