Important: The information in this document is obsolete and should not be used for new development.
DoVBLTask
Slot interrupt handlers for video cards should call theDoVBLTask
function to handle the execution of VBL tasks.
FUNCTION DoVBLTask (theSlot: Integer): OSErr;
theSlot
- Slot number corresponding to the vertical retrace queue whose tasks are to be executed.
DESCRIPTION
TheDoVBLTask
function decrements thevblCount
field of each task in the vertical retrace queue corresponding to thetheSlot
parameter (except for tasks whosevblCount
field already contains the value 0). The function executes a task if decrementing thevblCount
field for a task record results in a value of 0.If
theSlot
designates the slot of the primary video device, the position of the cursor is also updated.Slot interrupt handlers for video cards need to call this function to execute any tasks in the queue for that slot. You can also call this function if you need to simulate vertical retrace interrupts.
ASSEMBLY-LANGUAGE INFORMATION
The registers on entry and exit forDoVBLTask
are
Registers on entry D0 Slot number
Registers on exit D0 Result code To reduce overhead at interrupt time, instead of executing the
_DoVBLTask
trap, you can load the jump vectorjDoVBLTask
into an address register and execute aJSR
instruction using that register.RESULT CODES
noErr 0 No error slotNumErr -360 Invalid slot number