module Graphics.Rasterific.Compositor
( Compositor
, Modulable( .. )
, compositionDestination
, compositionAlpha
) where
import Data.Bits( unsafeShiftR )
import Data.Word( Word8, Word32 )
import Codec.Picture.Types( Pixel( .. ) )
type Compositor px =
(PixelBaseComponent px) ->
(PixelBaseComponent px) -> px -> px -> px
class Ord a => Modulable a where
emptyValue :: a
fullValue :: a
clampCoverage :: Float -> (a, a)
modulate :: a -> a -> a
alphaOver :: a -> a -> a -> a -> a
coverageModulate :: a -> a -> (a, a)
instance Modulable Word8 where
emptyValue = 0
fullValue = 255
clampCoverage f = (fromIntegral c, fromIntegral $ 255 c)
where c = toWord8 f
modulate c a = fromIntegral $ v `unsafeShiftR` 8
where fi :: Word8 -> Word32
fi = fromIntegral
v = fi c * fi a
coverageModulate c a = (clamped, fullValue clamped)
where
v = fromIntegral c * fromIntegral a :: Word32
clamped = fromIntegral $ (v + (v `unsafeShiftR` 8)) `unsafeShiftR` 8
alphaOver c ic b a = fromIntegral $ (v + (v `unsafeShiftR` 8)) `unsafeShiftR` 8
where fi :: Word8 -> Word32
fi = fromIntegral
v = fi c * fi a + fi b * fi ic + 128
toWord8 :: Float -> Int
toWord8 r = floor $ r * 255 + 0.5
compositionDestination :: (Pixel px, Modulable (PixelBaseComponent px))
=> Compositor px
compositionDestination c _ _ a = colorMap (modulate c) $ a
compositionAlpha :: (Pixel px, Modulable (PixelBaseComponent px))
=> Compositor px
compositionAlpha c ic
| c == emptyValue = const
| c == fullValue = \_ n -> n
| otherwise = mixWith (\_ -> alphaOver c ic)