/* Clutter.
 * An OpenGL based 'interactive canvas' library.
 * Authored By Matthew Allum  <mallum@openedhand.com>
 * Copyright (C) 2006-2007 OpenedHand
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <string.h>
#include <sys/types.h>
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif

#include <sys/stat.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <errno.h>

#include "clutter-backend-x11.h"
#include "clutter-stage-x11.h"
#include "clutter-x11.h"
#include <X11/extensions/Xcomposite.h>

#include "../clutter-event.h"
#include "../clutter-main.h"
#include "../clutter-debug.h"
#include "../clutter-private.h"

#include "cogl/cogl.h"

G_DEFINE_TYPE (ClutterBackendX11, clutter_backend_x11, CLUTTER_TYPE_BACKEND);

struct _ClutterX11XInputDevice
{
  ClutterInputDevice device;
#ifdef USE_XINPUT
  XDevice           *xdevice;
  XEventClass        xevent_list[5];   /* MAX 5 event types */
  int                num_events;
#endif
  ClutterX11InputDeviceType type; /* FIXME: generic to ClutterInputDevice? */
};

#ifdef USE_XINPUT
void  _clutter_x11_register_xinput ();
#endif


/* atoms; remember to add the code that assigns the atom value to
 * the member of the ClutterBackendX11 structure if you add an
 * atom name here. do not change the order!
 */
static const gchar *atom_names[] = {
  "_NET_WM_PING",
  "_NET_WM_STATE",
  "_NET_WM_STATE_FULLSCREEN",
  "_NET_WM_USER_TIME",
  "WM_PROTOCOLS",
  "WM_DELETE_WINDOW",
  "_XEMBED",
  "_XEMBED_INFO",
  "_NET_WM_NAME",
  "UTF8_STRING",
};

static const guint n_atom_names = G_N_ELEMENTS (atom_names);

/* singleton object */
static ClutterBackendX11 *backend_singleton = NULL;

/* various flags corresponding to pre init setup calls */
static gboolean _no_xevent_retrieval = FALSE;
static gboolean _enable_xinput = FALSE;
static Display  *_foreign_dpy = NULL;

/* options */
static gchar *clutter_display_name = NULL;
static gint clutter_screen = 0;
static gboolean clutter_synchronise = FALSE;

/* X error trap */
static int TrappedErrorCode = 0;
static int (* old_error_handler) (Display *, XErrorEvent *);

gboolean
clutter_backend_x11_pre_parse (ClutterBackend  *backend,
                               GError         **error)
{
  const gchar *env_string;

  /* we don't fail here if DISPLAY is not set, as the user
   * might pass the --display command line switch
   */
  env_string = g_getenv ("DISPLAY");
  if (env_string)
    {
      clutter_display_name = g_strdup (env_string);
      env_string = NULL;
    }

  return TRUE;
}

gboolean
clutter_backend_x11_post_parse (ClutterBackend  *backend,
                                GError         **error)
{
  ClutterBackendX11 *backend_x11 = CLUTTER_BACKEND_X11 (backend);

  if (_foreign_dpy)
    backend_x11->xdpy = _foreign_dpy;
  /*
   * Only open connection if not already set by prior call to
   * clutter_x11_set_display()
   */
  if (!backend_x11->xdpy)
    {
      if (clutter_display_name)
	{
	  CLUTTER_NOTE (BACKEND, "XOpenDisplay on `%s'",
			clutter_display_name);
	  backend_x11->xdpy = XOpenDisplay (clutter_display_name);
	}
      else
	{
	  g_set_error (error, CLUTTER_INIT_ERROR,
		       CLUTTER_INIT_ERROR_BACKEND,
		       "Unable to open display. You have to set the DISPLAY "
		       "environment variable, or use the --display command "
		       "line argument");
	  return FALSE;
	}
    }

  if (backend_x11->xdpy)
    {
      Atom atoms[n_atom_names];
      double dpi;

