1.1 Basic elements and data structures

1.1.5 The viewport hierarchy

All viewports and windows, including those created by the Window Tool Kit, are present in the viewport hierarchy. The root of the viewport hierarchy is the root viewport. The viewport hierarchy controls how viewports and windows overlap on the screen. A viewport or window can be the parent, child, or sibling of another viewport or window, and vice versa.

Certain functions allow you to manipulate the hierarchy and the relationships that exist between individual viewports. You can send character and graphics images to viewports or windows that are hidden by other viewports or windows, just as you can to any viewport or bitmap that is not visible on the screen. However, the changes to the bits on the viewport's bitmap remain invisible until the viewport is exposed by some means.

Note: The root viewport is not like other viewports and windows in that it does not have an associated bitmap, so no graphics operations can be performed on it. If you want to simulate graphics output on the root viewport, create a viewport that occludes the root viewport area and perform graphics operations on that viewport. See Chapter 2, "Bitmaps, Viewports, and Windows" for details on creating, moving, and reshaping bitmaps, viewports, and windows.

The Window Tool Kit - 9 SEP 1996

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