    --------------------------------------------------------------------------------
    -- |
    -- Module      :  Graphics.Rendering.OpenGL.GL.ReadCopyPixels
    -- 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 4.3 (Drawing, Reading, and Copying Pixels)
    -- of the OpenGL 2.1 specs.
    --
    --------------------------------------------------------------------------------

    module Graphics.Rendering.OpenGL.GL.ReadCopyPixels (
       -- * Reading Pixels
       readPixels, readBuffer,

       -- * Copying Pixels
       PixelCopyType(..), copyPixels
    ) where

    import Foreign.Ptr ( Ptr )
    import Graphics.Rendering.OpenGL.GL.BasicTypes ( GLenum, GLint, GLsizei )
    import Graphics.Rendering.OpenGL.GL.BufferMode (
       marshalBufferMode, unmarshalBufferMode )
    import Graphics.Rendering.OpenGL.GL.Framebuffer ( BufferMode(..) )
    import Graphics.Rendering.OpenGL.GL.CoordTrans ( Position(..), Size(..) )
    import Graphics.Rendering.OpenGL.GL.PixelData ( withPixelData )
    import Graphics.Rendering.OpenGL.GL.PixelRectangles ( PixelData )
    import Graphics.Rendering.OpenGL.GL.QueryUtils (
       GetPName(GetReadBuffer), getEnum1 )
    import Graphics.Rendering.OpenGL.GL.StateVar ( StateVar, makeStateVar )
    import Graphics.Rendering.OpenGL.GLU.ErrorsInternal ( recordInvalidValue )

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

    readPixels :: Position -> Size -> PixelData a -> IO ()
    readPixels (Position x y) (Size w h) pd =
       withPixelData pd $ glReadPixels x y w h

    foreign import CALLCONV unsafe "glReadPixels" glReadPixels ::
       GLint -> GLint -> GLsizei -> GLsizei -> GLenum -> GLenum -> Ptr a -> IO ()

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

    readBuffer :: StateVar BufferMode
    readBuffer =
       makeStateVar
          (getEnum1 unmarshalBufferMode GetReadBuffer)
          (maybe recordInvalidValue glReadBuffer . marshalBufferMode)

    foreign import CALLCONV unsafe "glReadBuffer" glReadBuffer :: GLenum -> IO ()

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

    data PixelCopyType =
         CopyColor
       | CopyDepth
       | CopyStencil
       deriving ( Eq, Ord, Show )

    marshalPixelCopyType :: PixelCopyType -> GLenum
    marshalPixelCopyType x = case x of
       CopyColor -> 0x1800
       CopyDepth -> 0x1801
       CopyStencil -> 0x1802

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

    copyPixels :: Position -> Size -> PixelCopyType -> IO ()
    copyPixels (Position x y) (Size w h) t =
       glCopyPixels x y w h (marshalPixelCopyType t)

    foreign import CALLCONV unsafe "glCopyPixels" glCopyPixels ::
       GLint -> GLint -> GLsizei -> GLsizei -> GLenum -> IO ()