joystick_init(3) Svgalib User Manual joystick_init(3)NAMEjoystick_init - open a joystick
SYNOPSIS
#include <vgajoystick.h>
typedef void (*__joystick_output) (const char *msg);
int joystick_init(int joydev, __joystick_output jo);
DESCRIPTION
This function opens a joystick device. A negative value is returned on
failure, otherwise the joystick was initialized. svgalib(7) supports
several joysticks. The corresponding device node names can be config‐
ured in libvga.config(5).
The joydev parameter indicates which joystick is to be initialized. As
of this writing svgalib support up to four joysticks joydev = 0 to joy‐
dev = 3, although I'm not aware of hardware and kernel drivers which
handle more than joysticks 0 and 1.
It is strongly encouraged that your program allows the user to cali‐
brate the joystick. This is controlled by the jo parameter. If it is
NULL, no calibration is performed. Otherwise, calibration is performed
and instructions are printed to the user by calling the user supplied
jo function. It is the responsibility of this function to print the NUL
and NL terminated message pointed to by msg to the user. The message
might contain embedded NL characters and will not extend 256 characters
including the terminating NUL.
Usually an fputs(msg, stdout); followed by fflush(stdout); will do, but
for your convenience you can perform the same by passing JOY_CALIB_STD‐
OUT for jo. gl_printf(3) is well suited for this job as well. However,
it needs some font setup first, so we do not provide a special pre‐
processor constant.
It is valid to initialize an already initialized joystick. This allows
you to recalibrate the joystick at any time. The module supports older
version 0.* as well as newer version 1.* joystick device protocols.
GENERAL CONCEPT
The joystick module is basically independent from the rest of svgalib.
You can easily use it in text mode only (but why would you do that?).
If used in a graphics mode, however, it will release the joystick
devices upon a VC switch s.t. several applications can share joysticks.
Unfortunately this does not work during joystick calibration. There‐
fore, you should lock the VC with vga_lockvc(3) while calibrating in
graphics mode.
Also, when using joysticks in textmode only, svgalib won't detect VC
switches and joysticks cannot be shared among applications.
joystick_close(3) releases opened joysticks.
joystick_update(3) queries the joysticks for position changes. Note
that you must busy wait for joystick events. At least the older ver‐
sion 0.* joystick devices do not allow to sleep and get informed about
new joystick events. Basically, this is a PC hardware issue in the
first place. Therefore, vga_waitevent(3) does not know about joysticks.
To use it, you must make it timeout after a few ms and actively query
the joystick for updates.
By default a handler deals with the joystick events. joy‐
stick_getaxis(3) and joystick_getbutton(3) plus several convenience
macros joystick_button1|2|3|4, joystick_getb1|2|3|4, joystick_x|y|z,
and joystick_getx|y|z allow to query the current status of the joystick
(as it was determined during the last joystick_update() call).
The functions joystick_getnumaxes(3) and joystick_getnumbuttons(3)
query the number of axes and buttons of a joystick.
Finally, you can (un)register an own handler for the joystick events
with joystick_sethandler(3) and joystick_setdefaulthandler(3)
The simple text demo joytest(6) and the more complex graphical
mjoytest(6) demo show the use of the joystick package in some more
detail.
CAVEATS
This function is only available in ELF versions of svgalib. Due to
backwards compatibility issues it cannot be used with shared a.out
libs.
Certain game ports seem to be unable to detect missing joysticks prop‐
erly. (This might also be a linux device driver issue). Anyway, is
using the joystick interface, allow a user of your application to spec‐
ify the number of joysticks to be used as well as to bail out the joy‐
stick calibration (when he is not able to press a button on a missing
joystick).
Usually <Ctrl>-C works, but you should not rely too much on it, as it
can be disabled. As a general guideline, maybe try to open and cali‐
brate joysticks while still in textmode. <Ctrl>-C will usually still
work then. If this succeeds, you may assume a joystick is there for any
following recalibrations in graphics mode.
SEE ALSOsvgalib(7), vgagl(7), libvga.config(5), joytest(6), mjoytest(6), joy‐
stick_close(3), joystick_update(3), joystick_sethandler(3), joy‐
stick_setdefaulthandler(3), joystick_getnumaxes(3), joystick_getnumbut‐
tons(3), joystick_getaxis(3), joystick_getbutton(3), joystick_but‐
ton1(3), joystick_getb1(3), joystick_x(3), joystick_getx(3).
AUTHOR
The svgalib joystick handler was mostly done by Daniel Engstr\"om
<daniel.engstrom@riksnett.no>. Multiple joystick, VC switching support
and code to glue it into svgalib by Michael Weller <eowmob@exp-
math.uni-essen.de>. Part of the code is based on code from C. Smith and
Vojtech Pavlik.
Svgalib 1.3.0 14 April 1998 joystick_init(3)
