feynman/src/compositor.c

/*
 *  Feynman -- Wayland compositor for GNU Emacs
 *
 * Copyright (c) 2022 Sameer Rahmani <lxsameer@gnu.org>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, version 2.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "compositor.h"

#include "utils.h"

#include <assert.h>
#include <wayland-server-core.h>
#include <wlr/backend.h>
#include <wlr/backend/interface.h>
#include <wlr/interfaces/wlr_output.h>
#include <wlr/render/wlr_renderer.h>

static void
/* cppcheck-suppress constParameter */
focus_view (struct feynman_view *view, struct wlr_surface *surface)
{
  /* Note: this function only deals with keyboard focus. */
  if (view == NULL)
    {
      return;
    }
  struct feynman_server *server    = view->server;
  struct wlr_seat *seat            = server->seat;
  struct wlr_surface *prev_surface = seat->keyboard_state.focused_surface;
  if (prev_surface == surface)
    {
      /* Don't re-focus an already focused surface. */
      return;
    }
  if (prev_surface)
    {
      /*
       * Deactivate the previously focused surface. This lets the client know
       * it no longer has focus and the client will repaint accordingly, e.g.
       * stop displaying a caret.
       */
      struct wlr_xdg_surface *previous = wlr_xdg_surface_from_wlr_surface (
          seat->keyboard_state.focused_surface);
      wlr_xdg_toplevel_set_activated (previous, false);
    }
  struct wlr_keyboard *keyboard = wlr_seat_get_keyboard (seat);
  /* Move the view to the front */
  wlr_scene_node_raise_to_top (view->scene_node);
  wl_list_remove (&view->link);
  wl_list_insert (&server->views, &view->link);
  /* Activate the new surface */
  wlr_xdg_toplevel_set_activated (view->xdg_surface, true);
  /*
   * Tell the seat to have the keyboard enter this surface. wlroots will keep
   * track of this and automatically send key events to the appropriate
   * clients without additional work on your part.
   */
  wlr_seat_keyboard_notify_enter (seat, view->xdg_surface->surface,
                                  keyboard->keycodes, keyboard->num_keycodes,
                                  &keyboard->modifiers);
}

static void
keyboard_handle_modifiers (struct wl_listener *listener, void *data)
{
  (void)data;
  /* This event is raised when a modifier key, such as shift or alt, is
   * pressed. We simply communicate this to the client. */
  struct feynman_keyboard *keyboard
      = wl_container_of (listener, keyboard, modifiers);
  /*
   * A seat can only have one keyboard, but this is a limitation of the
   * Wayland protocol - not wlroots. We assign all connected keyboards to the
   * same seat. You can swap out the underlying wlr_keyboard like this and
   * wlr_seat handles this transparently.
   */
  wlr_seat_set_keyboard (keyboard->server->seat, keyboard->device);
  /* Send modifiers to the client. */
  wlr_seat_keyboard_notify_modifiers (keyboard->server->seat,
                                      &keyboard->device->keyboard->modifiers);
}

static bool
handle_keybinding (struct feynman_server *server, xkb_keysym_t sym)
{
  /*
   * Here we handle compositor keybindings. This is when the compositor is
   * processing keys, rather than passing them on to the client for its own
   * processing.
   *
   * This function assumes Alt is held down.
   */
  switch (sym)
    {
    case XKB_KEY_Escape:
      wl_display_terminate (server->wl_display);
      break;
    case XKB_KEY_F1:
      /* Cycle to the next view */
      if (wl_list_length (&server->views) < 2)
        {
          break;
        }
      struct feynman_view *next_view
          = wl_container_of (server->views.prev, next_view, link);
      focus_view (next_view, next_view->xdg_surface->surface);
      break;
    default:
      return false;
    }
  return true;
}

static void
keyboard_handle_key (struct wl_listener *listener, void *data)
{
  /* This event is raised when a key is pressed or released. */
  struct feynman_keyboard *keyboard
      = wl_container_of (listener, keyboard, key);
  struct feynman_server *server        = keyboard->server;
  struct wlr_event_keyboard_key *event = data;
  struct wlr_seat *seat                = server->seat;

