Listen to touch events on the master device instead of slave.

Listening to touch events on the master prevents pointer emulation
events from being generated, alleviating the need to grab.

Grabbing on the slave device is buggy, and breaks pointer emulation
on all current servers that support XInput 2.2 due to a bug in the
server, and will also grab unwanted touch events.

For reference, see https://bugs.freedesktop.org/show_bug.cgi?id=78345

Reverts 2c65b78b400ec27e6e559829b9a970dca2df6669.  The idea of
enabling each touchscreen separately was introduced in
4dbf574b7acb7ae8f852219700afa95f8d568f0e; that aspect is also
reverted.

Change-Id: I30d36397aa4ff2fb7a8ad2bbb94c2a13abd472b4
Task-number: QTBUG-38625
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>

1 files changed, 13 insertions, 36 deletions

diff --git a/src/plugins/platforms/xcb/qxcbconnection_xi2.cpp b/src/plugins/platforms/xcb/qxcbconnection_xi2.cpp
index a574dcae6c..cf809b37e5 100644
--- a/src/plugins/platforms/xcb/qxcbconnection_xi2.cpp
+++ b/src/plugins/platforms/xcb/qxcbconnection_xi2.cpp
@@ -251,14 +251,13 @@ void QXcbConnection::xi2Select(xcb_window_t window)
     XIEventMask mask;
     mask.mask_len = sizeof(bitMask);
     mask.mask = xiBitMask;
-    // Enable each touchscreen
-    foreach (XInput2DeviceData *dev, m_touchDevices) {
-        mask.deviceid = dev->xiDeviceInfo->deviceid;
+    if (!m_touchDevices.isEmpty()) {
+        mask.deviceid = XIAllMasterDevices;
         Status result = XISelectEvents(xDisplay, window, &mask, 1);
-        // If we have XInput >= 2.2 and successfully enable a touchscreen, then
-        // it will provide touch only. In most other cases, there will be
-        // emulated mouse events from the driver. If not, then Qt must do its
-        // own mouse emulation to enable interaction with mouse-oriented QWidgets.
+        // If we select for touch events on the master pointer, XInput2
+        // will not synthesize mouse events. This means Qt must do it,
+        // which is also preferable, since Qt can control better when
+        // to do so.
         if (m_xi2Minor >= 2 && result == Success)
             has_touch_without_mouse_emulation = true;
     }
@@ -272,10 +271,10 @@ void QXcbConnection::xi2Select(xcb_window_t window)
     // similar handlers useless and we have no intention to infect
     // all the pure xcb code with Xlib-based XI2.
     if (!m_tabletData.isEmpty()) {
-        unsigned int tabletBitMask = bitMask;
+        unsigned int tabletBitMask;
         unsigned char *xiTabletBitMask = reinterpret_cast<unsigned char *>(&tabletBitMask);
         QVector<XIEventMask> xiEventMask(m_tabletData.count());
-        tabletBitMask |= XI_ButtonPressMask;
+        tabletBitMask = XI_ButtonPressMask;
         tabletBitMask |= XI_ButtonReleaseMask;
         tabletBitMask |= XI_MotionMask;
         tabletBitMask |= XI_PropertyEventMask;
@@ -294,24 +293,18 @@ void QXcbConnection::xi2Select(xcb_window_t window)
     // Enable each scroll device
     if (!m_scrollingDevices.isEmpty()) {
         QVector<XIEventMask> xiEventMask(m_scrollingDevices.size());
-        unsigned int scrollBitMask = 0;
+        unsigned int scrollBitMask;
         unsigned char *xiScrollBitMask = reinterpret_cast<unsigned char *>(&scrollBitMask);
+
         scrollBitMask = XI_MotionMask;
         scrollBitMask |= XI_ButtonReleaseMask;
-        bitMask |= XI_MotionMask;
-        bitMask |= XI_ButtonReleaseMask;
         int i=0;
         Q_FOREACH (const ScrollingDevice& scrollingDevice, m_scrollingDevices) {
             if (tabletDevices.contains(scrollingDevice.deviceId))
                 continue; // All necessary events are already captured.
             xiEventMask[i].deviceid = scrollingDevice.deviceId;
-            if (m_touchDevices.contains(scrollingDevice.deviceId)) {
-                xiEventMask[i].mask_len = sizeof(bitMask);
-                xiEventMask[i].mask = xiBitMask;
-            } else {
-                xiEventMask[i].mask_len = sizeof(scrollBitMask);
-                xiEventMask[i].mask = xiScrollBitMask;
-            }
+            xiEventMask[i].mask_len = sizeof(scrollBitMask);
+            xiEventMask[i].mask = xiScrollBitMask;
             i++;
         }
         XISelectEvents(xDisplay, window, xiEventMask.data(), i);
@@ -458,7 +451,7 @@ void QXcbConnection::xi2HandleEvent(xcb_ge_event_t *event)
                     fixed1616ToReal(xiDeviceEvent->root_x), fixed1616ToReal(xiDeviceEvent->root_y) );
 
             if (QXcbWindow *platformWindow = platformWindowFromId(xiDeviceEvent->event)) {
-                XInput2DeviceData *dev = deviceForId(xiEvent->deviceid);
+                XInput2DeviceData *dev = deviceForId(xiDeviceEvent->sourceid);
                 Q_ASSERT(dev);
                 const bool firstTouch = m_touchPoints.isEmpty();
                 if (xiEvent->evtype == XI_TouchBegin) {
@@ -563,22 +556,6 @@ void QXcbConnection::xi2HandleEvent(xcb_ge_event_t *event)
                     qDebug() << "   touchpoint "  << touchPoint.id << " state " << touchPoint.state << " pos norm " << touchPoint.normalPosition <<
                         " area " << touchPoint.area << " pressure " << touchPoint.pressure;
                 QWindowSystemInterface::handleTouchEvent(platformWindow->window(), xiEvent->time, dev->qtTouchDevice, m_touchPoints.values());
-                if (has_touch_without_mouse_emulation) {
-                    // We need to grab the touch event to prevent mouse emulation.
-                    if (xiEvent->evtype == XI_TouchBegin) {
-                        XIEventMask xieventmask;
-                        unsigned int bitMask = 0;
-                        unsigned char *xiBitMask = reinterpret_cast<unsigned char *>(&bitMask);
-                        xieventmask.deviceid = xiEvent->deviceid;
-                        xieventmask.mask = xiBitMask;
-                        xieventmask.mask_len = sizeof(bitMask);
-                        bitMask |= XI_TouchBeginMask;
-                        bitMask |= XI_TouchUpdateMask;
-                        bitMask |= XI_TouchEndMask;
-                        XIGrabDevice(static_cast<Display *>(m_xlib_display), xiEvent->deviceid, platformWindow->winId(), xiEvent->time, None, GrabModeAsync, GrabModeAsync, true, &xieventmask);
-                    } else if (xiEvent->evtype == XI_TouchEnd)
-                        XIUngrabDevice(static_cast<Display *>(m_xlib_display), xiEvent->deviceid, xiEvent->time);
-                }
                 if (touchPoint.state == Qt::TouchPointReleased)
                     // If a touchpoint was released, we can forget it, because the ID won't be reused.
                     m_touchPoints.remove(touchPoint.id);