SDL_syshaptic.c

/*
    SDL - Simple DirectMedia Layer
    Copyright (C) 2008 Edgar Simo

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2.1 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public
    License along with this library; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

    Sam Lantinga
    slouken@libsdl.org
*/
#include "SDL_config.h"

#ifdef SDL_HAPTIC_LINUX

#include "SDL_haptic.h"
#include "../SDL_syshaptic.h"
#include "SDL_joystick.h"
#include "../../joystick/SDL_sysjoystick.h"     /* For the real SDL_Joystick */
#include "../../joystick/linux/SDL_sysjoystick_c.h"     /* For joystick hwdata */

#include <unistd.h>             /* close */
#include <linux/input.h>        /* Force feedback linux stuff. */
#include <fcntl.h>              /* O_RDWR */
#include <limits.h>             /* INT_MAX */
#include <errno.h>              /* errno, strerror */
#include <math.h>               /* atan2 */

/* Just in case. */
#ifndef M_PI
#  define M_PI     3.14159265358979323846
#endif


#define MAX_HAPTICS  32         /* It's doubtful someone has more then 32 evdev */


/*
 * List of available haptic devices.
 */
static struct
{
    char *fname;                /* Dev path name (like /dev/input/event1) */
    SDL_Haptic *haptic;         /* Assosciated haptic. */
} SDL_hapticlist[MAX_HAPTICS];


/*
 * Haptic system hardware data.
 */
struct haptic_hwdata
{
    int fd;                     /* File descriptor of the device. */
    char *fname;                /* Points to the name in SDL_hapticlist. */
};


/*
 * Haptic system effect data.
 */
struct haptic_hweffect
{
    struct ff_effect effect;    /* The linux kernel effect structure. */
};



#define test_bit(nr, addr) \
   (((1UL << ((nr) & 31)) & (((const unsigned int *) addr)[(nr) >> 5])) != 0)
#define EV_TEST(ev,f) \
   if (test_bit((ev), features)) ret |= (f);
/*
 * Test whether a device has haptic properties.
 * Returns available properties or 0 if there are none.
 */
static int
EV_IsHaptic(int fd)
{
    unsigned int ret;
    unsigned long features[1 + FF_MAX / sizeof(unsigned long)];

    /* Ask device for what it has. */
    ret = 0;
    if (ioctl(fd, EVIOCGBIT(EV_FF, sizeof(features)), features) < 0) {
        SDL_SetError("Haptic: Unable to get device's features: %s",
                     strerror(errno));
        return -1;
    }

    /* Convert supported features to SDL_HAPTIC platform-neutral features. */
    EV_TEST(FF_CONSTANT, SDL_HAPTIC_CONSTANT);
    EV_TEST(FF_SINE, SDL_HAPTIC_SINE);
    EV_TEST(FF_SQUARE, SDL_HAPTIC_SQUARE);
    EV_TEST(FF_TRIANGLE, SDL_HAPTIC_TRIANGLE);
    EV_TEST(FF_SAW_UP, SDL_HAPTIC_SAWTOOTHUP);
    EV_TEST(FF_SAW_DOWN, SDL_HAPTIC_SAWTOOTHDOWN);
    EV_TEST(FF_RAMP, SDL_HAPTIC_RAMP);
    EV_TEST(FF_SPRING, SDL_HAPTIC_SPRING);
    EV_TEST(FF_FRICTION, SDL_HAPTIC_FRICTION);
    EV_TEST(FF_DAMPER, SDL_HAPTIC_DAMPER);
    EV_TEST(FF_INERTIA, SDL_HAPTIC_INERTIA);
    EV_TEST(FF_CUSTOM, SDL_HAPTIC_CUSTOM);
    EV_TEST(FF_GAIN, SDL_HAPTIC_GAIN);
    EV_TEST(FF_AUTOCENTER, SDL_HAPTIC_AUTOCENTER);

    /* Return what it supports. */
    return ret;
}


/*
 * Tests whether a device is a mouse or not.
 */
static int
EV_IsMouse(int fd)
{
    unsigned long argp[40];

