Kinks on interpolation

[ferfolio (Fernando Diaz)]

Hi everyone I’m getting some weird kink when I interpolate.
I’ve read other similar threads but didn’t help much.

First master

Second master

Interpolations:

Is there any way we can fix this?
Thank you!

[SCarewe (Sebastian Carewe)]

This is not fixable unless you use a different node structure.

Drawing help: Diagonals interpolation

You need to keep either the same angle or the same ratio (relative distance) between the 4 points forming each line. Rainer has Dekink Master Layers script for that. Also, Show Smooth Node Angle And Proportion plugin helps to measure it

I can’t find @jkutilek’s explanation anymore, he linked a very good resource a few months ago explaining the mathematics behind this. (Sorry for tagging you if it wasn’t you, Jens!)

Otherwise: https://twitter.com/RafalBuchner/status/965232476259004417

TLDR you’ll have to place the nodes from your first screenshot so that the angle of the handles stays the same.

[mekkablue (Rainer Erich Scheichelbauer)]

There is a chapter in the MM tutorials about kinks.

[ferfolio (Fernando Diaz)]

Thanks both, I found the solution by making the nodes in an angle instead of vertical as @SCarewe suggested.

[jkutilek (Jens Kutilek)]

@SCarewe I think you mean this post:

Variable straight slanted shape bug

For the relative angle of two lines not to change in interpolation, either the angle must stay the same, or the ratio of both line lengths must stay the same. It is better known when curves produce a kink in interpolation, as shown in “Designing Multiple Master Typefaces” (Adobe 1995, 1997), but is also true for lines. [Bildschirmfoto 2022-10-15 um 17.54.48] The problem is that not only the slant of the letters changes, but also the top bar of the T gets fatter.