#!/usr/bin/perl

  use strict;
  use CGI qw(:standard *table :nodebug);
  use Data::Dumper;

  #-------------------
  # Configuration

  my $NUM_STEPS = 32; # Number of colors in gradient
  my $WRAPPING  = 1;  # Makes the end match the beginning
  my $OUT_HTML  = 1;  # Output as HTML, otherwise Dumper

  #-------------------
  my $PI        = atan2(0, -1);
  my $USE_STEPS = $WRAPPING ? $NUM_STEPS : $NUM_STEPS * 2;
  my $EACH_STEP = $PI / $USE_STEPS;

  my $offs = make_offsets_random();
  my $grad = make_gradient($offs);

  if ($OUT_HTML) { output_html($offs, $grad); }
  else           { output_dump($offs, $grad); }

#-----------------------------------------------------------
sub make_gradient {

  my $offs = shift;

  my @grad;

  for my $i (0..$NUM_STEPS-1) {
    push @grad, make_rgb($i, $offs);
  }

  return \@grad;
}

#-----------------------------------------------------------
sub make_rgb {

  my $i    = shift;
  my $offs = shift;

  my $r = ($i + $offs->{r}) % $USE_STEPS;
  my $g = ($i + $offs->{g}) % $USE_STEPS;
  my $b = ($i + $offs->{b}) % $USE_STEPS;

  return
    sprintf "%2.2x%2.2x%2.2x",
      int(sin($r * $EACH_STEP) * 255),
      int(sin($g * $EACH_STEP) * 255),
      int(sin($b * $EACH_STEP) * 255);
}

#-----------------------------------------------------------
sub make_offsets_random {
  return {
    r => int(rand() * $USE_STEPS),
    g => int(rand() * $USE_STEPS),
    b => int(rand() * $USE_STEPS),
  };
}

#-----------------------------------------------------------
sub output_html {

  my $offs = shift;
  my $grad = shift;

  print header();
  print start_html();

  print start_table({-cellspacing=>0});

  my @rows;

  push @rows,
    Tr(td("Offsets $offs->{r} $offs->{g} $offs->{b}"));

  for my $i (@$grad) {
    push @rows, Tr(td({-bgcolor=>$i}, $i));
  }

  print join("\n", @rows);

  print end_table();
  print end_html();
}

#-----------------------------------------------------------
sub output_dump {

  my $offs = shift;
  my $grad = shift;

  print Dumper $offs;
  print Dumper $grad;
}