Overview

This chapter focuses on the environments where entities are displayed and function. Logical displays are conceptual objects that describe the operating environments to (and provide the frameworks for) the containment of their descendants. Descendant objects may be conceptual or physical, and provide the front end and interaction to the application. Multiple logical displays can exist for each M process, and each can describe the characteristics of different environments. Each display is a separate operating envelope for its descendants; their defined areas can overlap, but they cannot share information.

The characteristics of logical displays are described by attribute node values assigned to the Display SSVN (^$DI[SPLAY]), which contain the following information about their environments:

1. hardware capabilities including the presence of a keyboard, mouse, and pen device;

2. the contents of the clipboard;

3. the default characteristics to pass down to its descendants; and

4. the object where user actions are directed.

The characteristics of logical displays that are defined for different processes, and even in the same process, can have dissimilar properties.

The discussion of the logical display is broken down into several sections. The Creation and Modification section discusses how a logical display is created, how it interacts with its descendants, and how an application can modify it. The Display Attributes section presents the attributes available to define the characteristics of logical displays. The Implementation section shows an example of ^$DI and discusses its settings. After reading this chapter, the reader will know how to ascertain environmental characteristics of a logical...