Do layer checking in picture tree

src/Picture/Data.hs

@@ -36,6 +36,17 @@ instance Functor LTree where
     fmap f (LBranches ts) = LBranches $ (fmap (fmap f)) ts
     fmap f (LLeaf x) = LLeaf (f x)
 
+data RTree a b
+    = RBranches a [RTree a b]
+    | RLeaf b
+instance Foldable (RTree a) where
+    foldMap g (RBranches _ ts) = mconcat $ map (foldMap g) ts
+    foldMap g (RLeaf x)      = g x
+    {-# INLINE foldMap #-}
+instance Functor (RTree a) where
+    fmap f (RBranches i ts) = RBranches i $ (fmap (fmap f)) ts
+    fmap f (RLeaf x)      = RLeaf (f x)
+
 
 flat2 (x,y)     = [x,y]
 flat3 (x,y,z)   = [x,y,z]
@@ -67,6 +78,7 @@ data Picture
     | Color RGBA Picture
     | Pictures [Picture]
     | OverPic (Point3 -> Point3) (Float -> Float) (Point4 -> Point4) Picture
+    | OnLayer Int Picture
 
 
 blank :: Picture