--------------------------------------------------------------------------------
-- |
-- Module      :  Graphics.UI.GLUT.Initialization
-- Copyright   :  (c) Sven Panne 2002-2005
-- License     :  BSD-style (see the file libraries/GLUT/LICENSE)
-- 
-- Maintainer  :  sven.panne@aedion.de
-- Stability   :  stable
-- Portability :  portable
--
-- Actions and state variables in this module are used to initialize GLUT state.
-- The primary initialization routine is 'initialize', which should only be
-- called exactly once in a GLUT program. No other GLUT or OpenGL actions should
-- be called before 'initialize', apart from getting or setting the state
-- variables in this module.
--
-- The reason is that these state variables can be used to set default window
-- initialization state that might be modified by the command processing done in
-- 'initialize'. For example, 'initialWindowSize' can be set to @('Size'
-- 400 400)@ before 'initialize' is called to indicate 400 by 400 is the
-- program\'s default window size. Setting the initial window size or position
-- before 'initialize' allows the GLUT program user to specify the initial size
-- or position using command line arguments.
--
--------------------------------------------------------------------------------

module Graphics.UI.GLUT.Initialization (
   -- * Primary initialization
   initialize, getArgsAndInitialize,

   -- * Initial window geometry
   initialWindowPosition, initialWindowSize,

   -- * Setting the initial display mode (I)
   DisplayMode(..), initialDisplayMode, displayModePossible,

   -- * Setting the initial display mode (II)
   DisplayCapability(..), Relation(..), DisplayCapabilityDescription(..),
   initialDisplayCapabilities,

   -- * Controlling the creation of rendering contexts
   RenderingContext(..), renderingContext,

   -- * Direct\/indirect rendering
   DirectRendering(..), directRendering
) where

import Data.Bits ( Bits((.|.),(.&.)) )
import Data.List ( genericLength, intersperse )
import Foreign.C.String ( CString, withCString, peekCString )
import Foreign.C.Types ( CInt, CUInt )
import Foreign.Marshal.Array ( withArray0, peekArray )
import Foreign.Marshal.Utils ( with, withMany )
import Foreign.Ptr ( Ptr, nullPtr )
import Foreign.Storable ( Storable(..) )
import System.Environment ( getProgName, getArgs )
import Graphics.Rendering.OpenGL.GL.CoordTrans ( Position(..), Size(..) )
import Graphics.Rendering.OpenGL.GL.StateVar (
   GettableStateVar, makeGettableStateVar,
   SettableStateVar, makeSettableStateVar,
   StateVar, makeStateVar )
import Graphics.UI.GLUT.Constants (
   glut_INIT_WINDOW_X, glut_INIT_WINDOW_Y,
   glut_INIT_WINDOW_WIDTH, glut_INIT_WINDOW_HEIGHT,
   glut_RGBA, glut_RGB, glut_INDEX, glut_SINGLE, glut_DOUBLE, glut_ACCUM,
   glut_ALPHA, glut_DEPTH, glut_STENCIL, glut_MULTISAMPLE, glut_STEREO,
   glut_LUMINANCE, glut_AUX1, glut_AUX2, glut_AUX3, glut_AUX4,
   glut_INIT_DISPLAY_MODE,
   glut_DISPLAY_MODE_POSSIBLE,
   glut_RENDERING_CONTEXT, glut_CREATE_NEW_CONTEXT, glut_USE_CURRENT_CONTEXT,
   glut_DIRECT_RENDERING,
   glut_FORCE_INDIRECT_CONTEXT, glut_ALLOW_DIRECT_CONTEXT,
   glut_TRY_DIRECT_CONTEXT, glut_FORCE_DIRECT_CONTEXT )
import Graphics.UI.GLUT.QueryUtils ( simpleGet, glutSetOption )
import Graphics.UI.GLUT.Types ( Relation(..), relationToString )

