Delete me: The Filter Manager Introduction (Rev #2, changes)

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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 after to Wimp_Poll, be but called just before it the Wimp returns control back to a task. The reason reason-code code and data data-block block returned by Wimp_Poll can be modified if required before it they is are passed back to a task, task. or alternatively suppressed altogether.