Add better tracking of real stacking order

Wedging override-redirect windows into the constraint code in stack.c
results in Mutter getting confused about the stacking order of
these windows with respect to other windows, and may also in some
cases cause Mutter to restack override-redirect windows.

core/stack-tracker.c core/stack-tracker.h: MetaStackTracker - combine
  events received from the X server with local changes we have made
  to come up with the best possible idea of what the stacking order
  is at any one point in time.

core/screen.c core/screen-private.h: Create a MetaStackTracker for
  the screen.

core/display.c: Feed relevant events to MetaStackTracker

core/frame.c core/screen.c core/stack.c: When we make changes to the
  stacking order or add windows, record those changes immediatley
  in MetaStackTracker so we have the information without waiting
  for a round-trip.

include/ui.h ui/ui.c: meta_ui_create_frame_window add a return value
  for the X request serial used to create the window.

http://bugzilla.gnome.org/show_bug.cgi?id=585984

src/Makefile.am

@@ -70,6 +70,8 @@ mutter_SOURCES= 				\
 	core/session.h				\
 	core/stack.c				\
 	core/stack.h				\
+	core/stack-tracker.c			\
+	core/stack-tracker.h			\
 	core/util.c				\
 	include/util.h				\
 	core/window-props.c			\

src/core/display.c

@@ -2019,9 +2019,27 @@ event_callback (XEvent   *event,
     case VisibilityNotify:
       break;
     case CreateNotify:
+      {
+        MetaScreen *screen;
+
+        screen = meta_display_screen_for_root (display,
+                                               event->xcreatewindow.parent);
+        if (screen)
+          meta_stack_tracker_create_event (screen->stack_tracker,
+                                           &event->xcreatewindow);
+      }
       break;
       
     case DestroyNotify:
+      {
+        MetaScreen *screen;
+
+        screen = meta_display_screen_for_root (display,
+                                               event->xdestroywindow.event);
+        if (screen)
+          meta_stack_tracker_destroy_event (screen->stack_tracker,
+                                            &event->xdestroywindow);
+      }
       if (window)
         {
           /* FIXME: It sucks that DestroyNotify events don't come with
@@ -2135,8 +2153,30 @@ event_callback (XEvent   *event,
         }
       break;
     case ReparentNotify:
+      {
+        MetaScreen *screen;
+
+        screen = meta_display_screen_for_root (display,
+                                               event->xconfigure.event);
+        if (screen)
+          {
+            if (screen)
+              meta_stack_tracker_reparent_event (screen->stack_tracker,
+                                                 &event->xreparent);
+          }
+      }
       break;
     case ConfigureNotify:
+      if (event->xconfigure.event != event->xconfigure.window)
+        {
+          MetaScreen *screen;
+
+          screen = meta_display_screen_for_root (display,
+                                                 event->xconfigure.event);
+          if (screen)
+            meta_stack_tracker_configure_event (screen->stack_tracker,
+                                                &event->xconfigure);
+        }
       if (window && window->override_redirect)
 	meta_window_configure_notify (window, &event->xconfigure);
       else

src/core/frame.c

@@ -48,6 +48,7 @@ meta_window_ensure_frame (MetaWindow *window)
   MetaFrame *frame;
   XSetWindowAttributes attrs;
   Visual *visual;
+  gulong create_serial;
   
   if (window->frame)
     return;
@@ -105,7 +106,11 @@ meta_window_ensure_frame (MetaWindow *window)
                                                 frame->rect.y,
 						frame->rect.width,
 						frame->rect.height,
-						frame->window->screen->number);
+						frame->window->screen->number,
+                                                &create_serial);
+  meta_stack_tracker_record_add (window->screen->stack_tracker,
+                                 frame->xwindow,
+                                 create_serial);
 
   meta_verbose ("Frame for %s is 0x%lx\n", frame->window->desc, frame->xwindow);
   attrs.event_mask = EVENT_MASK;
@@ -141,6 +146,9 @@ meta_window_ensure_frame (MetaWindow *window)
   window->rect.x = 0;
   window->rect.y = 0;
 
