Inside Macintosh: Processes

Chapter 4 - Vertical Retrace Manager

Using the Vertical Retrace Manager

You can use the Vertical Retrace Manager to install VBL task records in and remove VBL task records from system-based or slot-based vertical retrace queues. To install a task record, you must first fill in some of its fields and then call either VInstall or SlotVInstall. See the next section, "Installing a VBL Task," for information on installing VBL tasks.

If it is to be executed more than once, a VBL task must access the task record and reset the value of the task record's vblCount field. The section "Accessing a Task Record at Interrupt Time" on page 4-12 describes this technique. To disable a task temporarily, you can simply set the vblCount field of its task record to 0. To remove a VBL task from its VBL queue, call VRemove if you installed the task by calling VInstall or call SlotVRemove if you installed the task by calling SlotVInstall.

If your VBL task needs to access your application global variables, you can put the application's A5 value or the global variables themselves into the second field of a record whose first field contains the VBL task itself. The sections "Accessing Application Global Variables in a VBL Task," beginning on page 4-13, and "Spinning the Cursor," beginning on page 4-16, explain these techniques.

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Subtopics

Installing a VBL Task

Accessing a Task Record at Interrupt Time

Accessing Application Global Variables in a VBL Task

Spinning the Cursor

Installing a Persistent VBL Task