Exciting topic for a blog post eh?
This maybe peculiar to OSX users of Inkscape but I have been using the software (for all sorts, including panel layout) for a couple of years and have NEVER been able to get the .HPGL export working.
I've lost count of the times I'd tried installing the required libs/python modules/scripts but it always refused to work.
That sis until last night, when I discovered this blog post and subsequent 'Inkscape fixer (scroll down to the bottom)'
Here's the link to the up-to-date PKG (the one linked from the blog is deprecated) that cures your Inkscape extension woes (it did for me, your mileage may vary of course). You also need to install libxml2 and lxml wrapper but you knew that already, right?
Now I can very easily knock up some vector art in Inkscape, save as .HPGL and import straight into FPD. For example when creating a 'scale' for a control knob:
(Well, apart from I'm trying to move away from Inkscape but so far I haven't found a solution to get .HPGL / .PLT files out of Sketchup - if anyone knows I'd be delighted to hear from you.)
vector inkscape design sketchup panel OSX HPGL fix