    /* Ask for supported features. */
    if (ioctl(fd, EVIOCGBIT(EV_KEY, sizeof(argp)), argp) < 0) {
        return -1;
    }

    /* Currently we only test for BTN_MOUSE which can give fake positives. */
    if (test_bit(BTN_MOUSE, argp) != 0) {
        return 1;
    }

    return 0;
}

/*
 * Initializes the haptic subsystem by finding available devices.
 */
int
SDL_SYS_HapticInit(void)
{
    const char joydev_pattern[] = "/dev/input/event%d";
    dev_t dev_nums[MAX_HAPTICS];
    char path[PATH_MAX];
    struct stat sb;
    int fd;
    int i, j, k;
    int duplicate;
    int numhaptics;

    numhaptics = 0;

    /* 
     * Limit amount of checks to MAX_HAPTICS since we may or may not have
     * permission to some or all devices.
     */
    i = 0;
    for (j = 0; j < MAX_HAPTICS; ++j) {

        snprintf(path, PATH_MAX, joydev_pattern, i++);

        /* check to see if file exists */
        if (stat(path, &sb) != 0)
            break;

        /* check for duplicates */
        duplicate = 0;
        for (k = 0; (k < numhaptics) && !duplicate; ++k) {
            if (sb.st_rdev == dev_nums[k]) {
                duplicate = 1;
            }
        }
        if (duplicate) {
            continue;
        }

        /* try to open */
        fd = open(path, O_RDWR, 0);
        if (fd < 0)
            continue;

#ifdef DEBUG_INPUT_EVENTS
        printf("Checking %s\n", path);
#endif

        /* see if it works */
        if (EV_IsHaptic(fd) > 0) {
            SDL_hapticlist[numhaptics].fname = SDL_strdup(path);
            SDL_hapticlist[numhaptics].haptic = NULL;
            dev_nums[numhaptics] = sb.st_rdev;
            ++numhaptics;
        }
        close(fd);
    }

    return numhaptics;
}


/*
 * Gets the name from a file descriptor.
 */
static const char *
SDL_SYS_HapticNameFromFD(int fd)
{
    static char namebuf[128];

    /* We use the evdev name ioctl. */
    if (ioctl(fd, EVIOCGNAME(sizeof(namebuf)), namebuf) <= 0) {
        return NULL;
    }

    return namebuf;
}


/*
 * Return the name of a haptic device, does not need to be opened.
 */
const char *
SDL_SYS_HapticName(int index)
{
    int fd;
    const char *name;

    /* Open the haptic device. */
    name = NULL;
    fd = open(SDL_hapticlist[index].fname, O_RDONLY, 0);

    if (fd >= 0) {

        name = SDL_SYS_HapticNameFromFD(fd);
        if (name == NULL) {
            /* No name found, return device character device */
            name = SDL_hapticlist[index].fname;
        }
    }
    close(fd);

    return name;
}


/*
 * Opens the haptic device from the file descriptor.
 */
static int
SDL_SYS_HapticOpenFromFD(SDL_Haptic * haptic, int fd)
{
    const char *name;

    /* Allocate the hwdata */
    haptic->hwdata = (struct haptic_hwdata *)
        SDL_malloc(sizeof(*haptic->hwdata));
    if (haptic->hwdata == NULL) {
        SDL_OutOfMemory();
        goto open_err;
    }
    SDL_memset(haptic->hwdata, 0, sizeof(*haptic->hwdata));

    /* Set the data. */
    haptic->hwdata->fd = fd;
    haptic->supported = EV_IsHaptic(fd);
    haptic->naxes = 2;          /* Hardcoded for now, not sure if it's possible to find out. */

    /* Set the effects */
    if (ioctl(fd, EVIOCGEFFECTS, &haptic->neffects) < 0) {
        SDL_SetError("Haptic: Unable to query device memory: %s",
                     strerror(errno));
        goto open_err;
    }
    haptic->nplaying = haptic->neffects;        /* Linux makes no distinction. */
    haptic->effects = (struct haptic_effect *)
        SDL_malloc(sizeof(struct haptic_effect) * haptic->neffects);
    if (haptic->effects == NULL) {
        SDL_OutOfMemory();
        goto open_err;
    }
    /* Clear the memory */
    SDL_memset(haptic->effects, 0,
               sizeof(struct haptic_effect) * haptic->neffects);

    return 0;

