{-# LANGUAGE TypeSynonymInstances #-}

module Graphics.ChalkBoard.Core 
	( -- * Pointwise operators.
	  interpBool 
	, sampleUI
	, withMask
	, withDefault
--	, choose
	  -- * Colors
	, alpha, withAlpha, unAlpha, transparent
	) where

-- This provided the internal functions, many of which are reflected into the "Observable", O.

import Graphics.ChalkBoard.Types
import Graphics.ChalkBoard.Utils

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

-- Pointwise operators

-- | Covert a Bool (mask point) into a unit interval.
interpBool :: Bool -> UI
interpBool True  = 1.0
interpBool False = 0.0

-- | sample a UI, giving a point of a mask.
sampleUI :: UI -> Bool
sampleUI n = n >= 0.5

-- | Use a mask to create a Just value, or Nothing.
withMask :: a -> (Bool -> Maybe a)
withMask a True  = Just a
withMask _ False = Nothing

-- | With a default if you do not have a Just.
withDefault :: a -> (Maybe a -> a)
withDefault a Nothing  = a
withDefault _ (Just b) = b

-- | 'choose' between two values.
choose :: a -> a -> (Bool -> a)
choose t  _f True  = t
choose _t f  False = f

------------------------------------------------------------------------------------------
-- Colors with alpha

alpha :: RGB -> RGBA
alpha (RGB r g b) = RGBA r g b 1

withAlpha :: RGB -> UI -> RGBA
withAlpha c a = RGBA r g b a
  where (RGB r g b) = c -- scale a c 
			-- turn off scaling

unAlpha :: RGBA -> RGB
unAlpha (RGBA r g b _) = RGB r g b

transparent :: RGBA 
transparent = RGBA 0 0 0 0