Update single selection to be under mouse while dragging

src/Dodge/Update/Input/InGame.hs

@@ -280,7 +280,7 @@ shiftInvItems ::
     IM.IntMap (SelectionItem a) ->
     World ->
     World
-shiftInvItems k x ab bn xs ss w = fromMaybe w $ do
+shiftInvItems k x ab bn xs ss w = setSelWhileDragging . fromMaybe w $ do
     let xk = fst x
     guard $ xk == k || xk + 1 == k || xk -1 == k
     (maxi,_) <- IS.maxView xs
@@ -295,6 +295,13 @@ shiftInvItems k x ab bn xs ss w = fromMaybe w $ do
             guard $ Just (k,maxi+1) < bn
             return $ shiftInvItemsDown k xs w
 
+setSelWhileDragging :: World -> World
+setSelWhileDragging w = fromMaybe w $ do
+    (i,_,xs) <- w ^? hud . hudElement . diSelection . _Just
+    (k,j) <- w ^? input . mouseContext . mcoMaybeSelect . _Just
+    guard $ i == k && j `IS.member` xs
+    return $ w & hud . hudElement . diSelection . _Just . _2 .~ j
+
 shiftInvItemsUp :: Int -> IS.IntSet -> World -> World
 shiftInvItemsUp j is w = IS.foldl' f w is
   where