      CLUTTER_NOTE (BACKEND, "Getting the X screen");

      if (clutter_screen == 0)
        backend_x11->xscreen = DefaultScreenOfDisplay (backend_x11->xdpy);
      else
        backend_x11->xscreen = ScreenOfDisplay (backend_x11->xdpy,
                                                clutter_screen);

      backend_x11->xscreen_num = XScreenNumberOfScreen (backend_x11->xscreen);

      backend_x11->xwin_root = RootWindow (backend_x11->xdpy,
                                           backend_x11->xscreen_num);

      backend_x11->display_name = g_strdup (clutter_display_name);

      dpi = (((double) DisplayHeight (backend_x11->xdpy, backend_x11->xscreen_num) * 25.4)
            / (double) DisplayHeightMM (backend_x11->xdpy, backend_x11->xscreen_num));

      clutter_backend_set_resolution (backend, dpi);

#ifdef USE_XINPUT
      _clutter_x11_register_xinput ();
#endif

      if (clutter_synchronise)
        XSynchronize (backend_x11->xdpy, True);

      XInternAtoms (backend_x11->xdpy,
                    (char **) atom_names, n_atom_names,
                    False, atoms);

      backend_x11->atom_NET_WM_PING = atoms[0];
      backend_x11->atom_NET_WM_STATE = atoms[1];
      backend_x11->atom_NET_WM_STATE_FULLSCREEN = atoms[2];
      backend_x11->atom_NET_WM_USER_TIME = atoms[3];
      backend_x11->atom_WM_PROTOCOLS = atoms[4];
      backend_x11->atom_WM_DELETE_WINDOW = atoms[5];
      backend_x11->atom_XEMBED = atoms[6];
      backend_x11->atom_XEMBED_INFO = atoms[7];
      backend_x11->atom_NET_WM_NAME = atoms[8];
      backend_x11->atom_UTF8_STRING = atoms[9];
    }

  g_free (clutter_display_name);

  CLUTTER_NOTE (BACKEND,
                "X Display `%s'[%p] opened (screen:%d, root:%u, dpi:%f)",
                backend_x11->display_name,
                backend_x11->xdpy,
                backend_x11->xscreen_num,
                (unsigned int) backend_x11->xwin_root,
                clutter_backend_get_resolution (backend));

  return TRUE;
}


static void
clutter_backend_x11_init_events (ClutterBackend *backend)
{
  CLUTTER_NOTE (EVENT, "initialising the event loop");

  if (!_no_xevent_retrieval)
    _clutter_backend_x11_events_init (backend);
}

static const GOptionEntry entries[] =
{
  {
    "display", 0,
    G_OPTION_FLAG_IN_MAIN,
    G_OPTION_ARG_STRING, &clutter_display_name,
    "X display to use", "DISPLAY"
  },
  {
    "screen", 0,
    G_OPTION_FLAG_IN_MAIN,
    G_OPTION_ARG_INT, &clutter_screen,
    "X screen to use", "SCREEN"
  },
  { "synch", 0,
    0,
    G_OPTION_ARG_NONE, &clutter_synchronise,
    "Make X calls synchronous", NULL,
  },
  { NULL }
};

void
clutter_backend_x11_add_options (ClutterBackend *backend,
                                 GOptionGroup   *group)
{
  g_option_group_add_entries (group, entries);
}

static void
clutter_backend_x11_finalize (GObject *gobject)
{
  ClutterBackendX11 *backend_x11 = CLUTTER_BACKEND_X11 (gobject);

  g_free (backend_x11->display_name);

  XCloseDisplay (backend_x11->xdpy);

  if (backend_singleton)
    backend_singleton = NULL;

  G_OBJECT_CLASS (clutter_backend_x11_parent_class)->finalize (gobject);
}

static void
clutter_backend_x11_dispose (GObject *gobject)
{
  ClutterBackendX11   *backend_x11 = CLUTTER_BACKEND_X11 (gobject);
  ClutterMainContext  *context;
  ClutterStageManager *stage_manager;

  CLUTTER_NOTE (BACKEND, "Disposing the of stages");

  context = clutter_context_get_default ();
  stage_manager = context->stage_manager;

  /* Destroy all of the stages. g_slist_foreach is used because the
     finalizer for the stages will remove the stage from the
     stage_manager's list and g_slist_foreach has some basic
     protection against this */
  g_slist_foreach (stage_manager->stages, (GFunc) clutter_actor_destroy, NULL);

  CLUTTER_NOTE (BACKEND, "Removing the event source");
  _clutter_backend_x11_events_uninit (CLUTTER_BACKEND (backend_x11));

