    {-
    Copyright (c) 2008, 2009
    Russell O'Connor

    Permission is hereby granted, free of charge, to any person obtaining a copy
    of this software and associated documentation files (the "Software"), to deal
    in the Software without restriction, including without limitation the rights
    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    copies of the Software, and to permit persons to whom the Software is
    furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be included in
    all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    THE SOFTWARE.
    -}
    -- |Datatypes for representing the human perception of colour.
    -- Includes common operations for blending and compositing colours.
    -- The most common way of creating colours is either by name
    -- (see "Data.Colour.Names") or by giving an sRGB triple
    -- (see "Data.Colour.SRGB").
    --
    -- Methods of specifying Colours can be found in
    --
    -- - "Data.Colour.SRGB"
    --
    -- - "Data.Colour.SRGB.Linear"
    --
    -- - "Data.Colour.CIE"
    --
    -- Colours can be specified in a generic 'Data.Colour.RGBSpace.RGBSpace'
    -- by using
    --
    -- - "Data.Colour.RGBSpace"

    --TODO
    -- - "Data.Colour.HDTV"
    --
    -- - "Data.Colour.SDTV"

    module Data.Colour
     (
    -- *Interfacing with Other Libraries\' Colour Spaces
    --
    -- |Executive summary: Always use "Data.Colour.SRGB" when interfacing with
    -- other libraries.
    -- Use 'Data.Colour.SRGB.toSRGB24' \/ 'Data.Colour.SRGB.sRGB24' when
    -- interfacing with libraries wanting 'Data.Word.Word8' per channel.
    -- Use 'Data.Colour.SRGB.toSRGB' \/ 'Data.Colour.SRGB.sRGB' when
    -- interfacing with libraries wanting 'Double' or 'Float' per channel.
    --
    -- Interfacing with the colour for other libraries, such as cairo
    -- (<http://www.haskell.org/gtk2hs/archives/category/cairo/>) and OpenGL
    -- (<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/OpenGL>),
    -- can be a challenge because these libraries often do not use colour spaces
    -- in a consistent way.
    -- The problem is that these libraries work in a device dependent colour
    -- space and give no indication what the colour space is.
    -- For most devices this colours space is implicitly the non-linear sRGB
    -- space.
    -- However, to make matters worse, these libraries also do their
    -- compositing and blending in the device colour space.
    -- Blending and compositing ought to be done in a linear colour space,
    -- but since the device space is typically non-linear sRGB, these libraries
    -- typically produce colour blends that are too dark.
    --
    -- (Note that "Data.Colour" is a device /independent/ colour space, and
    -- produces correct blends.
    -- e.g. compare @toSRGB (blend 0.5 lime red)@ with @RGB 0.5 0.5 0@)
    --
    -- Because these other colour libraries can only blend in device colour
    -- spaces, they are fundamentally broken and there is no \"right\" way
    -- to interface with them.
    -- For most libraries, the best one can do is assume they are working
    -- with an sRGB colour space and doing incorrect blends.
    -- In these cases use "Data.Colour.SRGB" to convert to and from the
    -- colour coordinates.  This is the best advice for interfacing with cairo.
    --
    -- When using OpenGL, the choice is less clear.
    -- Again, OpenGL usually does blending in the device colour space.
    -- However, because blending is an important part of proper shading, one
    -- may want to consider that OpenGL is working in a linear colour space,
    -- and the resulting rasters are improperly displayed.
    -- This is born out by the fact that OpenGL extensions that support
    -- sRGB do so by converting sRGB input\/output to linear colour coordinates
    -- for processing by OpenGL.
    --
    -- The best way to use OpenGL, is to use proper sRGB surfaces for textures
    -- and rendering.
    -- These surfaces will automatically convert to and from OpenGL's linear
    -- colour space.
    -- In this case, use "Data.Colour.SRGB.Linear" to interface OpenGL's linear
    -- colour space.
    --
    -- If not using proper surfaces with OpenGL, then you have a choice between
    -- having OpenGL do improper blending or improper display
    -- If you are using OpenGL for 3D shading, I recommend using
    -- "Data.Colour.SRGB.Linear" (thus choosing improper OpenGL display).
    -- If you are not using OpenGL for 3D shading, I recommend using
    -- "Data.Colour.SRGB" (thus choosing improper OpenGL blending).

