Intermediate Layers and Interpolation

Hello,

I am seeing some unexpected behavior in Glyphs 3 with intermediate layers I’ve created.

I have a glyph that inherits its metrics from the letter “H.” The lightest version of the H has 60 units on both sides. The boldest version of the H has 30 units on each side. The interpolated metrics for my intermediate layer with a weight of 300 has H(53) on the left and H(52) on the right. In theory, shouldn’t the H inherited value be exactly the same? Is it calculated and rounded independently for LSB and RSB?

Moreover, according to my math the value for the side bearing should be H(51) on both sides for an intermediate layer of weight 300. The difference between H(60) for the light weight and H(30) for the heavy weight is 30 units. If you have an intermediate layer with a weight of 300, the metric value should be 30% of the way between H(60) and H(30).

H(60) - H(30) = 30 Units.
30 Units * 0.3 = 9.
H(60) - 9 Units = H(51).

The one unit difference can’t be avoided as the leftmost point (that defines the LSB), the rightmost point and width (both together define the RSB) are rounded individually.
What are the axis values of your masters?

Hi Georg,

I just realized that my math is a bit off. I overlooked the fact that the axis extremes of 100 and 900 would offset the value a bit.

A difference of one unit is normal. Don’t worry about it. There will never be a situation where it will make a difference.