---

The ATS Server, Notifications, and Queries

The ATS server is a process that is responsible for maintaining the font database for Mac OS X. It activates and deactivates fonts, maintains and scales glyph outline data, maintains font caches, and communicates information about font availability between font clients and font utility applications. The ATS server ‘s role in font support in Mac OS X is shown in Figure 1-2.

The ATS server also handles font notifications. A font notification is a message from the ATS server that informs applications of changes in the font database. The ATS server passes the font activation and deactivation information to any application that has subscribed to receive notifications. Currently, the only types of notification an application can receive are the result of a global font activation or deactivation.

Applications that subscribe to notifications receive up-to-date information about the font database. Notifications eliminate the need for an application to check generation values and to periodically enumerate fonts and font families.

ATS supports the ability for ATS clients to send font queries. A font query is simply a message that is generated by an application in need of font information. Currently there is only one type of query supported—a query for a missing font. A missing-font query is generated automatically whenever an application looks for a font that is not currently active. If the ATS server does not have the queried font in the font database, the server passes the font query to any application that has signed up to handle queries. Typically this is a font utility, often a faceless process, specifically designed to handle font queries. If the font utility has access to the font, the utility can activate the font using the appropriate ATS function.

The query process is opaque to the application that needs a font. Query management is handled by the ATS server. To the requesting application, activation of the needed font is automatic.

---