.TH vga_waitevent 3 "27 July 1997" "Svgalib (>= 1.2.11)" "Svgalib User Manual"
.SH NAME
vga_waitevent \- wait for various I/O events
.SH SYNOPSIS

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

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

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

.I which
can be 0 or logical ored together from
.BR 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
.B fd_set
structures passed (see
.BR select (3)).
If you want
.B vga_waitevent()
to return after a timeout value pass a
.B struct timeval
with the desired value. If you are not interested in the
corresponding events you may pass
.B NULL
for any of the pointers.

If
.B NULL
is passed for
.IB "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
.B errno
for details. If a value >= 0 is returned it is a bitmask constructed using
.BR 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
.BR vga_waitevent() . vga_waitevent()
operates in raw as well as non-raw keyboard
mode. In the latter case use
.BR vga_getch (3)
not
.BR 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
.B fd_set
structures. If a
.RB non- NULL
.I timeout
is passed the remaining time is written into it on return.
If it is 0 a timeout occured. (again: cf.
.BR select (2))
Therefore, depending on context,
.BR vga_waitkey (3)
may return 0 if only special, non svgalib, events occured.

.SH EXAMPLES
If you want to wait blocking for a keypress OR a mouse event use:
.B 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:

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

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

You could do a similar thing by just calling

.B mouse_update();
.br
.B keyboard_update();

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

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

.SH BUGS
This function was introduced in 1.2.10. Unfortunately there was a typo in the first
implementation which broke the case where
.I input
was
.BR NULL .
Though fixed in 1.2.11 for optimal portability pass an empty
.B fd_set
instead of
.B 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
.B vga_waitevent
gets stuck and does no longer timeout. It is not clear if this is an svgalib bug, kernel
bug or general problem.

.SH SEE ALSO

.BR svgalib (7),
.BR vgagl (7),
.BR libvga.config (5),
.BR eventtest (6),
.BR mouse_getposition_6d (3),
.BR mouse_getx (3),
.BR mouse_update (3),
.BR mouse_waitforupdate (3),
.BR vga_getkey (3),
.BR vga_getch (3)

.SH 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.