vulkan-tutorial/src/Affection/Draw.hs

{-# LANGUAGE RecordWildCards #-}

-- | Module for drawing primitives
module Affection.Draw
  ( drawRect
  ) where

import Affection.Types (DrawType(..), Affection, GeglRectangle(..), liftIO)

import Foreign.C.Types

import qualified BABL as B

import qualified GEGL as G

-- | Draw a rectangle on target buffer
drawRect
  :: G.GeglBuffer  -- ^ Target buffer
  -> G.Color       -- ^ Color to draw in
  -> DrawType      -- ^ Draw type
  -> GeglRectangle -- ^ Dimensions of Rectangle
  -> IO ()
drawRect buf color (Fill) rect@G.GeglRectangle{..} =
  G.pixelPoke buf rect (B.PixelFormat B.RGBA B.CFdouble) G.GeglAccessReadWrite G.GeglAbyssNone $
    (\(x, y) ->
      let col = unsafeColorize color
      in 
        G.Pixel x y col
    )
drawRect buf color (Line size) rect@G.GeglRectangle{..} = do
  drawRect buf color Fill (G.GeglRectangle rectangleX rectangleY rectangleWidth size)
  drawRect buf color Fill (G.GeglRectangle rectangleX rectangleY size rectangleHeight)
  drawRect buf color Fill (G.GeglRectangle (rectangleX + rectangleWidth - size) rectangleY size rectangleHeight)
  drawRect buf color Fill (G.GeglRectangle rectangleX (rectangleY + rectangleHeight - size) rectangleWidth size)

-- | compute color for a single pixel
colorize
  :: (G.ComponentValue, G.ComponentValue, G.ComponentValue, G.ComponentValue) -- ^ Pixel information in buffer
  -> G.Color      -- ^ Color to draw over
  -> (G.ComponentValue, G.ComponentValue, G.ComponentValue, G.ComponentValue) -- ^ Resulting colour
colorize (rr, rg, rb, ra) col =
  let (G.CVdouble (CDouble br)) = rr
      (G.CVdouble (CDouble bg)) = rg
      (G.CVdouble (CDouble bb)) = rb
      (G.CVdouble (CDouble ba)) = ra
      (cr, cg, cb) = case col of
        G.RGBA r g b _ -> (r, g, b)
        G.RGB  r g b   -> (r, g, b)
      ca = case col of
        G.RGBA _ _ _ a -> a
        G.RGB  _ _ _   -> 1
      alpha = ca
      dst_a = ba
      da = alpha + dst_a * (1 - alpha)
      a_term = dst_a * (1 - alpha)
      red = cr * alpha + br * a_term
      gre = cg * alpha + bg * a_term
      blu = cb * alpha + bb * a_term
  in
    ( G.CVdouble $ CDouble $ red / da
    , G.CVdouble $ CDouble $ gre / da
    , G.CVdouble $ CDouble $ blu / da
    , G.CVdouble $ CDouble $ ca
    )

unsafeColorize col =
  let
    (r, g, b) = case col of
      G.RGBA cr cg cb _ -> (cr, cg, cb)
      G.RGB  cr cg cb   -> (cr, cg, cb)
    a = case col of
      G.RGBA _ _ _ ca -> ca
      G.RGB  _ _ _    -> 1
  in
    ( G.CVdouble $ CDouble $ r
    , G.CVdouble $ CDouble $ g
    , G.CVdouble $ CDouble $ b
    , G.CVdouble $ CDouble $ a
    )