    --------------------------------------------------------------------------------
    -- |
    -- Module      :  Graphics.Rendering.OpenGL.GL.Clipping
    -- 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 module corresponds to section 2.12 (Clipping) of the OpenGL 2.1 specs.
    --
    --------------------------------------------------------------------------------

    module Graphics.Rendering.OpenGL.GL.Clipping (
       ClipPlaneName(..), clipPlane, maxClipPlanes
    ) where

    import Foreign.Marshal.Alloc ( alloca )
    import Foreign.Marshal.Utils ( with )
    import Foreign.Ptr ( Ptr, castPtr )
    import Graphics.Rendering.OpenGL.GL.BasicTypes ( GLenum, GLsizei, GLdouble )
    import Graphics.Rendering.OpenGL.GL.Capability (
       EnableCap(CapClipPlane), makeStateVarMaybe )
    import Graphics.Rendering.OpenGL.GL.CoordTrans ( Plane(..) )
    import Graphics.Rendering.OpenGL.GL.PeekPoke ( peek1 )
    import Graphics.Rendering.OpenGL.GL.QueryUtils (
       GetPName(GetClipPlane,GetMaxClipPlanes),
       clipPlaneIndexToEnum, getDoublev, getSizei1 )
    import Graphics.Rendering.OpenGL.GL.StateVar (
       GettableStateVar, makeGettableStateVar, StateVar )
    import Graphics.Rendering.OpenGL.GLU.ErrorsInternal ( recordInvalidEnum )

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

    newtype ClipPlaneName = ClipPlaneName GLsizei
       deriving ( Eq, Ord, Show )

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

    clipPlane :: ClipPlaneName -> StateVar (Maybe (Plane GLdouble))
    clipPlane (ClipPlaneName i) =
       makeStateVarMaybe
          (return (CapClipPlane i))
          (alloca $ \buf -> do
              getDoublev (GetClipPlane i) (castPtr buf)
              peek1 id (buf :: Ptr (Plane GLdouble)))
          (\plane -> maybe recordInvalidEnum (with plane . glClipPlane)
                           (clipPlaneIndexToEnum i))

    foreign import CALLCONV unsafe "glClipPlane" glClipPlane ::
       GLenum -> Ptr (Plane GLdouble) -> IO ()

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

    maxClipPlanes :: GettableStateVar GLsizei
    maxClipPlanes = makeGettableStateVar (getSizei1 id GetMaxClipPlanes)