############################################################################
#
#	File:     glabels.icn
#
#	Subject:  Procedure to produce graph ticks
#
#	Author:   Ralph E. Griswold
#
#	Date:     May 2, 2001
#
############################################################################
#
#   This file is in the public domain.
#
############################################################################
#
#  glabels(min, max, nticks) produces a list of aesthetically pleasing labels
#  for graph ticks to cover a given range.  It is based on the algorithm
#  given by Paul S. Heckert in "Graphic Gems", Andrew S Glassner, ed.,
#  Academic Press, 1990.
#
############################################################################
#
#  Links: numbers
#
############################################################################

link numbers

procedure glabels(min, max, ntick)
   local d, graphmin, graphmax, nfrac, llist, x, nf, range

   if min = max then fail		# no can do

   range := nicenum(max - min)
   d := nicenum(range / (ntick - 1), 1)
   graphmin := floor(min / d) * d
   graphmax := ceil(max / d) * d
   nfrac := max(-floor(log(d, 10)), 0)
   llist := []
   every x := graphmin to graphmax + 0.5 * d by d do
     put(llist, x)

   return llist

end

procedure nicenum(x, round)
   local exp, f, nf

   exp := floor(log(x, 10))
   f := x / (10 ^ exp)
   if \round then {
      if f < 1.5 then nf := 1
      else if f < 3.0 then nf := 2
      else if f < 7 then nf := 5
      else nf := 10
      }
   else {
      if f <= 1 then nf := 1
      else if f <= 2 then nf := 2
      else if f <= 5 then nf := 5
      else nf := 10
      }

   return nf * (10 ^ exp)

end