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

-- | Given the program name and command line arguments, initialize the GLUT
-- library and negotiate a session with the window system. During this
-- process, 'initialize' may cause the termination of the GLUT program with an
-- error message to the user if GLUT cannot be properly initialized.
-- Examples of this situation include the failure to connect to the window
-- system, the lack of window system support for OpenGL, and invalid command
-- line options.
--
-- 'initialize' also processes command line options, but the specific options
-- parsed are window system dependent. Any command line arguments which are
-- not GLUT-specific are returned.
--
-- /X Implementation Notes:/ The X Window System specific options parsed by
-- 'initialize' are as follows:
--
-- * @-display /DISPLAY/@: Specify the X server to connect to. If not specified,
--   the value of the @DISPLAY@ environment variable is used.
--
-- * @-geometry /WxH+X+Y/@: Determines where windows should be created on the
--   screen. The parameter following @-geometry@ should be formatted as a
--   standard X geometry specification. The effect of using this option is to
--   change the GLUT initial size and initial position the same as if
--   'initialWindowSize' or 'initialWindowPosition' were modified directly.
--
-- * @-iconic@: Requests all top-level windows be created in an iconic state.
--
-- * @-indirect@: Force the use of indirect OpenGL rendering contexts.
--
-- * @-direct@: Force the use of direct OpenGL rendering contexts (not all GLX
--   implementations support direct rendering contexts). A fatal error is
--   generated if direct rendering is not supported by the OpenGL
--   implementation. If neither @-indirect@ or @-direct@ are used to force a
--   particular behavior, GLUT will attempt to use direct rendering if
--   possible and otherwise fallback to indirect rendering.
--
-- * @-gldebug@: After processing callbacks and\/or events, call
--   'Graphics.UI.GLUT.Debugging.reportErrors' to check if there are any pending
--   OpenGL errors. Using this option is helpful in detecting OpenGL run-time
--   errors.
--
-- * @-sync@: Enable synchronous X protocol transactions. This option makes
--   it easier to track down potential X protocol errors.

initialize :: String      -- ^ The program name.
           -> [String]    -- ^ The command line arguments
           -> IO [String] -- ^ Non-GLUT command line arguments
initialize prog args =
   with (1 + genericLength args) $ \argcBuf ->
   withMany withCString (prog : args) $ \argvPtrs ->
   withArray0 nullPtr argvPtrs $ \argvBuf -> do
   glutInit argcBuf argvBuf
   newArgc <- peek argcBuf
   newArgvPtrs <- peekArray (fromIntegral newArgc) argvBuf
   newArgv <- mapM peekCString newArgvPtrs
   return $ tail newArgv

foreign import ccall unsafe "glutInit" glutInit ::
   Ptr CInt -> Ptr CString -> IO ()

-- | Convenience action: Initialize GLUT, returning the program name and any
-- non-GLUT command line arguments.

getArgsAndInitialize :: IO (String, [String])
getArgsAndInitialize = do
   prog <- getProgName
   args <- getArgs
   nonGLUTArgs <- initialize prog args
   return (prog, nonGLUTArgs)

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

-- | Controls the /initial window position/.  Windows created by
-- 'Graphics.UI.GLUT.Window.createWindow' will be requested to be created with
-- the current /initial window position/. The initial value of the /initial
-- window position/ GLUT state is @'Size' (-1) (-1)@. If either the X or Y
-- component of the /initial window position/ is negative, the actual window
-- position is left to the window system to determine.
--
-- The intent of the /initial window position/ is to provide a suggestion to
-- the window system for a window\'s initial position. The window system is
-- not obligated to use this information. Therefore, GLUT programs should not
-- assume the window was created at the specified position.

initialWindowPosition :: StateVar Position
initialWindowPosition =
   makeStateVar getInitialWindowPosition setInitialWindowPosition

getInitialWindowPosition :: IO Position
getInitialWindowPosition = do
   x <- simpleGet fromIntegral glut_INIT_WINDOW_X
   y <- simpleGet fromIntegral glut_INIT_WINDOW_Y
   return $ Position x y

setInitialWindowPosition :: Position -> IO ()
setInitialWindowPosition (Position x y) =
    glutInitWindowPosition (fromIntegral x) (fromIntegral y)

foreign import ccall unsafe "glutInitWindowPosition" glutInitWindowPosition
   :: CInt -> CInt -> IO ()

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

-- | Controls the /initial window size/.  Windows created by
-- 'Graphics.UI.GLUT.Window.createWindow' will be requested to be created with
-- the current /initial window size/. The initial value of the /initial window
-- size/ GLUT state is @'Size' 300 300@. If either the width or the height
-- component of the /initial window size/ is non-positive, the actual window
-- size is left to the window system to determine.
--
-- The intent of the /initial window size/ is to provide a suggestion to the
-- window system for a window\'s initial size. The window system is not
-- obligated to use this information. Therefore, GLUT programs should not
-- assume the window was created at the specified size. A GLUT program should
-- use the window\'s reshape callback to determine the true size of the
-- window.

