2.8. Initiating Geometry Changes   

Parents, children, and clients each initiate geometry changes differently. Because a parent has absolute control of its children's geometry, it changes the geometry directly by calling XtMoveWidget, XtResizeWidget, or XtConfigureWidget. A child must ask its parent for a geometry change by calling XtMakeGeometryRequest or XtMakeResizeRequest. An application or other client code initiates a geometry change by calling XtSetValues on the appropriate geometry fields, thereby giving the widget the opportunity to modify or reject the client request before it gets propagated to the parent and the opportunity to respond appropriately to the parent's reply.

When a widget that needs to change its size, position, border width, or stacking depth asks its parent's geometry manager to make the desired changes, the geometry manager can allow the request, disallow the request, or suggest a compromise.

When the geometry manager is asked to change the geometry of a child, the geometry manager may also rearrange and resize any or all of the other children that it controls. The geometry manager can move children around freely using XtMoveWidget. When it resizes a child (that is, changes the width, height, or border width) other than the one making the request, it should do so by calling XtResizeWidget. The requesting child may be given special treatment. It can simultaneously move and resize a child with a single call to XtConfigureWidget.

Often, geometry managers find that they can satisfy a request only if they can reconfigure a widget that they are not in control of; in particular, the composite widget may want to change its own size. In this case, the geometry manager makes a request to its parent's geometry manager. Geometry requests can cascade this way to arbitrary depth.

Because such cascaded arbitration of widget geometry can involve extended negotiation, windows are not actually allocated to widgets at application startup until all widgets are satisfied with their geometry.


1. The Intrinsics treatment of stacking requests is deficient in several areas. Stacking requests for unrealized widgets are granted but will have no effect. In addition, there is no way to do an XtSetValues that will generate a stacking geometry request.

2. After a successful geometry request (one that returned XtGeometryYes), a widget does not know whether its resize procedure has been called. Widgets should have resize procedures that can be called more than once without ill effects.