  G_OBJECT_CLASS (clutter_backend_x11_parent_class)->dispose (gobject);
}

static GObject *
clutter_backend_x11_constructor (GType                  gtype,
                                 guint                  n_params,
                                 GObjectConstructParam *params)
{
  GObjectClass *parent_class;
  GObject *retval;

  if (!backend_singleton)
    {
      parent_class = G_OBJECT_CLASS (clutter_backend_x11_parent_class);
      retval = parent_class->constructor (gtype, n_params, params);

      backend_singleton = CLUTTER_BACKEND_X11 (retval);

      return retval;
    }

  g_warning ("Attempting to create a new backend object. This should "
             "never happen, so we return the singleton instance.");

  return g_object_ref (backend_singleton);
}

ClutterFeatureFlags
clutter_backend_x11_get_features (ClutterBackend *backend)
{
  return CLUTTER_FEATURE_STAGE_USER_RESIZE | CLUTTER_FEATURE_STAGE_CURSOR;
}

static void
clutter_backend_x11_class_init (ClutterBackendX11Class *klass)
{
  GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
  ClutterBackendClass *backend_class = CLUTTER_BACKEND_CLASS (klass);

  gobject_class->constructor = clutter_backend_x11_constructor;
  gobject_class->dispose = clutter_backend_x11_dispose;
  gobject_class->finalize = clutter_backend_x11_finalize;

  backend_class->pre_parse        = clutter_backend_x11_pre_parse;
  backend_class->post_parse       = clutter_backend_x11_post_parse;
  backend_class->init_events      = clutter_backend_x11_init_events;
  backend_class->add_options      = clutter_backend_x11_add_options;
  backend_class->get_features     = clutter_backend_x11_get_features;
}

static void
clutter_backend_x11_init (ClutterBackendX11 *backend_x11)
{
  ClutterBackend *backend = CLUTTER_BACKEND (backend_x11);

  /* FIXME: get from xsettings */
  clutter_backend_set_double_click_time (backend, 250);
  clutter_backend_set_double_click_distance (backend, 5);
  clutter_backend_set_resolution (backend, 96.0);
}

static int
error_handler(Display     *xdpy,
              XErrorEvent *error)
{
  TrappedErrorCode = error->error_code;
  return 0;
}

/**
 * clutter_x11_trap_x_errors:
 *
 * Traps every X error until clutter_x11_untrap_x_errors() is called.
 *
 * Since: 0.6
 */
void
clutter_x11_trap_x_errors (void)
{
  TrappedErrorCode  = 0;
  old_error_handler = XSetErrorHandler (error_handler);
}

/**
 * clutter_x11_untrap_x_errors:
 *
 * Removes the X error trap and returns the current status.
 *
 * Return value: the trapped error code, or 0 for success
 *
 * Since: 0.4
 */
gint
clutter_x11_untrap_x_errors (void)
{
  XSetErrorHandler (old_error_handler);

  return TrappedErrorCode;
}

/**
 * clutter_x11_get_default_display:
 *
 * Retrieves the pointer to the default display.
 *
 * Return value: the default display
 *
 * Since: 0.6
 */
Display *
clutter_x11_get_default_display (void)
{
  if (!backend_singleton)
    {
      g_critical ("X11 backend has not been initialised");
      return NULL;
    }

  return backend_singleton->xdpy;
}

/**
 * clutter_x11_set_display:
 * @xdpy: pointer to a X display connection.
 *
 * Sets the display connection Clutter should use; must be called
 * before clutter_init(), clutter_init_with_args() or other functions
 * pertaining Clutter's initialization process.
 *
 * If you are parsing the command line arguments by retrieving Clutter's
 * #GOptionGroup with clutter_get_option_group() and calling
 * g_option_context_parse() yourself, you should also call
 * clutter_x11_set_display() before g_option_context_parse().
 *
 * Since: 0.8
 */
void
clutter_x11_set_display (Display *xdpy)
{
  ClutterMainContext *ctx = clutter_context_get_default ();

  if (ctx->is_initialized)
    {
      g_critical ("Display connection already exists. You can only call "
		  "clutter_x11_set_display() once before clutter_init()\n");
      return;
    }

