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The Filter Manager Introduction
Programmer's Reference Manuals
» Part 7 - The Desktop
» The Filter Manager
» Introduction
The Filter Manager provides applications with the facility to register pre and post-filters. Filters are useful when a task needs to intercept events that may or may not be under the control of the task.
Filters do not need to be applied to a specific task as they can be assigned to respond to all tasks. Each filter is a routine that must have well defined entry and exit conditions.
Pre-Filters
A pre-filter is so-called because it is assigned to be called before a task calls Wimp_Poll. With a pre-filter, the event mask the task passes to Wimp_Poll can also be changed.
Post-Filters
A post-filter is so-called because it is assigned to be called just before the Wimp returns control back to a task. The reason-code and data-block returned by Wimp_Poll can be modified if required before they are passed back to a task.