xcb: when using XI2 for mouse, change state only on press and release

If the mouse event is synthesized from a touchscreen, since we're
using XI2 we've already delivered the actual touch event by the time
an XI_Motion event occurs.  It's bogus to treat the XI_Motion event
as a mouse press merely because XIMaskIsSet pretends that the mouse
button is pressed.  If the QPA motion event says that the button
is pressed, then QGuiApplicationPrivate::processMouseEvent() will
synthesize an extra mouse button event for the press, and another
for the release.

Task-number: QTBUG-56156
Change-Id: I937edfd8cc9aab5b21370036c4b42dc0c0a74b50
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

2 files changed, 17 insertions, 6 deletions

diff --git a/src/plugins/platforms/xcb/qxcbwindow.cpp b/src/plugins/platforms/xcb/qxcbwindow.cpp
index c81858c408..c703fbef22 100644
--- a/src/plugins/platforms/xcb/qxcbwindow.cpp
+++ b/src/plugins/platforms/xcb/qxcbwindow.cpp
@@ -2416,6 +2416,17 @@ static inline int fixed1616ToInt(FP1616 val)
     return int((qreal(val >> 16)) + (val & 0xFFFF) / (qreal)0xFFFF);
 }
 
+void QXcbWindow::handleXIMouseButtonState(const xcb_ge_event_t *event)
+{
+    QXcbConnection *conn = connection();
+    const xXIDeviceEvent *ev = reinterpret_cast<const xXIDeviceEvent *>(event);
+    if (ev->buttons_len > 0) {
+        unsigned char *buttonMask = (unsigned char *) &ev[1];
+        for (int i = 1; i <= 15; ++i)
+            conn->setButton(conn->translateMouseButton(i), XIMaskIsSet(buttonMask, i));
+    }
+}
+
 // With XI 2.2+ press/release/motion comes here instead of the above handlers.
 void QXcbWindow::handleXIMouseEvent(xcb_ge_event_t *event, Qt::MouseEventSource source)
 {
@@ -2431,12 +2442,6 @@ void QXcbWindow::handleXIMouseEvent(xcb_ge_event_t *event, Qt::MouseEventSource
 
     const Qt::MouseButton button = conn->xiToQtMouseButton(ev->detail);
 
-    if (ev->buttons_len > 0) {
-        unsigned char *buttonMask = (unsigned char *) &ev[1];
-        for (int i = 1; i <= 15; ++i)
-            conn->setButton(conn->translateMouseButton(i), XIMaskIsSet(buttonMask, i));
-    }
-
     const char *sourceName = 0;
     if (Q_UNLIKELY(lcQpaXInputEvents().isDebugEnabled())) {
         const QMetaObject *metaObject = qt_getEnumMetaObject(source);
@@ -2446,18 +2451,23 @@ void QXcbWindow::handleXIMouseEvent(xcb_ge_event_t *event, Qt::MouseEventSource
 
     switch (ev->evtype) {
     case XI_ButtonPress:
+        handleXIMouseButtonState(event);
         if (Q_UNLIKELY(lcQpaXInputEvents().isDebugEnabled()))
             qCDebug(lcQpaXInputEvents, "XI2 mouse press, button %d, time %d, source %s", button, ev->time, sourceName);
         conn->setButton(button, true);
         handleButtonPressEvent(event_x, event_y, root_x, root_y, ev->detail, modifiers, ev->time, source);
         break;
     case XI_ButtonRelease:
+        handleXIMouseButtonState(event);
         if (Q_UNLIKELY(lcQpaXInputEvents().isDebugEnabled()))
             qCDebug(lcQpaXInputEvents, "XI2 mouse release, button %d, time %d, source %s", button, ev->time, sourceName);
         conn->setButton(button, false);
         handleButtonReleaseEvent(event_x, event_y, root_x, root_y, ev->detail, modifiers, ev->time, source);
         break;
     case XI_Motion:
+        // Here we do NOT call handleXIMouseButtonState because we don't expect button state change to be bundled with motion.
+        // When a touchscreen is pressed, an XI_Motion event occurs in which XIMaskIsSet says the left button is pressed,
+        // but we don't want QGuiApplicationPrivate::processMouseEvent() to react by generating a mouse press event.
         if (Q_UNLIKELY(lcQpaXInputEvents().isDebugEnabled()))
             qCDebug(lcQpaXInputEvents, "XI2 mouse motion %d,%d, time %d, source %s", event_x, event_y, ev->time, sourceName);
         handleMotionNotifyEvent(event_x, event_y, root_x, root_y, modifiers, ev->time, source);
diff --git a/src/plugins/platforms/xcb/qxcbwindow.h b/src/plugins/platforms/xcb/qxcbwindow.h
index f62938ba8a..41dccbe4af 100644
--- a/src/plugins/platforms/xcb/qxcbwindow.h
+++ b/src/plugins/platforms/xcb/qxcbwindow.h
@@ -139,6 +139,7 @@ public:
     void handleFocusOutEvent(const xcb_focus_out_event_t *event) Q_DECL_OVERRIDE;
     void handlePropertyNotifyEvent(const xcb_property_notify_event_t *event) Q_DECL_OVERRIDE;
 #ifdef XCB_USE_XINPUT22
+    void handleXIMouseButtonState(const xcb_ge_event_t *);
     void handleXIMouseEvent(xcb_ge_event_t *, Qt::MouseEventSource source = Qt::MouseEventNotSynthesized) Q_DECL_OVERRIDE;
     void handleXIEnterLeave(xcb_ge_event_t *) Q_DECL_OVERRIDE;
 #endif