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Thu, 17 Sep 2009

The Happiness of Design Convergence


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Recently I've been having fun writing a plotting module for Perl 6. It's been really fun because adding new shiny things (titles, new chart types, whatever) has been relatively easy, and there was fast visual feedback.

However it's really just a toy module, lacking proper design. When I added legend boxes to one of the chart types (the lines plots), I noticed how much hassle it was, and that I needed code changes in many places to incorporate that feature into other chart types too - that's what you call "design smell".

So I thought about how to improve it, and the answer was quite obvious. Currently each thing that I plot (the data representation, the axis, ticks, labels, title, legend box) know where to place itself, so if I need more space for the legend box every piece has to adapt. Which is ugly.

Instead, I should just make each of them plot itself on to coordinates (0, 0), record their width and height, and later move (and possibly scale) them to fit onto the canvas (Note that I only planned that so far, I implemented the boxing only for a single component so far).

Flashback to the past: Shortly after announcing my very early SVG::Plot module masak pointed me to Scruffy, a small ruby based SVG plotting library that produces beautiful graphs. I looked into the source and found that it was spread into about 50 classes, all of which were short and sweet. I didn't really understand the code, mostly due to lack of Ruby reading skills, and lack of effort.

So I and others decided to port scruffy to Perl 6, the Perl 6 version will be called Tufte. And after re-reading the Scruffy source code I noticed that it was doing just what I planned for SVG::Plot: it encapsulates each graphical element into components (called Scruffy::Components::*). On top of that it allows multiple plots per canvas (the plots are called Scruffy::Layers::*), and allows arranging of them too.

So I was happy to come up with the same idea as the Scruffy hackers, independently, reassuring me that I actually port a nicely designed library ;-)

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