OpenType Variable Fonts
John Hudson (via Avi Drissman):
An OpenType variable font is one in which the equivalent of multiple individual fonts can be compactly packaged within a single font file. This is done by defining variations within the font, which constitute a single- or multi-axis design space within which many font instances can be interpolated. A variable font is a single font file that behaves like multiple fonts.
[…]
OpenType Font Variations builds on the model established in Apple’s TrueType GX variations in the mid-1990s, but has fully integrated that model into all aspects of the OpenType format, including OpenType Layout, and is available to both TrueType and Compact Font Format (CFF) flavours of OpenType.
[…]
However, unlike master-based interpolation technologies such as Adobe’s earlier multiple master format, an OpenType variable font contains only a single set of glyph outlines, and the other extremes or intermediate shapes are defined as deltas from those outlines.
