subwindow

A subwindow is a window that exists within the boundary of another window, known as its parent or container. It is part of a hierarchical window system in which the parent owns and manages the subwindow. Subwindows are typically positioned with coordinates relative to their parent and are clipped by the parent’s boundaries, meaning content outside the parent’s area is not displayed.

In most graphical user interfaces, subwindows are used to compose complex widgets and layouts. They can represent panels, toolbars, embedded views, or controls such as buttons and text fields. Some toolkits also support subwindows as internal frames or docked panels within a main window. In certain operating systems or toolkits, subwindows may be referred to as child windows or embedded widgets.

Key properties of subwindows include their relationship to the parent, their coordinate system, and their lifecycle. Events and painting are often constrained by the parent window, and destroying the parent typically destroys its subwindows. Subwindows inherit the parent’s visibility and can be shown, hidden, or moved as a group. The z-order of subwindows is usually managed within the parent, determining which one appears on top when windows overlap.

Common patterns involve using subwindows for modular UI components, such as a document editor window containing a subwindow for the text area, or an application with detachable panels. Some platforms also provide mechanisms for reparenting or embedding external windows as subwindows, enabling integration of diverse content within a single parent window.

Overall, subwindows enable structured, nested interfaces by allowing windows to be composed of smaller, coordinated parts under a single containment hierarchy.