src/haptic/linux/SDL_syshaptic.c

/*
  Simple DirectMedia Layer
  Copyright (C) 1997-2023 Sam Lantinga <slouken@libsdl.org>

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the authors be held liable for any damages
  arising from the use of this software.

  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.
*/
#include "../../SDL_internal.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 "../../core/linux/SDL_evdev_capabilities.h"
#include "../../core/linux/SDL_udev.h"

#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 <sys/stat.h>           /* stat */

/* 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 */

static int MaybeAddDevice(const char *path);
#if SDL_USE_LIBUDEV
static int MaybeRemoveDevice(const char *path);
static void haptic_udev_callback(SDL_UDEV_deviceevent udev_type, int udev_class, const char *devpath);
#endif /* SDL_USE_LIBUDEV */

/*
 * List of available haptic devices.
 */
typedef struct SDL_hapticlist_item
{
    char *fname;                /* Dev path name (like /dev/input/event1) */
    SDL_Haptic *haptic;         /* Associated haptic. */
    dev_t dev_num;
    struct SDL_hapticlist_item *next;
} SDL_hapticlist_item;


/*
 * 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. */
};

static SDL_hapticlist_item *SDL_hapticlist = NULL;
static SDL_hapticlist_item *SDL_hapticlist_tail = NULL;
static int numhaptics = 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) {
        return SDL_SetError("Haptic: Unable to get device's features: %s",
                            strerror(errno));
    }

    /* Convert supported features to SDL_HAPTIC platform-neutral features. */
    EV_TEST(FF_CONSTANT, SDL_HAPTIC_CONSTANT);
    EV_TEST(FF_SINE, SDL_HAPTIC_SINE);
    /* !!! FIXME: put this back when we have more bits in 2.1 */
    /* 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);
    EV_TEST(FF_RUMBLE, SDL_HAPTIC_LEFTRIGHT);

    /* 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";
    char path[PATH_MAX];
    int i, j;

    /*
     * 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) {

        SDL_snprintf(path, PATH_MAX, joydev_pattern, i++);
        MaybeAddDevice(path);
    }

#if SDL_USE_LIBUDEV
    if (SDL_UDEV_Init() < 0) {
        return SDL_SetError("Could not initialize UDEV");
    }

    if ( SDL_UDEV_AddCallback(haptic_udev_callback) < 0) {
        SDL_UDEV_Quit();
        return SDL_SetError("Could not setup haptic <-> udev callback");
    }

    /* Force a scan to build the initial device list */
    SDL_UDEV_Scan();
#endif /* SDL_USE_LIBUDEV */

    return numhaptics;
}

int
SDL_SYS_NumHaptics(void)
{
    return numhaptics;
}

static SDL_hapticlist_item *
HapticByDevIndex(int device_index)
{
    SDL_hapticlist_item *item = SDL_hapticlist;

    if ((device_index < 0) || (device_index >= numhaptics)) {
        return NULL;
    }

    while (device_index > 0) {
        SDL_assert(item != NULL);
        --device_index;
        item = item->next;
    }

    return item;
}

#if SDL_USE_LIBUDEV
static void haptic_udev_callback(SDL_UDEV_deviceevent udev_type, int udev_class, const char *devpath)
{
    if (devpath == NULL || !(udev_class & SDL_UDEV_DEVICE_JOYSTICK)) {
        return;
    }

    switch( udev_type )
    {
        case SDL_UDEV_DEVICEADDED:
            MaybeAddDevice(devpath);
            break;

        case SDL_UDEV_DEVICEREMOVED:
            MaybeRemoveDevice(devpath);
            break;

        default:
            break;
    }

}
#endif /* SDL_USE_LIBUDEV */

static int
MaybeAddDevice(const char *path)
{
    struct stat sb;
    int fd;
    int success;
    SDL_hapticlist_item *item;

    if (path == NULL) {
        return -1;
    }

    /* check to see if file exists */
    if (stat(path, &sb) != 0) {
        return -1;
    }

    /* check for duplicates */
    for (item = SDL_hapticlist; item != NULL; item = item->next) {
        if (item->dev_num == sb.st_rdev) {
            return -1;  /* duplicate. */
        }
    }

    /* try to open */
    fd = open(path, O_RDWR | O_CLOEXEC, 0);
    if (fd < 0) {
        return -1;
    }

