From some time ago , but I changed the calculus of the orbit ..
tB - TBGL module (Petr Schreiber) and O2 of course.  (3D animation)
the core is only :
 For k=1 To maxit
   dup=x
   x=x*x-y*y + cr
   y=dup*2*y + ci  
   orb=abs(x*y)
   If orb > 6 Then
    Exit For
   EndIf
  Next
  d=orb
best, Rob
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