So... how do other programs draw thick stroked lines?

Well, Synfig also has thick line drawing: http://wiki.synfig.org/wiki/Outline_Layer

Illustrator 5 also has a line thickness feature: http://www.video2brain.com/en/lessons/variable-width-strokes

I'm not sure about the algorithms they use though.

By the way, more feedback on Powerstrokes: - Closed-paths powerstrokes will often render strangely until you fiddle a bit with them. - Is it possible to either: a. Save the relative positions of the widths controls (to save the shape of the powerstroke) or b. Define the starting distance between the control point and the line center at least (basically when drawing very thin powerstrokes, the starting thickness can be a bit distracting)?

I'm trying to come up with a mock-up for line style management, to easily save and access all sorts of presets collections: - Powerstrokes - Pattern along Path (I'm finishing a mock-up proposal for on-canvas Pattern along Path editing) - Graph lines (a few arrowed and dotted lines. They're such a pain to set and unset right now) - Calligraphy (save presets as now, but with visual previews!) - [insert custom collections. Maybe presets from other tools]

They'll be accessed just like brush presets in MyPaint and Krita from a dialogue, except with longer previews.

For Powerstrokes, presets would allow the user to access various settings easily. But I'm hoping that it would also be possible to save and access preset Powerstrokes shapes, or at least of varying widths.

For example, suppose you're drawing eyelashes or hair highlights. You don't need to control the exact width of every line, but they do all need to be thin. See?