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

    /* see if it works */
    success = EV_IsHaptic(fd);
    close(fd);
    if (success <= 0) {
        return -1;
    }

    item = (SDL_hapticlist_item *) SDL_calloc(1, sizeof (SDL_hapticlist_item));
    if (item == NULL) {
        return -1;
    }

    item->fname = SDL_strdup(path);
    if (item->fname == NULL) {
        SDL_free(item);
        return -1;
    }

    item->dev_num = sb.st_rdev;

    /* TODO: should we add instance IDs? */
    if (SDL_hapticlist_tail == NULL) {
        SDL_hapticlist = SDL_hapticlist_tail = item;
    } else {
        SDL_hapticlist_tail->next = item;
        SDL_hapticlist_tail = item;
    }

    ++numhaptics;

    /* !!! TODO: Send a haptic add event? */

    return numhaptics;
}

#if SDL_USE_LIBUDEV
static int
MaybeRemoveDevice(const char* path)
{
    SDL_hapticlist_item *item;
    SDL_hapticlist_item *prev = NULL;

    if (path == NULL) {
        return -1;
    }

    for (item = SDL_hapticlist; item != NULL; item = item->next) {
        /* found it, remove it. */
        if (SDL_strcmp(path, item->fname) == 0) {
            const int retval = item->haptic ? item->haptic->index : -1;

            if (prev != NULL) {
                prev->next = item->next;
            } else {
                SDL_assert(SDL_hapticlist == item);
                SDL_hapticlist = item->next;
            }
            if (item == SDL_hapticlist_tail) {
                SDL_hapticlist_tail = prev;
            }

            /* Need to decrement the haptic count */
            --numhaptics;
            /* !!! TODO: Send a haptic remove event? */

            SDL_free(item->fname);
            SDL_free(item);
            return retval;
        }
        prev = item;
    }

    return -1;
}
#endif /* SDL_USE_LIBUDEV */

/*
 * 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)
{
    SDL_hapticlist_item *item;
    int fd;
    const char *name;

    item = HapticByDevIndex(index);
    /* Open the haptic device. */
    name = NULL;
    fd = open(item->fname, O_RDONLY | O_CLOEXEC, 0);

    if (fd >= 0) {

        name = SDL_SYS_HapticNameFromFD(fd);
        if (name == NULL) {
            /* No name found, return device character device */
            name = item->fname;
        }
        close(fd);
    }

    return name;
}


/*
 * Opens the haptic device from the file descriptor.
 */
static int
SDL_SYS_HapticOpenFromFD(SDL_Haptic * haptic, int fd)
{
    /* 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) {
        SDL_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;
    SDL_hapticlist_item *item;

    item = HapticByDevIndex(haptic->index);
    /* Open the character device */
    fd = open(item->fname, O_RDWR | O_CLOEXEC, 0);
    if (fd < 0) {
        return SDL_SetError("Haptic: Unable to open %s: %s",
                            item->fname, strerror(errno));
    }

    /* 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_strdup( item->fname );
    return 0;
}


/*
 * Opens a haptic device from first mouse it finds for usage.
 */
int
SDL_SYS_HapticMouse(void)
{
    int fd;
    int device_index = 0;
    SDL_hapticlist_item *item;

    for (item = SDL_hapticlist; item; item = item->next) {
        /* Open the device. */
        fd = open(item->fname, O_RDWR | O_CLOEXEC, 0);
        if (fd < 0) {
            return SDL_SetError("Haptic: Unable to open %s: %s",
                                item->fname, strerror(errno));
        }

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

        close(fd);

        ++device_index;
    }

    return -1;
}


/*
 * Checks to see if a joystick has haptic features.
 */
int
SDL_SYS_JoystickIsHaptic(SDL_Joystick * joystick)
{
#ifdef SDL_JOYSTICK_LINUX
    if (joystick->driver != &SDL_LINUX_JoystickDriver) {
        return SDL_FALSE;
    }
    if (EV_IsHaptic(joystick->hwdata->fd)) {
        return SDL_TRUE;
    }
#endif
    return SDL_FALSE;
}