initialWindowSize :: StateVar Size
initialWindowSize = makeStateVar getInitialWindowSize setInitialWindowSize

getInitialWindowSize :: IO Size
getInitialWindowSize = do
   w <- simpleGet fromIntegral glut_INIT_WINDOW_WIDTH
   h <- simpleGet fromIntegral glut_INIT_WINDOW_HEIGHT
   return $ Size w h

setInitialWindowSize :: Size -> IO ()
setInitialWindowSize (Size w h) =
   glutInitWindowSize (fromIntegral w) (fromIntegral h)

foreign import ccall unsafe "glutInitWindowSize" glutInitWindowSize ::
   CInt -> CInt -> IO ()

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

-- | A single aspect of a window which is to be created, used in conjunction
-- with 'initialDisplayMode'.

data DisplayMode
   = RGBAMode           -- ^ Select an RGBA mode window. This is the default if neither 'RGBAMode' nor 'IndexMode' are specified.
   | RGBMode            -- ^ An alias for 'RGBAMode'.
   | IndexMode          -- ^ Select a color index mode window. This overrides 'RGBAMode' if it is also specified.
   | LuminanceMode      -- ^ Select a window with a \"luminance\" color model. This model provides the functionality of OpenGL\'s
                        --   RGBA color model, but the green and blue components are not maintained in the frame buffer. Instead
                        --   each pixel\'s red component is converted to an index between zero and  'Graphics.UI.GLUT.Colormap.numColorMapEntries'
                        --   and looked up in a per-window color map to determine the color of pixels within the window. The initial
                        --   colormap of 'LuminanceMode' windows is initialized to be a linear gray ramp, but can be modified with GLUT\'s
                        --   colormap actions. /Implementation Notes:/ 'LuminanceMode' is not supported on most OpenGL platforms.
   | WithAlphaComponent -- ^ Select a window with an alpha component to the color buffer(s).
   | WithAccumBuffer    -- ^ Select a window with an accumulation buffer.
   | WithDepthBuffer    -- ^ Select a window with a depth buffer.
   | WithStencilBuffer  -- ^ Select a window with a stencil buffer.
   | WithAuxBuffers Int -- ^ (/freeglut only/) Select a window with /n/ (1 .. 4) auxiliary buffers. Any /n/ outside the range 1 .. 4 is a fatal error.
   | SingleBuffered     -- ^ Select a single buffered window. This is the default if neither 'DoubleBuffered' nor 'SingleBuffered' are specified.
   | DoubleBuffered     -- ^ Select a double buffered window. This overrides 'SingleBuffered' if it is also specified.
   | Multisampling      -- ^ Select a window with multisampling support. If multisampling is not available, a non-multisampling
                        --   window will automatically be chosen. Note: both the OpenGL client-side and server-side implementations
                        --   must support the @GLX_SAMPLE_SGIS@ extension for multisampling to be available.
   | Stereoscopic       -- ^ Select A Stereo Window.
   deriving ( Eq, Ord, Show )

marshalDisplayMode :: DisplayMode -> CUInt
marshalDisplayMode m = case m of
   RGBAMode -> glut_RGBA
   RGBMode -> glut_RGB
   IndexMode -> glut_INDEX
   SingleBuffered -> glut_SINGLE
   DoubleBuffered -> glut_DOUBLE
   WithAccumBuffer -> glut_ACCUM
   WithAlphaComponent -> glut_ALPHA
   WithDepthBuffer -> glut_DEPTH
   WithStencilBuffer -> glut_STENCIL
   WithAuxBuffers 1 -> glut_AUX1
   WithAuxBuffers 2 -> glut_AUX2
   WithAuxBuffers 3 -> glut_AUX3
   WithAuxBuffers 4 -> glut_AUX4
   WithAuxBuffers n ->
      error ("marshalDisplayMode: illegal number of auxiliary buffers: " ++ show n)
   Multisampling -> glut_MULTISAMPLE
   Stereoscopic -> glut_STEREO
   LuminanceMode -> glut_LUMINANCE

