    -- #hide
    --------------------------------------------------------------------------------
    -- |
    -- Module      :  Graphics.Rendering.OpenGL.GL.BufferMode
    -- 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 BufferMode.
    --
    --------------------------------------------------------------------------------

    module Graphics.Rendering.OpenGL.GL.BufferMode (
       BufferMode(..), marshalBufferMode, unmarshalBufferMode
    ) where

    import Graphics.Rendering.OpenGL.Raw.Core31
    import Graphics.Rendering.OpenGL.Raw.ARB.Compatibility ( gl_AUX0 )

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

    -- | The set of color buffers which are selected for reading and writing.

    data BufferMode =
         NoBuffers
         -- ^ No color buffers are selected.
       | FrontLeftBuffer
         -- ^ Only the front left color buffer is selected.
       | FrontRightBuffer
         -- ^ Only the front right color buffer is selected.
       | BackLeftBuffer
         -- ^ Only the  back left color buffer is selected.
       | BackRightBuffer
         -- ^ Only the back right color buffer is selected.
       | FrontBuffers
         -- ^ Only the front left and front right color buffers are selected. If
         -- there is no front right color buffer, only the front left color buffer
         -- is selected.
       | BackBuffers
         -- ^ Only the back left and back right color buffers are selected. If there
         -- is no back right color buffer, only the back left color buffer is
         -- selected.
       | LeftBuffers
         -- ^ Only the front left and back left color buffers are selected. If there
         -- is no back left color buffer, only the front left color buffer is
         -- selected.
       | RightBuffers
         -- ^ Only the front right and back right color buffers are selected. If
         -- there is no back right color buffer, only the front right color buffer
         -- is selected.
       | FrontAndBackBuffers
         -- ^ All the front and back color buffers (front left, front right, back
         -- left, back right) are selected. If there are no back color buffers, only
         -- the front left and front right color buffers are selected. If there are
         -- no right color buffers, only the front left and back left color buffers
         -- are selected. If there are no right or back color buffers, only the
         -- front left color buffer is selected.
       | AuxBuffer GLsizei
         -- ^ Only the given auxiliary color buffer no. /i/ is selected.
       deriving ( Eq, Ord, Show )

    marshalBufferMode :: BufferMode -> Maybe GLenum
    marshalBufferMode x = case x of
       NoBuffers -> Just gl_NONE
       FrontLeftBuffer -> Just gl_FRONT_LEFT
       FrontRightBuffer -> Just gl_FRONT_RIGHT
       BackLeftBuffer -> Just gl_BACK_LEFT
       BackRightBuffer -> Just gl_BACK_RIGHT
       FrontBuffers -> Just gl_FRONT
       BackBuffers -> Just gl_BACK
       LeftBuffers -> Just gl_LEFT
       RightBuffers -> Just gl_RIGHT
       FrontAndBackBuffers -> Just gl_FRONT_AND_BACK
       AuxBuffer i
          | fromIntegral i <= maxAuxBuffer -> Just (gl_AUX0 + fromIntegral i)
          | otherwise -> Nothing

    unmarshalBufferMode :: GLenum -> BufferMode
    unmarshalBufferMode x
       | x == gl_NONE = NoBuffers
       | x == gl_FRONT_LEFT = FrontLeftBuffer
       | x == gl_FRONT_RIGHT = FrontRightBuffer
       | x == gl_BACK_LEFT = BackLeftBuffer
       | x == gl_BACK_RIGHT = BackRightBuffer
       | x == gl_FRONT = FrontBuffers
       | x == gl_BACK = BackBuffers
       | x == gl_LEFT = LeftBuffers
       | x == gl_RIGHT = RightBuffers
       | x == gl_FRONT_AND_BACK = FrontAndBackBuffers
       | gl_AUX0 <= x && x <= gl_AUX0 + maxAuxBuffer = AuxBuffer (fromIntegral (x - gl_AUX0))
       | otherwise = error ("unmarshalBufferMode: illegal value " ++ show x)

    maxAuxBuffer :: GLenum
    maxAuxBuffer = 246