    /* Error handling */
  open_err:
    close(fd);
    if (haptic->hwdata != NULL) {
        free(haptic->hwdata);
        haptic->hwdata = NULL;
    }
    return -1;
}


/*
 * Opens a haptic device for usage.
 */
int
SDL_SYS_HapticOpen(SDL_Haptic * haptic)
{
    int fd;
    int ret;

    /* Open the character device */
    fd = open(SDL_hapticlist[haptic->index].fname, O_RDWR, 0);
    if (fd < 0) {
        SDL_SetError("Haptic: Unable to open %s: %s",
                     SDL_hapticlist[haptic->index], strerror(errno));
        return -1;
    }

    /* Try to create the haptic. */
    ret = SDL_SYS_HapticOpenFromFD(haptic, fd); /* Already closes on error. */
    if (ret < 0) {
        return -1;
    }

    /* Set the fname. */
    haptic->hwdata->fname = SDL_hapticlist[haptic->index].fname;
    return 0;
}


/*
 * Opens a haptic device from first mouse it finds for usage.
 */
int
SDL_SYS_HapticMouse(void)
{
    int fd;
    int i;

    for (i = 0; i < SDL_numhaptics; i++) {

        /* Open the device. */
        fd = open(SDL_hapticlist[i].fname, O_RDWR, 0);
        if (fd < 0) {
            SDL_SetError("Haptic: Unable to open %s: %s",
                         SDL_hapticlist[i], strerror(errno));
            return -1;
        }

        /* Is it a mouse? */
        if (EV_IsMouse(fd)) {
            close(fd);
            return i;
        }

        close(fd);
    }

    return -1;
}


/*
 * Checks to see if a joystick has haptic features.
 */
int
SDL_SYS_JoystickIsHaptic(SDL_Joystick * joystick)
{
    return EV_IsHaptic(joystick->hwdata->fd);
}


/*
 * Checks to see if the haptic device and joystick and in reality the same.
 */
int
SDL_SYS_JoystickSameHaptic(SDL_Haptic * haptic, SDL_Joystick * joystick)
{
    /* We are assuming linux is using evdev which should trump the old
     * joystick methods. */
    if (SDL_strcmp(joystick->hwdata->fname, haptic->hwdata->fname) == 0) {
        return 1;
    }
    return 0;
}


/*
 * Opens a SDL_Haptic from a SDL_Joystick.
 */
int
SDL_SYS_HapticOpenFromJoystick(SDL_Haptic * haptic, SDL_Joystick * joystick)
{
    int i;
    int fd;
    int ret;

    /* Find the joystick in the haptic list. */
    for (i = 0; i < MAX_HAPTICS; i++) {
        if (SDL_hapticlist[i].fname != NULL) {
            if (SDL_strcmp(SDL_hapticlist[i].fname, joystick->hwdata->fname)
                == 0) {
                haptic->index = i;
            }
        }
    }

    fd = open(joystick->hwdata->fname, O_RDWR, 0);
    ret = SDL_SYS_HapticOpenFromFD(haptic, fd); /* Already closes on error. */
    if (ret < 0) {
        return -1;
    }

    haptic->hwdata->fname = SDL_hapticlist[haptic->index].fname;
    return 0;
}


/*
 * Closes the haptic device.
 */
void
SDL_SYS_HapticClose(SDL_Haptic * haptic)
{
    if (haptic->hwdata) {

        /* Free effects. */
        SDL_free(haptic->effects);
        haptic->effects = NULL;
        haptic->neffects = 0;

        /* Clean up */
        close(haptic->hwdata->fd);

        /* Free */
        SDL_free(haptic->hwdata);
        haptic->hwdata = NULL;
    }

