How to create an EGL window in Wayland and set its position on screen?

Question

I have a working program that creates an EGL window in Wayland. I can control the window size, but not its position on the screen. Right now, if I set the size to match the size of the screen, it will run fullscreen but if I set anything less than that, it will just appear in a different random position every time.

I've read that the top surface can't be moved and that if I want to control the surface's position, I have to use a subsurface. However, I wasn't able to find any useful examples. Especially, I wasn't able to find any examples for EGL, which has some caviats.

Anyway, here's the important bit from my program:

static struct waylandContext {
    struct wl_display* display;
    struct wl_registry* registry;
    struct wl_compositor* compositor;
    struct wl_shell* shell;
    struct wl_surface* surface;
    struct wl_shell_surface* shell_surface;
    struct wl_egl_window* egl_window;
} wlContext;

static void registry_add_object(void* data, struct wl_registry* registry, uint32_t name, const char* interface, uint32_t version)
{
    if (!strcmp(interface, "wl_compositor")) {
        wlContext.compositor = wl_registry_bind(registry, name, &wl_compositor_interface, 1);
    } else if (!strcmp(interface, "wl_shell")) {
        wlContext.shell = wl_registry_bind(registry, name, &wl_shell_interface, 1);
    }
}

static void registry_remove_object(void* data, struct wl_registry* registry, uint32_t name)
{
}

static struct wl_registry_listener registry_listener = {
    &registry_add_object,
    &registry_remove_object
};

static void shell_surface_ping(void* data, struct wl_shell_surface* shell_surface, uint32_t serial)
{
    wl_shell_surface_pong(shell_surface, serial);
}

static void shell_surface_configure(void* data, struct wl_shell_surface* shell_surface, uint32_t edges, int32_t width, int32_t height)
{
    struct window* window = data;
    wl_egl_window_resize(wlContext.egl_window, width, height, 0, 0);
}

static void shell_surface_popup_done(void* data, struct wl_shell_surface* shell_surface)
{
}

static struct wl_shell_surface_listener shell_surface_listener = {
    &shell_surface_ping,
    &shell_surface_configure,
    &shell_surface_popup_done
};

static bool initWayland(int width, int height)
{
    wlContext.display = wl_display_connect(NULL);
    if (!wlContext.display) {
        fprintf(stderr, "failed to connect to display\n");
        return false;
    }

    wlContext.registry = wl_display_get_registry(wlContext.display);
    wl_registry_add_listener(wlContext.registry, &registry_listener, NULL);
    wl_display_dispatch(wlContext.display);
    wl_display_roundtrip(wlContext.display);

    wlContext.surface = wl_compositor_create_surface(wlContext.compositor);
    wlContext.shell_surface = wl_shell_get_shell_surface(wlContext.shell, wlContext.surface);
    wl_shell_surface_add_listener(wlContext.shell_surface, &shell_surface_listener, NULL);
    wl_shell_surface_set_toplevel(wlContext.shell_surface);
    wlContext.egl_window = wl_egl_window_create(wlContext.surface, width, height);

    return true;
}

I tried changing the code to this:

static struct waylandContext {
    struct wl_display* display;
    struct wl_registry* registry;
    struct wl_compositor* compositor;
    struct wl_subcompositor* subcompositor;
    struct wl_shell* shell;
    struct wl_surface* parent_surface;
    struct wl_surface* child_surface;
    struct wl_subsurface* subsurface;
    struct wl_shell_surface* shell_surface;
    struct wl_egl_window* egl_window;
    struct wl_egl_window* egl_window2;
} wlContext;

static void registry_add_object(void* data, struct wl_registry* registry, uint32_t name, const char* interface, uint32_t version)
{
    if (!strcmp(interface, "wl_compositor")) {
        wlContext.compositor = wl_registry_bind(registry, name, &wl_compositor_interface, 1);
    } else if (!strcmp(interface, "wl_subcompositor")) {
        wlContext.subcompositor = wl_registry_bind(registry, name, &wl_subcompositor_interface, 1);
    } else if (!strcmp(interface, "wl_shell")) {
        wlContext.shell = wl_registry_bind(registry, name, &wl_shell_interface, 1);
    }
}

static void registry_remove_object(void* data, struct wl_registry* registry, uint32_t name)
{
}

static struct wl_registry_listener registry_listener = {
    &registry_add_object,
    &registry_remove_object
};

static void shell_surface_ping(void* data, struct wl_shell_surface* shell_surface, uint32_t serial)
{
    wl_shell_surface_pong(shell_surface, serial);
}

static void shell_surface_configure(void* data, struct wl_shell_surface* shell_surface, uint32_t edges, int32_t width, int32_t height)
{
    struct window* window = data;
    wl_egl_window_resize(wlContext.egl_window, width, height, 0, 0);
}

static void shell_surface_popup_done(void* data, struct wl_shell_surface* shell_surface)
{
}

static struct wl_shell_surface_listener shell_surface_listener = {
    &shell_surface_ping,
    &shell_surface_configure,
    &shell_surface_popup_done
};

static bool initWayland(int width, int height)
{
    wlContext.display = wl_display_connect(NULL);
    if (!wlContext.display) {
        fprintf(stderr, "failed to connect to display\n");
        return false;
    }

    wlContext.registry = wl_display_get_registry(wlContext.display);
    wl_registry_add_listener(wlContext.registry, &registry_listener, NULL);
    wl_display_dispatch(wlContext.display);
    wl_display_roundtrip(wlContext.display);

    wlContext.parent_surface = wl_compositor_create_surface(wlContext.compositor);
    wlContext.shell_surface = wl_shell_get_shell_surface(wlContext.shell, wlContext.parent_surface);
    wl_shell_surface_add_listener(wlContext.shell_surface, &shell_surface_listener, NULL);
    wl_shell_surface_set_toplevel(wlContext.shell_surface);

    wlContext.child_surface = wl_compositor_create_surface(wlContext.compositor);
    wlContext.subsurface = wl_subcompositor_get_subsurface(wlContext.subcompositor, wlContext.child_surface, wlContext.parent_surface);

    wlContext.egl_window = wl_egl_window_create(wlContext.child_surface, width, height);

    return true;
}

Where I get subcompositor, create a child surface and create the EGL window from that child surface. However, this doesn't work and I'm not sure why.

Maybe I should add, how I work with EGL, but it's just standard stuff. After I create the EGL window, I have the regular sequence of calls like eglInitialize, eglCreateContext, etc. Then I create an OpenGL context, draw something and call eglSwapBuffers. When I do it with the subsurface, eglSwapBuffers runs once but nothing shows and then when I call eglSwapBuffers the second time, it freezes forever.