Improve the implementation of the _NET_WM_SYNC_REQUEST protocol

This change improves the synced resizes of xcb windows and adds support
for synced resizes of glx windows.

The QXcbWindow keeps a better track on whether the window manager
expects a sync and can be in one of three states:
* no sync required
* sync required, but configure notify event not yet received
* sync required and configured

By tracking this in the QXcbWindow itself the backing store can make
use of this information and doesn't need an own heuristic to decide
whether a sync is needed.

Also this allows to add support for synced resizes of windows with an
OpenGLSurface. This is accomplished by checking the sync state after
swapping buffers. As the OpenGL context may be bound to a background
thread the sync is done using a QueuedConnection to ensure that the
sync happens in the thread which created the xcb window.
So far this is only added for GLX.

This significantly improves the resize experience of QQuickWindow and
also the initial mapping with a composited window manager in case the
compositor uses the sync protocol to determine whether the window is
ready to get painted on screen.

Change-Id: Ied0261873043d785dec652d2821fc3638292fa36
Reviewed-by: Uli Schlachter <psychon@znc.in>
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>

8 files changed, 59 insertions, 16 deletions

diff --git a/src/plugins/platforms/xcb/qglxintegration.cpp b/src/plugins/platforms/xcb/qglxintegration.cpp
index f78d3bcc4e..9a56455940 100644
--- a/src/plugins/platforms/xcb/qglxintegration.cpp
+++ b/src/plugins/platforms/xcb/qglxintegration.cpp
@@ -390,6 +390,15 @@ void QGLXContext::swapBuffers(QPlatformSurface *surface)
     else
         glxDrawable = static_cast<QXcbWindow *>(surface)->xcb_window();
     glXSwapBuffers(DISPLAY_FROM_XCB(m_screen), glxDrawable);
+
+    if (surface->surface()->surfaceClass() == QSurface::Window) {
+        QXcbWindow *platformWindow = static_cast<QXcbWindow *>(surface);
+        // OpenGL context might be bound to a non-gui thread
+        // use QueuedConnection to sync the window from the platformWindow's thread
+        // as QXcbWindow is no QObject, a wrapper slot in QXcbConnection is used.
+        if (platformWindow->needsSync())
+            QMetaObject::invokeMethod(m_screen->connection(), "syncWindow", Qt::QueuedConnection, Q_ARG(QXcbWindow*, platformWindow));
+    }
 }
 
 void (*QGLXContext::getProcAddress(const QByteArray &procName)) ()
diff --git a/src/plugins/platforms/xcb/qxcbbackingstore.cpp b/src/plugins/platforms/xcb/qxcbbackingstore.cpp
index 57d6bc580b..ada5b0eedf 100644
--- a/src/plugins/platforms/xcb/qxcbbackingstore.cpp
+++ b/src/plugins/platforms/xcb/qxcbbackingstore.cpp
@@ -261,7 +261,6 @@ void QXcbShmImage::preparePaint(const QRegion &region)
 QXcbBackingStore::QXcbBackingStore(QWindow *window)
     : QPlatformBackingStore(window)
     , m_image(0)
-    , m_syncingResize(false)
 {
     QXcbScreen *screen = static_cast<QXcbScreen *>(window->screen()->handle());
     setConnection(screen->connection());
@@ -330,13 +329,10 @@ void QXcbBackingStore::flush(QWindow *window, const QRegion &region, const QPoin
 
     Q_XCB_NOOP(connection());
 
-    if (m_syncingResize) {
-        connection()->sync();
-        m_syncingResize = false;
+    if (platformWindow->needsSync())
         platformWindow->updateSyncRequestCounter();
-    } else {
+    else
         xcb_flush(xcb_connection());
-    }
 }
 
 #ifndef QT_NO_OPENGL
@@ -347,10 +343,8 @@ void QXcbBackingStore::composeAndFlush(QWindow *window, const QRegion &region, c
 
     Q_XCB_NOOP(connection());
 