/*
 * Checks to see if the haptic device and joystick are in reality the same.
 */
int
SDL_SYS_JoystickSameHaptic(SDL_Haptic * haptic, SDL_Joystick * joystick)
{
#ifdef SDL_JOYSTICK_LINUX
    if (joystick->driver != &SDL_LINUX_JoystickDriver) {
        return 0;
    }
    /* 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;
    }
#endif
    return 0;
}


/*
 * Opens a SDL_Haptic from a SDL_Joystick.
 */
int
SDL_SYS_HapticOpenFromJoystick(SDL_Haptic * haptic, SDL_Joystick * joystick)
{
#ifdef SDL_JOYSTICK_LINUX
    int device_index = 0;
    int fd;
    int ret;
    SDL_hapticlist_item *item;
    
    if (joystick->driver != &SDL_LINUX_JoystickDriver) {
        return -1;
    }
    /* Find the joystick in the haptic list. */
    for (item = SDL_hapticlist; item; item = item->next) {
        if (SDL_strcmp(item->fname, joystick->hwdata->fname) == 0) {
            break;
        }
        ++device_index;
    }
    haptic->index = device_index;

    if (device_index >= MAX_HAPTICS) {
        return SDL_SetError("Haptic: Joystick doesn't have Haptic capabilities");
    }

    fd = open(joystick->hwdata->fname, O_RDWR | O_CLOEXEC, 0);
    if (fd < 0) {
        return SDL_SetError("Haptic: Unable to open %s: %s",
                            joystick->hwdata->fname, strerror(errno));
    }
    ret = SDL_SYS_HapticOpenFromFD(haptic, fd); /* Already closes on error. */
    if (ret < 0) {
        return -1;
    }

    haptic->hwdata->fname = SDL_strdup( joystick->hwdata->fname );

    return 0;
#else
    return -1;
#endif
}


/*
 * 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->fname);
        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)
{
    SDL_hapticlist_item *item = NULL;
    SDL_hapticlist_item *next = NULL;

    for (item = SDL_hapticlist; item; item = next) {
        next = item->next;
        /* Opened and not closed haptics are leaked, this is on purpose.
         * Close your haptic devices after usage. */
        SDL_free(item->fname);
        SDL_free(item);
    }

#if SDL_USE_LIBUDEV
    SDL_UDEV_DelCallback(haptic_udev_callback);
    SDL_UDEV_Quit();
#endif /* SDL_USE_LIBUDEV */

    numhaptics = 0;
    SDL_hapticlist = NULL;
    SDL_hapticlist_tail = 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;
}


/*
 * Initializes the ff_effect usable direction from a SDL_HapticDirection.
 */
static int
SDL_SYS_ToDirection(Uint16 *dest, SDL_HapticDirection * src)
{
    Uint32 tmp;

    switch (src->type) {
    case SDL_HAPTIC_POLAR:
        /* Linux directions start from south.
                (and range from 0 to 0xFFFF)
                   Quoting include/linux/input.h, line 926:
                   Direction of the effect is encoded as follows:
                        0 deg -> 0x0000 (down)
                        90 deg -> 0x4000 (left)
                        180 deg -> 0x8000 (up)
                        270 deg -> 0xC000 (right)
                   The force pulls into the direction specified by Linux directions,
                   i.e. the opposite convention of SDL directions.
                    */
        tmp = ((src->dir[0] % 36000) * 0x8000) / 18000; /* convert to range [0,0xFFFF] */
        *dest = (Uint16) tmp;
        break;

    case SDL_HAPTIC_SPHERICAL:
            /*
                We convert to polar, because that's the only supported direction on Linux.
                The first value of a spherical direction is practically the same as a
                Polar direction, except that we have to add 90 degrees. It is the angle
                from EAST {1,0} towards SOUTH {0,1}.
                --> add 9000
                --> finally convert to [0,0xFFFF] as in case SDL_HAPTIC_POLAR.
            */
            tmp = ((src->dir[0]) + 9000) % 36000;    /* Convert to polars */
        tmp = (tmp * 0x8000) / 18000; /* convert to range [0,0xFFFF] */
        *dest = (Uint16) tmp;
        break;

