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