using casilda with gtk4-layer-shell for drop-down terminal

layer-shell.c

// toggle visibility with `kill -USR1 $(cat /tmp/casilda-tty.pid)` (assign this as the cmdline for a global hotkey)

#include "gtk4-layer-shell.h"
#include <gtk/gtk.h>
#include "casilda-compositor.h" // https://gitlab.gnome.org/jpu/casilda
#include <unistd.h>
#include <glib-unix.h>

GtkWidget *window;
#define TTY_SOCKET "/tmp/casilda-tty.sock"
#define TTY_PID "/tmp/casilda-tty.pid"

static gboolean on_signal_usr1(gpointer user_data) {
    if (window) {
        bool visible = !gtk_widget_get_visible(window);
        gtk_widget_set_visible(window, visible);
    }
    return G_SOURCE_CONTINUE;
}

static void activate (GtkApplication *app, G_GNUC_UNUSED gpointer  user_data)
{
    CasildaCompositor *compositor;

    window = gtk_application_window_new (app);
    GtkWindow* gtk_window = GTK_WINDOW(window);

    gtk_layer_init_for_window(gtk_window);
    gtk_layer_set_layer(gtk_window, GTK_LAYER_SHELL_LAYER_TOP);
    // gtk_layer_auto_exclusive_zone_enable(gtk_window);
    gtk_layer_set_keyboard_mode(gtk_window, GTK_LAYER_SHELL_KEYBOARD_MODE_ON_DEMAND);
    gtk_layer_set_margin(gtk_window, GTK_LAYER_SHELL_EDGE_LEFT, 20);
    gtk_layer_set_margin(gtk_window, GTK_LAYER_SHELL_EDGE_RIGHT, 20);
    gtk_layer_set_anchor(gtk_window, GTK_LAYER_SHELL_EDGE_TOP, TRUE);

    gtk_window_set_title(GTK_WINDOW (window), "Compositor");
    gtk_window_set_default_size(GTK_WINDOW (window), 1000, 600); // larger than 1000x600 some kind of limit??

    compositor = casilda_compositor_new(TTY_SOCKET);
    gtk_window_set_child(GTK_WINDOW (window), GTK_WIDGET (compositor));
    gtk_window_present(GTK_WINDOW (window));

    g_unix_signal_add(SIGUSR1, on_signal_usr1, NULL);

    GError *error = NULL;
    GSpawnFlags flags = G_SPAWN_DO_NOT_REAP_CHILD;
    gchar *argv[] = {"/usr/bin/ghostty", "--fullscreen", NULL};
    gchar *envp[] = {"GDK_BACKEND=wayland", "WAYLAND_DISPLAY=" TTY_SOCKET, NULL};
    GPid child_pid;

    if (!g_spawn_async(NULL, argv, envp, flags, NULL, NULL, &child_pid, &error)) {
        g_printerr("Failed to spawn process: %s\n", error->message);
        g_error_free(error);
        g_application_quit(G_APPLICATION(app));
        return;
    }
    g_child_watch_add(child_pid, (GChildWatchFunc)g_application_quit, app);
}

int main(int argc, char **argv) {
    g_autoptr(GtkApplication) app = NULL;

    app = gtk_application_new("org.gnome.casilda.compositor", G_APPLICATION_DEFAULT_FLAGS);
    g_signal_connect(app, "activate", G_CALLBACK (activate), NULL);

    FILE *file = fopen(TTY_PID, "w");
    if (file) {
        fprintf(file, "%d\n", getpid());
        fclose(file);
        g_print("PID written to %s\n", TTY_PID);
    } else {
        perror("Failed to write PID file");
    }

    return g_application_run(G_APPLICATION (app), argc, argv);
}

ref: ghostty-org/ghostty#4624 (comment)