Common.hs

{-# OPTIONS_HADDOCK hide #-}
module Graphics.Gloss.Internals.Render.Common where

import	Graphics.Rendering.OpenGL	       (($=))
import qualified Graphics.Rendering.OpenGL.GL	as GL
import Unsafe.Coerce


-- | The OpenGL library doesn't seem to provide a nice way convert
--	a Float to a GLfloat, even though they're the same thing
--	under the covers.  
--
--  Using realToFrac is too slow, as it doesn't get fused in at
--	least GHC 6.12.1
--
gf :: Float -> GL.GLfloat
{-# INLINE gf #-}
gf x = unsafeCoerce x


-- | Used for similar reasons to above
gsizei :: Int -> GL.GLsizei
{-# INLINE gsizei #-}
gsizei x = unsafeCoerce x


-- | Perform an OpenGL rendering action in the appropriate @ModelView@ context.
renderAction
	:: (Int, Int)  -- ^ Width and height of window.
	-> IO ()       -- ^ Action to perform.
	-> IO ()

renderAction (sizeX, sizeY) action
 = do
 	GL.matrixMode	$= GL.Projection
	GL.preservingMatrix
	 $ do
		-- setup the co-ordinate system
	 	GL.loadIdentity
		let (sx, sy)	= (fromIntegral sizeX / 2, fromIntegral sizeY / 2)

		GL.ortho (-sx) sx (-sy) sy 0 (-100)
	
		-- draw the world
		GL.matrixMode 	$= GL.Modelview 0
		action

		GL.matrixMode	$= GL.Projection
	
	GL.matrixMode	$= GL.Modelview 0