Simplify bullet movement

src/Dodge/Bullet.hs

@@ -22,10 +22,8 @@ import Data.Bifunctor
 updateBullet :: World -> Bullet -> (World, Maybe Bullet)
 updateBullet w bu
     | magV (_buVel bu) < 1 = (endspawn w, Nothing)
-    | otherwise =
+-- have to be slightly carefull not to accelerate bullets using magnets
-        second (fmap updateBulVel)
+    | otherwise = second (Just . updateBulVel) . hitEffFromBul w $ applyMagnetsToBul bu w
-            . hitEffFromBul w
-            $ applyMagnetsToBul bu w
   where
     endspawn = fromMaybe id $ do
         partspawn <- useBulletPayload bu
@@ -34,18 +32,19 @@ updateBullet w bu
 
 -- do we want this to drain energy from the deflection source?
 applyMagnetsToBul :: Bullet -> World -> Bullet
-applyMagnetsToBul bu =
+applyMagnetsToBul bu = foldl' doMagnetBuBu bu . _oldMagnets . _lWorld . _cWorld
-    foldl' (flip doMagnetBuBu) bu . _oldMagnets . _lWorld . _cWorld
 
-doMagnetBuBu :: Magnet -> Bullet -> Bullet
+doMagnetBuBu :: Bullet -> Magnet -> Bullet
-doMagnetBuBu mg bu = if isclose 
+doMagnetBuBu bu mg 
-    then case _mgField mg of
+    | notclose = bu
-        MagnetAlign -> bu & buVel %~ vecTurnTo (10 * pi / (d+40)) bpos mgalignpos
+    | otherwise = case _mgField mg of
-        MagnetDeflect -> bu & buVel %~ vecTurnTo (10 * pi / (d+40)) bpos mgdeflectpos
+        MagnetAlign -> doturntowards mgalignpos
-        MagnetAttract -> bu & buVel %~ vecTurnTo (10 * pi / (d+40)) bpos mpos
+        MagnetDeflect -> doturntowards mgdeflectpos
-        MagnetRepulse -> bu & buVel %~ vecTurnTo (10 * pi / (d+40)) bpos (2*bpos - mpos)
+        MagnetAttract -> doturntowards mpos
-    else bu
+        MagnetRepulse -> doturntowards (2*bpos - mpos)
   where
+    notclose = d > 100
+    doturntowards p = bu & buVel %~ vecTurnTo (10 * pi / (d+40)) bpos p
     bvel = bu ^. buVel
     mpos = mg ^. mgPos
     bpos = bu ^. buPos
@@ -56,7 +55,6 @@ doMagnetBuBu mg bu = if isclose
         | dotV bvel (bpos - mpos) > 0 = bpos - mpos
         | otherwise = mpos - bpos
     d = dist (bu ^. buPos) (mg ^. mgPos)
-    isclose = d < 100
 
 updateBulVel :: Bullet -> Bullet
 updateBulVel bt = bt & buVel .*.*~ _buDrag bt
@@ -155,10 +153,7 @@ makeFlak bu _ w = w & cWorld . lWorld . bullets .++~ [f x | x <- xs]
         ]
     g x v = v +.+ x *.* normalizeV (vNormal v)
 
-hitEffFromBul ::
+hitEffFromBul :: World -> Bullet -> (World, Bullet)
-    World ->
-    Bullet ->
-    (World, Maybe Bullet)
 hitEffFromBul w bu = case _buEffect bu of
     PenetrateBullet -> movePenBullet bu hitstream w
     BounceBullet -> case List.safeHead hitstream of
@@ -167,8 +162,7 @@ hitEffFromBul w bu = case _buEffect bu of
             dir <- bounceDir (hp, crwl)
             return
                 ( w
-                , Just $
+                , bu
-                    bu
                         & buPos .~ hp +.+ normalizeV (_buPos bu -.- hp)
                         & buVel %~ reflectIn dir
 --                        & buTrajectory .~ BasicBulletTrajectory
@@ -196,22 +190,18 @@ expireAndDamage ::
     Bullet ->
     [(Point2, Either Creature Wall)] ->
     World ->
-    (World, Maybe Bullet)
+    (World, Bullet)
 expireAndDamage bt things w = case List.safeHead things of
     Nothing -> (w, moveBullet bt)
-    Just x -> (damageThingHit bt x w, destroyAt (fst x) bt)
+    Just x -> (damageThingHit bt x w, stopBulletAt (fst x) bt)
 
-moveBullet :: Bullet -> Maybe Bullet
+moveBullet :: Bullet -> Bullet
-moveBullet pt =
+moveBullet pt = pt
-    Just $
-        pt
             & buPos %~ (+.+ _buVel pt)
             & buOldPos .~ _buPos pt
 
-destroyAt :: Point2 -> Bullet -> Maybe Bullet
+stopBulletAt :: Point2 -> Bullet -> Bullet
-destroyAt hitp pt =
+stopBulletAt hitp pt = pt
-    Just $
-        pt
             & buPos .~ hitp +.+ normalizeV (p -.- hitp)
             & buOldPos .~ p
             & buVel .~ 0
@@ -222,7 +212,7 @@ movePenBullet ::
     Bullet ->
     [(Point2, Either Creature Wall)] ->
     World ->
-    (World, Maybe Bullet)
+    (World, Bullet)
 movePenBullet bu hitstream w = case hitstream of
     [] -> (w, moveBullet bu)
     ((p, crwl) : strm) ->