UI Overview: 2 The GEOS User Interface

Most programmers who write applications for GEOS will have worked with other GUI systems. Some will even have worked with object-oriented systems. Using the GEOS UI, however, will be a new experience for nearly every programmer.

The GEOS user interface consists of a number of dynamic libraries containing object classes. Applications include objects of these classes to gain various types of functionality. In general, applications will use two different basic types of objects for their UI: Generic objects provide basic UI functionality including windows, menus, and dialog boxes, and their implementation on the screen is determined by GEOS. Visible objects provide more application-specific functionality and offer complete display control to the application.

Generic object classes are all based on the class GenClass . Applications will never use any objects of GenClass , but they will use many objects of its subclasses. A list of these subclasses is shown below, and each of these classes is described in Using the Generic Classes .

Visible object classes are subclassed from VisClass . VisClass may be used often by applications, as will its subclasses. The subclasses of VisClass are shown below, and each is described in Using the Visible Classes .

When to use the generic or visible objects is subject to many criteria. In order to learn more about each of these components of the UI, you should read the two sections following this one.

The GEOS UI also contains many features that will often be used by applications but which don't fall into either the generic or the visible world. These features are called "mechanisms" and include input management, geometry management, general change notification, and the clipboard and quick-transfer functions. As these mechanisms are not UI-specific but are only implemented within the UI libraries, they are documented elsewhere in this book.

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