Reload lastScrollPosition on window enter

We need the lastScrollPosition position to calculated scrolling deltas
on scroll events. Since the position is tied to the device and might
have changed while scroll events were send to other applications we need
to reload the value when mouse focus reenters our application.

Task-number: QTBUG-38274
Change-Id: Ic166648f8e7ae486288cbed339a057e3faa1ef2d
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>

3 files changed, 36 insertions, 0 deletions

diff --git a/src/plugins/platforms/xcb/qxcbconnection.h b/src/plugins/platforms/xcb/qxcbconnection.h
index a994c51c7d..13a0280baf 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.h
+++ b/src/plugins/platforms/xcb/qxcbconnection.h
@@ -454,6 +454,10 @@ public:
 
     QXcbSystemTrayTracker *systemTrayTracker();
 
+#ifdef XCB_USE_XINPUT2
+    void handleEnterEvent(const xcb_enter_notify_event_t *);
+#endif
+
 private slots:
     void processXcbEvents();
 
diff --git a/src/plugins/platforms/xcb/qxcbconnection_xi2.cpp b/src/plugins/platforms/xcb/qxcbconnection_xi2.cpp
index d80b49ccbb..d7b3c75aee 100644
--- a/src/plugins/platforms/xcb/qxcbconnection_xi2.cpp
+++ b/src/plugins/platforms/xcb/qxcbconnection_xi2.cpp
@@ -524,6 +524,35 @@ void QXcbConnection::xi2HandleEvent(xcb_ge_event_t *event)
     }
 }
 
+void QXcbConnection::handleEnterEvent(const xcb_enter_notify_event_t *)
+{
+#ifdef XCB_USE_XINPUT21
+    QHash<int, ScrollingDevice>::iterator it = m_scrollingDevices.begin();
+    const QHash<int, ScrollingDevice>::iterator end = m_scrollingDevices.end();
+    while (it != end) {
+        ScrollingDevice& scrollingDevice = it.value();
+        int nrDevices = 0;
+        XIDeviceInfo* xiDeviceInfo = XIQueryDevice(static_cast<Display *>(m_xlib_display), scrollingDevice.deviceId, &nrDevices);
+        if (nrDevices <= 0) {
+            it = m_scrollingDevices.erase(it);
+            continue;
+        }
+        for (int c = 0; c < xiDeviceInfo->num_classes; ++c) {
+            if (xiDeviceInfo->classes[c]->type == XIValuatorClass) {
+                XIValuatorClassInfo *vci = reinterpret_cast<XIValuatorClassInfo *>(xiDeviceInfo->classes[c]);
+                const int valuatorAtom = qatom(vci->label);
+                if (valuatorAtom == QXcbAtom::RelHorizScroll || valuatorAtom == QXcbAtom::RelHorizWheel)
+                    scrollingDevice.lastScrollPosition.setX(vci->value);
+                else if (valuatorAtom == QXcbAtom::RelVertScroll || valuatorAtom == QXcbAtom::RelVertWheel)
+                    scrollingDevice.lastScrollPosition.setY(vci->value);
+            }
+        }
+        XIFreeDeviceInfo(xiDeviceInfo);
+        ++it;
+    }
+#endif
+}
+
 void QXcbConnection::xi2HandleScrollEvent(void *event, ScrollingDevice &scrollingDevice)
 {
 #ifdef XCB_USE_XINPUT21
diff --git a/src/plugins/platforms/xcb/qxcbwindow.cpp b/src/plugins/platforms/xcb/qxcbwindow.cpp
index 5a2002f1d4..ad7e99bd49 100644
--- a/src/plugins/platforms/xcb/qxcbwindow.cpp
+++ b/src/plugins/platforms/xcb/qxcbwindow.cpp
@@ -1778,6 +1778,9 @@ public:
 void QXcbWindow::handleEnterNotifyEvent(const xcb_enter_notify_event_t *event)
 {
     connection()->setTime(event->time);
+#ifdef XCB_USE_XINPUT2
+    connection()->handleEnterEvent(event);
+#endif
 
     if ((event->mode != XCB_NOTIFY_MODE_NORMAL && event->mode != XCB_NOTIFY_MODE_UNGRAB)
         || event->detail == XCB_NOTIFY_DETAIL_VIRTUAL