    case SDL_HAPTIC_CARTESIAN:
        if (!src->dir[1])
            *dest = (src->dir[0] >= 0 ? 0x4000 : 0xC000);
        else if (!src->dir[0])
            *dest = (src->dir[1] >= 0 ? 0x8000 : 0);
        else {
            float f = SDL_atan2(src->dir[1], src->dir[0]);    /* Ideally we'd use fixed point math instead of floats... */
                    /*
                      SDL_atan2 takes the parameters: Y-axis-value and X-axis-value (in that order)
                       - Y-axis-value is the second coordinate (from center to SOUTH)
                       - X-axis-value is the first coordinate (from center to EAST)
                        We add 36000, because SDL_atan2 also returns negative values. Then we practically
                        have the first spherical value. Therefore we proceed as in case
                        SDL_HAPTIC_SPHERICAL and add another 9000 to get the polar value.
                      --> add 45000 in total
                      --> finally convert to [0,0xFFFF] as in case SDL_HAPTIC_POLAR.
                    */
                tmp = (((Sint32) (f * 18000. / M_PI)) + 45000) % 36000;
            tmp = (tmp * 0x8000) / 18000; /* convert to range [0,0xFFFF] */
            *dest = (Uint16) tmp;
        }
        break;
    case SDL_HAPTIC_STEERING_AXIS:
        *dest = 0x4000;
        break;
    default:
        return SDL_SetError("Haptic: Unsupported direction type.");
    }

    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)
{
    SDL_HapticConstant *constant;
    SDL_HapticPeriodic *periodic;
    SDL_HapticCondition *condition;
    SDL_HapticRamp *ramp;
    SDL_HapticLeftRight *leftright;

    /* 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;
        if (SDL_SYS_ToDirection(&dest->direction, &constant->direction) == -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:
    /* !!! FIXME: put this back when we have more bits in 2.1 */
    /* case SDL_HAPTIC_SQUARE: */
    case SDL_HAPTIC_TRIANGLE:
    case SDL_HAPTIC_SAWTOOTHUP:
    case SDL_HAPTIC_SAWTOOTHDOWN:
        periodic = &src->periodic;

        /* Header */
        dest->type = FF_PERIODIC;
        if (SDL_SYS_ToDirection(&dest->direction, &periodic->direction) == -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;
        /* !!! FIXME: put this back when we have more bits in 2.1 */
        /* 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;
        /* Linux phase is defined in interval "[0x0000, 0x10000[", corresponds with "[0deg, 360deg[" phase shift. */
        dest->u.periodic.phase = ((Uint32)periodic->phase * 0x10000U) / 36000;

        /* 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 = condition->right_sat[0];
        dest->u.condition[0].left_saturation = 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 = condition->deadband[0];
        dest->u.condition[0].center = condition->center[0];
        /* Y axis */
        dest->u.condition[1].right_saturation = condition->right_sat[1];
        dest->u.condition[1].left_saturation = 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 = 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;
        if (SDL_SYS_ToDirection(&dest->direction, &ramp->direction) == -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;

    case SDL_HAPTIC_LEFTRIGHT:
        leftright = &src->leftright;

        /* Header */
        dest->type = FF_RUMBLE;
        dest->direction = 0;

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

        /* Trigger */
        dest->trigger.button = 0;
        dest->trigger.interval = 0;

        /* Rumble (Linux expects 0-65535, so multiply by 2) */
        dest->u.rumble.strong_magnitude = CLAMP(leftright->large_magnitude) * 2;
        dest->u.rumble.weak_magnitude = CLAMP(leftright->small_magnitude) * 2;

        break;


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

    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) {
        return SDL_OutOfMemory();
    }

    /* 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:
    SDL_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) {
        return SDL_SetError("Haptic: Error updating the effect: %s",
                            strerror(errno));
    }

    /* 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) {
        return SDL_SetError("Haptic: Unable to run the effect: %s", strerror(errno));
    }

    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) {
        return SDL_SetError("Haptic: Unable to stop the effect: %s",
                            strerror(errno));
    }

    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) {
        return SDL_SetError("Haptic: Error getting device status.");
    }

    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) {
        return SDL_SetError("Haptic: Error setting gain: %s", strerror(errno));
    }

    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) {
        return SDL_SetError("Haptic: Error setting autocenter: %s", strerror(errno));
    }

    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) {
                return SDL_SetError
                    ("Haptic: Error while trying to stop all playing effects.");
            }
        }
    }
    return 0;
}

#endif /* SDL_HAPTIC_LINUX */

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