User Guide

If you want to interpolate another rectangle that is 50% of
the way between them (the gray rectangle on the right),
you draw lines connecting the corresponding points of the
two figures to be interpolated, then mark a point on each line
that is 50% of the way from the outer point to the inner
point. Connecting those points gives us the gray interpolated
figure. You could interpolate 25% by marking the point
25% of the way from the outer to the inner point (or from
the inner to the outer—it depends on how we set up the
interpolate operation).
So far, the process is fairly simple. Now let’s consider what
can go wrong if the points of the two master figures don’t
correspond (like not having the path direction correct or the
ordering of points be the same). The points in Figure 2
again have been numbered so you can see what is going on.
The only change from the first example is that the inner
figure has its points permuted (or reordered) slightly. You
should remember this rule: Connect like-numbered points,
then add a point halfway between the connected points,
and connect those halfway points. Note in the example
how unlike the desired rectangle the resulting diamond
shape appears. It is likely that you will see something
similar as you begin using “Font Blend” to make fonts.
Clearly this is not an interpolate bug; Fontographer does
exactly what it is supposed to do mathematically, and
exactly what you asked it to do when you permuted the
points.
Other aspects of blending make it a little difficult to use, but
follow clearly from the mathematics. Consider the case
Fontographer User's Manual
10: Expert Advice Page #10