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

-- | Controls the /initial display mode/ used when creating top-level windows,
-- subwindows, and overlays to determine the OpenGL display mode for the
-- to-be-created window or overlay.
--
-- Note that 'RGBAMode' selects the RGBA color model, but it does not request any
-- bits of alpha (sometimes called an /alpha buffer/ or /destination alpha/)
-- be allocated. To request alpha, specify 'WithAlphaComponent'. The same
-- applies to 'LuminanceMode'.

initialDisplayMode :: StateVar [DisplayMode]
initialDisplayMode = makeStateVar getInitialDisplayMode setInitialDisplayMode

getInitialDisplayMode :: IO [DisplayMode]
getInitialDisplayMode = simpleGet i2dms glut_INIT_DISPLAY_MODE

i2dms :: CInt -> [DisplayMode]
i2dms bitfield =
   [ c | c <- [ RGBAMode, RGBMode, IndexMode, SingleBuffered, DoubleBuffered,
                WithAccumBuffer, WithAlphaComponent, WithDepthBuffer,
                WithStencilBuffer, WithAuxBuffers 1, WithAuxBuffers 2,
                WithAuxBuffers 3, WithAuxBuffers 4, Multisampling, Stereoscopic,
                LuminanceMode ]
       , (fromIntegral bitfield .&. marshalDisplayMode c) /= 0 ]

setInitialDisplayMode :: [DisplayMode] -> IO ()
setInitialDisplayMode = glutInitDisplayMode . toBitfield marshalDisplayMode

toBitfield :: (Bits b) => (a -> b) -> [a] -> b
toBitfield marshal = foldl (.|.) 0 . map marshal

foreign import ccall unsafe "glutInitDisplayMode" glutInitDisplayMode ::
   CUInt -> IO ()

-- | Contains 'True' if the /current display mode/ is supported, 'False'
-- otherwise.

displayModePossible :: GettableStateVar Bool
displayModePossible =
   makeGettableStateVar $ simpleGet (/= 0) glut_DISPLAY_MODE_POSSIBLE

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

-- | Capabilities for 'initialDisplayCapabilities', most of them are extensions
-- of the constructors of 'DisplayMode'.

