Right, it is between the masters, here’s a diagram:
That works perfectly in a variable font, but I’m not super sure what’s the best way to reliably calculate the same intermediate (semi-red) values for the static instances’ filter, that would match how GPOS does it. In other words what would that function be?
GPOS_value = get_GPOS_for_axes(weight = 25, width = 30)
Do you just interpolate it in one dimension and then in the other? What about the open corners?