Greetings,
I’m sure you already know this, but Synfig is AWESOME.
Outlines can taper off suddenly because of the miter limit in Synfig. So, I used the Onto blend method as a “hack” that fixed the convex miters. The Alpha Over blend method can be used to fix the concave miters.
I do not know how to describe the process, so I will just give you an example file. Note the usage of blend methods and width points on the CURVE_HACK layers.
Good luck,
Charlie
CurvyMiters.sifz (5.58 KB)