    -- *Colour type
      Colour
     ,colourConvert
     ,black

     ,AlphaColour
     ,opaque, withOpacity
     ,transparent
     ,alphaColourConvert
     ,alphaChannel

     -- *Colour operations
     -- |These operations allow combine and modify existing colours
     ,AffineSpace(..), blend

     ,ColourOps(..)
     ,dissolve, atop
     )
    where

    import Data.Char
    import Data.Colour.Internal
    import qualified Data.Colour.SRGB.Linear
    import Data.Colour.CIE.Chromaticity (app_prec, infix_prec)

    instance (Fractional a, Show a) => Show (Colour a) where
      showsPrec :: Int -> Colour a -> ShowS
    showsPrec d :: Int
    d c :: Colour a
    c = Bool -> ShowS -> ShowS
    showParen (Int
    d Int -> Int -> Bool
    forall a. Ord a => a -> a -> Bool
    > Int
    app_prec) ShowS
    showStr
       where
        showStr :: ShowS
    showStr = String -> ShowS
    showString String
    linearConstructorQualifiedName
                ShowS -> ShowS -> ShowS
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . String -> ShowS
    showString " " ShowS -> ShowS -> ShowS
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (Int -> a -> ShowS
    forall a. Show a => Int -> a -> ShowS
    showsPrec (Int
    app_precInt -> Int -> Int
    forall a. Num a => a -> a -> a
    +1) a
    r)
                ShowS -> ShowS -> ShowS
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . String -> ShowS
    showString " " ShowS -> ShowS -> ShowS
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (Int -> a -> ShowS
    forall a. Show a => Int -> a -> ShowS
    showsPrec (Int
    app_precInt -> Int -> Int
    forall a. Num a => a -> a -> a
    +1) a
    g)
                ShowS -> ShowS -> ShowS
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . String -> ShowS
    showString " " ShowS -> ShowS -> ShowS
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (Int -> a -> ShowS
    forall a. Show a => Int -> a -> ShowS
    showsPrec (Int
    app_precInt -> Int -> Int
    forall a. Num a => a -> a -> a
    +1) a
    b)
        Data.Colour.SRGB.Linear.RGB r :: a
    r g :: a
    g b :: a
    b = Colour a -> RGB a
    forall a. Fractional a => Colour a -> RGB a
    Data.Colour.SRGB.Linear.toRGB Colour a
    c

    instance (Fractional a, Read a) => Read (Colour a) where
      readsPrec :: Int -> ReadS (Colour a)
    readsPrec d :: Int
    d r :: String
    r = Bool -> ReadS (Colour a) -> ReadS (Colour a)
    forall a. Bool -> ReadS a -> ReadS a
    readParen (Int
    d Int -> Int -> Bool
    forall a. Ord a => a -> a -> Bool
    > Int
    app_prec)
                      (\r :: String
    r -> [(a -> a -> a -> Colour a
    forall a. Fractional a => a -> a -> a -> Colour a
    Data.Colour.SRGB.Linear.rgb a
    r0 a
    g0 a
    b0,String
    t)
                             |(name :: String
    name,s :: String
    s) <- String -> [(String, String)]
    mylex String
    r
                             ,String
    name String -> [String] -> Bool
    forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool
    `elem` [String
    linearConstructorName
                                          ,String
    linearConstructorQualifiedName]
                             ,(r0 :: a
    r0,s0 :: String
    s0) <- Int -> ReadS a
    forall a. Read a => Int -> ReadS a
    readsPrec (Int
    app_precInt -> Int -> Int
    forall a. Num a => a -> a -> a
    +1) String
    s
                             ,(g0 :: a
    g0,s1 :: String
    s1) <- Int -> ReadS a
    forall a. Read a => Int -> ReadS a
    readsPrec (Int
    app_precInt -> Int -> Int
    forall a. Num a => a -> a -> a
    +1) String
    s0
                             ,(b0 :: a
    b0,t :: String
    t)  <- Int -> ReadS a
    forall a. Read a => Int -> ReadS a
    readsPrec (Int
    app_precInt -> Int -> Int
    forall a. Num a => a -> a -> a
    +1) String
    s1]) String
    r
       where
        mylex :: String -> [(String, String)]
    mylex = (String, String) -> [(String, String)]
    forall (m :: * -> *) a. Monad m => a -> m a
    return
              ((String, String) -> [(String, String)])
    -> (String -> (String, String)) -> String -> [(String, String)]
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (Char -> Bool) -> String -> (String, String)
    forall a. (a -> Bool) -> [a] -> ([a], [a])
    span (\c :: Char
    c -> Char -> Bool
    isAlphaNum Char
    c Bool -> Bool -> Bool
    || Char
    c Char -> String -> Bool
    forall (t :: * -> *) a. (Foldable t, Eq a) => a -> t a -> Bool
    `elem` "._'")
              (String -> (String, String)) -> ShowS -> String -> (String, String)
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (Char -> Bool) -> ShowS
    forall a. (a -> Bool) -> [a] -> [a]
    dropWhile Char -> Bool
    isSpace