-    if (m_syncingResize) {
-        QXcbWindow *platformWindow = static_cast<QXcbWindow *>(window->handle());
-        connection()->sync();
-        m_syncingResize = false;
+    QXcbWindow *platformWindow = static_cast<QXcbWindow *>(window->handle());
+    if (platformWindow->needsSync()) {
         platformWindow->updateSyncRequestCounter();
     } else {
         xcb_flush(xcb_connection());
@@ -376,8 +370,6 @@ void QXcbBackingStore::resize(const QSize &size, const QRegion &)
     delete m_image;
     m_image = new QXcbShmImage(screen, size, win->depth(), win->imageFormat());
     Q_XCB_NOOP(connection());
-
-    m_syncingResize = true;
 }
 
 extern void qt_scrollRectInImage(QImage &img, const QRect &rect, const QPoint &offset);
diff --git a/src/plugins/platforms/xcb/qxcbbackingstore.h b/src/plugins/platforms/xcb/qxcbbackingstore.h
index 19a5ac62d0..af3c004c2d 100644
--- a/src/plugins/platforms/xcb/qxcbbackingstore.h
+++ b/src/plugins/platforms/xcb/qxcbbackingstore.h
@@ -72,7 +72,6 @@ public:
 
 private:
     QXcbShmImage *m_image;
-    bool m_syncingResize;
 };
 
 QT_END_NAMESPACE
diff --git a/src/plugins/platforms/xcb/qxcbconnection.cpp b/src/plugins/platforms/xcb/qxcbconnection.cpp
index f5f6c712c5..1b72bb0da1 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.cpp
+++ b/src/plugins/platforms/xcb/qxcbconnection.cpp
@@ -1833,6 +1833,11 @@ QXcbSystemTrayTracker *QXcbConnection::systemTrayTracker()
     return m_systemTrayTracker;
 }
 
+void QXcbConnection::syncWindow(QXcbWindow *window)
+{
+    window->updateSyncRequestCounter();
+}
+
 QXcbConnectionGrabber::QXcbConnectionGrabber(QXcbConnection *connection)
     :m_connection(connection)
 {
diff --git a/src/plugins/platforms/xcb/qxcbconnection.h b/src/plugins/platforms/xcb/qxcbconnection.h
index 6e511356c4..f96541318c 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.h
+++ b/src/plugins/platforms/xcb/qxcbconnection.h
@@ -464,6 +464,9 @@ public:
     void handleEnterEvent(const xcb_enter_notify_event_t *);
 #endif
 
+public slots:
+    void syncWindow(QXcbWindow *window);
+
 private slots:
     void processXcbEvents();
 
diff --git a/src/plugins/platforms/xcb/qxcbintegration.cpp b/src/plugins/platforms/xcb/qxcbintegration.cpp
index 0bab341914..ddb164bf07 100644
--- a/src/plugins/platforms/xcb/qxcbintegration.cpp
+++ b/src/plugins/platforms/xcb/qxcbintegration.cpp
@@ -127,6 +127,7 @@ QXcbIntegration::QXcbIntegration(const QStringList &parameters, int &argc, char
     : m_services(new QGenericUnixServices)
     , m_instanceName(0)
 {
+    qRegisterMetaType<QXcbWindow*>();
 #ifdef XCB_USE_XLIB
     XInitThreads();
 #endif
diff --git a/src/plugins/platforms/xcb/qxcbwindow.cpp b/src/plugins/platforms/xcb/qxcbwindow.cpp
index 3645b6469a..a46fe437d8 100644
--- a/src/plugins/platforms/xcb/qxcbwindow.cpp
+++ b/src/plugins/platforms/xcb/qxcbwindow.cpp
@@ -200,6 +200,7 @@ QXcbWindow::QXcbWindow(QWindow *window)
     , m_eglSurface(0)
 #endif
     , m_lastWindowStateEvent(-1)
+    , m_syncState(NoSyncNeeded)
 {
     m_screen = static_cast<QXcbScreen *>(window->screen()->handle());
 
@@ -367,7 +368,12 @@ void QXcbWindow::create()
     properties[propertyCount++] = atom(QXcbAtom::WM_TAKE_FOCUS);
     properties[propertyCount++] = atom(QXcbAtom::_NET_WM_PING);
 
