[x11] Disable synchronized resizing for Xwayland < 1.21

In case Xwayland does not use multiple buffers, the currently attached
buffer is going to be destroyed if the frame window is resized. It may
render the previous and the current window pixmap invalid and thus result
in visual artifacts when an X11 client is being interactively resized.

In order to avoid the visual artifacts, this change disables support for
synchronized resizing for X11 clients if the version of Xwayland is less
than the version in which Xwayland started using multiple buffers, i.e.
1.21.

Differential Revision: https://phabricator.kde.org/D29250

CMakeLists.txt

@@ -509,6 +509,7 @@ set(kwin_SRCS
     xcbutils.cpp
     xdgshellclient.cpp
     xkb.cpp
+    xwaylandclient.cpp
     xwl/xwayland_interface.cpp
 )
 

workspace.cpp

@@ -62,6 +62,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "xcbutils.h"
 #include "main.h"
 #include "decorations/decorationbridge.h"
+#include "xwaylandclient.h"
 // KDE
 #include <KConfig>
 #include <KConfigGroup>
@@ -528,7 +529,12 @@ void Workspace::setupClientConnections(AbstractClient *c)
 X11Client *Workspace::createClient(xcb_window_t w, bool is_mapped)
 {
     StackingUpdatesBlocker blocker(this);
-    X11Client *c = new X11Client();
+    X11Client *c = nullptr;
+    if (kwinApp()->operationMode() == Application::OperationModeX11) {
+        c = new X11Client();
+    } else {
+        c = new XwaylandClient();
+    }
     setupClientConnections(c);
     if (X11Compositor *compositor = X11Compositor::self()) {
         connect(c, &X11Client::blockingCompositingChanged, compositor, &X11Compositor::updateClientCompositeBlocking);

x11client.cpp

@@ -2342,10 +2342,20 @@ void X11Client::getIcons()
     setIcon(icon);
 }
 
+/**
+ * Returns \c true if X11Client wants to throttle resizes; otherwise returns \c false.
+ */
+bool X11Client::wantsSyncCounter() const
+{
+    return true;
+}
+
 void X11Client::getSyncCounter()
 {
     if (!Xcb::Extensions::self()->isSyncAvailable())
         return;
+    if (!wantsSyncCounter())
+        return;
 
     Xcb::Property syncProp(false, window(), atoms->net_wm_sync_request_counter, XCB_ATOM_CARDINAL, 0, 1);
     const xcb_sync_counter_t counter = syncProp.value<xcb_sync_counter_t>(XCB_NONE);

x11client.h

@@ -85,6 +85,8 @@ class KWIN_EXPORT X11Client : public AbstractClient
     Q_PROPERTY(bool clientSideDecorated READ isClientSideDecorated NOTIFY clientSideDecoratedChanged)
 public:
     explicit X11Client();
+    ~X11Client() override; ///< Use destroyClient() or releaseWindow()
+
     xcb_window_t wrapperId() const;
     xcb_window_t inputId() const { return m_decoInputExtent; }
     xcb_window_t frameId() const override;
@@ -320,6 +322,7 @@ public:
     const SyncRequest &syncRequest() const {
         return m_syncRequest;
     }
+    virtual bool wantsSyncCounter() const;
     void handleSync();
 
     static void cleanupX11();
@@ -333,9 +336,6 @@ private Q_SLOTS:
     void shadeUnhover();
 
 private:
-    // Use Workspace::createClient()
-    ~X11Client() override; ///< Use destroyClient() or releaseWindow()
-
     // Handlers for X11 events
     bool mapRequestEvent(xcb_map_request_event_t *e);
     void unmapNotifyEvent(xcb_unmap_notify_event_t *e);

xwaylandclient.cpp

@@ -0,0 +1,37 @@
+/********************************************************************
+ KWin - the KDE window manager
+ This file is part of the KDE project.
+
+Copyright (C) 2020 Vlad Zahorodnii <vlad.zahorodnii@kde.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; 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, see <http://www.gnu.org/licenses/>.
+*********************************************************************/
+
+#include "xwaylandclient.h"
+
+namespace KWin
+{
+
+bool XwaylandClient::wantsSyncCounter() const
+{
+    // When the frame window is resized, the attached buffer will be destroyed by
+    // Xwayland, causing unexpected invalid previous and current window pixmaps.
+    // With the addition of multiple window buffers in Xwayland 1.21, X11 clients
+    // are no longer able to destroy the buffer after it's been committed and not
+    // released by the compositor yet.
+    static const quint32 xwaylandVersion = xcb_get_setup(connection())->release_number;
+    return xwaylandVersion >= 12100000;
+}
+
+} // namespace KWin

xwaylandclient.h

@@ -0,0 +1,39 @@
+/********************************************************************
+ KWin - the KDE window manager
+ This file is part of the KDE project.
+
+Copyright (C) 2020 Vlad Zahorodnii <vlad.zahorodnii@kde.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; 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, see <http://www.gnu.org/licenses/>.
+*********************************************************************/
+
+#pragma once
+
+#include "x11client.h"
+
+namespace KWin
+{
+
+/**
+ * The XwaylandClient class represents a managed Xwayland client.
+ */
+class XwaylandClient : public X11Client
+{
+    Q_OBJECT
+
+public:
+    bool wantsSyncCounter() const override;
+};
+
+} // namespace KWin