  /* Translate libinput keycode -> xkbcommon */
  uint32_t keycode = event->keycode + 8;
  /* Get a list of keysyms based on the keymap for this keyboard */
  const xkb_keysym_t *syms;
  int nsyms = xkb_state_key_get_syms (keyboard->device->keyboard->xkb_state,
                                      keycode, &syms);

  bool handled       = false;
  uint32_t modifiers = wlr_keyboard_get_modifiers (keyboard->device->keyboard);
  if ((modifiers & WLR_MODIFIER_ALT)
      && event->state == WL_KEYBOARD_KEY_STATE_PRESSED)
    {
      /* If alt is held down and this button was _pressed_, we attempt to
       * process it as a compositor keybinding. */
      for (int i = 0; i < nsyms; i++)
        {
          handled = handle_keybinding (server, syms[i]);
        }
    }

  if (!handled)
    {
      /* Otherwise, we pass it along to the client. */
      wlr_seat_set_keyboard (seat, keyboard->device);
      wlr_seat_keyboard_notify_key (seat, event->time_msec, event->keycode,
                                    event->state);
    }
}

static void
server_new_keyboard (struct feynman_server *server,
                     struct wlr_input_device *device)
{
  struct feynman_keyboard *keyboard
      = calloc (1, sizeof (struct feynman_keyboard));
  keyboard->server = server;
  keyboard->device = device;

  /* We need to prepare an XKB keymap and assign it to the keyboard. This
   * assumes the defaults (e.g. layout = "us"). */
  struct xkb_context *context = xkb_context_new (XKB_CONTEXT_NO_FLAGS);
  struct xkb_keymap *keymap
      = xkb_keymap_new_from_names (context, NULL, XKB_KEYMAP_COMPILE_NO_FLAGS);

  wlr_keyboard_set_keymap (device->keyboard, keymap);
  xkb_keymap_unref (keymap);
  xkb_context_unref (context);
  wlr_keyboard_set_repeat_info (device->keyboard, 25, 600);

  /* Here we set up listeners for keyboard events. */
  keyboard->modifiers.notify = keyboard_handle_modifiers;
  wl_signal_add (&device->keyboard->events.modifiers, &keyboard->modifiers);
  keyboard->key.notify = keyboard_handle_key;
  wl_signal_add (&device->keyboard->events.key, &keyboard->key);

  wlr_seat_set_keyboard (server->seat, device);

  /* And add the keyboard to our list of keyboards */
  wl_list_insert (&server->keyboards, &keyboard->link);
}

static void
server_new_pointer (struct feynman_server *server,
                    struct wlr_input_device *device)
{
  /* We don't do anything special with pointers. All of our pointer handling
   * is proxied through wlr_cursor. On another compositor, you might take this
   * opportunity to do libinput configuration on the device to set
   * acceleration, etc. */
  wlr_cursor_attach_input_device (server->cursor, device);
}

static void
server_new_input (struct wl_listener *listener, void *data)
{
  /* This event is raised by the backend when a new input device becomes
   * available. */
  struct feynman_server *server
      = wl_container_of (listener, server, new_input);
  struct wlr_input_device *device = data;
  switch (device->type)
    {
    case WLR_INPUT_DEVICE_KEYBOARD:
      server_new_keyboard (server, device);
      break;
    case WLR_INPUT_DEVICE_POINTER:
      server_new_pointer (server, device);
      break;
    default:
      break;
    }
  /* We need to let the wlr_seat know what our capabilities are, which is
   * communiciated to the client. In Feynman we always have a cursor, even if
   * there are no pointer devices, so we always include that capability. */
  uint32_t caps = WL_SEAT_CAPABILITY_POINTER;
  if (!wl_list_empty (&server->keyboards))
    {
      caps |= WL_SEAT_CAPABILITY_KEYBOARD;
    }
  wlr_seat_set_capabilities (server->seat, caps);
}

static void
seat_request_cursor (struct wl_listener *listener, void *data)
{
  struct feynman_server *server
      = wl_container_of (listener, server, request_cursor);
  /* This event is raised by the seat when a client provides a cursor image */
  struct wlr_seat_pointer_request_set_cursor_event *event = data;
  struct wlr_seat_client *focused_client
      = server->seat->pointer_state.focused_client;
  /* This can be sent by any client, so we check to make sure this one is
   * actually has pointer focus first. */
  if (focused_client == event->seat_client)
    {
      /* Once we've vetted the client, we can tell the cursor to use the
       * provided surface as the cursor image. It will set the hardware cursor
       * on the output that it's currently on and continue to do so as the
       * cursor moves between outputs. */
      wlr_cursor_set_surface (server->cursor, event->surface, event->hotspot_x,
                              event->hotspot_y);
    }
}

