From f163a15b133b6726bb52907dbe68df5605056a8f Mon Sep 17 00:00:00 2001
From: "Owen W. Taylor" <otaylor@fishsoup.net>
Date: Wed, 10 Sep 2014 13:06:28 -0400
Subject: [PATCH] MetaStackTracker: optimize out unnecessary X restacking

We have a quite accurate view of the X stack, so there's no good reason to ask
the X server to do restacking that has no effect. (Restackings that have no
effect on either X windows or Wayland windows were generally optimized out in
the synchronization code, but in other cases like moving an X window that is
only beneath Wayland windows to the top of the stack we would make such
requests.)

Removing such requests:
 - Is a small efficiency win in itself
 - Allows us to immediately go ahead and apply Wayland changes to the verified stack
 - Prevents queued Wayland changes piling up waiting for an X event that will never
   be received, since the X server will not send confirmation of no-op restacks.

Since such operations may still have an effect on the relative stacking of X
and Wayland windows, we need to continue applying them to the local stack.

https://bugzilla.gnome.org/show_bug.cgi?id=736559
---
 src/core/stack-tracker.c | 54 +++++++++++++++++++++++-----------------
 1 file changed, 31 insertions(+), 23 deletions(-)

diff --git a/src/core/stack-tracker.c b/src/core/stack-tracker.c
index c916e0f9d..9de84e15d 100644
--- a/src/core/stack-tracker.c
+++ b/src/core/stack-tracker.c
@@ -534,11 +534,11 @@ stack_tracker_apply_prediction (MetaStackTracker *tracker,
 {
   gboolean free_at_end = FALSE;
 
-  /* If this is a wayland operation then it's implicitly verified so
-   * we can apply it immediately so long as it doesn't depend on any
-   * unverified X operations...
+  /* If this operation doesn't involve restacking X windows then it's
+   * implicitly verified. We can apply it immediately unless there
+   * are outstanding X restacks that haven't yet been confirmed.
    */
-  if (!META_STACK_ID_IS_X11 (op->any.window) &&
+  if (op->any.serial == 0 &&
       tracker->unverified_predictions->length == 0)
     {
       if (meta_stack_op_apply (tracker, op, tracker->verified_stack, APPLY_DEFAULT))
@@ -976,19 +976,23 @@ meta_stack_tracker_lower_below (MetaStackTracker *tracker,
   if (META_STACK_ID_IS_X11 (window))
     {
       XWindowChanges changes;
-      serial = XNextRequest (tracker->screen->display->xdisplay);
+      changes.sibling = sibling ? find_x11_sibling_upwards (tracker, sibling) : None;
 
-      meta_error_trap_push (tracker->screen->display);
+      if (changes.sibling != find_x11_sibling_upwards (tracker, window))
+        {
+          serial = XNextRequest (tracker->screen->display->xdisplay);
 
-      changes.sibling = sibling ? find_x11_sibling_upwards (tracker,sibling) : None;
-      changes.stack_mode = changes.sibling ? Below : Above;
+          meta_error_trap_push (tracker->screen->display);
 
-      XConfigureWindow (tracker->screen->display->xdisplay,
-                        window,
-                        (changes.sibling ? CWSibling : 0) | CWStackMode,
-                        &changes);
+          changes.stack_mode = changes.sibling ? Below : Above;
 
-      meta_error_trap_pop (tracker->screen->display);
+          XConfigureWindow (tracker->screen->display->xdisplay,
+                            window,
+                            (changes.sibling ? CWSibling : 0) | CWStackMode,
+                            &changes);
+
+          meta_error_trap_pop (tracker->screen->display);
+        }
     }
 
   meta_stack_tracker_record_lower_below (tracker,
@@ -1013,19 +1017,23 @@ meta_stack_tracker_raise_above (MetaStackTracker *tracker,
   if (META_STACK_ID_IS_X11 (window))
     {
       XWindowChanges changes;
-      serial = XNextRequest (tracker->screen->display->xdisplay);
-
-      meta_error_trap_push (tracker->screen->display);
-
       changes.sibling = sibling ? find_x11_sibling_downwards (tracker, sibling) : None;
-      changes.stack_mode = changes.sibling ? Above : Below;
 
-      XConfigureWindow (tracker->screen->display->xdisplay,
-                        (Window)window,
-                        (changes.sibling ? CWSibling : 0) | CWStackMode,
-                        &changes);
+      if (changes.sibling != find_x11_sibling_downwards (tracker, window))
+        {
+          serial = XNextRequest (tracker->screen->display->xdisplay);
 
-      meta_error_trap_pop (tracker->screen->display);
+          meta_error_trap_push (tracker->screen->display);
+
+          changes.stack_mode = changes.sibling ? Above : Below;
+
+          XConfigureWindow (tracker->screen->display->xdisplay,
+                            (Window)window,
+                            (changes.sibling ? CWSibling : 0) | CWStackMode,
+                            &changes);
+
+          meta_error_trap_pop (tracker->screen->display);
+        }
     }
 
   meta_stack_tracker_record_raise_above (tracker, window,