Library for colours

See also the more sophisticated colour package on Hackage.

Simple thing for working on colours in the RGB colours space. (The intention being that each component is in the interval 0 ≤ x ≤ 1.) You could just use tuples, but this library provides simple colour arithmetic.

module Colour where

data Colour = Colour {red, green, blue :: Double} deriving (Eq, Show)

cmap :: (Double -> Double) -> Colour -> Colour
cmap f (Colour r g b) = Colour (f r) (f g) (f b)

czip :: (Double -> Double -> Double) -> Colour -> Colour -> Colour
czip f (Colour r1 g1 b1) (Colour r2 g2 b2) = Colour (f r1 r2) (f g1 g2) (f b1 b2)

cfold :: (Double -> Double -> Double) -> Colour -> Double
cfold f (Colour r g b) = r `f` g `f` b

cpromote :: Double -> Colour
cpromote x = Colour x x x

instance Num Colour where
  (+) = czip (+)
  (-) = czip (-)
  (*) = czip (*)
  negate = cmap negate
  abs    = cmap abs
  signum = cmap signum
  fromInteger x = cpromote (fromInteger x)

instance Fractional Colour where
  (/) = czip (/)
  recip = cmap recip
  fromRational x = cpromote (fromRational x)

clip :: (Num n, Ord n) => n -> n
clip n
  | n < 0 = 0
  | n > 1 = 1
  | otherwise = n

cclip :: Colour -> Colour
cclip = cmap clip