xcb: rewrite auto-repeat key detection logic

It's unclear what the original code was doing. It relied on 'm_release'
which could never be 'false' (ref. QTBUG-69679). It was subtracting event
times and comparing with arbitrary '10'. On X11 auto-repeat keys can be
detected by checking time and keycode of the current release event and
the next event in the queue. If an event is an auto-repeat, then next event
in the queue will be a key press with matching time and keycode.

Verified that auto-repeat was unreliable in Qt 4 as well. With this patch
auto-repeat works as expected.

Added support for Xlib's XPeekEvent in our XCB implementation QXcbConnection::checkEvent():

"The XPeekEvent() function returns the first event from the event queue,
but it does not remove the event from the queue."

Sneaking in one variable renaming: "string" -> "text", to match the QKeyEvent::text().

Task-number: QTBUG-57335
Task-number: QTBUG-69679
Change-Id: I0a23f138287f57eaaecf1a009bd939e7e0e23269
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

1 files changed, 4 insertions, 3 deletions

diff --git a/src/plugins/platforms/xcb/qxcbconnection.h b/src/plugins/platforms/xcb/qxcbconnection.h
index 24719a6c31..697b509bf0 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.h
+++ b/src/plugins/platforms/xcb/qxcbconnection.h
@@ -441,7 +441,7 @@ public:
     QXcbWindow *platformWindowFromId(xcb_window_t id);
 
     template<typename Functor>
-    inline xcb_generic_event_t *checkEvent(Functor &&filter);
+    inline xcb_generic_event_t *checkEvent(Functor &&filter, bool removeFromQueue = true);
 
     typedef bool (*PeekFunc)(QXcbConnection *, xcb_generic_event_t *);
     void addPeekFunc(PeekFunc f);
@@ -735,14 +735,15 @@ Q_DECLARE_TYPEINFO(QXcbConnection::TabletData, Q_MOVABLE_TYPE);
 #endif
 
 template<typename Functor>
-xcb_generic_event_t *QXcbConnection::checkEvent(Functor &&filter)
+xcb_generic_event_t *QXcbConnection::checkEvent(Functor &&filter, bool removeFromQueue)
 {
     QXcbEventArray *eventqueue = m_reader->lock();
 
     for (int i = 0; i < eventqueue->size(); ++i) {
         xcb_generic_event_t *event = eventqueue->at(i);
         if (event && filter(event, event->response_type & ~0x80)) {
-            (*eventqueue)[i] = nullptr;
+            if (removeFromQueue)
+                (*eventqueue)[i] = nullptr;
             m_reader->unlock();
             return event;
         }