swaystick/swaystick.c

/*
 * swaystick: control Sway with a DualSense gamepad
 * Copyright (c) 2024 Jeremy Baxter.
 */

#include <sys/wait.h>
#include <linux/joystick.h>

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

/* DualSense button mapping */
enum DSButton {
	DS_CROSS = 0,
	DS_CIRCLE = 1,
	DS_TRIANGLE = 2,
	DS_SQUARE = 3,
	DS_L1 = 4,
	DS_R1 = 5,
	DS_L2 = 6,
	DS_R2 = 7,
	DS_CREATE = 8,
	DS_OPTIONS = 9,
	DS_PLAYSTATION = 10,
	DS_LSTICK = 11,
	DS_RSTICK = 12
};

int
read_event(int fd, struct js_event *event)
{
	ssize_t bytes;

	bytes = read(fd, event, sizeof(*event));

	if (bytes == sizeof(*event))
		return 0;

	return -1;
}

size_t
get_axis_count(int fd)
{
	__u8 axes;

	if (ioctl(fd, JSIOCGAXES, &axes) == -1)
		return 0;

	return axes;
}

size_t
get_button_count(int fd)
{
	__u8 buttons;
	if (ioctl(fd, JSIOCGBUTTONS, &buttons) == -1)
		return 0;

	return buttons;
}

char *
make_move_command(int pos, int x)
{
	char *buffer;
	size_t len;

	len = 32;
	buffer = malloc(len * sizeof(char));

	snprintf(buffer, len, "move %s %d",
			 x ? "right" : "down",
			 pos / 2000);

	return buffer;
}

char *
make_resize_command(int pos, int x)
{
	char *buffer;
	size_t len;

	len = 32;
	buffer = malloc(len * sizeof(char));

	snprintf(buffer, len, "resize %s %s %d",
			 pos > 0 ? "grow" : "shrink",
			 x ? "width" : "height",
			 pos / 2000);

	return buffer;
}

void
swaymsg(const char *msg)
{
	const char *prog = "swaymsg";
	pid_t child;
	int wstatus;

	child = fork();
	switch (child) {
	case -1:
		perror("fork");
		break;
	case 0:
		if (execlp(prog, prog, msg, NULL) == -1)
			perror("execlp");
		break;
	default:
		if (wait(&wstatus) == -1)
			perror("wait");
	}
}

struct axis_state {
	short x, y;
};

/**
 * Keeps track of the current axis state.
 *
 * NOTE: This function assumes that axes are numbered starting from 0,
 * and that the X axis is an even number, and the Y axis is an odd number.
 * However, this is usually a safe assumption.
 *
 * Returns the axis that the event indicated.
 */
size_t
get_axis_state(struct js_event *event, struct axis_state axes[3])
{
	size_t axis = event->number / 2;

	if (axis < 3) {
		if (event->number % 2 == 0)
			axes[axis].x = event->value;
		else
			axes[axis].y = event->value;
	}

	return axis;
}

int
main(int argc, char *argv[])
{
	struct axis_state axes[3] = {0};
	struct js_event event;
	const char *device;
	size_t axis;
	int js;
	int moving;

	moving = 0;

	if (argc > 1)
		device = argv[1];
	else
		device = "/dev/input/js0";

	js = open(device, O_RDONLY);

	if (js == -1)
		perror(device);

	/* This loop will exit if the controller is unplugged. */
	while (read_event(js, &event) == 0) {
		if (moving)
			swaymsg("move position cursor");

		switch (event.type) {
		case JS_EVENT_BUTTON:
			if (event.value) { /* pressed */
				switch (event.number) {
				case DS_CROSS:
					swaymsg("kill");
					break;
				case DS_TRIANGLE:
					moving = 1;
					break;
				case DS_LSTICK:
					swaymsg("focus prev");
					break;
				case DS_RSTICK:
					swaymsg("focus next");
					break;
				default: break;
				}
				break;
			}
			/* released */
			switch (event.number) {
			case DS_CIRCLE:
				swaymsg("focus mode_toggle");
				break;
			case DS_TRIANGLE:
				moving = 0;
				break;
			case DS_SQUARE:
				swaymsg("floating toggle");
				break;
			case DS_L1:
				swaymsg("workspace prev");
				break;
			case DS_R1:
				swaymsg("workspace next");
				break;
			case DS_CREATE:
				swaymsg("layout tabbed");
				break;
			case DS_OPTIONS:
				swaymsg("layout toggle split");
				break;
			case DS_PLAYSTATION:
				swaymsg("exec 'emacsclient -c'");
				break;
			default: break;
			}
			break;
		case JS_EVENT_AXIS:
			axis = get_axis_state(&event, axes);

			if (axis > 2)
				break;
			/* no activity? */
			if (axes[axis].x > -2000 && axes[axis].x < 2000
				&& axes[axis].y > -2000 && axes[axis].y < 2000)
				break;

			if (axis == 0) { /* left X/Y */
				swaymsg(make_move_command(axes[axis].x, 1));
				swaymsg(make_move_command(axes[axis].y, 0));
			}
		default:
			/* ignore init events */
			break;
		}
	}

	close(js);
	return 0;
}