I've also written a vector graphics game demo which uses this curve, and the Bézier curve methods in the below post, for object motion. The differences in plot density along the curve create natural-looking trails (e.g. for comets, or exhaust).

{-# LANGUAGE NoMonomorphismRestriction #-} import Data.Bits ((.|.), shiftL) import Control.Arrow ((***), (&&&)) import Graphics.UI.SDL as SDL import Graphics.UI.SDL.Primitives (pixel) (xres, yres, zz) = (1050, 1050, round *** round) main = withInit [InitVideo] $ do w <- setVideoMode xres yres 32 [NoFrame] enableEvent SDLMouseMotion False setCaption "Butterfly Curve" "Butterfly Curve" fillRect w (Just $ Rect 0 0 xres yres) $ Pixel 0 plot w $ center $ scale curve loop w [] where scale = map ((150 *) *** (* 150)) center = map (((xres / 2) +) *** (+ ((yres + 190) / 2))) curve = map (f &&& (negate . g)) ts where ts = [-999, -998.99.. 999] f t = sin t * (e ** cos t - 2 * cos (4*t) - h (t / 12)) g t = cos t * (e ** cos t - 2 * cos (4*t) - h (t / 12)) h = foldr1 (.) $ replicate 5 sin e = exp 1 plot w = mapM_ (f . zz) where f (x,y) = pixel w (fromIntegral x) (fromIntegral y) $ Pixel rgb where rgb = rgb' .|. shiftL (255 `div` (max x y `div` min x y)) 8 rgb' = rgb'' .|. shiftL (255 `div` (xres `div` x)) 16 rgb'' = 0xFF .|. shiftL (255 `div` (yres `div` y)) 24 loop w ps = do delay 128 event <- pollEvent case event of KeyUp (Keysym SDLK_ESCAPE _ _) -> return () _ -> loop w ps

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