-    m_usingSyncProtocol = m_screen->syncRequestSupported() && window()->surfaceType() != QSurface::OpenGLSurface;
+    m_usingSyncProtocol = m_screen->syncRequestSupported();
+#if !defined(XCB_USE_GLX)
+    // synced resize only implemented on GLX
+    if (window()->supportsOpenGL())
+        m_usingSyncProtocol = false;
+#endif
 
     if (m_usingSyncProtocol)
         properties[propertyCount++] = atom(QXcbAtom::_NET_WM_SYNC_REQUEST);
@@ -1596,6 +1602,8 @@ void QXcbWindow::handleClientMessageEvent(const xcb_client_message_event_t *even
             connection()->setTime(event->data.data32[1]);
             m_syncValue.lo = event->data.data32[2];
             m_syncValue.hi = event->data.data32[3];
+            if (m_usingSyncProtocol)
+                m_syncState = SyncReceived;
 #ifndef QT_NO_WHATSTHIS
         } else if (event->data.data32[0] == atom(QXcbAtom::_NET_WM_CONTEXT_HELP)) {
             QWindowSystemInterface::handleEnterWhatsThisEvent();
@@ -1669,6 +1677,9 @@ void QXcbWindow::handleConfigureNotifyEvent(const xcb_configure_notify_event_t *
         QWindowSystemInterface::handleExposeEvent(window(), QRect(QPoint(), geometry().size()));
     }
 
+    if (m_usingSyncProtocol && m_syncState == SyncReceived)
+        m_syncState = SyncAndConfigureReceived;
+
     m_dirtyFrameMargins = true;
 }
 
@@ -1945,12 +1956,17 @@ void QXcbWindow::handleFocusOutEvent(const xcb_focus_out_event_t *)
 
 void QXcbWindow::updateSyncRequestCounter()
 {
+    if (m_syncState != SyncAndConfigureReceived) {
+        // window manager does not expect a sync event yet.
+        return;
+    }
     if (m_usingSyncProtocol && (m_syncValue.lo != 0 || m_syncValue.hi != 0)) {
         Q_XCB_CALL(xcb_sync_set_counter(xcb_connection(), m_syncCounter, m_syncValue));
-        connection()->sync();
+        xcb_flush(xcb_connection());
 
         m_syncValue.lo = 0;
         m_syncValue.hi = 0;
+        m_syncState = NoSyncNeeded;
     }
 }
 
@@ -2173,4 +2189,9 @@ void QXcbWindow::setAlertState(bool enabled)
     }
 }
 
+bool QXcbWindow::needsSync() const
+{
+    return m_syncState == SyncAndConfigureReceived;
+}
+
 QT_END_NAMESPACE
diff --git a/src/plugins/platforms/xcb/qxcbwindow.h b/src/plugins/platforms/xcb/qxcbwindow.h
index 12d17023fb..b924ee27e5 100644
--- a/src/plugins/platforms/xcb/qxcbwindow.h
+++ b/src/plugins/platforms/xcb/qxcbwindow.h
@@ -144,13 +144,17 @@ public:
 
     void handleMouseEvent(xcb_timestamp_t time, const QPoint &local, const QPoint &global, Qt::KeyboardModifiers modifiers);
 
-    void updateSyncRequestCounter();
     void updateNetWmUserTime(xcb_timestamp_t timestamp);
 
 #if defined(XCB_USE_EGL)
     QXcbEGLSurface *eglSurface() const;
 #endif
 
+    bool needsSync() const;
+
+public Q_SLOTS:
+    void updateSyncRequestCounter();
+
 private:
     void changeNetWmState(bool set, xcb_atom_t one, xcb_atom_t two = 0);
     NetWmStates netWmStates();
@@ -217,8 +221,17 @@ private:
 
     xcb_visualid_t m_visualId;
     int m_lastWindowStateEvent;
+
+    enum SyncState {
+        NoSyncNeeded,
+        SyncReceived,
+        SyncAndConfigureReceived
+    };
+    SyncState m_syncState;
 };
 
 QT_END_NAMESPACE
 
+Q_DECLARE_METATYPE(QXcbWindow*)
+
 #endif