static void
seat_request_set_selection (struct wl_listener *listener, void *data)
{
  /* This event is raised by the seat when a client wants to set the selection,
   * usually when the user copies something. wlroots allows compositors to
   * ignore such requests if they so choose, but in feynman we always honor
   */
  struct feynman_server *server
      = wl_container_of (listener, server, request_set_selection);
  struct wlr_seat_request_set_selection_event *event = data;
  wlr_seat_set_selection (server->seat, event->source, event->serial);
}

static struct feynman_view *
desktop_view_at (struct feynman_server *server, double lx, double ly,
                 struct wlr_surface **surface, double *sx, double *sy)
{
  /* This returns the topmost node in the scene at the given layout coords.
   * we only care about surface nodes as we are specifically looking for a
   * surface in the surface tree of a feynman_view. */
  struct wlr_scene_node *node
      = wlr_scene_node_at (&server->scene->node, lx, ly, sx, sy);
  if (node == NULL || node->type != WLR_SCENE_NODE_SURFACE)
    {
      return NULL;
    }
  *surface = wlr_scene_surface_from_node (node)->surface;
  /* Find the node corresponding to the feynman_view at the root of this
   * surface tree, it is the only one for which we set the data field. */
  while (node != NULL && node->data == NULL)
    {
      node = node->parent;
    }
  /* cppcheck-suppress nullPointerRedundantCheck */
  return node->data;
}

static void
process_cursor_move (struct feynman_server *server, uint32_t time)
{
  (void)time;
  /* Move the grabbed view to the new position. */
  struct feynman_view *view = server->grabbed_view;
  view->x                   = server->cursor->x - server->grab_x;
  view->y                   = server->cursor->y - server->grab_y;
  wlr_scene_node_set_position (view->scene_node, view->x, view->y);
}

static void
process_cursor_resize (struct feynman_server *server, uint32_t time)
{
  (void)time;
  /*
   * Resizing the grabbed view can be a little bit complicated, because we
   * could be resizing from any corner or edge. This not only resizes the view
   * on one or two axes, but can also move the view if you resize from the top
   * or left edges (or top-left corner).
   *
   * Note that I took some shortcuts here. In a more fleshed-out compositor,
   * you'd wait for the client to prepare a buffer at the new size, then
   * commit any movement that was prepared.
   */
  struct feynman_view *view = server->grabbed_view;
  double border_x           = server->cursor->x - server->grab_x;
  double border_y           = server->cursor->y - server->grab_y;
  int new_left              = server->grab_geobox.x;
  int new_right  = server->grab_geobox.x + server->grab_geobox.width;
  int new_top    = server->grab_geobox.y;
  int new_bottom = server->grab_geobox.y + server->grab_geobox.height;

  if (server->resize_edges & WLR_EDGE_TOP)
    {
      new_top = border_y;
      if (new_top >= new_bottom)
        {
          new_top = new_bottom - 1;
        }
    }
  else if (server->resize_edges & WLR_EDGE_BOTTOM)
    {
      new_bottom = border_y;
      if (new_bottom <= new_top)
        {
          new_bottom = new_top + 1;
        }
    }
  if (server->resize_edges & WLR_EDGE_LEFT)
    {
      new_left = border_x;
      if (new_left >= new_right)
        {
          new_left = new_right - 1;
        }
    }
  else if (server->resize_edges & WLR_EDGE_RIGHT)
    {
      new_right = border_x;
      if (new_right <= new_left)
        {
          new_right = new_left + 1;
        }
    }

  struct wlr_box geo_box;
  wlr_xdg_surface_get_geometry (view->xdg_surface, &geo_box);
  view->x = new_left - geo_box.x;
  view->y = new_top - geo_box.y;
  wlr_scene_node_set_position (view->scene_node, view->x, view->y);

  int new_width  = new_right - new_left;
  int new_height = new_bottom - new_top;
  wlr_xdg_toplevel_set_size (view->xdg_surface, new_width, new_height);
}

static void
process_cursor_motion (struct feynman_server *server, uint32_t time)
{
  /* If the mode is non-passthrough, delegate to those functions. */
  if (server->cursor_mode == FEYNMAN_CURSOR_MOVE)
    {
      process_cursor_move (server, time);
      return;
    }
  else if (server->cursor_mode == FEYNMAN_CURSOR_RESIZE)
    {
      process_cursor_resize (server, time);
      return;
    }

