History

The ideas behind OpenType have been in the making since 1991 when Apple released its QuickDraw GX system. This, as with OpenType, concentrated heavily on adding typographic support, such as extended support for ligatures, alternative numerals and fractions. QuickDraw GX found little support amongst application developers and quietly disappeared, but the seeds were sewn.

In 1995 Microsoft developed TrueType Open (an extension of the already popular TrueType font format) for the Arabic and Indic language markets, to enable more intricate and culturally acceptable typography for these complex script systems. 1996 finally saw Adobe and Microsoft agreeing on a common font format to end the font wars.

Advantages

OpenType has four major advantages over other font formats:

• The same font file works on any platform that supports OpenType. There is no difference between a Mac and Windows OpenType font.
• Each font is only one file. Some other formats split outlines, metrics and kerning information over multiple files.
• Unicode is used throughout, allowing multiple languages and script systems to all be available from a single font file.
• The font designer and engineer can include advanced typographic features that allow compatible applications to give access to context-sensitve and user-selectable presentation forms and features.

Compatibility

Dalton Maag favours TrueType-based OpenType fonts. The format allows us to control the screen display (QuDOS) to a high degree. They also degrade gracefully (losing advanced typographic features, but preserving Unicode support) on older versions of Windows without the need for third-party add-ons. Mac OS X also fully supports .ttf OpenType files. With additional engineering and wrapping the .ttf into a Mac suitcase, they can be made to work under Mac OS 8.5 and 9. Fonts labelled .otf work under Mac OS 8.5 and OS 9 with the help of ATM 4.6.2 or later and under Mac OS X natively. Only Windows 2000 and later support this flavour natively.

Features

For the designer, the availability of typographic features is particularly interesting. For example, the type designer can create true small caps and make them available to the user by a simple option from any compatible application's OpenType menu or toolbar. If the font is changed to one that doesn't implement the small cap feature, the text, as it is still intact, reverts to its normal form - the integrity of the information in the document is preserved.

Versions & Flavours

OpenType fonts come in two different flavours. OpenType fonts labelled .ttf contain TrueType outlines and are fully backwards compatible with OSes and applications that support TrueType fonts, whilst fonts labelled .otf contain CFF (compressed PostScript) outlines [1]. Structurally, both flavours are the same and the difference ought to be transparent to the user[2].

[1] .otf files can contain TrueType outlines, but this is discouraged as it breaks backwards compatibility with applications that support TrueType only.
[2] Some Windows applications view CFF-based OpenType fonts as "printer fonts" and refuse to display them. This is a bad assumption on the part of the application's developer.