Interpolating points

When instructions are used to change the position of a few of the points in a character outline, the curves that make up the character may become kinked or otherwise distorted. It may be desirable to smooth out the resulting curve. This smoothing out process is actually a redistribution of all points that have not been moved so that their positions relative to the moved points remain consistent.

To assist in managing the shape of outlines, the interpreter uses the concept of touching a point. Whenever an instruction has the effect of moving a point, that point is marked as touched in the x-direction or y-direction or both. The IUP instruction will affect only untouched points. It is possible to explicitly untouch a point so that it will be affected by an interpolation instruction.