  /* Otherwise, find the view under the pointer and send the event along. */
  double sx, sy;
  struct wlr_seat *seat       = server->seat;
  struct wlr_surface *surface = NULL;
  struct feynman_view *view   = desktop_view_at (
        server, server->cursor->x, server->cursor->y, &surface, &sx, &sy);
  if (!view)
    {
      /* If there's no view under the cursor, set the cursor image to a
       * default. This is what makes the cursor image appear when you move it
       * around the screen, not over any views. */
      wlr_xcursor_manager_set_cursor_image (server->cursor_mgr, "left_ptr",
                                            server->cursor);
    }
  if (surface)
    {
      /*
       * Send pointer enter and motion events.
       *
       * The enter event gives the surface "pointer focus", which is distinct
       * from keyboard focus. You get pointer focus by moving the pointer over
       * a window.
       *
       * Note that wlroots will avoid sending duplicate enter/motion events if
       * the surface has already has pointer focus or if the client is already
       * aware of the coordinates passed.
       */
      wlr_seat_pointer_notify_enter (seat, surface, sx, sy);
      wlr_seat_pointer_notify_motion (seat, time, sx, sy);
    }
  else
    {
      /* Clear pointer focus so future button events and such are not sent to
       * the last client to have the cursor over it. */
      wlr_seat_pointer_clear_focus (seat);
    }
}

static void
server_cursor_motion (struct wl_listener *listener, void *data)
{
  /* This event is forwarded by the cursor when a pointer emits a _relative_
   * pointer motion event (i.e. a delta) */
  struct feynman_server *server
      = wl_container_of (listener, server, cursor_motion);
  struct wlr_event_pointer_motion *event = data;
  /* The cursor doesn't move unless we tell it to. The cursor automatically
   * handles constraining the motion to the output layout, as well as any
   * special configuration applied for the specific input device which
   * generated the event. You can pass NULL for the device if you want to move
   * the cursor around without any input. */
  wlr_cursor_move (server->cursor, event->device, event->delta_x,
                   event->delta_y);
  process_cursor_motion (server, event->time_msec);
}

static void
server_cursor_motion_absolute (struct wl_listener *listener, void *data)
{
  /* This event is forwarded by the cursor when a pointer emits an _absolute_
   * motion event, from 0..1 on each axis. This happens, for example, when
   * wlroots is running under a Wayland window rather than KMS+DRM, and you
   * move the mouse over the window. You could enter the window from any edge,
   * so we have to warp the mouse there. There is also some hardware which
   * emits these events. */
  struct feynman_server *server
      = wl_container_of (listener, server, cursor_motion_absolute);
  struct wlr_event_pointer_motion_absolute *event = data;
  wlr_cursor_warp_absolute (server->cursor, event->device, event->x, event->y);
  process_cursor_motion (server, event->time_msec);
}

static void
server_cursor_button (struct wl_listener *listener, void *data)
{
  /* This event is forwarded by the cursor when a pointer emits a button
   * event. */
  struct feynman_server *server
      = wl_container_of (listener, server, cursor_button);
  struct wlr_event_pointer_button *event = data;
  /* Notify the client with pointer focus that a button press has occurred */
  wlr_seat_pointer_notify_button (server->seat, event->time_msec,
                                  event->button, event->state);
  double sx, sy;
  struct wlr_surface *surface = NULL;
  struct feynman_view *view   = desktop_view_at (
        server, server->cursor->x, server->cursor->y, &surface, &sx, &sy);
  if (event->state == WLR_BUTTON_RELEASED)
    {
      /* If you released any buttons, we exit interactive move/resize mode. */
      server->cursor_mode = FEYNMAN_CURSOR_PASSTHROUGH;
    }
  else
    {
      /* Focus that client if the button was _pressed_ */
      focus_view (view, surface);
    }
}

