NX2navi/runtime/input_hd_pair.c

// HD rumble for a pair of Joy-Con (input_hd_pair.h).
//
// SDL presents a left and a right Joy-Con as one gamepad and drives its two halves at fixed frequencies; the call
// that hands a Switch controller raw rumble data (input.c hd_tick, SDL_SendGamepadEffect) is refused for the combined
// gamepad. So for a pair this file writes the rumble output report itself, through SDL's HID interface, to the two
// HID devices SDL also has open:
// - Each Joy-Con is opened a second time (the system shares a HID device between handles) and gets output report
//   0x10 (rumble_hd.c rumble_hd_report), 49 bytes, the length of a Bluetooth output report. A Joy-Con by itself has no
//   other connection: its USB charging grip is another product id and is left to the motors' path.
// - The report carries a number that goes round 0..15. Each handle here counts its own; the controller plays a report
//   whatever number it carries, so SDL's count for its own reports is not disturbed.
// - While HD rumble is on, input.c makes no dual-motor call for the gamepad (input_rumble), so these reports are the
//   only rumble the Joy-Con get. SDL still writes its own commands (player lights, sensors on), which carry the rumble
//   value SDL last set, the one at rest: such a command silences the actuators until the next report from here, at most
//   RUMBLE_HD_REFRESH_NS later.
// - A report holds a left and a right value and a Joy-Con plays the one of its side; both halves get the same value
//   here, so nothing depends on which half a Joy-Con reads.
// With several pairs connected the first left and the first right Joy-Con listed are taken.
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <SDL3/SDL.h>

#include "input_hd_pair.h"
#include "platform/platform.h"

enum { VID_NINTENDO = 0x057E, PID_JOYCON_LEFT = 0x2006, PID_JOYCON_RIGHT = 0x2007, BLUETOOTH_REPORT = 49 };

static PlatMutex path_lock = PLAT_MUTEX_INIT;   // guards path[]
static char *path[2];                           // the HID paths hd_pair_find saw last: left, right
static PlatMutex dev_lock = PLAT_MUTEX_INIT;    // guards dev[] and number[], and is held across a write
static SDL_hid_device *dev[2];
static unsigned number[2];                      // the next report's number, per device
static volatile int32_t ended;                  // hd_pair_end ran: hd_pair_write, under dev_lock, writes nothing

int hd_pair_find(void) {
    char *found[2] = {NULL, NULL};
    SDL_hid_device_info *list = SDL_hid_enumerate(VID_NINTENDO, 0);
    for (SDL_hid_device_info *d = list; d; d = d->next) {
        int s = d->product_id == PID_JOYCON_LEFT ? 0 : d->product_id == PID_JOYCON_RIGHT ? 1 : -1;
        if (s >= 0 && !found[s] && d->path) found[s] = strdup(d->path);
    }
    SDL_hid_free_enumeration(list);
    int both = found[0] && found[1];
    plat_mutex_lock(&path_lock);
    for (int s = 0; s < 2; s++) {
        free(path[s]);
        path[s] = both ? found[s] : NULL;
        if (!both) free(found[s]);
    }
    plat_mutex_unlock(&path_lock);
    return both;
}

// Under dev_lock.
static void close_devices(void) {
    for (int s = 0; s < 2; s++) {
        if (dev[s]) SDL_hid_close(dev[s]);
        dev[s] = NULL;
    }
}

// Under dev_lock: one report with v in both halves to device s. 1 when the whole report was taken.
static int write_side(int s, const uint8_t v[RUMBLE_HD_SIDE]) {
    uint8_t data[RUMBLE_HD_DATA], report[BLUETOOTH_REPORT];
    memcpy(data, v, RUMBLE_HD_SIDE);
    memcpy(data + RUMBLE_HD_SIDE, v, RUMBLE_HD_SIDE);
    rumble_hd_report(data, number[s]++, report, sizeof report);
    return SDL_hid_write(dev[s], report, sizeof report) == (int)sizeof report;
}

int hd_pair_write(const uint8_t data[RUMBLE_HD_DATA]) {
    int ok = 1;
    plat_mutex_lock(&dev_lock);
    if (__atomic_load_n(&ended, __ATOMIC_ACQUIRE)) {   // under the write's lock: no stop between this and the write
        plat_mutex_unlock(&dev_lock);
        SDL_SetError("HD rumble has ended");
        return 0;
    }
    if (!dev[0] || !dev[1]) {
        close_devices();
        char *p[2];
        plat_mutex_lock(&path_lock);
        for (int s = 0; s < 2; s++) p[s] = path[s] ? strdup(path[s]) : NULL;
        plat_mutex_unlock(&path_lock);
        if (!p[0] || !p[1]) ok = 0, SDL_SetError("the two Joy-Con are not both listed as HID devices");
        for (int s = 0; s < 2 && ok; s++) {
            dev[s] = SDL_hid_open_path(p[s]);
            number[s] = 0;
            if (!dev[s]) ok = 0;
        }
        free(p[0]);
        free(p[1]);
    }
    for (int s = 0; s < 2 && ok; s++) ok = write_side(s, data + s * RUMBLE_HD_SIDE);
    if (!ok) close_devices();
    plat_mutex_unlock(&dev_lock);
    return ok;
}

int hd_pair_is_open(void) {
    plat_mutex_lock(&dev_lock);
    int open = dev[0] && dev[1];
    plat_mutex_unlock(&dev_lock);
    return open;
}

void hd_pair_close(int neutral, unsigned wait_ms) {
    if (!wait_ms) plat_mutex_lock(&dev_lock);
    else {
        int got = 0;
        for (unsigned i = 0; i < wait_ms && !(got = plat_mutex_trylock(&dev_lock)); i++) plat_wait_ns(1000000);
        if (!got) return;
    }
    for (int s = 0; s < 2 && neutral; s++)
        if (dev[s]) write_side(s, rumble_hd_neutral);
    close_devices();
    plat_mutex_unlock(&dev_lock);
}

void hd_pair_end(unsigned wait_ms) {
    __atomic_store_n(&ended, 1, __ATOMIC_RELEASE);   // before the lock: a write that holds it now is the last one
    hd_pair_close(1, wait_ms);
}