# usage:
#   $iter = range(\@fromRGB, \@toRGB, \@weights, $size);

#   my $iter = range(
#     [0,0,0] => [255,255,255],
#     [ (1) x 100 ],
#     255
#   );
#   
#   while (my ($rgb_ref, $width) = $iter->()) { ... }

sub range {
  my ($from,$to,$w,$s) = @_;
  my $i = 0;
  my @steps = map +($to->[$_] - $from->[$_])/$#$w, 0..2;
  my $c = $from;
  my $f = 0;

  $i += $_ for @$w;

  # this (CRUFTILY) converts an array of floats
  # with a sum of X to an array of ints that still
  # has that same sum of X

  $w = [ map {
    my $v = $f + $s*$_/$i;
    $f = $v - int($v);
    int $v
  } @$w ];
  $w->[-1] += $f;

  sub {{
    my $ret = [ @$c ];
    return if !@$w;
    $c = [ map $steps[$_] + $c->[$_], 0..2 ];
    return ($ret, shift @$w) if $w->[0];
    shift @$w, redo;
  }};
}