static void
server_cursor_axis (struct wl_listener *listener, void *data)
{
  /* This event is forwarded by the cursor when a pointer emits an axis event,
   * for example when you move the scroll wheel. */
  struct feynman_server *server
      = wl_container_of (listener, server, cursor_axis);
  struct wlr_event_pointer_axis *event = data;
  /* Notify the client with pointer focus of the axis event. */
  wlr_seat_pointer_notify_axis (server->seat, event->time_msec,
                                event->orientation, event->delta,
                                event->delta_discrete, event->source);
}

static void
server_cursor_frame (struct wl_listener *listener, void *data)
{
  (void)data;
  /* This event is forwarded by the cursor when a pointer emits an frame
   * event. Frame events are sent after regular pointer events to group
   * multiple events together. For instance, two axis events may happen at the
   * same time, in which case a frame event won't be sent in between. */
  struct feynman_server *server
      = wl_container_of (listener, server, cursor_frame);
  /* Notify the client with pointer focus of the frame event. */
  wlr_seat_pointer_notify_frame (server->seat);
}

static void
output_frame (struct wl_listener *listener, void *data)
{
  (void)data;
  /* This function is called every time an output is ready to display a frame,
   * generally at the output's refresh rate (e.g. 60Hz). */
  struct feynman_output *output = wl_container_of (listener, output, frame);
  struct wlr_scene *scene       = output->server->scene;

  struct wlr_scene_output *scene_output
      = wlr_scene_get_scene_output (scene, output->wlr_output);

  /* Render the scene if needed and commit the output */
  wlr_scene_output_commit (scene_output);

  struct timespec now;
  clock_gettime (CLOCK_MONOTONIC, &now);
  wlr_scene_output_send_frame_done (scene_output, &now);
}

static void
server_new_output (struct wl_listener *listener, void *data)
{
  /* This event is raised by the backend when a new output (aka a display or
   * monitor) becomes available. */
  struct feynman_server *server
      = wl_container_of (listener, server, new_output);
  struct wlr_output *wlr_output = data;

  /* Configures the output created by the backend to use our allocator
   * and our renderer. Must be done once, before commiting the output */
  wlr_output_init_render (wlr_output, server->allocator, server->renderer);

  /* Some backends don't have modes. DRM+KMS does, and we need to set a mode
   * before we can use the output. The mode is a tuple of (width, height,
   * refresh rate), and each monitor supports only a specific set of modes. We
   * just pick the monitor's preferred mode, a more sophisticated compositor
   * would let the user configure it. */
  if (!wl_list_empty (&wlr_output->modes))
    {
      struct wlr_output_mode *mode = wlr_output_preferred_mode (wlr_output);
      wlr_output_set_mode (wlr_output, mode);
      wlr_output_enable (wlr_output, true);
      if (!wlr_output_commit (wlr_output))
        {
          return;
        }
    }

  /* Allocates and configures our state for this output */
  struct feynman_output *output = calloc (1, sizeof (struct feynman_output));
  output->wlr_output            = wlr_output;
  output->server                = server;
  /* Sets up a listener for the frame notify event. */
  output->frame.notify = output_frame;
  wl_signal_add (&wlr_output->events.frame, &output->frame);
  wl_list_insert (&server->outputs, &output->link);

  /* Adds this to the output layout. The add_auto function arranges outputs
   * from left-to-right in the order they appear. A more sophisticated
   * compositor would let the user configure the arrangement of outputs in the
   * layout.
   *
   * The output layout utility automatically adds a wl_output global to the
   * display, which Wayland clients can see to find out information about the
   * output (such as DPI, scale factor, manufacturer, etc).
   */
  wlr_output_layout_add_auto (server->output_layout, wlr_output);
}

static void
xdg_toplevel_map (struct wl_listener *listener, void *data)
{
  (void)data;
  /* Called when the surface is mapped, or ready to display on-screen. */
  struct feynman_view *view = wl_container_of (listener, view, map);

  wl_list_insert (&view->server->views, &view->link);

  focus_view (view, view->xdg_surface->surface);
}

static void
xdg_toplevel_unmap (struct wl_listener *listener, void *data)
{
  (void)data;
  /* Called when the surface is unmapped, and should no longer be shown. */
  struct feynman_view *view = wl_container_of (listener, view, unmap);

