SDL/src/haptic/linux/SDL_syshaptic.c

/*
  Simple DirectMedia Layer
  Copyright (C) 1997-2024 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_syshaptic.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
#include <string.h>      // strerror
#include <sys/stat.h>    // stat

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

static bool MaybeAddDevice(const char *path);
#ifdef SDL_USE_LIBUDEV
static bool 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
{
    SDL_HapticID instance_id;
    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 Uint32 EV_IsHaptic(int fd)
{
    unsigned long features[1 + FF_MAX / sizeof(unsigned long)];
    Uint32 ret = 0;

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

    // 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);
    EV_TEST(FF_RUMBLE, SDL_HAPTIC_LEFTRIGHT);

    // Return what it supports.
    return ret;
}

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

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

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

    return true;
}

/*
 * Initializes the haptic subsystem by finding available devices.
 */
bool 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) {
        (void)SDL_snprintf(path, PATH_MAX, joydev_pattern, i++);
        MaybeAddDevice(path);
    }

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

    if (!SDL_UDEV_AddCallback(haptic_udev_callback)) {
        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 true;
}

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;
}

static SDL_hapticlist_item *HapticByInstanceID(SDL_HapticID instance_id)
{
    SDL_hapticlist_item *item;
    for (item = SDL_hapticlist; item; item = item->next) {
        if (instance_id == item->instance_id) {
            return item;
        }
    }
    return NULL;
}

#ifdef SDL_USE_LIBUDEV
static void haptic_udev_callback(SDL_UDEV_deviceevent udev_type, int udev_class, const char *devpath)
{
    if (!devpath || !(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 bool MaybeAddDevice(const char *path)
{
    struct stat sb;
    int fd;
    Uint32 supported;
    SDL_hapticlist_item *item;

    if (!path) {
        return false;
    }

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

    // get file status
    if (fstat(fd, &sb) != 0) {
        close(fd);
        return false;
    }

    // check for duplicates
    for (item = SDL_hapticlist; item; item = item->next) {
        if (item->dev_num == sb.st_rdev) {
            close(fd);
            return false; // duplicate.
        }
    }

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

    // see if it works
    supported = EV_IsHaptic(fd);
    close(fd);
    if (!supported) {
        return false;
    }

    item = (SDL_hapticlist_item *)SDL_calloc(1, sizeof(SDL_hapticlist_item));
    if (!item) {
        return false;
    }

    item->instance_id = SDL_GetNextObjectID();
    item->fname = SDL_strdup(path);
    if (!item->fname) {
        SDL_free(item);
        return false;
    }

    item->dev_num = sb.st_rdev;

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

    ++numhaptics;

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

    return true;
}

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

    if (!path) {
        return false;
    }

    for (item = SDL_hapticlist; item; item = item->next) {
        // found it, remove it.
        if (SDL_strcmp(path, item->fname) == 0) {
            const bool result = item->haptic ? true : false;

            if (prev) {
                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 result;
        }
        prev = item;
    }

    return false;
}
#endif // SDL_USE_LIBUDEV

/*
 * Return the instance ID of a haptic device, does not need to be opened.
 */
SDL_HapticID SDL_SYS_HapticInstanceID(int index)
{
    SDL_hapticlist_item *item;

    item = HapticByDevIndex(index);
    if (item) {
        return item->instance_id;
    }
    return 0;
}

/*
 * 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 = NULL;

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

        if (fd >= 0) {

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

/*
 * Opens the haptic device from the file descriptor.
 */
static bool SDL_SYS_HapticOpenFromFD(SDL_Haptic *haptic, int fd)
{
    // Allocate the hwdata
    haptic->hwdata = (struct haptic_hwdata *)
        SDL_calloc(1, sizeof(*haptic->hwdata));
    if (!haptic->hwdata) {
        goto open_err;
    }

    // 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) {
        goto open_err;
    }
    // Clear the memory
    SDL_memset(haptic->effects, 0,
               sizeof(struct haptic_effect) * haptic->neffects);

    return true;

    // Error handling
open_err:
    close(fd);
    if (haptic->hwdata) {
        SDL_free(haptic->hwdata);
        haptic->hwdata = NULL;
    }
    return false;
}

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

    item = HapticByInstanceID(haptic->instance_id);
    // 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.
    if (!SDL_SYS_HapticOpenFromFD(haptic, fd)) {
        // Already closes on error.
        return false;
    }

