import Control.Arrow ((***)) import Control.Monad (void, liftM3, when) import Data.Bits (shift) import Data.Numbers.Primes (primes) import Graphics.UI.SDL as SDL (xres, yres) = (800, 800) main = withInit [InitVideo] $ do win <- setVideoMode xres yres 32 [] fillRect win (Just $ Rect 0 0 xres yres) (Pixel 0) enableEvent SDLMouseMotion False setCaption "Prime Curve" "Prime Curve" run win (xres `div` 2, yres `div` 2) [1..] nesw rgbs where nesw = cycle $ map f [(0,-1), (1,0), (0,1), (-1,0)] f (x,y) = (x+) *** (+y) run w p (n:ns) (d:ds) (c:cs) = do drawCell w p c let ds' = if prime n then ds else d:ds when (n `mod` 13 == 0) $ SDL.flip w e <- pollEvent case e of KeyUp (Keysym SDLK_ESCAPE _ _) -> void save _ -> run w (d p) ns ds' cs where prime n = n `elem` takeWhile (< n + 1) primes save = saveBMP w "out.bmp" >> print n drawCell w p c = draw p =<< createRGBSurface [SWSurface] 1 1 32 0 0 0 0 where rect x y = Just $ Rect x y 1 1 draw (x,y) s = do fillRect s (rect 0 0) (Pixel c) blitSurface s (rect 0 0) w (rect x y) rgbs = cycle . map f $ liftM3 (,,) ns ns ns where ns = [151, 153.. 255] f (r,g,b) = shift r 16 + shift g 8 + b

## Sunday, January 26, 2014

### prime curve

This curve is created, Logo-style, by the trail of a turtle that makes a clockwise quarter-turn at every prime iteration; the screenshot shows the curve after about 730000 steps.

Labels:
integer sequences,
logo graphics

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