    /* Clear the rest. */
    SDL_memset(haptic, 0, sizeof(SDL_Haptic));
}


/* 
 * Clean up after system specific haptic stuff
 */
void
SDL_SYS_HapticQuit(void)
{
    int i;

    for (i = 0; SDL_hapticlist[i].fname != NULL; i++) {
        /* Opened and not closed haptics are leaked, this is on purpose.
         * Close your haptic devices after usage. */

        SDL_free(SDL_hapticlist[i].fname);
    }
    SDL_hapticlist[0].fname = NULL;
}


/*
 * Converts an SDL button to a ff_trigger button.
 */
static Uint16
SDL_SYS_ToButton(Uint16 button)
{
    Uint16 ff_button;

    ff_button = 0;

    /*
     * Not sure what the proper syntax is because this actually isn't implemented
     * in the current kernel from what I've seen (2.6.26).
     */
    if (button != 0) {
        ff_button = BTN_GAMEPAD + button - 1;
    }

    return ff_button;
}


/*
 * Returns the ff_effect usable direction from a SDL_HapticDirection.
 */
static Uint16
SDL_SYS_ToDirection(SDL_HapticDirection * dir)
{
    Uint32 tmp;
    float f;                    /* Ideally we'd use fixed point math instead of floats... */

    switch (dir->type) {
    case SDL_HAPTIC_POLAR:
        /* Linux directions are inverted. */
        tmp = (((18000 + dir->dir[0]) % 36000) * 0xFFFF) / 36000;
        return (Uint16) tmp;

    case SDL_HAPTIC_CARTESIAN:
        /* We must invert "x" and "y" to go clockwise. */
        f = atan2(dir->dir[0], dir->dir[1]);
        tmp = (int) (f * 18000. / M_PI) % 36000;
        tmp = (tmp * 0xFFFF) / 36000;
        return (Uint16) tmp;

    case SDL_HAPTIC_SPHERICAL:
        tmp = (36000 - dir->dir[0]) + 27000;    /* Convert to polars */
        tmp = (((18000 + tmp) % 36000) * 0xFFFF) / 36000;
        return (Uint16) tmp;

    default:
        SDL_SetError("Haptic: Unsupported direction type.");
        return (Uint16) - 1;
    }

    return 0;
}


#define  CLAMP(x)    (((x) > 32767) ? 32767 : x)
/*
 * Initializes the linux effect struct from a haptic_effect.
 * Values above 32767 (for unsigned) are unspecified so we must clamp.
 */
static int
SDL_SYS_ToFFEffect(struct ff_effect *dest, SDL_HapticEffect * src)
{
    Uint32 tmp;
    SDL_HapticConstant *constant;
    SDL_HapticPeriodic *periodic;
    SDL_HapticCondition *condition;
    SDL_HapticRamp *ramp;

    /* Clear up */
    SDL_memset(dest, 0, sizeof(struct ff_effect));

    switch (src->type) {
    case SDL_HAPTIC_CONSTANT:
        constant = &src->constant;

        /* Header */
        dest->type = FF_CONSTANT;
        dest->direction = SDL_SYS_ToDirection(&constant->direction);
        if (dest->direction == (Uint16) - 1)
            return -1;

        /* Replay */
        dest->replay.length = (constant->length == SDL_HAPTIC_INFINITY) ?
            0 : CLAMP(constant->length);
        dest->replay.delay = CLAMP(constant->delay);

        /* Trigger */
        dest->trigger.button = SDL_SYS_ToButton(constant->button);
        dest->trigger.interval = CLAMP(constant->interval);

        /* Constant */
        dest->u.constant.level = constant->level;

        /* Envelope */
        dest->u.constant.envelope.attack_length =
            CLAMP(constant->attack_length);
        dest->u.constant.envelope.attack_level =
            CLAMP(constant->attack_level);
        dest->u.constant.envelope.fade_length = CLAMP(constant->fade_length);
        dest->u.constant.envelope.fade_level = CLAMP(constant->fade_level);

        break;

    case SDL_HAPTIC_SINE:
    case SDL_HAPTIC_SQUARE:
    case SDL_HAPTIC_TRIANGLE:
    case SDL_HAPTIC_SAWTOOTHUP:
    case SDL_HAPTIC_SAWTOOTHDOWN:
        periodic = &src->periodic;

