# "Composite and Constraint Widgets

These widgets may contain arbitrary widget children. They implement a policy for the size and location of their children.

Box

  This widget will pack its children as tightly as possible in non-overlapping rows.

Dialog

  An implementation of a commonly used interaction semantic to prompt for auxiliary input from the user, such as a filename.

Form

  A more sophisticated layout widget that allows the children to specify their positions relative to the other children, or to the edges of the Form.

Paned

  Allows children to be tiled vertically or horizontally. Controls are also provided to allow the user to dynamically resize the individual panes.

Porthole

  Allows viewing of a managed child which is as large as, or larger than its parent, typically under control of a Panner widget.

Tree

  Provides geometry management of widgets arranged in a directed, acyclic graph.

Viewport

  Consists of a frame, one or two scrollbars, and an inner window. The inner window can contain all the data that is to be displayed. This inner window will be clipped by the frame with the scrollbars controlling which section of the inner window is currently visible.

The geometry management semantics provided by the X Toolkit give full control of the size and position of a widget to the parent of that widget. While the children are allowed to request a certain size or location, it is the parent who makes the final decision. Many of the composite widgets here will deny any geometry request from their children by default. If a child widget is not getting the expected size or location, it is most likely the parent disallowing a request, or implementing semantics slightly different than those expected by the application programmer.

If the application wishes to change the size or location of any widget it should make a call to `XtSetValues`. This will allow the widget to ask its parent for the new size or location. As noted above the parent is allowed to refuse this request, and the child must live with the result. If the application is unable to achieve the desired semantics, then perhaps it should use a different composite widget. Under no circumstances should an application programmer resort to `XtMoveWidget` or `XtResizeWidget`; these functions are exclusively for the use of Composite widget implementors.

For more information on geometry management consult the X Toolkit Intrinsics - C Language Interface.