@letterror There is a challenge I have been struggling with for many years, though:

Let’s say the user (i.e. font maker) has a given setup with multiple axes, and then decides to scale everything linearly in one dimension. For example, scaling one axis by factor 10 by adding a zero to the coordinate for all points. They would (rightly) expect that this does not affect the final result.

As far as I can tell, Delauney violates this requirement.

(Don’t shoot the messenger, I am hating this requirement myself but I consider it as inevitable.)

@letterror Not sure what to make of this.

In font interpolation, unlike in geo sciences, the relative scales of most dimensions are arbitrary.

It seems the implications were not clear.

If the scaling of an axis affects the visible result, then, as a font maker, I will play around with different scalings, trying to find the one that gives the best results. For several axes at once. This could be quite tedious.

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@letterror There are some axes which can’t be re-scaled easily, though. For example, the weight axis nowadays is expected to range from 100 to 1000, while the width axis is typically scaled at 50 (compressed) to 100 (regular). This means the width axis has a built-in dominance of roughly 1:10 over the weight axis. Only because someone, a long time ago, decided that 400 is regular and 700 is bold. Had they decided that 40 is regular and 70 is bold then our interpolated fonts would look differently. I am not prepared to accept that.

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@letterror Each master has coordinates, a tuple of values, of course. Same for the interpolated instance(s).

Let’s say in my font project, I have a foo axis that goes from 0 to 100. Then I decide that I want it to go from 0 to 1000 instead. I will simply add a zero to the foo value of each master and each instance. I’d expect that the interpolations remain perfectly identical.