eidolon/Scale.hs

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2017-03-24 16:49:11 +00:00
-- eidolon -- A simple gallery in Haskell and Yesod
-- Copyright (C) 2015-2016 Amedeo Molnár
--
-- This program is free software: you can redistribute it and/or modify
-- it under the terms of the GNU Affero General Public License as published
-- by the Free Software Foundation, either version 3 of the License, or
-- (at your option) any later version.
--
-- This program is distributed in the hope that it will be useful,
-- but WITHOUT ANY WARRANTY; without even the implied warranty of
-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
-- GNU Affero General Public License for more details.
--
-- You should have received a copy of the GNU Affero General Public License
-- along with this program. If not, see <http://www.gnu.org/licenses/>.
module Scale
(scaleBilinearAlpha
) where
import Import
import Codec.Picture
import Control.Monad.ST
import qualified Codec.Picture.Types as M
scaleBilinearAlpha
:: Int -- ^ Desired width
-> Int -- ^ Desired height
-> Image PixelRGBA8 -- ^ Original image
-> Image PixelRGBA8 -- ^ Scaled image
scaleBilinearAlpha width height img@Image {..} = runST $ do
mimg <- M.newMutableImage width height
let sx, sy :: Float
sx = fromIntegral imageWidth / fromIntegral width
sy = fromIntegral imageHeight / fromIntegral height
go x' y'
| x' >= width = go 0 (y' + 1)
| y' >= height = M.unsafeFreezeImage mimg
| otherwise = do
let xf = fromIntegral x' * sx
yf = fromIntegral y' * sy
x, y :: Int
x = floor xf
y = floor yf
δx = xf - fromIntegral x
δy = yf - fromIntegral y
pixelAt' i j =
if i >= imageWidth || j >= imageHeight
then PixelRGBA8 0 0 0 0
else pixelAt img i j
writePixel mimg x' y' $
mulp (pixelAt' x y) ((1 - δx) * (1 - δy)) `addp`
mulp (pixelAt' (x + 1) y) (δx * (1 - δy)) `addp`
mulp (pixelAt' x (y + 1)) ((1 - δx) * δy) `addp`
mulp (pixelAt' (x + 1) (y + 1)) (δx * δy)
go (x' + 1) y'
go 0 0
mulp :: PixelRGBA8 -> Float -> PixelRGBA8
mulp pixel x = colorMap (floor . (* x) . fromIntegral) pixel
{-# INLINE mulp #-}
addp :: PixelRGBA8 -> PixelRGBA8 -> PixelRGBA8
addp = mixWith (const f)
where
f x y = fromIntegral $
(0xff :: Pixel8) `min` (fromIntegral x + fromIntegral y)