-- | The Face module just contains the definition of the 'Face' data
--   type and its two typeclass instances.
--
module Face (
  Face(..),
  center )
where

import Point ( Point, scale )

data Face = Face { v0 :: !Point,
                   v1 :: !Point,
                   v2 :: !Point,
                   v3 :: !Point }
          deriving (Eq)

instance Show Face where
    show (Face v0' v1' v2' v3') =
      "Face:\n" ++
        "  v0: " ++ (show v0') ++ "\n" ++
        "  v1: " ++ (show v1') ++ "\n" ++
        "  v2: " ++ (show v2') ++ "\n" ++
        "  v3: " ++ (show v3') ++ "\n"

-- | Returns the center of the given face. Since a face is just
--   square, we can average the four vertices to find its center. This
--   is useful because the center of a face is always a vertex of a
--   tetrahedron.
center :: Face -> Point
center (Face v0' v1' v2' v3') =
  (v0' + v1' + v2' + v3') `scale` (1/4)