source: git/src/gdtconvert

#!/usr/bin/perl -w

#  gdtconvert
#
#  Converter for POV-Ray gradient files produced by The Gimp
#
#  Copyright (C) 2002 Mark R. Shinwell
#
#  This program is free software; you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation; either version 2 of the License, or
#  (at your option) any later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this program; if not, see
#  <https://www.gnu.org/licenses/>.

use strict;

my $points = 13;
my $prev = -1.0;
my $interval = 1.0 / ($points-1);
my $next = 0.0;
my $pr = 0;
my $pg = 0;
my $pb = 0;
my $prevpos = 0.0;
my $outputr = "";
my $outputg = "";
my $outputb = "";
while (my $l = <>) {
   if ($l =~ /.*\[(\d\.\d+) color rgbt <(\d\.\d+), (\d\.\d+), (\d\.\d+).*/) {
       if ($prev != $1) {
           my $r = int($2 * 255);
           my $g = int($3 * 255);
           my $b = int($4 * 255);
           my $pos = $1;
           while ($pos >= $next) {
               if ($prev == -1.0) {
                   $outputr = $r;
                   $outputg = $g;
                   $outputb = $b;
               }
               else {
                   my $faralong = $next - $prevpos;
                   my $total = $pos - $prevpos;
                   my $frac = $faralong / $total;

                   my $newr = $pr + int(($r - $pr) * $frac);
                   my $newg = $pg + int(($g - $pg) * $frac);
                   my $newb = $pb + int(($b - $pb) * $frac);
                   
                   $outputr = "$outputr, $newr";
                   $outputg = "$outputg, $newg";
                   $outputb = "$outputb, $newb";
               }
               $next += $interval;
           }
           $pr = $r;
           $pg = $g;
           $pb = $b;
           $prevpos = $pos;
       }
       $prev = $1;
   }
}

print "/* Generated by $0 */\n";
print "static const unsigned char REDS[]   = {$outputr, 230};\n";
print "static const unsigned char GREENS[] = {$outputg, 230};\n";
print "static const unsigned char BLUES[]  = {$outputb, 230};\n";