Go right over and read John Hudson’s explanation of the OpenType Variable Font format. Three quick but very interesting quotes:
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.
At the core of OpenType Font Variations are tables that define the design space and how it is presented to users. Some of these tables have been directly adapted from Apple’s TrueType GX architecture, but have been revised and enhanced.
The idea of fonts containing interpolable design space and named or dynamic instances is not new. OpenType variable fonts build directly on the technology introduced to TrueType by Apple in the QuickDraw GX graphics environment.
If you are old enough to remember QuickDraw GX, one of the coolest demo features was the font variation slider in the long gone LightningDraw GX app (Laris Software): select text, move slider, instant seamless on the fly font variations.
Dave Opstad, one of the original TrueType GX font engineers at Apple, should be feeling proud. Thank you Dave (and the GX team) for taking the heat and drawing that line in the sand. It made a difference after all.
Update: It is one thing to create a new font specification. It is quite another how it is implemented in the operating system. One last quote from John Hudson:
Apple, characteristically, are least forthcoming about future plans, but they have a head start on variable font support in their TrueType GX infrastructure, and have played an active role in bringing the technology to OpenType.
It is true that all the Apple Advanced Typography (AAT) font tables have been there since the QuickDraw GX days. Apple’s own support of AAT, at least from the Japanese font side, has sometimes been robust, sometimes not. You could almost hear Apple engineers arguing: “let’s go all in with OpenType layout” vs. “AAT still has things that OpenType layout does not.” The good thing is this has all been put to rest. The TrueType GX model and AAT tables are incorporated and carried forward in OpenType variable font technology. Everybody benefits.
The big questions are when will Apple add support for OpenType variable fonts in iOS, macOS, etc., and how. Will developers have to dig down into Core Text, or will Apple push it as high up as they can and make it easy?
One thing is certain: for the text layout and font development crowd, WWDC 2017 or 2018, is going to be very interesting.