AWAIT_RETRACE(3G)

NAME

await_retrace − wait 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);

DESCRIPTION

INPUT PARAMETER

fildes 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 from the lower-right corner of the display to the upper-left corner. Vertical blanking time is device dependent, ranging from 1 ms to 0.1 ms on current devices. During vertical blanking, any needed changes to the frame buffer, control registers, or color map (such as when double-buffering) do not appear on the CRT, and thus do not produce any flicker and/or picture distortion.

It should also be noted that the await_retrace procedure may wait up to one full retrace cycle, (1/60 second on most displays). This procedure should only be used when making changes that can be completed in a very short time and which are not done more often than 1/60th of a second, such as when performing double buffering or cursor dragging. This procedure should not be used between primitives when drawing a picture because it can slow processing speeds considerably with no visible improvement in the display.

The display_enable command calls await_retrace before changing its state.

Some devices may not support this procedure.

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