This repository contains a single variable font file with support the limited glyph set A-Z, a-z, and 1 (plus a normal space and .notdef). This font was created to test CFF2 rasterization when the ordering of horizontal or veritcal stems changes as a result of elements moving relative to one another in different instances.
The CFF specification requires that, within a given CharString, the lists of vertical and horizontal stems be stored in sort order (by the start of the stem). The original CFF2 specification did not add to or modify this requirement, although stems sizes and positions could now be variable.
In some variable glyph designs the stem of one element might cross another. if the requirement were that stems must stay ordered in all regions of designspace, one or the other of those stems would need to be removed. Because it is desirable to support hinting of both stems in such cases, Adobe has proposed loosening the requirement so that stems for the default instance must be in order, but can change order in other regions of designspace.
The limited font built from this repository, which is based on glyphs copied
from Source-Serif, tests such cases. The two axes—wght and opsz—from Source
Serif are retained. An additional posi axis causes an accent-like element to
move from bottom to top, or left to right, relative to a letter. As a result of
that movement the stem(s) of the accent-like element cross stems of the letter.
The font can be used to test existing CFF2 rasterizers to determine how fonts encoded according to the modified specification will behave. So far, Adobe's testing with both its own CoolType rasterizer and the open source FreeType rasterizer indicate that the glyphs render the same way regardless of the accent position. This suggests that those implementations are not depending on the ordering of the stems when rasterizing (e.g. doing a binary search for matching stems rather than a linear scan). Any such rasterizer already complies with the proposed change to the specification.