        /* Header */
        dest->type = FF_PERIODIC;
        dest->direction = SDL_SYS_ToDirection(&periodic->direction);
        if (dest->direction == (Uint16) - 1)
            return -1;

        /* Replay */
        dest->replay.length = (periodic->length == SDL_HAPTIC_INFINITY) ?
            0 : CLAMP(periodic->length);
        dest->replay.delay = CLAMP(periodic->delay);

        /* Trigger */
        dest->trigger.button = SDL_SYS_ToButton(periodic->button);
        dest->trigger.interval = CLAMP(periodic->interval);

        /* Periodic */
        if (periodic->type == SDL_HAPTIC_SINE)
            dest->u.periodic.waveform = FF_SINE;
        else if (periodic->type == SDL_HAPTIC_SQUARE)
            dest->u.periodic.waveform = FF_SQUARE;
        else if (periodic->type == SDL_HAPTIC_TRIANGLE)
            dest->u.periodic.waveform = FF_TRIANGLE;
        else if (periodic->type == SDL_HAPTIC_SAWTOOTHUP)
            dest->u.periodic.waveform = FF_SAW_UP;
        else if (periodic->type == SDL_HAPTIC_SAWTOOTHDOWN)
            dest->u.periodic.waveform = FF_SAW_DOWN;
        dest->u.periodic.period = CLAMP(periodic->period);
        dest->u.periodic.magnitude = periodic->magnitude;
        dest->u.periodic.offset = periodic->offset;
        /* Phase is calculated based of offset from period and then clamped. */
        tmp = ((periodic->phase % 36000) * dest->u.periodic.period) / 36000;
        dest->u.periodic.phase = CLAMP(tmp);

        /* Envelope */
        dest->u.periodic.envelope.attack_length =
            CLAMP(periodic->attack_length);
        dest->u.periodic.envelope.attack_level =
            CLAMP(periodic->attack_level);
        dest->u.periodic.envelope.fade_length = CLAMP(periodic->fade_length);
        dest->u.periodic.envelope.fade_level = CLAMP(periodic->fade_level);

        break;

    case SDL_HAPTIC_SPRING:
    case SDL_HAPTIC_DAMPER:
    case SDL_HAPTIC_INERTIA:
    case SDL_HAPTIC_FRICTION:
        condition = &src->condition;

        /* Header */
        if (condition->type == SDL_HAPTIC_SPRING)
            dest->type = FF_SPRING;
        else if (condition->type == SDL_HAPTIC_DAMPER)
            dest->type = FF_DAMPER;
        else if (condition->type == SDL_HAPTIC_INERTIA)
            dest->type = FF_INERTIA;
        else if (condition->type == SDL_HAPTIC_FRICTION)
            dest->type = FF_FRICTION;
        dest->direction = 0;    /* Handled by the condition-specifics. */

        /* Replay */
        dest->replay.length = (condition->length == SDL_HAPTIC_INFINITY) ?
            0 : CLAMP(condition->length);
        dest->replay.delay = CLAMP(condition->delay);

        /* Trigger */
        dest->trigger.button = SDL_SYS_ToButton(condition->button);
        dest->trigger.interval = CLAMP(condition->interval);

        /* Condition */
        /* X axis */
        dest->u.condition[0].right_saturation =
            CLAMP(condition->right_sat[0]);
        dest->u.condition[0].left_saturation = CLAMP(condition->left_sat[0]);
        dest->u.condition[0].right_coeff = condition->right_coeff[0];
        dest->u.condition[0].left_coeff = condition->left_coeff[0];
        dest->u.condition[0].deadband = CLAMP(condition->deadband[0]);
        dest->u.condition[0].center = condition->center[0];
        /* Y axis */
        dest->u.condition[1].right_saturation =
            CLAMP(condition->right_sat[1]);
        dest->u.condition[1].left_saturation = CLAMP(condition->left_sat[1]);
        dest->u.condition[1].right_coeff = condition->right_coeff[1];
        dest->u.condition[1].left_coeff = condition->left_coeff[1];
        dest->u.condition[1].deadband = CLAMP(condition->deadband[1]);
        dest->u.condition[1].center = condition->center[1];