  wl_list_remove (&view->link);
}

static void
xdg_toplevel_handler (struct wl_listener *listener, void *data)
{
  (void)data;
  /* Called when the surface is destroyed and should never be shown again. */
  struct feynman_view *view = wl_container_of (listener, view, destroy);

  wl_list_remove (&view->map.link);
  wl_list_remove (&view->unmap.link);
  wl_list_remove (&view->destroy.link);
  wl_list_remove (&view->request_move.link);
  wl_list_remove (&view->request_resize.link);

  free (view);
}

static void
begin_interactive (struct feynman_view *view, enum feynman_cursor_mode mode,
                   uint32_t edges)
{
  /* This function sets up an interactive move or resize operation, where the
   * compositor stops propegating pointer events to clients and instead
   * consumes them itself, to move or resize windows. */
  struct feynman_server *server = view->server;
  struct wlr_surface *focused_surface
      = server->seat->pointer_state.focused_surface;
  if (view->xdg_surface->surface
      != wlr_surface_get_root_surface (focused_surface))
    {
      /* Deny move/resize requests from unfocused clients. */
      return;
    }
  server->grabbed_view = view;
  server->cursor_mode  = mode;

  if (mode == FEYNMAN_CURSOR_MOVE)
    {
      server->grab_x = server->cursor->x - view->x;
      server->grab_y = server->cursor->y - view->y;
    }
  else
    {
      struct wlr_box geo_box;
      wlr_xdg_surface_get_geometry (view->xdg_surface, &geo_box);

      double border_x = (view->x + geo_box.x)
                        + ((edges & WLR_EDGE_RIGHT) ? geo_box.width : 0);
      double border_y = (view->y + geo_box.y)
                        + ((edges & WLR_EDGE_BOTTOM) ? geo_box.height : 0);
      server->grab_x = server->cursor->x - border_x;
      server->grab_y = server->cursor->y - border_y;

      server->grab_geobox = geo_box;
      server->grab_geobox.x += view->x;
      server->grab_geobox.y += view->y;

      server->resize_edges = edges;
    }
}

static void
xdg_toplevel_request_move (struct wl_listener *listener, void *data)
{
  (void)data;
  /* This event is raised when a client would like to begin an interactive
   * move, typically because the user clicked on their client-side
   * decorations. Note that a more sophisticated compositor should check the
   * provided serial against a list of button press serials sent to this
   * client, to prevent the client from requesting this whenever they want. */
  struct feynman_view *view = wl_container_of (listener, view, request_move);
  begin_interactive (view, FEYNMAN_CURSOR_MOVE, 0);
}

static void
xdg_toplevel_request_resize (struct wl_listener *listener, void *data)
{
  /* This event is raised when a client would like to begin an interactive
   * resize, typically because the user clicked on their client-side
   * decorations. Note that a more sophisticated compositor should check the
   * provided serial against a list of button press serials sent to this
   * client, to prevent the client from requesting this whenever they want. */
  struct wlr_xdg_toplevel_resize_event *event = data;
  struct feynman_view *view = wl_container_of (listener, view, request_resize);
  begin_interactive (view, FEYNMAN_CURSOR_RESIZE, event->edges);
}

static void
server_new_xdg_surface (struct wl_listener *listener, void *data)
{
  /* This event is raised when wlr_xdg_shell receives a new xdg surface from a
   * client, either a toplevel (application window) or popup. */
  struct feynman_server *server
      = wl_container_of (listener, server, new_xdg_surface);
  struct wlr_xdg_surface *xdg_surface = data;

  /* We must add xdg popups to the scene graph so they get rendered. The
   * wlroots scene graph provides a helper for this, but to use it we must
   * provide the proper parent scene node of the xdg popup. To enable this,
   * we always set the user data field of xdg_surfaces to the corresponding
   * scene node. */
  if (xdg_surface->role == WLR_XDG_SURFACE_ROLE_POPUP)
    {
      struct wlr_xdg_surface *parent
          = wlr_xdg_surface_from_wlr_surface (xdg_surface->popup->parent);
      struct wlr_scene_node *parent_node = parent->data;
      xdg_surface->data
          = wlr_scene_xdg_surface_create (parent_node, xdg_surface);
      return;
    }
  assert (xdg_surface->role == WLR_XDG_SURFACE_ROLE_TOPLEVEL);