data DisplayCapability
   = DisplayRGBA  -- ^ Number of bits of red, green, blue, and alpha in the RGBA
                  --   color buffer. Default is \"'IsAtLeast' @1@\" for red,
                  --   green, blue, and alpha capabilities, and \"'IsEqualTo'
                  --   @1@\" for the RGBA color model capability.
   | DisplayRGB   -- ^ Number of bits of red, green, and blue in the RGBA color
                  --   buffer and zero bits of alpha color buffer precision.
                  --   Default is \"'IsAtLeast' @1@\" for the red, green, and
                  --   blue capabilities, and \"'IsNotLessThan' @0@\" for alpha
                  --   capability, and \"'IsEqualTo' @1@\" for the RGBA color
                  --   model capability.
   | DisplayRed   -- ^ Red color buffer precision in bits. Default is
                  --   \"'IsAtLeast' @1@\".
   | DisplayGreen -- ^ Green color buffer precision in bits. Default is
                  --   \"'IsAtLeast' @1@\".
   | DisplayBlue  -- ^ Blue color buffer precision in bits. Default is
                  --   \"'IsAtLeast' @1@\".
   | DisplayIndex -- ^ Boolean if the color model is color index or not. True is
                  --   color index. Default is \"'IsAtLeast' @1@\".
   | DisplayBuffer -- ^ Number of bits in the color index color buffer. Default
                  --   is \"'IsAtLeast' @1@\".
   | DisplaySingle -- ^ Boolean indicate the color buffer is single buffered.
                  --   Default is \"'IsEqualTo' @1@\".
   | DisplayDouble -- ^ Boolean indicating if the color buffer is double
                  --   buffered. Default is \"'IsEqualTo' @1@\".
   | DisplayAccA  -- ^ Red, green, blue, and alpha accumulation buffer precision
                  --   in  bits. Default is \"'IsAtLeast' @1@\" for red, green,
                  --   blue, and alpha capabilities.
   | DisplayAcc   -- ^ Red, green, and green accumulation buffer precision in
                  --   bits and zero bits of alpha accumulation buffer precision.
                  --   Default is \"'IsAtLeast' @1@\" for red, green, and blue
                  --   capabilities, and \"'IsNotLessThan' @0@\" for the alpha
                  --   capability.
   | DisplayAlpha -- ^ Alpha color buffer precision in bits. Default is
                  --   \"'IsAtLeast' @1@\".
   | DisplayDepth -- ^ Number of bits of precsion in the depth buffer. Default
                  --   is \"'IsAtLeast' @12@\".
   | DisplayStencil -- ^ Number of bits in the stencil buffer. Default is
                  --   \"'IsNotLessThan' @1@\".
   | DisplaySamples -- ^ Indicates the number of multisamples to use based on
                  --   GLX\'s @SGIS_multisample@ extension (for antialiasing).
                  --   Default is \"'IsNotGreaterThan' @4@\". This default means
                  --   that a GLUT application can request multisampling if
                  --   available by simply specifying \"'With' 'DisplaySamples'\".
   | DisplayStereo -- ^ Boolean indicating the color buffer is supports
                  --   OpenGL-style stereo. Default is \"'IsEqualTo' @1@\".
   | DisplayLuminance -- ^ Number of bits of red in the RGBA and zero bits of green,
                  --   blue (alpha not specified) of color buffer precision.
                  --   Default is \"'IsAtLeast' @1@\" for the red capabilitis,
                  --   and \"'IsEqualTo' @0@\" for the green and blue
                  --   capabilities, and \"'IsEqualTo' @1@\" for the RGBA color
                  --   model capability, and, for X11, \"'IsEqualTo' @1@\" for
                  --   the 'DisplayXStaticGray' capability. SGI InfiniteReality (and
                  --   other future machines) support a 16-bit luminance (single
                  --   channel) display mode (an additional 16-bit alpha channel
                  --   can also be requested). The red channel maps to gray
                  --   scale and green and blue channels are not available. A
                  --   16-bit precision luminance display mode is often
                  --   appropriate for medical imaging applications. Do not
                  --   expect many machines to support extended precision
                  --   luminance display modes.
   | DisplayAux   -- ^ (/freeglut only/) Number of auxiliary buffers. Default is
                  --   \"'IsEqualTo' @1@\".
   | DisplayNum   -- ^ A special capability name indicating where the value
                  --   represents the Nth frame buffer configuration matching
                  --   the description string. When not specified,
                  --   'initialDisplayCapabilities' also uses the first
                  --   (best matching) configuration. 'Num' requires a relation
                  --   and numeric value.
   | DisplayConformant -- ^ Boolean indicating if the frame buffer configuration is
                  --   conformant or not. Conformance information is based on
                  --   GLX\'s @EXT_visual_rating@ extension if supported. If the
                  --   extension is not supported, all visuals are assumed
                  --   conformant. Default is \"'IsEqualTo' @1@\".
   | DisplaySlow  -- ^ Boolean indicating if the frame buffer configuration is
                  --   slow or not. Slowness information is based on GLX\'s
                  --   @EXT_visual_rating@ extension if supported. If the
                  --   extension is not supported, all visuals are assumed fast.
                  --   Note that slowness is a relative designation relative to
                  --   other frame buffer configurations available. The intent
                  --   of the slow capability is to help programs avoid frame
                  --   buffer configurations that are slower (but perhaps higher
                  --   precision) for the current machine. Default is
                  --   \"'IsAtLeast' @0@\". This default means that slow visuals
                  --   are used in preference to fast visuals, but fast visuals
                  --   will still be allowed.
   | DisplayWin32PFD -- ^ Only recognized on GLUT implementations for Win32, this
                  --   capability name matches the Win32 Pixel Format Descriptor
                  --   by number. 'DisplayWin32PFD' can only be used with 'Where'.
   | DisplayXVisual -- ^ Only recongized on GLUT implementations for the X Window
                  --   System, this capability name matches the X visual ID by
                  --   number. 'DisplayXVisual' requires a relation and numeric value.
   | DisplayXStaticGray -- ^ Only recongized on GLUT implementations for the X Window
                  --   System, boolean indicating if the frame buffer
                  --   configuration\'s X visual is of type @StaticGray@.
                  --   Default is \"'IsEqualTo' @1@\".
   | DisplayXGrayScale -- ^ Only recongized on GLUT implementations for the X Window
                  --   System, boolean indicating if the frame buffer
                  --   configuration\'s X visual is of type @GrayScale@. Default
                  --   is \"'IsEqualTo' @1@\".
   | DisplayXStaticColor -- ^ Only recongized on GLUT implementations for the X Window
                  --   System, boolean indicating if the frame buffer
                  --   configuration\'s X visual is of type @StaticColor@.
                  --   Default is \"'IsEqualTo' @1@\".
   | DisplayXPseudoColor -- ^ Only recongized on GLUT implementations for the X Window
                  --   System, boolean indicating if the frame buffer
                  --   configuration\'s X visual is of type @PsuedoColor@.
                  --   Default is \"'IsEqualTo' @1@\".
   | DisplayXTrueColor -- ^ Only recongized on GLUT implementations for the X Window
                  --   System, boolean indicating if the frame buffer
                  --   configuration\'s X visual is of type @TrueColor@. Default
                  --   is \"'IsEqualTo' @1@\".
   | DisplayXDirectColor -- ^ Only recongized on GLUT implementations for the X Window
                  --   System, boolean indicating if the frame buffer
                  --   configuration\'s X visual is of type @DirectColor@.
                  --   Default is \"'IsEqualTo' @1@\".
   deriving ( Eq, Ord, Show )