        /*
         * There is no envelope in the linux force feedback api for conditions.
         */

        break;

    case SDL_HAPTIC_RAMP:
        ramp = &src->ramp;

        /* Header */
        dest->type = FF_RAMP;
        dest->direction = SDL_SYS_ToDirection(&ramp->direction);
        if (dest->direction == (Uint16) - 1)
            return -1;

        /* Replay */
        dest->replay.length = (ramp->length == SDL_HAPTIC_INFINITY) ?
            0 : CLAMP(ramp->length);
        dest->replay.delay = CLAMP(ramp->delay);

        /* Trigger */
        dest->trigger.button = SDL_SYS_ToButton(ramp->button);
        dest->trigger.interval = CLAMP(ramp->interval);

        /* Ramp */
        dest->u.ramp.start_level = ramp->start;
        dest->u.ramp.end_level = ramp->end;

        /* Envelope */
        dest->u.ramp.envelope.attack_length = CLAMP(ramp->attack_length);
        dest->u.ramp.envelope.attack_level = CLAMP(ramp->attack_level);
        dest->u.ramp.envelope.fade_length = CLAMP(ramp->fade_length);
        dest->u.ramp.envelope.fade_level = CLAMP(ramp->fade_level);

        break;


    default:
        SDL_SetError("Haptic: Unknown effect type.");
        return -1;
    }

    return 0;
}


/*
 * Creates a new haptic effect.
 */
int
SDL_SYS_HapticNewEffect(SDL_Haptic * haptic, struct haptic_effect *effect,
                        SDL_HapticEffect * base)
{
    struct ff_effect *linux_effect;

    /* Allocate the hardware effect */
    effect->hweffect = (struct haptic_hweffect *)
        SDL_malloc(sizeof(struct haptic_hweffect));
    if (effect->hweffect == NULL) {
        SDL_OutOfMemory();
        return -1;
    }

    /* Prepare the ff_effect */
    linux_effect = &effect->hweffect->effect;
    if (SDL_SYS_ToFFEffect(linux_effect, base) != 0) {
        goto new_effect_err;
    }
    linux_effect->id = -1;      /* Have the kernel give it an id */

    /* Upload the effect */
    if (ioctl(haptic->hwdata->fd, EVIOCSFF, linux_effect) < 0) {
        SDL_SetError("Haptic: Error uploading effect to the device: %s",
                     strerror(errno));
        goto new_effect_err;
    }

    return 0;

  new_effect_err:
    free(effect->hweffect);
    effect->hweffect = NULL;
    return -1;
}


/*
 * Updates an effect.
 *
 * Note: Dynamically updating the direction can in some cases force
 * the effect to restart and run once.
 */
int
SDL_SYS_HapticUpdateEffect(SDL_Haptic * haptic,
                           struct haptic_effect *effect,
                           SDL_HapticEffect * data)
{
    struct ff_effect linux_effect;

    /* Create the new effect */
    if (SDL_SYS_ToFFEffect(&linux_effect, data) != 0) {
        return -1;
    }
    linux_effect.id = effect->hweffect->effect.id;

    /* See if it can be uploaded. */
    if (ioctl(haptic->hwdata->fd, EVIOCSFF, &linux_effect) < 0) {
        SDL_SetError("Haptic: Error updating the effect: %s",
                     strerror(errno));
        return -1;
    }

    /* Copy the new effect into memory. */
    SDL_memcpy(&effect->hweffect->effect, &linux_effect,
               sizeof(struct ff_effect));

    return effect->hweffect->effect.id;
}


/*
 * Runs an effect.
 */
int
SDL_SYS_HapticRunEffect(SDL_Haptic * haptic, struct haptic_effect *effect,
                        Uint32 iterations)
{
    struct input_event run;

