If what you're looking for is just a reference line, it'd be pretty easy to hack in, I think. There may be a bug or two in this (though it works in a trivial test case), but I'd think something along these lines would work: 

# assuming $graph has already been set up and plotted
my $y_value = 42; # desired y-value for reference line 
my $y_coord = ( $graph->val_to_pixel(0,$y_value,0) )[1];
my $GD = $graph->{graph};
my $red = $GD->colorResolve(255,0,0);
$GD->line($graph->{left},$y_coord,$graph->{right},$y_coord,$red);

[download]

Not that I've been thinking about precisely that problem, recently, or anything like that. ;-)


If God had meant us to fly, he would *never* have given us the railroads.
    --Michael Flanders

In reply to Re: Alternative for GD::Graph? by ChemBoy
in thread Alternative for GD::Graph? by jbrugger

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.