displayCapabilityToString :: DisplayCapability -> String
displayCapabilityToString x = case x of
   DisplayRGBA         -> "rgba"
   DisplayRGB          -> "rgb"
   DisplayRed          -> "red"
   DisplayGreen        -> "green"
   DisplayBlue         -> "blue"
   DisplayIndex        -> "index"
   DisplayBuffer       -> "buffer"
   DisplaySingle       -> "single"
   DisplayDouble       -> "double"
   DisplayAccA         -> "acca"
   DisplayAcc          -> "acc"
   DisplayAlpha        -> "alpha"
   DisplayDepth        -> "depth"
   DisplayStencil      -> "stencil"
   DisplaySamples      -> "samples"
   DisplayStereo       -> "stereo"
   DisplayLuminance    -> "luminance"
   DisplayAux          -> "aux"
   DisplayNum          -> "num"
   DisplayConformant   -> "conformant"
   DisplaySlow         -> "slow"
   DisplayWin32PFD     -> "win32pfd"
   DisplayXVisual      -> "xvisual"
   DisplayXStaticGray  -> "xstaticgray"
   DisplayXGrayScale   -> "xgrayscale"
   DisplayXStaticColor -> "xstaticcolor"
   DisplayXPseudoColor -> "xpseudocolor"
   DisplayXTrueColor   -> "xtruecolor"
   DisplayXDirectColor -> "xdirectcolor"

-- | A single capability description for 'initialDisplayCapabilities'.

data DisplayCapabilityDescription
   = Where DisplayCapability Relation Int
     -- ^ A description of a capability with a specific relation to a numeric
     --   value.
   | With  DisplayCapability
     -- ^ When the relation and numeric value are not specified, each capability
     --   has a different default, see the different constructors of
     --   'DisplayCapability'.
   deriving ( Eq, Ord, Show )

displayCapabilityDescriptionToString ::  DisplayCapabilityDescription -> String
displayCapabilityDescriptionToString (Where c r i) =
   displayCapabilityToString c ++ relationToString r ++ show i
displayCapabilityDescriptionToString (With c) = displayCapabilityToString c

-- | Controls the /initial display mode/ used when creating top-level windows,
-- subwindows, and overlays to determine the OpenGL display mode for the
-- to-be-created window or overlay. It is described by a list of zero or more
-- capability descriptions, which are translated into a set of criteria used to
-- select the appropriate frame buffer configuration. The criteria are matched
-- in strict left to right order of precdence. That is, the first specified
-- criterion (leftmost) takes precedence over the later criteria for non-exact
-- criteria ('IsGreaterThan', 'IsLessThan', etc.). Exact criteria ('IsEqualTo',
-- 'IsNotEqualTo') must match exactly so precedence is not relevant.
--
-- Unspecified capability descriptions will result in unspecified criteria being
-- generated. These unspecified criteria help 'initialDisplayCapabilities'
-- behave sensibly with terse display mode descriptions.
--
-- Here is an example using 'initialDisplayCapabilities':
--
-- @
--    initialDisplayCapabilities $= [ With  DisplayRGB,
--                                    Where DisplayDepth IsAtLeast 16,
--                                    With  DisplaySamples,
--                                    Where DisplayStencil IsNotLessThan 2,
--                                    With  DisplayDouble ]
-- @
--
-- The above call requests a window with an RGBA color model (but requesting
-- no bits of alpha), a depth buffer with at least 16 bits of precision but
-- preferring more, multisampling if available, at least 2 bits of stencil
-- (favoring less stencil to more as long as 2 bits are available), and double
-- buffering.

