    -- #hide
    --------------------------------------------------------------------------------
    -- |
    -- Module      :  Graphics.Rendering.OpenGL.GL.ComparisonFunction
    -- Copyright   :  (c) Sven Panne 2002-2009
    -- 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 ComparisonFunction.
    --
    --------------------------------------------------------------------------------

    module Graphics.Rendering.OpenGL.GL.ComparisonFunction (
       ComparisonFunction(..), marshalComparisonFunction,
       unmarshalComparisonFunction
    ) where

    import Graphics.Rendering.OpenGL.Raw.Core31

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

    data ComparisonFunction =
         Never
       | Less
       | Equal
       | Lequal
       | Greater
       | Notequal
       | Gequal
       | Always
       deriving ( Eq, Ord, Show )

    marshalComparisonFunction :: ComparisonFunction -> GLenum
    marshalComparisonFunction x = case x of
       Never -> gl_NEVER
       Less -> gl_LESS
       Equal -> gl_EQUAL
       Lequal -> gl_LEQUAL
       Greater -> gl_GREATER
       Notequal -> gl_NOTEQUAL
       Gequal -> gl_GEQUAL
       Always -> gl_ALWAYS

    unmarshalComparisonFunction :: GLenum -> ComparisonFunction
    unmarshalComparisonFunction x
       | x == gl_NEVER = Never
       | x == gl_LESS = Less
       | x == gl_EQUAL = Equal
       | x == gl_LEQUAL = Lequal
       | x == gl_GREATER = Greater
       | x == gl_NOTEQUAL = Notequal
       | x == gl_GEQUAL = Gequal
       | x == gl_ALWAYS = Always
       | otherwise = error ("unmarshalComparisonFunction: illegal value " ++ show x)