#!/usr/bin/perl

  use strict;
  use GD;
  use POSIX;

  #---------------------------------------
  # conf

  my $conf = {

    image => {
      x_size => 320,
      y_size => 320,
    },

    palette => {
      num_colors => int(rand(56) + 8),
      set_points => [
        [0, 0, 0],
        [int(rand(255)), int(rand(255)), int(rand(255))],
        [0, 0, 0],
        [255, 255, 255],
        [0, 0, 0],
        [int(rand(255)), int(rand(255)), int(rand(255))],
      ],
      repeat => rand(1.5) + .5,
    },

    moire => {
      num_lines  => int(rand(7)) + 2,
      repeat_min => 4,
      repeat_max => 8,
      wrap_prob  => rand(),
      turn_prob  => rand(),
      plot       => int(rand(2)),
    },
  };


  #---------------------------------------
  # init

  my $palette = setup_palette($conf->{palette});
  my $moire   = setup_moire($conf->{moire});
  my $image   = new GD::Image($conf->{image}{x_size}, $conf->{image}{y_size});

  for my $col (@$palette) {
    $image->colorAllocate($col->[0], $col->[1], $col->[2]);
  }

  #---------------------------------------
  # go

  make_image($conf, $moire, $image);

  #print "Content-Type: image/png \n\n";
  print $image->png();

#-----------------------------------------------------------
sub make_image {

  my $conf  = shift;
  my $moire = shift;
  my $image = shift;

  my $x_pix = 1 / $conf->{image}{x_size};
  my $y_pix = 1 / $conf->{image}{y_size};

  my $max;

  for my $line (@$moire) {
    if ($line->{wrap}) { $max += 1; }
    else               { $max += .5; }
  }

  for my $xi (0..$conf->{image}{x_size}-1) {
    my $x = $xi * $x_pix;

    for my $yi (0..$conf->{image}{y_size}-1) {
      my $y = $yi * $y_pix;

      my $tot;

      for my $line (@$moire) {

        my $val = $x + $y * $line->{grad};
           $val = $val * $line->{mult};
           $val = $val - floor($val);

        if ($line->{wrap}) {
          if ($val > .5) { $val = 1 - $val; }
        }

        if ($line->{turn}) { $val = 1 - $val; }

        $tot += $val;
      }

      $tot = $conf->{moire}{plot}
             ? ($tot / $max) * $conf->{palette}{repeat}
             : $tot / @$moire;

      my $ci = $tot * $conf->{palette}{num_colors};

      $image->setPixel($xi, $yi, $ci % $conf->{palette}{num_colors});
    }
  }
}

#-----------------------------------------------------------
sub setup_moire {

  my $conf = shift;

  my @lines;

  for (1..$conf->{num_lines}) {

    my $line = {};
    push (@lines, $line);

    $line->{mult} = rand($conf->{repeat_max} - $conf->{repeat_min});
    $line->{mult} = int($line->{mult} + $conf->{repeat_min});

    $line->{wrap} = (rand() < $conf->{wrap_prob}) ? 1 : 0;
    $line->{turn} = (rand() < $conf->{turn_prob}) ? 1 : 0;

    $line->{grad} = rand(2);

    if ($line->{grad} > 1) {
      $line->{grad} = 1 / ($line->{grad} - 1);
    }

    if (int(rand(2))) { $line->{grad} *= -1; }
  }

  return \@lines;
}

#-----------------------------------------------------------
sub setup_palette {

  my $conf = shift;

  my @palette_colors;
  my @palette_indexs;

  push @{$conf->{set_points}}, $conf->{set_points}[0];

  my $rate = $conf->{num_colors} / $#{$conf->{set_points}};

  for my $i (0 .. $#{$conf->{set_points}}) {
    my $j = int($i * $rate);
    push @palette_indexs, $j;
    $palette_colors[$j] = $conf->{set_points}[$i];
  }

  for my $i (0 .. $#palette_indexs - 1) {
    my $beg = $palette_indexs[$i];
    my $end = $palette_indexs[$i+1];
    interpolate(\@palette_colors, $beg, $end);
  }

  pop @palette_colors;

  return \@palette_colors;
}

#-----------------------------------------------------------
sub interpolate {

  my $colors = shift;
  my $beg    = shift;
  my $end    = shift;

  my $steps = $end - $beg;

  my $r_start = $colors->[$beg][0];
  my $r_range = $colors->[$end][0] - $colors->[$beg][0];
  my $r_slope = $r_range / $steps;

  my $g_start = $colors->[$beg][1];
  my $g_range = $colors->[$end][1] - $colors->[$beg][1];
  my $g_slope = $g_range / $steps;

  my $b_start = $colors->[$beg][2];
  my $b_range = $colors->[$end][2] - $colors->[$beg][2];
  my $b_slope = $b_range / $steps;

  for my $i (1..$steps-1) {
    my $j = $i + $beg;
    $colors->[$j][0] = int($r_start + ($i * $r_slope));
    $colors->[$j][1] = int($g_start + ($i * $g_slope));
    $colors->[$j][2] = int($b_start + ($i * $b_slope));
  }
}