From 28e39706a1a922d5c1054ad3243bac8b2708dc56 Mon Sep 17 00:00:00 2001
From: Giulio Camuffo <giulio.camuffo@jollamobile.com>
Date: Wed, 22 Apr 2015 13:39:39 +0300
Subject: [PATCH] Add a way to filter window system events

This change introduces the class QWindowSystemEventHandler
which can be used to hook into QWindowSystemInterfacePrivate to
filter and dispatch window system events.
One use case is to intercept key events from the underlying system
in QtCompositor and feed them into the xkbcommon state, and to modify
the events based on the resulting state.

Change-Id: I829eb7d960420135990fb0f6db54c14eea3e8e48
Reviewed-by: Laszlo Agocs <laszlo.agocs@theqtcompany.com>
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>
---
 src/gui/kernel/qwindowsysteminterface.cpp | 34 +++++++++++++++++++++++++++++--
 src/gui/kernel/qwindowsysteminterface_p.h | 13 ++++++++++++
 2 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/src/gui/kernel/qwindowsysteminterface.cpp b/src/gui/kernel/qwindowsysteminterface.cpp
index 850b69d..2ea1ccd 100644
--- a/src/gui/kernel/qwindowsysteminterface.cpp
+++ b/src/gui/kernel/qwindowsysteminterface.cpp
@@ -48,6 +48,7 @@ QElapsedTimer QWindowSystemInterfacePrivate::eventTime;
 bool QWindowSystemInterfacePrivate::synchronousWindowsSystemEvents = false;
 QWaitCondition QWindowSystemInterfacePrivate::eventsFlushed;
 QMutex QWindowSystemInterfacePrivate::flushEventMutex;
+QWindowSystemEventHandler *QWindowSystemInterfacePrivate::eventHandler;
 
 //------------------------------------------------------------
 //
@@ -621,14 +622,32 @@ bool QWindowSystemInterface::sendWindowSystemEvents(QEventLoop::ProcessEventsFla
                 QWindowSystemInterfacePrivate::getWindowSystemEvent();
         if (!event)
             break;
-        nevents++;
-        QGuiApplicationPrivate::processWindowSystemEvent(event);
+
+        if (QWindowSystemInterfacePrivate::eventHandler) {
+            if (QWindowSystemInterfacePrivate::eventHandler->sendEvent(event))
+                nevents++;
+        } else {
+            nevents++;
+            QGuiApplicationPrivate::processWindowSystemEvent(event);
+        }
         delete event;
     }
 
     return (nevents > 0);
 }
 
+void QWindowSystemInterfacePrivate::installWindowSystemEventHandler(QWindowSystemEventHandler *handler)
+{
+    if (!eventHandler)
+        eventHandler = handler;
+}
+
+void QWindowSystemInterfacePrivate::removeWindowSystemEventhandler(QWindowSystemEventHandler *handler)
+{
+    if (eventHandler == handler)
+        eventHandler = 0;
+}
+
 void QWindowSystemInterface::setSynchronousWindowsSystemEvents(bool enable)
 {
     QWindowSystemInterfacePrivate::synchronousWindowsSystemEvents = enable;
@@ -852,4 +871,15 @@ Q_GUI_EXPORT  void qt_handleTouchEvent(QWindow *w, QTouchDevice *device,
     QWindowSystemInterface::handleTouchEvent(w, device, touchPointList(points), mods);
 }
 
+QWindowSystemEventHandler::~QWindowSystemEventHandler()
+{
+    QWindowSystemInterfacePrivate::removeWindowSystemEventhandler(this);
+}
+
+bool QWindowSystemEventHandler::sendEvent(QWindowSystemInterfacePrivate::WindowSystemEvent *e)
+{
+    QGuiApplicationPrivate::processWindowSystemEvent(e);
+    return true;
+}
+
 QT_END_NAMESPACE
diff --git a/src/gui/kernel/qwindowsysteminterface_p.h b/src/gui/kernel/qwindowsysteminterface_p.h
index 2ec402a..f51c726 100644
--- a/src/gui/kernel/qwindowsysteminterface_p.h
+++ b/src/gui/kernel/qwindowsysteminterface_p.h
@@ -54,6 +54,8 @@
 
 QT_BEGIN_NAMESPACE
 
+class QWindowSystemEventHandler;
+
 class Q_GUI_EXPORT QWindowSystemInterfacePrivate {
 public:
     enum EventType {
@@ -487,6 +489,17 @@ public:
     static QMutex flushEventMutex;
 
     static QList<QTouchEvent::TouchPoint> convertTouchPoints(const QList<QWindowSystemInterface::TouchPoint> &points, QEvent::Type *type);
+
+    static void installWindowSystemEventHandler(QWindowSystemEventHandler *handler);
+    static void removeWindowSystemEventhandler(QWindowSystemEventHandler *handler);
+    static QWindowSystemEventHandler *eventHandler;
+};
+
+class Q_GUI_EXPORT QWindowSystemEventHandler
+{
+public:
+    virtual ~QWindowSystemEventHandler();
+    virtual bool sendEvent(QWindowSystemInterfacePrivate::WindowSystemEvent *event);
 };
 
 QT_END_NAMESPACE
-- 
2.6.4