+  meta_stack_tracker_record_remove (window->screen->stack_tracker,
+                                    window->xwindow,
+                                    XNextRequest (window->display->xdisplay));
   XReparentWindow (window->display->xdisplay,
                    window->xwindow,
                    frame->xwindow,
@@ -199,6 +207,9 @@ meta_window_destroy_frame (MetaWindow *window)
                   "Incrementing unmaps_pending on %s for reparent back to root\n", window->desc);
       window->unmaps_pending += 1;
     }
+  meta_stack_tracker_record_add (window->screen->stack_tracker,
+                                 window->xwindow,
+                                 XNextRequest (window->display->xdisplay));
   XReparentWindow (window->display->xdisplay,
                    window->xwindow,
                    window->screen->xroot,

src/core/screen-private.h

@@ -36,6 +36,7 @@
 #include "display-private.h"
 #include "screen.h"
 #include <X11/Xutil.h>
+#include "stack-tracker.h"
 #include "alttabhandler.h"
 #include "ui.h"
 
@@ -94,6 +95,7 @@ struct _MetaScreen
   GList *workspaces;
 
   MetaStack *stack;
+  MetaStackTracker *stack_tracker;
 
   MetaCursor current_cursor;
 

src/core/screen.c

@@ -439,11 +439,15 @@ create_guard_window (Display *xdisplay, MetaScreen *screen)
 {
   XSetWindowAttributes attributes;
   Window guard_window;
+  gulong create_serial;
   
   attributes.event_mask = NoEventMask;
   attributes.override_redirect = True;
   attributes.background_pixel = BlackPixel (xdisplay, screen->number);
 
+  /* We have to call record_add() after we have the new window ID,
+   * so save the serial for the CreateWindow request until then */
+  create_serial = XNextRequest(xdisplay);
   guard_window =
     XCreateWindow (xdisplay,
 		   screen->xroot,
@@ -457,6 +461,13 @@ create_guard_window (Display *xdisplay, MetaScreen *screen)
 		   CopyFromParent, /* visual */
 		   CWEventMask|CWOverrideRedirect|CWBackPixel,
 		   &attributes);
+  meta_stack_tracker_record_add (screen->stack_tracker,
+                                 guard_window,
+                                 create_serial);
+
+  meta_stack_tracker_record_lower (screen->stack_tracker,
+                                   guard_window,
+                                   XNextRequest (xdisplay));
   XLowerWindow (xdisplay, guard_window);
   XMapWindow (xdisplay, guard_window);
   return guard_window;
@@ -730,6 +741,7 @@ meta_screen_new (MetaDisplay *display,
   screen->ws_popup = NULL;
   
   screen->stack = meta_stack_new (screen);
+  screen->stack_tracker = meta_stack_tracker_new (screen);
 
   meta_prefs_add_listener (prefs_changed_callback, screen);
 
@@ -807,6 +819,7 @@ meta_screen_free (MetaScreen *screen,
   meta_ui_free (screen->ui);
 
   meta_stack_free (screen->stack);
+  meta_stack_tracker_free (screen->stack_tracker);
 
   meta_error_trap_push_with_return (screen->display);
   XSelectInput (screen->display->xdisplay, screen->xroot, 0);

