import qualified Graphics.UI.Gtk as Gtk
import Graphics.UI.Gtk (AttrOp((:=)))
import qualified Graphics.UI.Gtk.OpenGL as GtkGL

import Graphics.Rendering.OpenGL as GL

animationWaitTime = 3

-- OpenGL polygon-function for drawing stuff.
display = do
  loadIdentity
  color (Color3 1 1 1 :: Color3 GLfloat)
  -- Instead of glBegin ... glEnd there is renderPrimitive.  
  renderPrimitive Polygon $ do
    vertex (Vertex3 0.25 0.25 0.0 :: Vertex3 GLfloat)
    vertex (Vertex3 0.75 0.25 0.0 :: Vertex3 GLfloat)
    vertex (Vertex3 0.75 0.75 0.0 :: Vertex3 GLfloat)
    vertex (Vertex3 0.25 0.75 0.0 :: Vertex3 GLfloat)

main :: IO ()
main = do
  Gtk.initGUI
  -- Initialise the Gtk+ OpenGL extension
  -- (including reading various command line parameters)
  GtkGL.initGL

  -- We need a OpenGL frame buffer configuration to be able to create other
  -- OpenGL objects.
  glconfig <- GtkGL.glConfigNew [GtkGL.GLModeRGBA,
                                 GtkGL.GLModeDepth,
                                 GtkGL.GLModeDouble]

  -- Create an OpenGL drawing area widget
  canvas <- GtkGL.glDrawingAreaNew glconfig

  Gtk.widgetSetSizeRequest canvas 250 250

  -- Initialise some GL setting just before the canvas first gets shown
  -- (We can't initialise these things earlier since the GL resources that
  -- we are using wouldn't heve been setup yet)
  Gtk.onRealize canvas $ GtkGL.withGLDrawingArea canvas $ \_ -> do
    clearColor $= (Color4 0.0 0.0 0.0 0.0)
    matrixMode $= Projection
    loadIdentity
    ortho 0.0 1.0 0.0 1.0 (-1.0) 1.0
    depthFunc $= Just Less
    drawBuffer $= BackBuffers
 
  -- Set the repaint handler
  Gtk.onExpose canvas $ \_ -> do
    GtkGL.withGLDrawingArea canvas $ \glwindow -> do
      GL.clear [GL.DepthBuffer, GL.ColorBuffer]
      display
      GtkGL.glDrawableSwapBuffers glwindow
    return True
 
  -- Setup the animation
  Gtk.timeoutAddFull (do
      Gtk.widgetQueueDraw canvas
      return True)
    Gtk.priorityDefaultIdle animationWaitTime
 
  --------------------------------
  -- Setup the rest of the GUI:
  --
  -- Objects
  window <- Gtk.windowNew
  button <- Gtk.buttonNew
  exitButton <- Gtk.buttonNew
  vbox <- Gtk.vBoxNew False 4

  --Wrench them together

  Gtk.set window [ Gtk.containerBorderWidth := 10,
                   Gtk.containerChild := vbox,
                   Gtk.windowTitle := "Pioneer" ]
  Gtk.set button [ Gtk.buttonLabel := "Hello World" ]
  Gtk.set exitButton [ Gtk.buttonLabel := "Quit" ]
  Gtk.set vbox [
                   Gtk.containerChild := canvas,
                   Gtk.containerChild := button,
                   Gtk.containerChild := exitButton
                ]

  Gtk.onClicked button (putStrLn "Hello World")
  Gtk.onClicked exitButton Gtk.mainQuit
  Gtk.onDestroy window Gtk.mainQuit
  Gtk.widgetShowAll window
  Gtk.mainGUI