  /* Allocate a feynman_view for this surface */
  struct feynman_view *view = calloc (1, sizeof (struct feynman_view));
  view->server              = server;
  view->xdg_surface         = xdg_surface;
  view->scene_node = wlr_scene_xdg_surface_create (&view->server->scene->node,
                                                   view->xdg_surface);
  view->scene_node->data = view;
  xdg_surface->data      = view->scene_node;

  /* Listen to the various events it can emit */
  view->map.notify = xdg_toplevel_map;
  wl_signal_add (&xdg_surface->events.map, &view->map);
  view->unmap.notify = xdg_toplevel_unmap;
  wl_signal_add (&xdg_surface->events.unmap, &view->unmap);
  view->destroy.notify = xdg_toplevel_handler;
  wl_signal_add (&xdg_surface->events.destroy, &view->destroy);

  /* cotd */
  struct wlr_xdg_toplevel *toplevel = xdg_surface->toplevel;
  view->request_move.notify         = xdg_toplevel_request_move;
  wl_signal_add (&toplevel->events.request_move, &view->request_move);
  view->request_resize.notify = xdg_toplevel_request_resize;
  wl_signal_add (&toplevel->events.request_resize, &view->request_resize);
}

int
init_feynman_server (emacs_env *env, struct feynman_server *server)
{
  wlr_log_init (WLR_DEBUG, NULL);

  /* The Wayland display is managed by libwayland. It handles accepting
   * clients from the Unix socket, manging Wayland globals, and so on. */
  server->wl_display = wl_display_create ();
  /* The backend is a wlroots feature which abstracts the underlying input and
   * output hardware. The autocreate option will choose the most suitable
   * backend based on the current environment, such as opening an X11 window
   * if an X11 server is running. */
  server->backend = wlr_backend_autocreate (server->wl_display);

  /* Autocreates a renderer, either Pixman, GLES2 or Vulkan for us. The user
   * can also specify a renderer using the WLR_RENDERER env var.
   * The renderer is responsible for defining the various pixel formats it
   * supports for shared memory, this configures that for clients. */
  server->renderer = wlr_renderer_autocreate (server->backend);
  wlr_renderer_init_wl_display (server->renderer, server->wl_display);

  /* Autocreates an allocator for us.
   * The allocator is the bridge between the renderer and the backend. It
   * handles the buffer creation, allowing wlroots to render onto the
   * screen */
  server->allocator
      = wlr_allocator_autocreate (server->backend, server->renderer);

  /* This creates some hands-off wlroots interfaces. The compositor is
   * necessary for clients to allocate surfaces and the data device manager
   * handles the clipboard. Each of these wlroots interfaces has room for you
   * to dig your fingers in and play with their behavior if you want. Note that
   * the clients cannot set the selection directly without compositor approval,
   * see the handling of the request_set_selection event below.*/
  wlr_compositor_create (server->wl_display, server->renderer);
  wlr_data_device_manager_create (server->wl_display);

  /* Creates an output layout, which a wlroots utility for working with an
   * arrangement of screens in a physical layout. */
  server->output_layout = wlr_output_layout_create ();

  /* Configure a listener to be notified when new outputs are available on the
   * backend. */
  wl_list_init (&server->outputs);
  server->new_output.notify = server_new_output;
  wl_signal_add (&server->backend->events.new_output, &server->new_output);

  /* Create a scene graph. This is a wlroots abstraction that handles all
   * rendering and damage tracking. All the compositor author needs to do
   * is add things that should be rendered to the scene graph at the proper
   * positions and then call wlr_scene_output_commit() to render a frame if
   * necessary.
   */
  server->scene = wlr_scene_create ();
  wlr_scene_attach_output_layout (server->scene, server->output_layout);

  /* Set up the xdg-shell. The xdg-shell is a Wayland protocol which is used
   * for application windows. For more detail on shells, refer to my article:
   *
   * https://drewdevault.com/2018/07/29/Wayland-shells.html
   */
  wl_list_init (&server->views);
  server->xdg_shell              = wlr_xdg_shell_create (server->wl_display);
  server->new_xdg_surface.notify = server_new_xdg_surface;
  wl_signal_add (&server->xdg_shell->events.new_surface,
                 &server->new_xdg_surface);