src/core/stack-tracker.c

@@ -0,0 +1,630 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
+
+/*
+ * Copyright (C) 2009 Red Hat, Inc.
+ *
+ * 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; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * 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, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+ * 02111-1307, USA.
+ */
+
+#include <config.h>
+
+#include <string.h>
+
+#include "screen-private.h"
+#include "stack-tracker.h"
+#include "util.h"
+
+/* The complexity here comes from resolving two competing factors:
+ *
+ *  - We need to have a view of the stacking order that takes into
+ *    account everything we have done without waiting for events
+ *    back from the X server; we don't want to draw intermediate
+ *    partially-stacked stack states just because we haven't received
+ *    some notification yet.
+ *
+ *  - Only the X server has an accurate view of the complete stacking;
+ *    when we make a request to restack windows, we don't know how
+ *    it will affect override-redirect windows, because at any point
+ *    applications may restack these windows without our involvement.
+ *
+ * The technique we use is that we keep three sets of information:
+ *
+ *  - The stacking order on the server as known from the last
+ *    event we received.
+ *  - A queue of stacking requests that *we* made subsequent to
+ *    that last event.
+ *  - A predicted stacking order, derived from applying the queued
+ *    requests to the last state from the server.
+ *
+ * When we receive a new event: a) we compare the serial in the event to
+ * the serial of the queued requests and remove any that are now
+ * no longer pending b) drop the predicted stacking order to recompute
+ * it at the next opportunity.
+ *
+ * Possible optimizations:
+ *  Keep the stacks as an array + reverse-mapping hash table to avoid
+ *    linear lookups.
+ *  Keep the stacks as a GList + reverse-mapping hash table to avoid
+ *    linear lookups and to make restacking constant-time.
+ */
+
+typedef union _MetaStackOp MetaStackOp;
+
+typedef enum {
+  STACK_OP_ADD,
+  STACK_OP_REMOVE,
+  STACK_OP_RAISE_ABOVE,
+  STACK_OP_LOWER_BELOW
+} MetaStackOpType;
+
+/* MetaStackOp represents a "stacking operation" - a change to
+ * apply to a window stack. Depending on the context, it could
+ * either reflect a request we have sent to the server, or a
+ * notification event we received from the X server.
+ */
+union _MetaStackOp
+{
+  struct {
+    MetaStackOpType type;
+    gulong serial;
+  } any;
+  struct {
+    MetaStackOpType type;
+    gulong serial;
+    Window window;
+  } add;
+  struct {
+    MetaStackOpType type;
+    gulong serial;
+    Window window;
+  } remove;
+  struct {
+    MetaStackOpType type;
+    gulong serial;
+    Window window;
+    Window sibling;
+  } raise_above;
+  struct {
+    MetaStackOpType type;
+    gulong serial;
+    Window window;
+    Window sibling;
+  } lower_below;
+};
+
+struct _MetaStackTracker
+{
+  MetaScreen *screen;
+
+  /* This is the last state of the stack as based on events received
+   * from the X server.
+   */
+  GArray *server_stack;
+
+  /* This is the serial of the last request we made that was reflected
+   * in server_stack
+   */
+  gulong server_serial;
+
+  /* This is a queue of requests we've made to change the stacking order,
+   * where we haven't yet gotten a reply back from the server.
+   */
+  GQueue *queued_requests;
+
+  /* This is how we think the stack is, based on server_stack, and
+   * on requests we've made subsequent to server_stack
+   */
+  GArray *predicted_stack;
+};
+
+static void
+meta_stack_op_dump (MetaStackOp *op,
+		    const char  *prefix,
+		    const char  *suffix)
+{
+  switch (op->any.type)
+    {
+    case STACK_OP_ADD:
+      meta_topic (META_DEBUG_STACK, "%sADD(%#lx; %ld)%s",
+		  prefix, op->add.window, op->any.serial, suffix);
+      break;
+    case STACK_OP_REMOVE:
+      meta_topic (META_DEBUG_STACK, "%sREMOVE(%#lx; %ld)%s",
+		  prefix, op->add.window, op->any.serial, suffix);
+      break;
+    case STACK_OP_RAISE_ABOVE:
+      meta_topic (META_DEBUG_STACK, "%sRAISE_ABOVE(%#lx, %#lx; %ld)%s",
+		  prefix,