    // Set the fname.
    haptic->hwdata->fname = SDL_strdup(item->fname);
    return true;
}

/*
 * 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.
 */
bool SDL_SYS_JoystickIsHaptic(SDL_Joystick *joystick)
{
#ifdef SDL_JOYSTICK_LINUX
    SDL_AssertJoysticksLocked();

    if (joystick->driver != &SDL_LINUX_JoystickDriver) {
        return false;
    }
    if (EV_IsHaptic(joystick->hwdata->fd)) {
        return true;
    }
#endif
    return false;
}

/*
 * Checks to see if the haptic device and joystick are in reality the same.
 */
bool SDL_SYS_JoystickSameHaptic(SDL_Haptic *haptic, SDL_Joystick *joystick)
{
#ifdef SDL_JOYSTICK_LINUX
    SDL_AssertJoysticksLocked();

    if (joystick->driver != &SDL_LINUX_JoystickDriver) {
        return false;
    }
    /* 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 true;
    }
#endif
    return false;
}

/*
 * Opens a SDL_Haptic from a SDL_Joystick.
 */
bool SDL_SYS_HapticOpenFromJoystick(SDL_Haptic *haptic, SDL_Joystick *joystick)
{
#ifdef SDL_JOYSTICK_LINUX
    int fd;
    SDL_hapticlist_item *item;
    const char *name;

    SDL_AssertJoysticksLocked();

    if (joystick->driver != &SDL_LINUX_JoystickDriver) {
        return false;
    }
    // Find the joystick in the haptic list.
    for (item = SDL_hapticlist; item; item = item->next) {
        if (SDL_strcmp(item->fname, joystick->hwdata->fname) == 0) {
            haptic->instance_id = item->instance_id;
            break;
        }
    }

    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));
    }
    if (!SDL_SYS_HapticOpenFromFD(haptic, fd)) {
        // Already closes on error.
        return false;
    }

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

    name = SDL_SYS_HapticNameFromFD(fd);
    if (name) {
        haptic->name = SDL_strdup(name);
    }
    return true;
#else
    return false;
#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);
    }

#ifdef 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 bool SDL_SYS_ToDirection(Uint16 *dest, const SDL_HapticDirection *src)
{
    Uint32 tmp;

    switch (src->type) {
    case SDL_HAPTIC_POLAR:
        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_atan2f(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 * 18000.0 / SDL_PI_D)) + 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 true;
}

#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 bool SDL_SYS_ToFFEffect(struct ff_effect *dest, const SDL_HapticEffect *src)
{
    const SDL_HapticConstant *constant;
    const SDL_HapticPeriodic *periodic;
    const SDL_HapticCondition *condition;
    const SDL_HapticRamp *ramp;
    const 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)) {
            return false;
        }

        // 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;
        if (!SDL_SYS_ToDirection(&dest->direction, &periodic->direction)) {
            return false;
        }

        // 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;
        // 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)) {
            return false;
        }

        // 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 true;
}

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

    // Allocate the hardware effect
    effect->hweffect = (struct haptic_hweffect *)
        SDL_calloc(1, sizeof(struct haptic_hweffect));
    if (!effect->hweffect) {
        return false;
    }

    // Prepare the ff_effect
    linux_effect = &effect->hweffect->effect;
    if (!SDL_SYS_ToFFEffect(linux_effect, base)) {
        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 true;

new_effect_err:
    SDL_free(effect->hweffect);
    effect->hweffect = NULL;
    return false;
}

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

    // Create the new effect
    if (!SDL_SYS_ToFFEffect(&linux_effect, data)) {
        return false;
    }
    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 true;
}

/*
 * Runs an effect.
 */
bool 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 true;
}

/*
 * Stops an effect.
 */
bool 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 true;
}

/*
 * 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 1;
#endif

    SDL_Unsupported();
    return -1;
}

/*
 * Sets the gain.
 */
bool 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 true;
}

/*
 * Sets the autocentering.
 */
bool 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 true;
}

/*
 * Pausing is not supported atm by linux.
 */
bool SDL_SYS_HapticPause(SDL_Haptic *haptic)
{
    return SDL_Unsupported();
}

/*
 * Unpausing is not supported atm by linux.
 */
bool SDL_SYS_HapticResume(SDL_Haptic *haptic)
{
    return SDL_Unsupported();
}

/*
 * Stops all the currently playing effects.
 */
bool 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 true;
}

#endif // SDL_HAPTIC_LINUX