OpenType font variations
Ask any graphic designer: The key to communicating your ideas concisely and effectively is good typography. Designers make use of a variety of font weights and styles to make your message stand out clearly. The problem has been that all those weights and styles—bold, semibold, regular, display, caption—are separate font files, which increases application size and slows down web page load times, especially on mobile phones. OpenType Font Variations provide all the weights and styles of a full font family in a single, compact file to improve applications size and web site responsiveness.
A variable font file supports more than typical font instances like bold and condensed: it also can generate a smooth continuum of styles between them (e.g. semi-semi-bold, or very-slightly-condensed). This great variety makes possible a number of responsive typography features that can produce really polished layouts. Web sites can make fine adjustments font width to fit headlines to column widths without wrapping or ugly whitespace; applications can adjust fonts to match the pixel density of devices, creating an excellent looking design from low resolution monitors to smartphones. In his article on responsive typography, Nick Sherman has described many other scenarios in which variable fonts could help.
OpenType Font Variations marries the font variations technology created by Apple for QuickDraw GX with the richness OpenType, including its advanced layout capabilities of OpenType Layout and the choice of outline formats. A variable font contains three main components: Each font file contains a single set of outlines that forms the basis for the typeface family. It also includes a set of design axes, such as weight, width, optical size, or more, to describe the ways that the font family varies. Finally, it includes a set of deltas that describe how the outline shapes, kerning, mark positioning, and metrics change across those axes. When applications or web sites use a variable font, they choose a particular style within the ranges of the design axes, and the operating system will apply the appropriate deltas and OpenType substitutions to create an ephemeral, virtual font for rendering text in that style. A variable font can also provide a set of pre-defined styles, called named instances, which will surface just like traditional static fonts in operating systems that support variable fonts.
John Hudson has written an excellent article with more details of the mechanics of variable fonts. The specification of OpenType Variations is available in version 1.8 (or later) of the OpenType specification.
Variable fonts are supported by current versions of Windows, MacOS, and Android, as well as all major web browsers. Windows currently includes the variable font Bahnschrift, and more will be coming in future releases.
Microsoft and its collaborators hope that OpenType Font Variations will create a new font platform on which developers and designers can create a new level of typographic richness while also providing better solutions for their customers.