+                  op->raise_above.window, op->raise_above.sibling,
+                  op->any.serial,
+                  suffix);
+      break;
+    case STACK_OP_LOWER_BELOW:
+      meta_topic (META_DEBUG_STACK, "%sLOWER_BELOW(%#lx, %#lx; %ld)%s",
+		  prefix,
+                  op->lower_below.window, op->lower_below.sibling,
+                  op->any.serial,
+                  suffix);
+      break;
+    }
+}
+
+static void
+meta_stack_tracker_dump (MetaStackTracker *tracker)
+{
+  guint i;
+  GList *l;
+
+  meta_topic (META_DEBUG_STACK, "MetaStackTracker state (screen=%d)\n", tracker->screen->number);
+  meta_push_no_msg_prefix ();
+  meta_topic (META_DEBUG_STACK, "  server_serial: %ld\n", tracker->server_serial);
+  meta_topic (META_DEBUG_STACK, "  server_stack: ");
+  for (i = 0; i < tracker->server_stack->len; i++)
+    meta_topic (META_DEBUG_STACK, "  %#lx", g_array_index (tracker->server_stack, Window, i));
+  if (tracker->predicted_stack)
+    {
+      meta_topic (META_DEBUG_STACK, "\n  predicted_stack: ");
+      for (i = 0; i < tracker->predicted_stack->len; i++)
+	meta_topic (META_DEBUG_STACK, "  %#lx", g_array_index (tracker->predicted_stack, Window, i));
+    }
+  meta_topic (META_DEBUG_STACK, "\n  queued_requests: [");
+  for (l = tracker->queued_requests->head; l; l = l->next)
+    {
+      MetaStackOp *op = l->data;
+      meta_stack_op_dump (op, "", l->next ? ", " : "");
+    }
+  meta_topic (META_DEBUG_STACK, "]\n");
+  meta_pop_no_msg_prefix ();
+}
+
+static void
+meta_stack_op_free (MetaStackOp *op)
+{
+  g_slice_free (MetaStackOp, op);
+}
+
+static int
+find_window (GArray *stack,
+	     Window  window)
+{
+  guint i;
+
+  for (i = 0; i < stack->len; i++)
+    if (g_array_index (stack, Window, i) == window)
+      return i;
+
+  return -1;
+}
+
+static void
+move_window_above (GArray *stack,
+                   Window  window,
+                   int     old_pos,
+                   int     above_pos)
+{
+  int i;
+
+  if (old_pos < above_pos)
+    {
+      for (i = old_pos; i < above_pos; i++)
+	g_array_index (stack, Window, i) = g_array_index (stack, Window, i + 1);
+
+      g_array_index (stack, Window, above_pos) = window;
+    }
+  else if (old_pos > above_pos + 1)
+    {
+      for (i = old_pos; i > above_pos + 1; i--)
+	g_array_index (stack, Window, i) = g_array_index (stack, Window, i - 1);
+
+      g_array_index (stack, Window, above_pos + 1) = window;
+    }
+}
+
+static void
+meta_stack_op_apply (MetaStackOp *op,
+		     GArray      *stack)
+{
+  switch (op->any.type)
+    {
+    case STACK_OP_ADD:
+      {
+	int old_pos = find_window (stack, op->add.window);
+	if (old_pos >= 0)
+	  {
+	    g_warning ("STACK_OP_ADD: window %#lx already in stack",
+		       op->add.window);
+	    return;
+	  }
+
+	g_array_append_val (stack, op->add.window);
+	break;
+      }
+    case STACK_OP_REMOVE:
+      {
+	int old_pos = find_window (stack, op->remove.window);
+	if (old_pos < 0)
+	  {
+	    g_warning ("STACK_OP_REMOVE: window %#lx not in stack",
+		       op->remove.window);
+	    return;
+	  }
+
+	g_array_remove_index (stack, old_pos);
+	break;
+      }
+    case STACK_OP_RAISE_ABOVE:
+      {
+	int old_pos = find_window (stack, op->raise_above.window);
+	int above_pos;
+	if (old_pos < 0)
+	  {
+	    g_warning ("STACK_OP_RAISE_ABOVE: window %#lx not in stack",
+		       op->raise_above.window);
+	    return;
+	  }
+
+	if (op->raise_above.sibling != None)
+	  {
+	    above_pos = find_window (stack, op->raise_above.sibling);
+	    if (above_pos < 0)
+	      {
+		g_warning ("STACK_OP_RAISE_ABOVE: sibling window %#lx not in stack",
+			   op->raise_above.sibling);
+		return;
+	      }
+	  }
+	else
+	  {
+	    above_pos = -1;
+	  }
+
+	move_window_above (stack, op->raise_above.window, old_pos, above_pos);
+	break;
+      }
+    case STACK_OP_LOWER_BELOW:
+      {
+	int old_pos = find_window (stack, op->lower_below.window);
+	int above_pos;
+	if (old_pos < 0)
+	  {
+	    g_warning ("STACK_OP_LOWER_BELOW: window %#lx not in stack",
+		       op->lower_below.window);
+	    return;
+	  }
+
+	if (op->lower_below.sibling != None)
+	  {
+	    int below_pos = find_window (stack, op->lower_below.sibling);
+	    if (below_pos < 0)
+	      {
+		g_warning ("STACK_OP_LOWER_BELOW: sibling window %#lx not in stack",
