{-
   ColorMatrix.hs (adapted from colormatrix.c which is (c) Silicon Graphics, Inc.)
   Copyright (c) Sven Panne 2002-2018 <svenpanne@gmail.com>
   This file is part of HOpenGL and distributed under a BSD-style license
   See the file libraries/GLUT/LICENSE

   This program uses the color matrix to exchange the color channels of an image.

     Red   -> Green
     Green -> Blue
     Blue  -> Red
-}

import System.Exit ( exitWith, ExitCode(ExitSuccess) )
import Graphics.UI.GLUT
import ReadImage

myInit :: IO ()
myInit = do
   m <- newMatrix ColumnMajor [ 0, 1, 0, 0,
                                0, 0, 1, 0,
                                1, 0, 0, 0,
                                0, 0, 0, 1 ]
   rowAlignment Unpack $= 1
   clearColor $= Color4 0 0 0 0
   matrixMode $= Color
   matrix Nothing $= (m :: GLmatrix GLfloat)
   matrixMode $= Modelview 0

display :: Size -> PixelData a -> DisplayCallback
display size pixels = do
   clear [ ColorBuffer ]
   -- resolve overloading, not needed in "real" programs
   let rasterPos2i = rasterPos :: Vertex2 GLint -> IO ()
   rasterPos2i (Vertex2 1 1)
   drawPixels size pixels
   flush

reshape :: ReshapeCallback
reshape size@(Size w h) = do
   viewport $= (Position 0 0, size)
   matrixMode $= Projection
   loadIdentity
   ortho 0 (fromIntegral w) 0 (fromIntegral h) (-1) 1
   matrixMode $= Modelview 0

keyboard :: KeyboardMouseCallback
keyboard (Char '\27') Down _ _ = exitWith ExitSuccess
keyboard _            _    _ _ = return ()

-- Main Loop: Open window with initial window size, title bar, RGBA display
-- mode, and handle input events.
main :: IO ()
main = do
   (progName, args) <- getArgsAndInitialize
   (size, pixels) <- readImage (if null args then "Data/leeds.bin" else head args)
   initialDisplayMode $= [ SingleBuffered, RGBMode ]
   initialWindowSize $= size
   initialWindowPosition $= Position 100 100
   _ <- createWindow progName
   myInit
   reshapeCallback $= Just reshape
   keyboardMouseCallback $= Just keyboard
   displayCallback $= display size pixels
   mainLoop