    linearConstructorQualifiedName :: String
    linearConstructorQualifiedName = "Data.Colour.SRGB.Linear.rgb"
    linearConstructorName :: String
    linearConstructorName = "rgb"

    instance (Fractional a, Show a, Eq a) => Show (AlphaColour a) where
      showsPrec :: Int -> AlphaColour a -> ShowS
    showsPrec d :: Int
    d ac :: AlphaColour a
    ac | a
    a a -> a -> Bool
    forall a. Eq a => a -> a -> Bool
    == 0 = String -> ShowS
    showString "transparent"
                     | Bool
    otherwise = Bool -> ShowS -> ShowS
    showParen (Int
    d Int -> Int -> Bool
    forall a. Ord a => a -> a -> Bool
    > Int
    infix_prec) ShowS
    showStr
       where
        showStr :: ShowS
    showStr = Int -> Colour a -> ShowS
    forall a. Show a => Int -> a -> ShowS
    showsPrec (Int
    infix_precInt -> Int -> Int
    forall a. Num a => a -> a -> a
    +1) Colour a
    c
                ShowS -> ShowS -> ShowS
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . String -> ShowS
    showString " `withOpacity` "
                ShowS -> ShowS -> ShowS
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . Int -> a -> ShowS
    forall a. Show a => Int -> a -> ShowS
    showsPrec (Int
    infix_precInt -> Int -> Int
    forall a. Num a => a -> a -> a
    +1) a
    a
        a :: a
    a = AlphaColour a -> a
    forall a. AlphaColour a -> a
    alphaChannel AlphaColour a
    ac
        c :: Colour a
    c = AlphaColour a -> Colour a
    forall a. Fractional a => AlphaColour a -> Colour a
    colourChannel AlphaColour a
    ac

    instance (Fractional a, Read a) => Read (AlphaColour a) where
      readsPrec :: Int -> ReadS (AlphaColour a)
    readsPrec d :: Int
    d r :: String
    r = [(AlphaColour a
    forall a. Num a => AlphaColour a
    transparent,String
    s)|("transparent",s :: String
    s) <- String -> [(String, String)]
    lex String
    r]
                   [(AlphaColour a, String)]
    -> [(AlphaColour a, String)] -> [(AlphaColour a, String)]
    forall a. [a] -> [a] -> [a]
    ++ Bool -> ReadS (AlphaColour a) -> ReadS (AlphaColour a)
    forall a. Bool -> ReadS a -> ReadS a
    readParen (Int
    d Int -> Int -> Bool
    forall a. Ord a => a -> a -> Bool
    > Int
    infix_prec)
                      (\r :: String
    r -> [(Colour a
    c Colour a -> a -> AlphaColour a
    forall a. Num a => Colour a -> a -> AlphaColour a
    `withOpacity` a
    o,String
    s)
                             |(c :: Colour a
    c,r0 :: String
    r0) <- Int -> ReadS (Colour a)
    forall a. Read a => Int -> ReadS a
    readsPrec (Int
    infix_precInt -> Int -> Int
    forall a. Num a => a -> a -> a
    +1) String
    r
                             ,("`",r1 :: String
    r1) <- String -> [(String, String)]
    lex String
    r0
                             ,("withOpacity",r2 :: String
    r2) <- String -> [(String, String)]
    lex String
    r1
                             ,("`",r3 :: String
    r3) <- String -> [(String, String)]
    lex String
    r2
                             ,(o :: a
    o,s :: String
    s)  <- Int -> ReadS a
    forall a. Read a => Int -> ReadS a
    readsPrec (Int
    infix_precInt -> Int -> Int
    forall a. Num a => a -> a -> a
    +1) String
    r3]) String
    r