+			   op->lower_below.sibling);
+		return;
+	      }
+
+	    above_pos = below_pos - 1;
+	  }
+	else
+	  {
+	    above_pos = stack->len - 1;
+	  }
+
+	move_window_above (stack, op->lower_below.window, old_pos, above_pos);
+	break;
+      }
+    }
+}
+
+static GArray *
+copy_stack (Window *windows,
+	    guint   n_windows)
+{
+  GArray *stack = g_array_new (FALSE, FALSE, sizeof (Window));
+
+  g_array_set_size (stack, n_windows);
+  memcpy (stack->data, windows, sizeof (Window) * n_windows);
+
+  return stack;
+}
+
+MetaStackTracker *
+meta_stack_tracker_new (MetaScreen *screen)
+{
+  MetaStackTracker *tracker;
+  Window ignored1, ignored2;
+  Window *children;
+  guint n_children;
+
+  tracker = g_new0 (MetaStackTracker, 1);
+  tracker->screen = screen;
+
+  tracker->server_serial = XNextRequest (screen->display->xdisplay);
+
+  XQueryTree (screen->display->xdisplay,
+              screen->xroot,
+              &ignored1, &ignored2, &children, &n_children);
+  tracker->server_stack = copy_stack (children, n_children);
+  XFree (children);
+
+  tracker->queued_requests = g_queue_new ();
+
+  return tracker;
+}
+
+void
+meta_stack_tracker_free (MetaStackTracker *tracker)
+{
+  g_array_free (tracker->server_stack, TRUE);
+  if (tracker->predicted_stack)
+    g_array_free (tracker->predicted_stack, TRUE);
+
+  g_queue_foreach (tracker->queued_requests, (GFunc)meta_stack_op_free, NULL);
+  g_queue_free (tracker->queued_requests);
+  tracker->queued_requests = NULL;
+}
+
+static void
+stack_tracker_queue_request (MetaStackTracker *tracker,
+			     MetaStackOp      *op)
+{
+  meta_stack_op_dump (op, "Queueing: ", "\n");
+  g_queue_push_tail (tracker->queued_requests, op);
+  if (tracker->predicted_stack)
+    meta_stack_op_apply (op, tracker->predicted_stack);
+  meta_stack_tracker_dump (tracker);
+}
+
+void
+meta_stack_tracker_record_add (MetaStackTracker *tracker,
+			       Window            window,
+			       gulong            serial)
+{
+  MetaStackOp *op = g_slice_new (MetaStackOp);
+
+  op->any.type = STACK_OP_ADD;
+  op->any.serial = serial;
+  op->add.window = window;
+
+  stack_tracker_queue_request (tracker, op);
+}
+
+void
+meta_stack_tracker_record_remove (MetaStackTracker *tracker,
+				  Window            window,
+				  gulong            serial)
+{
+  MetaStackOp *op = g_slice_new (MetaStackOp);
+
+  op->any.type = STACK_OP_REMOVE;
+  op->any.serial = serial;
+  op->remove.window = window;
+
+  stack_tracker_queue_request (tracker, op);
+}
+
+void
+meta_stack_tracker_record_restack_windows (MetaStackTracker *tracker,
+					   Window           *windows,
+					   int               n_windows,
+					   gulong            serial)
+{
+  int i;
+
+  /* XRestackWindows() isn't actually a X requests - it's broken down
+   * by XLib into a series of XConfigureWindow(StackMode=below); we
+   * mirror that exactly here.
+   *
+   * Aside: Having a separate StackOp for this would be possible to
+   * get some extra efficiency in memory allocation and in applying
+   * the op, at the expense of a code complexity. Implementation hint
+   * for that - keep op->restack_window.n_complete, and when receiving
+   * events with intermediate serials, set n_complete rather than
+   * removing the op from the queue.
+   */
+  for (i = 0; i < n_windows - 1; i++)
+    meta_stack_tracker_record_lower_below (tracker, windows[i + 1], windows[i],
+					   serial + i);
+}
+
+void
+meta_stack_tracker_record_raise_above (MetaStackTracker *tracker,
+				       Window            window,
+				       Window            sibling,
+				       gulong            serial)
+{
+  MetaStackOp *op = g_slice_new (MetaStackOp);
+
+  op->any.type = STACK_OP_RAISE_ABOVE;
+  op->any.serial = serial;
+  op->raise_above.window = window;
+  op->raise_above.sibling = sibling;
+
+  stack_tracker_queue_request (tracker, op);
+}
+
+void
+meta_stack_tracker_record_lower_below (MetaStackTracker *tracker,
+				       Window            window,
+				       Window            sibling,
+				       gulong            serial)
+{
+  MetaStackOp *op = g_slice_new (MetaStackOp);
+
+  op->any.type = STACK_OP_LOWER_BELOW;
+  op->any.serial = serial;
+  op->lower_below.window = window;
