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Symbian Developer Library

SYMBIAN OS V9.4

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Drawing and redrawing

The window server maintains the screen display taking into account the region, ordinal position, visibility and shadow requirements of all displayable windows. The display may be updated for several reasons:

All window server applications must be able to perform application-initiated drawing. Most also need to handle redraws due to regions of their windows becoming invalid.

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Application-initiated drawing

When an application model changes, as a result of a user command or some other reason, it may be necessary for that application to update the display. In this case, the application initiates a draw sequence to one or more of its windows. When this draw sequence has finished on a particular window, that window will be a valid reflection of the model.

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Window server-initiated redrawing

When a window is moved, resized, or otherwise manipulated by an application, it may cause parts of other windows to become invalid so that they must be redrawn. The window server maintains a list of all invalid regions and causes them to be redrawn in one of several ways:

This latter case requires the application to redraw the region of the RWindow that is now invalid. All applications which use RWindows must be able to redraw reliably.