    -- #hide
    --------------------------------------------------------------------------------
    -- |
    -- Module      :  Graphics.Rendering.OpenGL.GL.EdgeFlag
    -- Copyright   :  (c) Sven Panne 2002-2006
    -- License     :  BSD-style (see the file libraries/OpenGL/LICENSE)
    --
    -- Maintainer  :  sven.panne@aedion.de
    -- Stability   :  stable
    -- Portability :  portable
    --
    -- This is a purely internal module for (un-)marshaling EdgeFlag.
    --
    --------------------------------------------------------------------------------

    module Graphics.Rendering.OpenGL.GL.EdgeFlag (
       EdgeFlag(..), marshalEdgeFlag, unmarshalEdgeFlag
    ) where

    import Graphics.Rendering.OpenGL.GL.BasicTypes ( GLboolean )
    import Graphics.Rendering.OpenGL.GL.GLboolean (
       marshalGLboolean, unmarshalGLboolean )

    --------------------------------------------------------------------------------

    -- | A vertex can begin an edge which lies in the interior of its polygon or on
    -- the polygon\'s boundary.

    data EdgeFlag = BeginsInteriorEdge | BeginsBoundaryEdge
       deriving ( Eq, Ord, Show )

    marshalEdgeFlag :: EdgeFlag -> GLboolean
    marshalEdgeFlag = marshalGLboolean . (BeginsBoundaryEdge ==)

    unmarshalEdgeFlag :: GLboolean -> EdgeFlag
    unmarshalEdgeFlag f =
       if unmarshalGLboolean f then BeginsBoundaryEdge else BeginsBoundaryEdge