Allow for bullet drag

src/Dodge/Particle/Bullet/Update.hs

@@ -10,23 +10,21 @@ import Dodge.WorldEvent.ThingsHit
 import Geometry
 --import Geometry.Vector3D
 
+import Data.Bifunctor
 import Control.Lens
 {-
 Update for a generic bullet.
 -}
 mvBullet :: World -> Particle -> (World, Maybe Particle)
 mvBullet w bt 
-    | t <= 0 = wAnd Nothing
-    | t <  4 = wAnd $ Just $ bt
-        & btPassThrough' .~ Nothing
-        & btTrail' .~ (p:p:ps)
-        & btTimer' -~ 1                      
---    | otherwise = hiteff bt (thingsHitExceptCr3D' mcr (addZ 20 p) (addZ 20 (p +.+ vel)) w) w
-    | otherwise = hiteff bt (thingsHitExceptCr mcr p (p +.+ vel) w) w
+    | t <= 0 || magV (_btVel' bt) < 1 = wAnd Nothing
+    | otherwise = second (fmap dodrag) $ hiteff bt (thingsHitExceptCr mcr p (p +.+ vel) w) w
   where 
+    dodrag = btVel' %~ (drag *.*)
+    drag = _btDrag bt
     wAnd    = (w,)
     mcr     = _btPassThrough' bt
-    (p:ps)  = _btTrail' bt
+    (p:_)  = _btTrail' bt
     vel     = _btVel' bt
     hiteff  = _btHitEffect' bt
     t       = _btTimer' bt