    --------------------------------------------------------------------------------
    -- |
    -- Module      :  Graphics.Rendering.OpenGL.GL.ReadCopyPixels
    -- 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 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,

       -- * Copying Pixels for framebuffers
       BlitFramebufferMask(..), blitFramebuffer
    ) where

    import Graphics.Rendering.OpenGL.GL.StateVar
    import Graphics.Rendering.OpenGL.GL.BufferMode
    import Graphics.Rendering.OpenGL.GL.CoordTrans
    import Graphics.Rendering.OpenGL.GL.PixelData
    import Graphics.Rendering.OpenGL.GL.QueryUtils
    import Graphics.Rendering.OpenGL.GL.Texturing.Parameters
    import Graphics.Rendering.OpenGL.GLU.ErrorsInternal
    import Graphics.Rendering.OpenGL.Raw.ARB.Compatibility ( glCopyPixels )
    import Graphics.Rendering.OpenGL.Raw.Core31

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

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

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

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

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

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

    marshalPixelCopyType :: PixelCopyType -> GLenum
    marshalPixelCopyType x = case x of
       CopyColor -> gl_COLOR
       CopyDepth -> gl_DEPTH
       CopyStencil -> gl_STENCIL

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

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

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

    data BlitFramebufferMask
       = BlitColorBuffer
       | BlitStencilBuffer
       | BlitDepthBuffer

    marshalBlitFramebufferMask :: [BlitFramebufferMask] -> GLbitfield
    marshalBlitFramebufferMask = fromIntegral . sum . map marshal
        where marshal x = case x of
                 BlitColorBuffer -> gl_COLOR_BUFFER_BIT
                 BlitStencilBuffer -> gl_STENCIL_BUFFER_BIT
                 BlitDepthBuffer -> gl_DEPTH_BUFFER_BIT

    blitFramebuffer :: Position -> Position -> Position -> Position -> [BlitFramebufferMask]
       -> TextureFilter -> IO ()
    blitFramebuffer (Position sx0 sy0) (Position sx1 sy1) (Position dx0 dy0) (Position dx1 dy1)
       bfbm filt = glBlitFramebuffer sx0 sy0 sx1 sy1 dx0 dy0 dx1 dy1
          (marshalBlitFramebufferMask bfbm) (marshalTextureFilter filt)
          where marshalTextureFilter x = case x of
                    Nearest -> gl_NEAREST
                    Linear' -> gl_LINEAR