+  op->lower_below.sibling = sibling;
+
+  stack_tracker_queue_request (tracker, op);
+}
+
+void
+meta_stack_tracker_record_lower (MetaStackTracker *tracker,
+				 Window            window,
+				 gulong            serial)
+{
+  meta_stack_tracker_record_raise_above (tracker, window, None, serial);
+}
+
+static void
+stack_tracker_event_received (MetaStackTracker *tracker,
+			      MetaStackOp      *op)
+{
+  meta_stack_op_dump (op, "Stack op event received: ", "\n");
+
+  if (op->any.serial < tracker->server_serial)
+    return;
+
+  tracker->server_serial = op->any.serial;
+
+  meta_stack_op_apply (op, tracker->server_stack);
+
+  while (tracker->queued_requests->head)
+    {
+      MetaStackOp *queued_op = tracker->queued_requests->head->data;
+      if (queued_op->any.serial > op->any.serial)
+	break;
+
+      g_queue_pop_head (tracker->queued_requests);
+      meta_stack_op_free (queued_op);
+    }
+
+  if (tracker->predicted_stack)
+    {
+      g_array_free (tracker->predicted_stack, TRUE);
+      tracker->predicted_stack = NULL;
+    }
+
+  meta_stack_tracker_dump (tracker);
+}
+
+void
+meta_stack_tracker_create_event (MetaStackTracker    *tracker,
+				 XCreateWindowEvent  *event)
+{
+  MetaStackOp op;
+
+  op.any.type = STACK_OP_ADD;
+  op.any.serial = event->serial;
+  op.add.window = event->window;
+
+  stack_tracker_event_received (tracker, &op);
+}
+
+void
+meta_stack_tracker_destroy_event (MetaStackTracker    *tracker,
+				  XDestroyWindowEvent *event)
+{
+  MetaStackOp op;
+
+  op.any.type = STACK_OP_REMOVE;
+  op.any.serial = event->serial;
+  op.remove.window = event->window;
+
+  stack_tracker_event_received (tracker, &op);
+}
+
+void
+meta_stack_tracker_reparent_event (MetaStackTracker    *tracker,
+				   XReparentEvent      *event)
+{
+  if (event->parent == event->event)
+    {
+      MetaStackOp op;
+
+      op.any.type = STACK_OP_ADD;
+      op.any.serial = event->serial;
+      op.add.window = event->window;
+
+      stack_tracker_event_received (tracker, &op);
+    }
+  else
+    {
+      MetaStackOp op;
+
+      op.any.type = STACK_OP_REMOVE;
+      op.any.serial = event->serial;
+      op.remove.window = event->window;
+
+      stack_tracker_event_received (tracker, &op);
+    }
+}
+
+void
+meta_stack_tracker_configure_event (MetaStackTracker    *tracker,
+				    XConfigureEvent     *event)
+{
+  MetaStackOp op;
+
+  op.any.type = STACK_OP_RAISE_ABOVE;
+  op.any.serial = event->serial;
+  op.raise_above.window = event->window;
+  op.raise_above.sibling = event->above;
+
+  stack_tracker_event_received (tracker, &op);
+}
+
+/**
+ * meta_stack_tracker_get_stack:
+ * @tracker: a #MetaStackTracker
+ * @windows: location to store list of windows, or %NULL
+ * @n_windows: location to store count of windows, or %NULL
+ *
+ * Returns the most current view we have of the stacking order
+ * of the children of the root window. The returned array contains
+ * everything: InputOnly windows, override-redirect windows,
+ * hidden windows, etc. Some of these will correspond to MetaWindow
+ * objects, others won't.
+ *
+ * Assuming that no other clients have made requests that change
+ * the stacking order since we last received a notification, the
+ * returned list of windows is exactly that you'd get as the
+ * children when calling XQueryTree() on the root window.
+ */
+void
+meta_stack_tracker_get_stack (MetaStackTracker *tracker,
+			      Window          **windows,
+			      int              *n_windows)
+{
+  GArray *stack;
+
+  if (tracker->queued_requests->length == 0)
+    {
+      stack = tracker->server_stack;
+    }
+  else
+    {
+      if (tracker->predicted_stack == NULL)
+        {
+          GList *l;
+
+          tracker->predicted_stack = copy_stack ((Window *)tracker->server_stack->data,
+                                                 tracker->server_stack->len);
+          for (l = tracker->queued_requests->head; l; l = l->next)
+            {
+              MetaStackOp *op = l->data;
+              meta_stack_op_apply (op, tracker->predicted_stack);
+            }
+        }
+
+      stack = tracker->predicted_stack;
+    }
+
+  if (windows)
+    *windows = (Window *)stack->data;
+  if (n_windows)
+    *n_windows = stack->len;
+}