  _foreign_dpy= xdpy;
}

/**
 * clutter_x11_enable_xinput:
 *
 * Enables the use of the XInput extension if present on connected
 * XServer and support built into Clutter.  XInput allows for multiple
 * pointing devices to be used. This must be called before
 * clutter_init().
 *
 * You should use #clutter_x11_has_xinput to see if support was enabled.
 *
 * Since: 0.8
 */
void
clutter_x11_enable_xinput ()
{
  ClutterMainContext *ctx = clutter_context_get_default ();

  if (ctx->is_initialized)
    {
      g_warning  ("clutter_x11_enable_xinput should "
                  "be called before clutter_init");
      return;
    }

  _enable_xinput = TRUE;
}

/**
 * clutter_x11_disable_event_retrieval
 *
 * Disables retrieval of X events in the main loop. Use to create event-less
 * canvas or in conjunction with clutter_x11_handle_event.
 *
 * This function can only be called before calling clutter_init().
 *
 * Since: 0.8
 */
void
clutter_x11_disable_event_retrieval (void)
{
  ClutterMainContext *ctx = clutter_context_get_default ();

  if (ctx->is_initialized)
    {
      g_warning  ("clutter_x11_disable_event_retrieval should "
                  "be called before clutter_init");
      return;
    }

  _no_xevent_retrieval = TRUE;
}

/**
 * clutter_x11_has_event_retrieval
 *
 * Queries the X11 backend to check if event collection has been disabled.
 *
 * Return value: TRUE if event retrival has been disabled. FALSE otherwise.
 *
 * Since: 0.8
 */
gboolean
clutter_x11_has_event_retrieval (void)
{
  return !_no_xevent_retrieval;
}

/**
 * clutter_x11_get_default_screen:
 *
 * Gets the number of the default X Screen object.
 *
 * Return value: the number of the default screen
 *
 * Since: 0.6
 */
int
clutter_x11_get_default_screen (void)
{
  if (!backend_singleton)
    {
      g_critical ("X11 backend has not been initialised");
      return 0;
    }

  return backend_singleton->xscreen_num;
}

/**
 * clutter_x11_get_root_window:
 *
 * Retrieves the root window.
 *
 * Return value: the id of the root window
 *
 * Since: 0.6
 */
Window
clutter_x11_get_root_window (void)
{
  if (!backend_singleton)
    {
      g_critical ("X11 backend has not been initialised");
      return None;
    }

  return backend_singleton->xwin_root;
}

/**
 * clutter_x11_add_filter:
 * @func: a filter function
 * @data: user data to be passed to the filter function, or %NULL
 *
 * Adds an event filter function.
 *
 * Since: 0.6
 */
void
clutter_x11_add_filter (ClutterX11FilterFunc func,
                        gpointer             data)
{
  ClutterX11EventFilter *filter;

  g_return_if_fail (func != NULL);

  if (!backend_singleton)
    {
      g_critical ("X11 backend has not been initialised");
      return;
    }

  filter = g_new0 (ClutterX11EventFilter, 1);
  filter->func = func;
  filter->data = data;

  backend_singleton->event_filters =
    g_slist_append (backend_singleton->event_filters, filter);

  return;
}

/**
 * clutter_x11_remove_filter:
 * @func: a filter function
 * @data: user data to be passed to the filter function, or %NULL
 *
 * Removes the given filter function.
 *
 * Since: 0.6
 */
void
clutter_x11_remove_filter (ClutterX11FilterFunc func,
                           gpointer             data)
{
  GSList                *tmp_list, *this;
  ClutterX11EventFilter *filter;

  g_return_if_fail (func != NULL);

  tmp_list = backend_singleton->event_filters;

  while (tmp_list)
    {
      filter   = tmp_list->data;
      this     =  tmp_list;
      tmp_list = tmp_list->next;

      if (filter->func == func && filter->data == data)
        {
          backend_singleton->event_filters =
            g_slist_remove_link (backend_singleton->event_filters, this);

          g_slist_free_1 (this);
          g_free (filter);

          return;
        }
    }
}

#ifdef USE_XINPUT

void
_clutter_x11_register_xinput ()
{
  XDeviceInfo *xdevices = NULL;
  XDeviceInfo *info = NULL;

  XDevice *xdevice = NULL;

