    -- #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.GL.BasicTypes ( GLenum )

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

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

    marshalComparisonFunction :: ComparisonFunction -> GLenum
    marshalComparisonFunction x = case x of
       Never -> 0x200
       Less -> 0x201
       Equal -> 0x202
       Lequal -> 0x203
       Greater -> 0x204
       Notequal -> 0x205
       Gequal -> 0x206
       Always -> 0x207

    unmarshalComparisonFunction :: GLenum -> ComparisonFunction
    unmarshalComparisonFunction x
       | x == 0x200 = Never
       | x == 0x201 = Less
       | x == 0x202 = Equal
       | x == 0x203 = Lequal
       | x == 0x204 = Greater
       | x == 0x205 = Notequal
       | x == 0x206 = Gequal
       | x == 0x207 = Always
       | otherwise = error ("unmarshalComparisonFunction: illegal value " ++ show x)