Scroll the viewport around the character

Scroll the viewport so that the character is never less than 5 away from
the edge of the screen.

This was super easy, thanks Brick!

src/Xanthous/Entities/Character.hs

@@ -5,6 +5,7 @@ module Xanthous.Entities.Character
 --------------------------------------------------------------------------------
 import Xanthous.Prelude
 import Test.QuickCheck
+import Brick
 --------------------------------------------------------------------------------
 import Xanthous.Entities
 --------------------------------------------------------------------------------
@@ -12,7 +13,16 @@ import Xanthous.Entities
 data Character = Character
   deriving stock (Show, Eq, Ord, Generic)
   deriving anyclass (CoArbitrary, Function)
-  deriving Draw via (DrawCharacter "@" Character)
+
+scrollOffset :: Int
+scrollOffset = 5
+
+-- deriving Draw via (DrawCharacter "@" Character)
+instance Draw Character where
+  draw _ = visibleRegion rloc rreg $ str "@"
+    where
+      rloc = Location (negate scrollOffset, negate scrollOffset)
+      rreg = (2 * scrollOffset, 2 * scrollOffset)
 
 instance Entity Character where
   blocksVision _ = False