Hi, I'm making variable fonts with FOSSs(free open source softwares).
i use fontforge(both GUI and python api to design and prepare masters), notepad++, fonttools(name records modification, format conversion, ttx,...), fontmake(generate variable fonts and instances) and python scripts(regex, automation,...).
there is 2 problems about interpolation of masters, which are related to varlib(a part of fontmake) limitations:
1- anisotropic interpolation(multiply a number to x and y delta values) it's usefull to contrast regulations, especially in sans serif fonts.
2- Extrapolation(going out of designspace borders mathematically): fontforge has this ability but it's not working for opentype GPOS(mark anchors coordinates, kerning values,...).
apparently MutatorMath with ufoprocessor could handle these problems but i couldn't find how...
Could anyone please help me to find a solution or working examples?(i know Glyphs, fontlab 7, robofont(?), FontCreator(?),... have these abilities, I'm searching for opensource solutions).