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Svgalib 1.3.0
14 April 1998


Development tools for the SVGAlib graphics library


joystick_init - open a joystick


#include <vgajoystick.h>
typedef void (*__joystick_output) (const char *msg);
int joystick_init(int joydev, __joystick_output jo);


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 configured 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 joydev = 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 calibrate 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_STDOUT 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 preprocessor 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.


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. Therefore, 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 version 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. joystick_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.


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 properly. (This might also be a linux device driver issue). Anyway, is using the joystick interface, allow a user of your application to specify the number of joysticks to be used as well as to bail out the joystick 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 calibrate 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.


svgalib(7), vgagl(7), libvga.config(5), joytest(6), mjoytest(6), joystick_close(3), joystick_update(3), joystick_sethandler(3), joystick_setdefaulthandler(3), joystick_getnumaxes(3), joystick_getnumbuttons(3), joystick_getaxis(3), joystick_getbutton(3), joystick_button1(3), joystick_getb1(3), joystick_x(3), joystick_getx(3).


The svgalib joystick handler was mostly done by Daniel Engstr\"om <>. Multiple joystick, VC switching support and code to glue it into svgalib by Michael Weller <>. Part of the code is based on code from C. Smith and Vojtech Pavlik.
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