G'MIC filter "Crease"

#@gui Crease : fx_crease,fx_crease(0)
#@gui : Amplitude = float(30,0,300)
#@gui : Frequency (%) = float(10,0,100)
#@gui : Boundary = choice(3,"Transparent","Nearest","Periodic","Mirror")
#@gui : sep = separator(), note = note("<small>Author: <i>David Tschumperl&#233;</i>.      Latest update: <i>2018/01/22</i>.</small>")
fx_crease :
  repeat $! l[$>]
    if {!$3} to_a fi
    2,2,1,2,{"const w1 = w#-1-1; const h1 = h#-1 - 1; [ 0,w1,0,w1,0,0,h1,h1 ];"}
    r. {0,D=$2*[w,h]%;[max(D[0],1),max(D[1],1)]},1,2,3 noise. $1,1
    r. ..,..,1,2,3 warp.. .,0,1,$3 rm.
  endl done