    /* Prepare to run the effect */
    run.type = EV_FF;
    run.code = effect->hweffect->effect.id;
    /* We don't actually have infinity here, so we just do INT_MAX which is pretty damn close. */
    run.value = (iterations > INT_MAX) ? INT_MAX : iterations;

    if (write(haptic->hwdata->fd, (const void *) &run, sizeof(run)) < 0) {
        SDL_SetError("Haptic: Unable to run the effect: %s", strerror(errno));
        return -1;
    }

    return 0;
}


/*
 * Stops an effect.
 */
int
SDL_SYS_HapticStopEffect(SDL_Haptic * haptic, struct haptic_effect *effect)
{
    struct input_event stop;

    stop.type = EV_FF;
    stop.code = effect->hweffect->effect.id;
    stop.value = 0;

    if (write(haptic->hwdata->fd, (const void *) &stop, sizeof(stop)) < 0) {
        SDL_SetError("Haptic: Unable to stop the effect: %s",
                     strerror(errno));
        return -1;
    }

    return 0;
}


/*
 * Frees the effect.
 */
void
SDL_SYS_HapticDestroyEffect(SDL_Haptic * haptic, struct haptic_effect *effect)
{
    if (ioctl(haptic->hwdata->fd, EVIOCRMFF, effect->hweffect->effect.id) < 0) {
        SDL_SetError("Haptic: Error removing the effect from the device: %s",
                     strerror(errno));
    }
    SDL_free(effect->hweffect);
    effect->hweffect = NULL;
}


/*
 * Gets the status of a haptic effect.
 */
int
SDL_SYS_HapticGetEffectStatus(SDL_Haptic * haptic,
                              struct haptic_effect *effect)
{
#if 0                           /* Not supported atm. */
    struct input_event ie;

    ie.type = EV_FF;
    ie.type = EV_FF_STATUS;
    ie.code = effect->hweffect->effect.id;

    if (write(haptic->hwdata->fd, &ie, sizeof(ie)) < 0) {
        SDL_SetError("Haptic: Error getting device status.");
        return -1;
    }

    return 0;
#endif

    return -1;
}


/*
 * Sets the gain.
 */
int
SDL_SYS_HapticSetGain(SDL_Haptic * haptic, int gain)
{
    struct input_event ie;

    ie.type = EV_FF;
    ie.code = FF_GAIN;
    ie.value = (0xFFFFUL * gain) / 100;

    if (write(haptic->hwdata->fd, &ie, sizeof(ie)) < 0) {
        SDL_SetError("Haptic: Error setting gain: %s", strerror(errno));
        return -1;
    }

    return 0;
}


/*
 * Sets the autocentering.
 */
int
SDL_SYS_HapticSetAutocenter(SDL_Haptic * haptic, int autocenter)
{
    struct input_event ie;

    ie.type = EV_FF;
    ie.code = FF_AUTOCENTER;
    ie.value = (0xFFFFUL * autocenter) / 100;

    if (write(haptic->hwdata->fd, &ie, sizeof(ie)) < 0) {
        SDL_SetError("Haptic: Error setting autocenter: %s", strerror(errno));
        return -1;
    }

    return 0;
}


/*
 * Pausing is not supported atm by linux.
 */
int
SDL_SYS_HapticPause(SDL_Haptic * haptic)
{
    return -1;
}


/*
 * Unpausing is not supported atm by linux.
 */
int
SDL_SYS_HapticUnpause(SDL_Haptic * haptic)
{
    return -1;
}


/*
 * Stops all the currently playing effects.
 */
int
SDL_SYS_HapticStopAll(SDL_Haptic * haptic)
{
    int i, ret;

    /* Linux does not support this natively so we have to loop. */
    for (i = 0; i < haptic->neffects; i++) {
        if (haptic->effects[i].hweffect != NULL) {
            ret = SDL_SYS_HapticStopEffect(haptic, &haptic->effects[i]);
            if (ret < 0) {
                SDL_SetError
                    ("Haptic: Error while trying to stop all playing effects.");
                return -1;
            }
        }
    }
    return 0;
}


#endif /* SDL_HAPTIC_LINUX */