    -- #hide
    --------------------------------------------------------------------------------
    -- |
    -- Module      :  Graphics.Rendering.OpenGL.Raw.Extensions
    -- Copyright   :  (c) Sven Panne 2009
    -- License     :  BSD-style (see the file LICENSE)
    --
    -- Maintainer  :  sven.panne@aedion.de
    -- Stability   :  stable
    -- Portability :  portable
    --
    -- This internal module offers convenience functions and re-exports for OpenGL
    -- extension loading.
    --
    --------------------------------------------------------------------------------

    module Graphics.Rendering.OpenGL.Raw.Extensions (
       Invoker, getExtensionEntry,
       FunPtr, unsafePerformIO
    ) where

    import Foreign.Marshal.Error
    import Foreign.Ptr
    import Graphics.Rendering.OpenGL.Raw.GetProcAddress
    import System.IO.Unsafe

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

    type Invoker a = FunPtr a -> a

    getExtensionEntry :: String -> String -> IO (FunPtr a)
    getExtensionEntry extensionNameString extensionEntry =
       throwIfNullFunPtr ("unknown OpenGL extension entry " ++ extensionEntry ++
                          ", check for " ++ extensionNameString) $
          getProcAddressWithSuffixes extensionEntry extensionSuffixes

    throwIfNullFunPtr :: String -> IO (FunPtr a) -> IO (FunPtr a)
    throwIfNullFunPtr = throwIf (== nullFunPtr) . const

    -- non-ARB extension suffixes are in descending order of number of extensions
    extensionSuffixes :: [String]
    extensionSuffixes = [
       "", "ARB", "EXT", "NV", "SGIX", "SGIS", "ATI", "APPLE", "SUN", "OES", "IBM",
       "MESA", "HP", "SGI", "OML", "AMD", "3DFX", "WIN", "PGI", "INTEL", "INGR",
       "GREMEDY", "SUNX", "S3", "REND", "MESAX" ]