{-# LANGUAGE CPP #-}
{- |
   Module      :  Graphics.Win32.LayeredWindow
   Copyright   :  2012-2013 shelarcy
   License     :  BSD-style

   Maintainer  :  shelarcy@gmail.com
   Stability   :  Provisional
   Portability :  Non-portable (Win32 API)

   Provides LayeredWindow functionality.
-}
module Graphics.Win32.LayeredWindow where
import Control.Monad    ( void )
import Data.Bits        ( (.|.) )
import Foreign.Ptr      ( Ptr )
import Graphics.Win32.GDI.AlphaBlend ( BLENDFUNCTION )
import Graphics.Win32 hiding ( c_SetWindowLongPtr )
import Graphics.Win32.Compat ( c_SetWindowLongPtr, c_GetWindowLongPtr )

#define _WIN32_WINNT 0x0500
#include <windows.h>

toLayeredWindow :: HWND -> IO ()
toLayeredWindow w = do
  flg <- c_GetWindowLongPtr w gWL_EXSTYLE
  void $ c_SetWindowLongPtr w gWL_EXSTYLE (flg .|. (fromIntegral wS_EX_LAYERED))

-- test w =  c_SetLayeredWindowAttributes w 0 128 lWA_ALPHA

gWL_EXSTYLE :: INT
gWL_EXSTYLE = #const GWL_EXSTYLE

wS_EX_LAYERED :: WindowStyleEx
wS_EX_LAYERED = #const WS_EX_LAYERED

lWA_COLORKEY, lWA_ALPHA :: DWORD
lWA_COLORKEY = #const LWA_COLORKEY
lWA_ALPHA    = #const LWA_ALPHA

foreign import WINDOWS_CCONV unsafe "windows.h SetLayeredWindowAttributes"
  c_SetLayeredWindowAttributes :: HWND -> COLORREF -> BYTE -> DWORD -> IO BOOL

foreign import WINDOWS_CCONV unsafe "windows.h GetLayeredWindowAttributes"
  c_GetLayeredWindowAttributes :: HWND -> COLORREF -> Ptr BYTE -> Ptr DWORD -> IO BOOL

foreign import WINDOWS_CCONV unsafe "windows.h UpdateLayeredWindow"
  c_UpdateLayeredWindow :: HWND -> HDC -> Ptr POINT -> Ptr SIZE ->  HDC -> Ptr POINT -> COLORREF -> Ptr BLENDFUNCTION -> DWORD -> IO BOOL

#{enum DWORD,
 , uLW_ALPHA    = ULW_ALPHA
 , uLW_COLORKEY = ULW_COLORKEY
 , uLW_OPAQUE   = ULW_OPAQUE
 }