xcb: Use _NET_FRAME_EXTENTS to get frame margins

Some window managers don't reparent the client window into the frame,
so the old method of calculating frame margins by the geometries of the
window and it's frame window is not suitable for them. Use it only as a
fallback.

Change-Id: Ie4d62370425effef4dd91bf27d98e3746e8a375e
Task-number: QTBUG-2280
Reviewed-by: Gatis Paeglis <gatis.paeglis@digia.com>
Reviewed-by: Uli Schlachter <psychon@znc.in>

3 files changed, 20 insertions, 0 deletions

diff --git a/src/plugins/platforms/xcb/qxcbconnection.cpp b/src/plugins/platforms/xcb/qxcbconnection.cpp
index b8b665157b..4e558f9447 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.cpp
+++ b/src/plugins/platforms/xcb/qxcbconnection.cpp
@@ -1578,6 +1578,7 @@ static const char * xcb_atomnames = {
     "_KDE_NET_WM_WINDOW_TYPE_OVERRIDE\0"
 
     "_KDE_NET_WM_FRAME_STRUT\0"
+    "_NET_FRAME_EXTENTS\0"
 
     "_NET_STARTUP_INFO\0"
     "_NET_STARTUP_INFO_BEGIN\0"
diff --git a/src/plugins/platforms/xcb/qxcbconnection.h b/src/plugins/platforms/xcb/qxcbconnection.h
index 291193612c..348af5f155 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.h
+++ b/src/plugins/platforms/xcb/qxcbconnection.h
@@ -194,6 +194,7 @@ namespace QXcbAtom {
         _KDE_NET_WM_WINDOW_TYPE_OVERRIDE,
 
         _KDE_NET_WM_FRAME_STRUT,
+        _NET_FRAME_EXTENTS,
 
         _NET_STARTUP_INFO,
         _NET_STARTUP_INFO_BEGIN,
diff --git a/src/plugins/platforms/xcb/qxcbwindow.cpp b/src/plugins/platforms/xcb/qxcbwindow.cpp
index 6e021ced23..9c5609bb8d 100644
--- a/src/plugins/platforms/xcb/qxcbwindow.cpp
+++ b/src/plugins/platforms/xcb/qxcbwindow.cpp
@@ -745,6 +745,22 @@ void QXcbWindow::setGeometry(const QRect &rect)
 QMargins QXcbWindow::frameMargins() const
 {
     if (m_dirtyFrameMargins) {
+        if (connection()->wmSupport()->isSupportedByWM(atom(QXcbAtom::_NET_FRAME_EXTENTS))) {
+            xcb_get_property_cookie_t cookie = xcb_get_property(xcb_connection(), false, m_window,
+                                                                atom(QXcbAtom::_NET_FRAME_EXTENTS), XCB_ATOM_CARDINAL, 0, 4);
+            QScopedPointer<xcb_get_property_reply_t, QScopedPointerPodDeleter> reply(
+                xcb_get_property_reply(xcb_connection(), cookie, NULL));
+            if (reply && reply->type == XCB_ATOM_CARDINAL && reply->format == 32 && reply->value_len == 4) {
+                quint32 *data = (quint32 *)xcb_get_property_value(reply.data());
+                // _NET_FRAME_EXTENTS format is left, right, top, bottom
+                m_frameMargins = QMargins(data[0], data[2], data[1], data[3]);
+                m_dirtyFrameMargins = false;
+                return m_frameMargins;
+            }
+        }
+
+        // _NET_FRAME_EXTENTS property is not available, so
+        // walk up the window tree to get the frame parent
         xcb_window_t window = m_window;
         xcb_window_t parent = m_window;
 
@@ -2385,6 +2401,8 @@ void QXcbWindow::handlePropertyNotifyEvent(const xcb_property_notify_event_t *ev
             m_windowState = newState;
         }
         return;
+    } else if (event->atom == atom(QXcbAtom::_NET_FRAME_EXTENTS)) {
+        m_dirtyFrameMargins = true;
     } else if (event->atom == atom(QXcbAtom::_NET_WORKAREA) && xcbScreen() && event->window == xcbScreen()->root()) {
         xcbScreen()->updateGeometry(event->time);
     }