0.2.0

What is it?

SVG::Graph is a loose port of the Perl SVG::TT:Graph package. It is a toolkit for generating SVG data graphs, which are a species of plot that are oriented toward displaying statistical data.

Actually, I just made all of that up. Graphs differ from plots (as far as I can tell) in that one of the columns can be non-numeric data. Graphs are the sorts of things that spreadsheets generate. Feel free to email me with concise definitions of Graphs and Plots.

Screenshot

Gotta have one.

The SVG output by SVG::Graph uses CSS for styling, and a depressing number of SVG viewers don't do CSS correctly yet. If the above image is entirely black, your SVG viewer doesn't handle CSS properly. If the above image doesn't display at all, your browser probably doesn't understand SVG. The Adobe plugin does, as does Batik.

Why use it?

If you're a Ruby programmer, you can't use SVG::TT::Graph directly. This package is for you.

If you want one of the features that this package has that the Perl version doesn't, and you don't mind doing your graph code in Ruby, then this package is for you.

If you're a Perl wienie or you have something against Ruby, use SVG::TT::Graph. If it doesn't provide you with the features you want, hack it yourself.

Getting it

The source archives contain the example script(s) and an install script. Documentation must be downloaded separately.

Why?

The SVG::TT:Graph package is just fine. It lacked a couple of features that I wanted, and it was in Perl1, so I re-implemented it.

SVG::Graph is not a straight port of SVG::TT::Graph, because the Perl version uses templates, and I don't believe that this is a job for templates. Templates are great when you have lots of context containing a little bit of evaluated code, but the Graph classes are mostly code with a little SVG; therefore, it makes more sense (and is a hell of a lot more readable) to have the SVG embedded in the code rather than vice versa. However, much of the logic was directly cut and paste out of SVG::TT::Graph, so at least the first few versions of SVG::Graph borrowed heavily from the Perl version.

In fact i version 0.2.0 I completely refactored the code to make it more modularized. As a result, the core Graph class contains most of the graph drawing primatives, and the specializations only draw the plot itself. This results in many fewer lines of code, and that code is more robust.

I intend SVG::Graph to have more features than SVG::TT::Graph, which is the main reason for the re-implementation. One such feature is the ability to change the stacking of the data sets. For instance, SVG::Graph allows you to place the data bars from multiple data sets on the same graph side-by-side, rather than overlapping.

SVG::Graph is probably incomplete. In fact, the first release contained two graph styles: Bar, and BarHorizontal. Version 0.2.0 added a Line graph, and the number of styles will grow.

Dependancies

REXML 3.0+, or Ruby 1.8+. If you want to use the SVG compression feature, which generates zlib compressed SVGs, you must also have the Ruby zlib library installed.

Usage

There's API documentation available, either online or for download. Or, you can use rdoc to generate it yourself. The API documentation is pretty comprehensive (Leo Lapworth did a really good job on the docs, and I stole most of them), and there's an example application in the main directory.

Bugs

SVG::Graph probably contains bugs. In fact, it is probably mostly bugs, held together with some working code around them. In particular, SVG::Graph is probably really intolerant of *your* bugs, and is likely entirely unhelpful in helping you track down problems. We can only pray that this situation improves2. Email me, and I'll fix them. If the package ever gets popular, I'll set up a bug page3.

1)

Perl is from Hell. The language is bad enough, but working with the package system -- CPAN, etc. -- is an excercize in masochism. I'd rather chew on glass.

2)

Prayer is much more effective when accompanied by sums of cash sent to the author.

3)

Watch: five years from now, when SVG::Graph is a core Ruby package, and it consists of a half million lines of code, and the United Nations depends on it for all of it's graphing needs, and the Linux kernel itself depends on it for its install process -- this documentation will be largely unchanged, and although I'll have long since set up a bug page, I won't have changed that paragraph.