  /*
   * Creates a cursor, which is a wlroots utility for tracking the cursor
   * image shown on screen.
   */
  server->cursor = wlr_cursor_create ();
  wlr_cursor_attach_output_layout (server->cursor, server->output_layout);

  /* Creates an xcursor manager, another wlroots utility which loads up
   * Xcursor themes to source cursor images from and makes sure that cursor
   * images are available at all scale factors on the screen (necessary for
   * HiDPI support). We add a cursor theme at scale factor 1 to begin with. */
  server->cursor_mgr = wlr_xcursor_manager_create (NULL, 24);
  wlr_xcursor_manager_load (server->cursor_mgr, 1);

  /*
   * wlr_cursor *only* displays an image on screen. It does not move around
   * when the pointer moves. However, we can attach input devices to it, and
   * it will generate aggregate events for all of them. In these events, we
   * can choose how we want to process them, forwarding them to clients and
   * moving the cursor around. More detail on this process is described in my
   * input handling blog post:
   *
   * https://drewdevault.com/2018/07/17/Input-handling-in-wlroots.html
   *
   * And more comments are sprinkled throughout the notify functions above.
   */
  server->cursor_motion.notify = server_cursor_motion;
  wl_signal_add (&server->cursor->events.motion, &server->cursor_motion);
  server->cursor_motion_absolute.notify = server_cursor_motion_absolute;
  wl_signal_add (&server->cursor->events.motion_absolute,
                 &server->cursor_motion_absolute);
  server->cursor_button.notify = server_cursor_button;
  wl_signal_add (&server->cursor->events.button, &server->cursor_button);
  server->cursor_axis.notify = server_cursor_axis;
  wl_signal_add (&server->cursor->events.axis, &server->cursor_axis);
  server->cursor_frame.notify = server_cursor_frame;
  wl_signal_add (&server->cursor->events.frame, &server->cursor_frame);

  /*
   * Configures a seat, which is a single "seat" at which a user sits and
   * operates the computer. This conceptually includes up to one keyboard,
   * pointer, touch, and drawing tablet device. We also rig up a listener to
   * let us know when new input devices are available on the backend.
   */
  wl_list_init (&server->keyboards);
  server->new_input.notify = server_new_input;
  wl_signal_add (&server->backend->events.new_input, &server->new_input);
  server->seat = wlr_seat_create (server->wl_display, "seat0");
  server->request_cursor.notify = seat_request_cursor;
  wl_signal_add (&server->seat->events.request_set_cursor,
                 &server->request_cursor);
  server->request_set_selection.notify = seat_request_set_selection;
  wl_signal_add (&server->seat->events.request_set_selection,
                 &server->request_set_selection);

  /* Add a Unix socket to the Wayland display. */
  const char *socket = wl_display_add_socket_auto (server->wl_display);
  if (!socket)
    {
      wlr_backend_destroy (server->backend);
      em_error (env, "Failed to create a unix socket!");
      return 1;
    }

  /* Start the backend. This will enumerate outputs and inputs, become the DRM
   * master, etc */
  if (!wlr_backend_start (server->backend))
    {
      wlr_backend_destroy (server->backend);
      wl_display_destroy (server->wl_display);
      em_error (env, "Couldn't start the backend");
      return 2;
    }

  /* Set the WAYLAND_DISPLAY environment variable to our socket */
  setenv ("WAYLAND_DISPLAY", socket, true);

  /* Run the Wayland event loop. This does not return until you exit the
   * compositor. Starting the backend rigged up all of the necessary event
   * loop configuration to listen to libinput events, DRM events, generate
   * frame events at the refresh rate, and so on. */
  em_message (env, "Running Wayland compositor on WAYLAND_DISPLAY=%s", socket);
  wlr_log (WLR_INFO, "Running Wayland compositor on WAYLAND_DISPLAY=%s",
           socket);

  return 0;
}

void
start_feynman (struct feynman_server *server)
{
  assert (server);
  wl_display_run (server->wl_display);
}

void
stop_feynman (emacs_env *env, struct feynman_server *server)
{
  (void)env;

  wl_display_terminate (server->wl_display);
  /* Once wl_display_run returns, we shut down the server-> */
  wl_display_destroy_clients (server->wl_display);
  wl_display_destroy (server->wl_display);
}