Callbacks

When an OnTheSpot input method is implemented, only the client can insert or delete preedit data in place and possibly scroll existing text. This means the echo of the keystrokes has to be achieved by the client itself, tightly coupled with the input method logic.

When a keystroke is entered, the client calls the XmbLookupString() or XwcLookupString() function. At this point, in the OnTheSpot case, the echo of the keystroke in the preedit has not yet been done. Before returning to the client logic that handles the input characters, the lookup function must call the echoing logic for inserting the new keystroke. If the keystrokes entered so far make up a character, the keystrokes entered need to be deleted, and the composed character is returned. The result is that, while being called by client code, input method logic has to call back to the client before it returns. The client code, that is, a callback routine, is called from the input method logic.

There are a number of cases where the input method logic has to call back the client. Each of those cases is associated with a well-defined callback action. It is possible for the client to specify, for each input context, which callback is to be called for each action.

There are also callbacks provided for feedback of status information and a callback to initiate a geometry request for an input method.