I just found your application, and I'm stunned. You've done a great job. I'm the lead developer of another application called SciGraphica (http://scigraphica.sourceforge.net) and GtkExtra, a package of widgets for (among other things) plotting 2d, contour, 3d, and polar plots. SciGraphica is built on top of gtkextra and it's not competing with matplot in the sense that it aims at having a GUI based program ala Microcal Origin, with spreadsheets for editing and manipulating the data. I hope you agree that we can learn from each others experiences with algorithms, etc. This is precisely why I'm contacting you, guys!
I have to confess that my contour and 3d plots are pretty "raw" in the sense that the algorithms I use are quite primitive and slow. I basicaly generate a delaunay triangulation and cut the triangles with planes, and draw the resulting polygons. I was wondering if you guys could give me some feedback about a good algorithm for plotting 2d contour plots, or at least, tell me where to look in your code to see if I can learn from it. Whare are the actual engines to plot the pie charts and contours, for instance?
I hope you guys don't mind sharing info with me, actually this is one of the reasons for doing OSS. I hope we can enjoy a fruitful communication. All the best, and congratulations again for your project.
PS: If by any chance you feel inclined to trying SG, I suggest you to go directly for the CVS code, since the latest release is not very stable.