vga_waitevent

Section: Svgalib User Manual (3)
Updated: 27 July 1997
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NAME

vga_waitevent - wait for various I/O events

SYNOPSIS

#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>
#include <vga.h>

int vga_waitevent(int which, fd_set *input, fd_set *output , fd_set *except, struct timeval *timeout)

DESCRIPTION

This is the only function allowing you to wait for keyboard AND mouse events. It is based on the select(2) library function, so for deep understanding of vga_waitevent() look at select(2) as well.

which can be 0 or logical ored together from VGA_MOUSEEVENT and VGA_KEYEVENT. If you are interested in waiting for file descriptors having input available or being ready for new write data or being in an exceptional condition (urgent data arrived on a TCP stream) set the corresponding bits in the fd_set structures passed (see select(3)). If you want vga_waitevent() to return after a timeout value pass a struct timeval with the desired value. If you are not interested in the corresponding events you may pass NULL for any of the pointers.

If NULL is passed for timeout vga_waitevent() will not time out but block until any of the other events occurs. If the integer returned is < 0 an error occurred. Check the global variable errno for details. If a value >= 0 is returned it is a bitmask constructed using VGA_MOUSEEVENT and VGA_KEYEVENT to show which of these events occured.

If any of these two occured the appropriate update functions are already called by vga_waitevent().vga_waitevent() operates in raw as well as non-raw keyboard mode. In the latter case use vga_getch(3) not vga_getkey(3) to read the newly arrived keys.

Any of the file related conditions being met will be signalled by setting exactly the bits for files that met the conditions in the corresponding fd_set structures. If a non-NULL timeout is passed the remaining time is written into it on return. If it is 0 a timeout occured. (again: cf. select(2)) Therefore, depending on context, vga_waitkey(3) may return 0 if only special, non svgalib, events occured.

EXAMPLES

If you want to wait blocking for a keypress OR a mouse event use: vga_waitevent(VGA_MOUSEEVENT | VGA_KEYEVENT, NULL, NULL, NULL, NULL);

If you want to wait for a keypress OR a mouse event but non-blocking use:

#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>
#include <vga.h>

struct timeval timeout;
timeout.tv_sec = 0;
timeout.tv_usec = 0;
vga_waitevent(VGA_MOUSEEVENT | VGA_KEYEVENT, NULL, NULL, NULL, &timeout);

You could do a similar thing by just calling

mouse_update();
keyboard_update();

though. There is no such counterpart for the first example.

Finally, there is a very nice eventtest(6) demo showing most capabilities of vga_waitevent().

BUGS

This function was introduced in 1.2.10. Unfortunately there was a typo in the first implementation which broke the case where input was NULL. Though fixed in 1.2.11 for optimal portability pass an empty fd_set instead of NULL as first argument.

When not running in background mode, that is, the svgalib applcation is suspended while the VC is switched away, it seems vga_waitevent gets stuck and does no longer timeout. It is not clear if this is an svgalib bug, kernel bug or general problem.

AUTHOR

This manual page was edited by Michael Weller <eowmob@exp-math.uni-essen.de>. The exact source of the referenced function as well as of the original documentation is unknown.

It is very likely that both are at least to some extent are due to Harm Hanemaayer <H.Hanemaayer@inter.nl.net>.

Occasionally this might be wrong. I hereby asked to be excused by the original author and will happily accept any additions or corrections to this first version of the svgalib manual.

This document was created by man2html, using the manual pages.
Time: 02:49:05 GMT, April 19, 2024