initialDisplayCapabilities :: SettableStateVar [DisplayCapabilityDescription]
initialDisplayCapabilities =
   makeSettableStateVar $ \caps ->
      withCString
         (concat . intersperse " " . map displayCapabilityDescriptionToString $
          caps)
         glutInitDisplayString

foreign import ccall unsafe "glutInitDisplayString" glutInitDisplayString ::
  CString -> IO ()

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

-- | How rendering context for new windows are created.

data RenderingContext
   = -- | Create a new context via @glXCreateContext@ or @wglCreateContext@
     --   (default).
     CreateNewContext
   | -- | Re-use the current rendering context.
     UseCurrentContext
   deriving ( Eq, Ord, Show )

marshalRenderingContext :: RenderingContext -> CInt
marshalRenderingContext CreateNewContext  = glut_CREATE_NEW_CONTEXT
marshalRenderingContext UseCurrentContext = glut_USE_CURRENT_CONTEXT

unmarshalRenderingContext :: CInt -> RenderingContext
unmarshalRenderingContext r
   | r == glut_CREATE_NEW_CONTEXT  = CreateNewContext
   | r == glut_USE_CURRENT_CONTEXT = UseCurrentContext
   | otherwise = error "unmarshalRenderingContext"

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

-- | (/freeglut only/) Controls the creation of rendering contexts for new
-- windows.

renderingContext :: StateVar RenderingContext
renderingContext =
   makeStateVar
      (simpleGet unmarshalRenderingContext glut_RENDERING_CONTEXT)
      (glutSetOption glut_RENDERING_CONTEXT . marshalRenderingContext)

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

-- | The kind of GLX rendering context used. Direct rendering provides a
-- performance advantage in some implementations. However, direct rendering
-- contexts cannot be shared outside a single process, and they may be unable
-- to render to GLX pixmaps.

data DirectRendering
   = -- | Rendering is always done through the X server. This corresponds to
     -- the command line argument @-indirect@, see 'initialize'.
     ForceIndirectContext
   | -- | Try to use direct rendering, silently using indirect rendering if this
     -- is not possible.
     AllowDirectContext
   | -- | Try to use direct rendering, issue a warning and use indirect
     -- rendering if this is not possible.
     TryDirectContext
   | -- | Try to use direct rendering, issue an error and terminate the program
     -- if this is not possible.This corresponds to the command line argument
     -- @-direct@, see 'initialize'.
     ForceDirectContext
   deriving ( Eq, Ord, Show )

marshalDirectRendering :: DirectRendering -> CInt
marshalDirectRendering x = case x of
   ForceIndirectContext -> glut_FORCE_INDIRECT_CONTEXT
   AllowDirectContext -> glut_ALLOW_DIRECT_CONTEXT
   TryDirectContext -> glut_TRY_DIRECT_CONTEXT
   ForceDirectContext -> glut_FORCE_DIRECT_CONTEXT

unmarshalDirectRendering :: CInt -> DirectRendering
unmarshalDirectRendering x
   | x == glut_FORCE_INDIRECT_CONTEXT = ForceIndirectContext
   | x == glut_ALLOW_DIRECT_CONTEXT = AllowDirectContext
   | x == glut_TRY_DIRECT_CONTEXT = TryDirectContext
   | x == glut_FORCE_DIRECT_CONTEXT = ForceDirectContext
   | otherwise = error ("unmarshalDirectRendering: illegal value " ++ show x)

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

-- | (/freeglut on X11 only/) Controls which kind of rendering context is
-- created when a new one is required.

directRendering :: StateVar DirectRendering
directRendering =
   makeStateVar
      (simpleGet unmarshalDirectRendering glut_DIRECT_RENDERING)
      (glutSetOption glut_DIRECT_RENDERING . marshalDirectRendering)
