In pre-Mac OS X versions of the Macintosh operating system, the Appearance Manager controlled the overall look of the Mac GUI widgets and supported several themes. The Appearance Manager was originally developed for Apple's failed Copland project, but with the cancellation of this project the system was moved into newer versions of the Mac OS, notably bundled with Mac OS 8 and 9. However, the Appearance Manager is also available free as part of a downloadable SDK for System 7. The current version of the operating system, Mac OS X, no longer directly supports the Appearance Manager.
The Appearance Manager is implemented as an abstraction layer between the Control Manager and QuickDraw. Previously, controls made direct QuickDraw calls to draw user interface elements such as buttons, scrollbars, window title bars, etc. With the Appearance Manager, these elements are abstracted into a series of APIs that draw the item as a distinct entity on behalf of the client code, thus relieving the Control Manager of the task. This extra level of indirection allows the system to support the concept of switchable "themes", since client code simply requests the image of an interface element (a button or scroll bar, for example) and draws its appearance. Kaleidoscope, a 3rd party application, was the first to utilize this functionality with via "scheme" files, followed by an updated Appearance Control Panel in Mac OS 8.5, which acted similarly via "theme" files. Schemes and themes are similar in concept, but they are not internally compatible. The Appearance Manager remains as part of Carbon, but switchable themes are no longer supported in Mac OS X.
Read more about Appearance Manager: Appearance Themes, Typography, Shareware Products
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