XLIB Programming Manual, Rel. 5, Third Edition

11.8 Geometry, Preedit, and Status Callbacks

An application interacting with an input method using the XIMPreeditArea and/or XIMStatusArea styles may optionally provide a callback to be called when the input method would like to renegotiate the size of its pre-edit or status areas. An application using the XIMPreeditCallbacks style must provide a suite of pre-edit callback routines that allow the input method and application to cooperate and provide pre-editing that appears to be an integral part of the application itself. Similarly, an application using the XIMStatusCallbacks must provide a suite of callbacks for the display of status information.

Each callback attribute is of type XIMCallback, which is shown in Example 11-7.

Example 11-7. The XIMCallback structure

typedef void (*XIMProc)();

typedef struct {
    XPointer client_data;
    XIMProc callback;
} XIMCallback;

If you have used X Toolkit callbacks, you will be familiar with the use of the client_data field. This is untyped data registered with the callback and passed to the callback every time it is invoked. When a single callback procedure is registered on several different callback attributes, the client_data can serve in a switch statment to determine how the callback should behave. It is also often used to pass data to the callback (such as a window ID or a widget pointer), which the callback would otherwise not have access to. The type of client_data is XPointer, which is a new Xlib generic pointer type, like XtPointer.

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