src/core/stack-tracker.h

@@ -0,0 +1,86 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
+
+/**
+ * \file stack-tracker.h  Track stacking order for compositor
+ *
+ * MetaStackTracker maintains the most accurate view we have at a
+ * given point of time of the ordering of the children of the root
+ * window (including override-redirect windows.) This is used to order
+ * the windows when the compositor draws them.
+ *
+ * By contrast, MetaStack is responsible for keeping track of how we
+ * think that windows *should* be ordered.  For windows we manage
+ * (non-override-redirect windows), the two stacking orders will be
+ * the same.
+ */
+
+/*
+ * Copyright (C) 2009 Red Hat, Inc.
+ *
+ * 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; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * 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, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+ * 02111-1307, USA.
+ */
+
+#ifndef META_STACK_TRACKER_H
+#define META_STACK_TRACKER_H
+
+#include "screen.h"
+
+typedef struct _MetaStackTracker MetaStackTracker;
+
+MetaStackTracker *meta_stack_tracker_new  (MetaScreen       *screen);
+void              meta_stack_tracker_free (MetaStackTracker *tracker);
+
+/* These functions are called when we make an X call that changes the
+ * stacking order; this allows MetaStackTracker to predict stacking
+ * order before it receives events back from the X server */
+void meta_stack_tracker_record_add             (MetaStackTracker *tracker,
+						Window            window,
+                                                gulong            serial);
+void meta_stack_tracker_record_remove          (MetaStackTracker *tracker,
+						Window            window,
+                                                gulong            serial);
+void meta_stack_tracker_record_restack_windows (MetaStackTracker *tracker,
+						Window           *windows,
+						int               n_windows,
+                                                gulong            serial);
+void meta_stack_tracker_record_raise_above     (MetaStackTracker *tracker,
+						Window            window,
+						Window            sibling,
+                                                gulong            serial);
+void meta_stack_tracker_record_lower_below    (MetaStackTracker *tracker,
+						Window            window,
+						Window            sibling,
+                                                gulong            serial);
+void meta_stack_tracker_record_lower           (MetaStackTracker *tracker,
+						Window            window,
+                                                gulong            serial);
+
+/* These functions are used to update the stack when we get events
+ * reflecting changes to the stacking order */
+void meta_stack_tracker_create_event    (MetaStackTracker    *tracker,
+					 XCreateWindowEvent  *event);
+void meta_stack_tracker_destroy_event   (MetaStackTracker    *tracker,
+					 XDestroyWindowEvent *event);
+void meta_stack_tracker_reparent_event  (MetaStackTracker    *tracker,
+					 XReparentEvent      *event);
+void meta_stack_tracker_configure_event (MetaStackTracker    *tracker,
+					 XConfigureEvent     *event);
+
+void meta_stack_tracker_get_stack (MetaStackTracker *tracker,
+				   Window          **windows,
+				   int              *n_windows);
+
+#endif /* META_STACK_TRACKER_H */

src/core/stack.c

@@ -1033,6 +1033,10 @@ raise_window_relative_to_managed_windows (MetaScreen *screen,
           changes.stack_mode = Above;
 