  XInputClassInfo *xclass_info = NULL;
  XExtensionVersion *ext;

  gint num_devices = 0;
  gint num_events = 0;
  gint i = 0, j = 0;
  gboolean have_an_xpointer = FALSE;

  ClutterBackendX11      *x11b;
  ClutterX11XInputDevice *device = NULL;

  ClutterMainContext  *context;

  if (!backend_singleton)
    {
      g_critical ("X11 backend has not been initialised");
      return;
    }

  if (!_enable_xinput)
    {
      CLUTTER_NOTE (BACKEND, "Not enabling XInput");
      return;
    }

  context = clutter_context_get_default ();

  backend_singleton->have_xinput = TRUE;

  ext = XGetExtensionVersion(backend_singleton->xdpy, INAME);

  if (!ext || (ext == (XExtensionVersion*) NoSuchExtension))
    {
      backend_singleton->have_xinput = FALSE;
      return;
    }

  x11b = backend_singleton;

  xdevices = XListInputDevices (x11b->xdpy, &num_devices);

  CLUTTER_NOTE (BACKEND, "%d XINPUT devices found", num_devices);

  if (num_devices == 0)
    {
      backend_singleton->have_xinput = FALSE;
      return;
    }

  for (i = 0; i < num_devices; i++)
  {
    num_events = 0;
    info = xdevices + i;

    CLUTTER_NOTE (BACKEND, "Considering %li with type %d",
                  info->id, info->use);

    /* Only want 'raw' devices themselves not virtual ones */
    if (info->use == IsXExtensionPointer ||
        /*info->use == IsXExtensionKeyboard || XInput is broken */
        info->use == IsXExtensionDevice)
    {
      clutter_x11_trap_x_errors ();
      xdevice = XOpenDevice (x11b->xdpy, info->id);
      if (clutter_x11_untrap_x_errors () || xdevice == NULL)
        continue;

      /* Create the appropriate Clutter device */
      device = g_new0 (ClutterX11XInputDevice, 1);
      context->input_devices = g_slist_append (context->input_devices, device);

      device->device.id = info->id;

      /* FIXME: some kind of general device_init() call should do below */
      device->device.click_count = 0;
      device->device.previous_time = 0;
      device->device.previous_x = -1;
      device->device.previous_y = -1;
      device->device.previous_button_number = -1;

      device->xdevice = xdevice;
      device->num_events = 0;

      switch (info->use)
      {
        case IsXExtensionPointer:
          device->type = CLUTTER_X11_XINPUT_POINTER_DEVICE;
          have_an_xpointer = TRUE;
          break;
        /* XInput is broken:
        case IsXExtensionKeyboard:
          device->type = CLUTTER_X11_XINPUT_KEYBOARD_DEVICE;
          break;*/
        case IsXExtensionDevice:
          device->type = CLUTTER_X11_XINPUT_EXTENSION_DEVICE;
          break;
      }

      CLUTTER_NOTE (BACKEND, "Registering XINPUT device with XID: %li",
                    xdevice->device_id);

      /* We must go through all the classes supported by this device and
       * register the appropriate events we want. Each class only appears
       * once. We need to store the types with the stage since they are
       * created dynamically by the server. They are not device specific.
       */
      for (j = 0; j < xdevice->num_classes; j++)
      {
        xclass_info = xdevice->classes + j;

        switch (xclass_info->input_class)
        {
#if 0
      /* We do not do XInput keyboard events yet, since it is broken */
          case KeyClass:
            DeviceKeyPress (xdevice,
                x11b->event_types [CLUTTER_X11_XINPUT_KEY_PRESS_EVENT],
                device->xevent_list [num_events]);
            num_events++;

            DeviceKeyRelease (xdevice,
                x11b->event_types [CLUTTER_X11_XINPUT_KEY_RELEASE_EVENT],
                device->xevent_list [num_events]);
            num_events++;
            break;
#endif

          case ButtonClass:
            DeviceButtonPress (xdevice,
                x11b->event_types [CLUTTER_X11_XINPUT_BUTTON_PRESS_EVENT],
                device->xevent_list [num_events]);
            num_events++;

