diff --git a/moffy-samples-gtk4-run.cabal b/moffy-samples-gtk4-run.cabal
--- a/moffy-samples-gtk4-run.cabal
+++ b/moffy-samples-gtk4-run.cabal
@@ -5,7 +5,7 @@
 -- see: https://github.com/sol/hpack
 
 name:           moffy-samples-gtk4-run
-version:        0.1.0.0
+version:        0.2.0.0
 synopsis:       Package to run moffy samples - Gtk4 version
 description:    Please see the README on GitHub at <https://github.com/YoshikuniJujo/moffy-samples-gtk4-run#readme>
 category:       Control
@@ -71,6 +71,7 @@
       base >=4.7 && <5
     , c-enum
     , c-struct
+    , containers
     , exception-hierarchy
     , moffy
     , moffy-samples-events
@@ -99,6 +100,7 @@
       base >=4.7 && <5
     , c-enum
     , c-struct
+    , containers
     , exception-hierarchy
     , moffy
     , moffy-samples-events
diff --git a/src/Control/Moffy/Samples/Followbox/Run/Gtk4.hs b/src/Control/Moffy/Samples/Followbox/Run/Gtk4.hs
--- a/src/Control/Moffy/Samples/Followbox/Run/Gtk4.hs
+++ b/src/Control/Moffy/Samples/Followbox/Run/Gtk4.hs
@@ -32,27 +32,32 @@
 import Control.Moffy.Samples.Viewable.Shape
 import Data.OneOfThem
 
+import Data.Map qualified as M
+import Control.Moffy.Samples.Event.Area qualified as A
+
 runFollowbox :: String -> Sig s FollowboxEv T.View () -> IO ()
 runFollowbox brws sig = runFollowbox_ brws Nothing $ viewToView <$%> sig
 
 runFollowbox_ :: String -> Maybe GithubNameToken -> Sig s FollowboxEv View () -> IO ()
 runFollowbox_ brws tkn sig = do
+	va <- atomically $ newTVar M.empty
 	(cer, ceo, cv) <- atomically $
 		(,,) <$> newTChan <*> newTChan <*> newTChan
-	_ <- forkIO $ runFollowboxGen cer ceo brws tkn cv (sig >> emit Stopped)
+	_ <- forkIO $ runFollowboxGen cer ceo va brws tkn cv (sig >> emit Stopped)
 	runSingleWin cer ceo cv
 
 runFollowboxGen ::
-	TChan (EvReqs (CalcTextExtents :- GuiEv)) -> TChan (EvOccs (CalcTextExtents :- GuiEv)) -> String ->
+	TChan (EvReqs (CalcTextExtents :- GuiEv)) -> TChan (EvOccs (CalcTextExtents :- GuiEv)) ->
+	TVar (M.Map Int (A.Point, A.Point)) -> String ->
 	Maybe GithubNameToken -> TChan x -> Sig s FollowboxEv x r -> IO r
-runFollowboxGen cr c brs mgnt c' s = do
-	(r, _) <- interpretSt (handleFollowbox (cr, c) brs mgnt) c' s (initialFollowboxState $ mkStdGen 8)
+runFollowboxGen cr c va brs mgnt c' s = do
+	(r, _) <- interpretSt (handleFollowbox va (cr, c) brs mgnt) c' s (initialFollowboxState $ mkStdGen 8)
 	pure r
 
-handleFollowbox ::
+handleFollowbox :: TVar (M.Map Int (A.Point, A.Point)) ->
 	(TChan (EvReqs (CalcTextExtents :- GuiEv)), TChan (EvOccs (CalcTextExtents :- GuiEv))) -> Browser ->
 	Maybe GithubNameToken -> HandleF IO (CalcTextExtents :- GuiEv :+: FollowboxEv)
-handleFollowbox = handleFollowboxWith (uncurry . handle)
+handleFollowbox va f = handleFollowboxWith (uncurry . handle) f va
 
 viewToView :: T.View -> View
 viewToView (T.View vs) = View $ (view1ToView1 `apply`) <$> vs