           meta_error_trap_push (screen->display);
+          meta_stack_tracker_record_raise_above (screen->stack_tracker,
+                                                 xwindow,
+                                                 children[i],
+                                                 XNextRequest (screen->display->xdisplay));
           XConfigureWindow (screen->display->xdisplay,
                             xwindow,
                             CWSibling | CWStackMode,
@@ -1051,6 +1055,9 @@ raise_window_relative_to_managed_windows (MetaScreen *screen,
        * to be sure we're below any override redirect windows.
        */
       meta_error_trap_push (screen->display);
+      meta_stack_tracker_record_lower (screen->stack_tracker,
+                                       xwindow,
+                                       XNextRequest (screen->display->xdisplay));
       XLowerWindow (screen->display->xdisplay,
                     xwindow);
       meta_error_trap_pop (screen->display, FALSE);
@@ -1159,10 +1166,16 @@ stack_sync_to_server (MetaStack *stack)
       meta_topic (META_DEBUG_STACK, "Don't know last stack state, restacking everything\n");
 
       if (root_children_stacked->len > 0)
+        {
+          meta_stack_tracker_record_restack_windows (stack->screen->stack_tracker,
+                                                     (Window *) root_children_stacked->data,
+                                                     root_children_stacked->len,
+                                                     XNextRequest (stack->screen->display->xdisplay));
           XRestackWindows (stack->screen->display->xdisplay,
                            (Window *) root_children_stacked->data,
                            root_children_stacked->len);
         }
+    }
   else if (root_children_stacked->len > 0)
     {
       /* Try to do minimal window moves to get the stack in order */
@@ -1224,6 +1237,9 @@ stack_sync_to_server (MetaStack *stack)
                   meta_topic (META_DEBUG_STACK, "Placing window 0x%lx below 0x%lx\n",
                               *newp, last_window);
 
+                  meta_stack_tracker_record_lower_below (stack->screen->stack_tracker,
+                                                         *newp, last_window,
+                                                         XNextRequest (stack->screen->display->xdisplay));
                   XConfigureWindow (stack->screen->display->xdisplay,
                                     *newp,
                                     CWSibling | CWStackMode,
@@ -1246,13 +1262,23 @@ stack_sync_to_server (MetaStack *stack)
            */
           if (newp != new_stack)
             --newp;
+          meta_stack_tracker_record_restack_windows (stack->screen->stack_tracker,
+                                                     (Window *) newp, new_end - newp,
+                                                     XNextRequest (stack->screen->display->xdisplay));
           XRestackWindows (stack->screen->display->xdisplay,
                            (Window *) newp, new_end - newp);
         }
     }
 
   /* Push hidden windows to the bottom of the stack under the guard window */
+  meta_stack_tracker_record_lower (stack->screen->stack_tracker,
+                                   stack->screen->guard_window,
+                                   XNextRequest (stack->screen->display->xdisplay));
   XLowerWindow (stack->screen->display->xdisplay, stack->screen->guard_window);
+  meta_stack_tracker_record_restack_windows (stack->screen->stack_tracker,
+                                             (Window *)all_hidden->data,
+                                             all_hidden->len,
+                                             XNextRequest (stack->screen->display->xdisplay));
   XRestackWindows (stack->screen->display->xdisplay,
 		   (Window *)all_hidden->data,
 		   all_hidden->len);

src/include/ui.h

@@ -76,7 +76,8 @@ Window meta_ui_create_frame_window (MetaUI *ui,
 				    gint y,
 				    gint width,
 				    gint height,
-				    gint screen_no);
+				    gint screen_no,
+                                    gulong *create_serial);
 void meta_ui_destroy_frame_window (MetaUI *ui,
 				   Window  xwindow);
 void meta_ui_move_resize_frame (MetaUI *ui,

src/ui/ui.c

@@ -159,7 +159,8 @@ meta_ui_create_frame_window (MetaUI *ui,
 			     gint y,
 			     gint width,
 			     gint height,
-			     gint screen_no)
+			     gint screen_no,
+                             gulong *create_serial)
 {
   GdkDisplay *display = gdk_x11_lookup_xdisplay (xdisplay);
   GdkScreen *screen = gdk_display_get_screen (display, screen_no);
@@ -208,6 +209,12 @@ meta_ui_create_frame_window (MetaUI *ui,
 
   attributes_mask = GDK_WA_X | GDK_WA_Y | GDK_WA_VISUAL | GDK_WA_COLORMAP;
 
+  /* We make an assumption that gdk_window_new() is going to call
+   * XCreateWindow as it's first operation; this seems to be true currently
+   * as long as you pass in a colormap.
+   */
+  if (create_serial)
+    *create_serial = XNextRequest (xdisplay);
   window =
     gdk_window_new (gdk_screen_get_root_window(screen),
 		    &attrs, attributes_mask);