            DeviceButtonRelease (xdevice,
                x11b->event_types [CLUTTER_X11_XINPUT_BUTTON_RELEASE_EVENT],
                device->xevent_list [num_events]);
            num_events++;
            break;

          case ValuatorClass:
            DeviceMotionNotify (xdevice,
                x11b->event_types [CLUTTER_X11_XINPUT_MOTION_NOTIFY_EVENT],
                                   device->xevent_list [num_events]);
            num_events++;
            break;
        }
      }

      if (info->use == IsXExtensionPointer && num_events > 0)
        have_an_xpointer = TRUE;

      device->num_events  = num_events;
    }
  }

  XFree (xdevices);

  if (!have_an_xpointer)
    {
      /* Something is likely wrong with Xinput setup so we basically
       * abort here and fall back to lofi regular xinput.
      */
      g_warning ("No usuable XInput pointing devices found");
      backend_singleton->have_xinput = FALSE;
      g_slist_free (context->input_devices);
      context->input_devices = NULL;
    }
}

void
_clutter_x11_unregister_xinput ()
{

}

void
_clutter_x11_select_events (Window xwin)
{
  GSList *list_it;
  ClutterX11XInputDevice *device = NULL;

  ClutterMainContext  *context;

  context = clutter_context_get_default ();

  if (!backend_singleton)
    {
      g_critical ("X11 backend has not been initialised");
      return;
    }

  for (list_it = context->input_devices;
       list_it != NULL;
       list_it = list_it->next)
  {
    device = (ClutterX11XInputDevice *)list_it->data;

    XSelectExtensionEvent (backend_singleton->xdpy,
                           xwin,
                           device->xevent_list,
                           device->num_events);
  }
}

ClutterX11XInputDevice *
_clutter_x11_get_device_for_xid (XID id)
{
  GSList *list_it;
  ClutterX11XInputDevice *device = NULL;
  ClutterMainContext  *context;

  context = clutter_context_get_default ();

  if (!backend_singleton)
    {
      g_critical ("X11 backend has not been initialised");
      return NULL;
    }

  for (list_it = context->input_devices;
       list_it != NULL;
       list_it = list_it->next)
  {
    device = (ClutterX11XInputDevice *)list_it->data;

    if (device->xdevice->device_id == id)
      return device;
  }

  return NULL;
}
#endif

/* FIXME: This nasty little func needs moving elsewhere.. */
GSList*
clutter_x11_get_input_devices (void)
{
  ClutterMainContext  *context;

#ifdef USE_XINPUT
  if (!backend_singleton)
    {
      g_critical ("X11 backend has not been initialised");
      return NULL;
    }

  context = clutter_context_get_default ();

  return context->input_devices;
#else
  return NULL;
#endif
}

/**
 * clutter_x11_get_input_device_type:
 * @device: a #ClutterX11XInputDevice
 *
 * Retrieves the type of @device.
 *
 * Return value: the type of the device
 *
 * Since: 0.8
 */
ClutterX11InputDeviceType
clutter_x11_get_input_device_type (ClutterX11XInputDevice *device)
{
  return device->type;
}

/**
 * clutter_x11_has_xinput:
 *
 * Gets whether Clutter has XInput support.
 *
 * Return value: %TRUE if Clutter was compiled with XInput support
 *   and XInput support is available at run time.
 *
 * Since: 0.8
 */
gboolean
clutter_x11_has_xinput (void)
{
#ifdef USE_XINPUT
  if (!backend_singleton)
    {
      g_critical ("X11 backend has not been initialised");
      return FALSE;
    }

  return backend_singleton->have_xinput;
#else
  return FALSE;
#endif
}

gboolean
clutter_x11_has_composite_extension (void)
{
  static gboolean                 have_composite = FALSE, done_check = FALSE;
  int                             error = 0, event = 0;
  Display                        *dpy;

  if (done_check)
    return have_composite;

  if (!backend_singleton)
    {
      g_critical ("X11 backend has not been initialised");
      return FALSE;
    }

  dpy = clutter_x11_get_default_display();

  if (XCompositeQueryExtension (dpy, &event, &error))
    {
      int major = 0, minor = 0;
      if (XCompositeQueryVersion (dpy, &major, &minor))
        {
          if (major >= 0 && minor >= 3)
            have_composite = TRUE;
        }
    }

  done_check = TRUE;

  return have_composite;
}