Main.hs

{-# LANGUAGE OverloadedStrings #-}

-- A nifty animated fractal of a tree, superimposed on a background
--      of three red rectangles.
import Brillo


main :: IO ()
main =
  animate
    (InWindow "Zen" (800, 600) (5, 5))
    (greyN 0.2)
    frame


-- Produce one frame of the animation.
frame :: Float -> Picture
frame timeS =
  Pictures
    -- the red rectangles
    [ Translate 0 150 backRec
    , Translate 0 0 backRec
    , Translate 0 (-150) backRec
    , -- the tree
      Translate 0 (-150) $ treeFrac 7 timeS
    ]


-- One of the red backing rectangles, with a white outline.
backRec :: Picture
backRec =
  Pictures
    [ Color red (rectangleSolid 400 100)
    , Color white (rectangleWire 400 100)
    ]


-- The color for the outline of the tree's branches.
treeOutline :: Color
treeOutline = makeColor 0.3 0.3 1.0 1.0


-- The color for the shading of the tree's branches.
--      The Alpha here is set to 0.5 so the branches are partly transparent.
treeColor :: Color
treeColor = makeColor 0.0 1.0 0.0 0.5


-- The tree fractal.
--  The position of the branches changes depending on the animation time
--  as well as the iteration number of the fractal.
treeFrac :: Int -> Float -> Picture
treeFrac 0 _ = Blank
treeFrac n timeS =
  Pictures
    [ Color treeColor $ rectangleUpperSolid 20 300
    , Color treeOutline $ rectangleUpperWire 20 300
    , Translate 0 30 $
        Rotate (200 * sin timeS / (fromIntegral n)) $
          Scale 0.9 0.9 $
            treeFrac (n - 1) timeS
    , Translate 0 70 $
        Rotate (-200 * sin timeS / (fromIntegral n)) $
          Scale 0.8 0.8 $
            treeFrac (n - 1) timeS
    ]