AWAIT_RETRACE(3G)

NAME

await_retrace − waits for vertical retrace on raster scanning devices.

SYNOPSIS

C SYNTAX

void await_retrace(fildes);
int fildes;

FORTRAN77 SYNTAX

subroutine await_retrace(fildes)
integer*4 fildes

PASCAL SYNTAX

procedure await_retrace(fildes:integer);

HP-UX COMPATIBILITY

Level: HP-UX/STANDARD

Origin: HP

DESCRIPTION

INPUT PARAMETER

fildes
is an integer file descriptor returned by gopen when an I/O path to a graphics device is opened.

DISCUSSION

Await_retrace waits in a busy loop until vertical blanking begins on raster scan CRT devices. Vertical blanking is the part of the retrace cycle when the electron beam is turned off and moved form the lower right corner of the display to the upper left corner. This time is very device dependent, however on current devices it ranges from 1 ms to 0.1 ms. During this time, any changes to the frame buffer, control registers, or color map will not be seen on the CRT. This makes it possible to make changes, such as needed when double buffering, to the frame buffer, control registers, or color map without getting any flicker and/or picture distortion.

It should also be noted that the await_retrace procedure may wait up to one full retrace cycle, on most displays this is 1/60th of a second. This procedure should only be used when making changes which can be done in a small amount of time, and are not done more often then 1/60th of a second, such as double buffering or cursor dragging. This procedure should not be used between primitives when drawing a picture, since it may have a very negative performance penalty and make no visible improvement in the display.

The display_enable command calls await_retrace before changing it’s state.

Some devices may not support this operation.

Museum

Related Articles