Implement texture atlas, details on why it works unclear

src/Picture/Tree.hs

@@ -14,7 +14,7 @@ import Data.Maybe (isNothing)
 -- consider generalising to alternative rather than using LTree
 -- | Transform a picture into a tree of renderable objects
 picToLTree 
-    :: Maybe Int -- ^ Layer filter. Draw if 'Nothing' or when value is the same as at the leaf.
+    :: Maybe Int -- ^ Layer filter. Draw 'Nothing' when value is the same as at the leaf.
     -> Picture
     -> LTree RenderType
 {-# INLINE picToLTree #-}