Focus Management

Languages with large numbers of characters (such as Japanese and Chinese) require an input method that allows the user to compose characters in that language interactively. This is because, for these languages, there are many more characters than can be reasonably mapped to a terminal keyboard.

The interactive process of composing characters in such languages is called preediting. The preediting itself is handled by the input method. However, the user interface of the preediting is determined by the system environment. An interface needs to exist between the input method and the system environment. This is done through the VendorShell widget of the system environment.

Figure 4-3 illustrates a case with Japanese preediting. The string shown in reverse video is the string in preediting. This string can be moved across different windows by giving focus to the particular window. However, only one preediting session can occur at one time.

Figure 4-3 Japanese preediting example

For an example of focus management, suppose a TopLevelShell widget (a subclass of the VendorShell widget) has an XmBulletinBoard widget child (MainWindow area), which has five XmText widgets as children. Assume the locale requires the preedit area, and assume the OverTheSpot mode is specified. Because the VendorShell widget manages only one instance of an input method, you can run only one preedit area at a time inside the TopLevelShell widget. If the focus is moved from one Text widget to another, the current preedit string under construction is also moved on top of the Text widget that currently has focus. Processing of keys to the old Text widget is suspended temporarily. Subsequent interface of the input method, such as the delivery of the string at preedit completion, is made to the new, focused Text widget.

The string being preedited can be moved to the location of the focus; for example, by clicking the mouse.

A string that the end user is finished preediting and that is already confirmed cannot be reconverted. Once the string is composed, it is committed. Committing a string means that it is moved from the preedit area to the focus point of the client.