art with code

2008-09-01

Adaptive blur filter Mandelbrot

To finish off today's Mandelbrot madness, here's a version that does a ghetto 2D box filter with kernel size controlled by the second image (i.e. blur more where second image is white, don't blur where it's black.) Using a second core gives an 80% speed boost.



open Prelude

let niter = 255
let limit = 4.0

let mandelbrot x y w h =
let cr = 2.0 *. x /. w -. 1.5 in
let ci = 2.0 *. y /. h -. 1.0 in
let rec aux i zr zi = if i >= niter then 0 else
let nzr = zr *. zr -. zi *. zi +. cr
and nzi = 2.0 *. zr *. zi +. ci in
if nzr *. nzr +. nzi *. nzi > limit then 255-i
else aux (i+1) nzr nzi in
aux 0 0.0 0.0

let draw_fractal xoff yoff w h =
pbinit (fun i ->
let y, x = quot_rem i w in
mandelbrot (float (xoff+x)) (float (yoff+y)) (float w) (float h)
) (w*h)

let blend a b w h =
let c = pbinit (fun i ->
let y, x = quot_rem i w in
let r = ord (suget b i) / 32 in
let x1 = max (x-r) 0
and x2 = min (x+r) (w-1) in
saverage (ssub (y*w+x1) (x2-x1+1) a)
) (slen a) in
pbinit (fun i ->
let y, x = quot_rem i w in
let r = ord (suget b i) / 32 in
let y1 = max (y-r) 0
and y2 = min (y+r) (h-1) in
saverage (ssubStride w (y1*w+x) (y2-y1+1) c)
) (slen a)

let square_fractal d =
let frac1 = draw_fractal 0 0 d d in
let frac2 = draw_fractal (d/4) (-d/4) d d in
let header = sprintf "P5 %i %i 255\n" d d in
header ^ (blend frac1 frac2 d d)

let () =
let img = square_fractal (parseInt Sys.argv.(1)) in
output_string stdout img
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