xcb: don't compress tablet motion events

7edd10e6c added this compression feature, but it's not a good idea for
drawing-tablet applications, because smooth drawing depends on receiving
every movement of the stylus.

Also show the device ID in qt.qpa.input.devices category logging.

[ChangeLog][X11] The new X event compression feature that was added in
5.6.0 no longer applies to motion events from drawing tablets.

Task-number: QTBUG-44964
Change-Id: Icd2ca8ca77d8f80c2f39160c74208db10e382501
Reviewed-by: Gatis Paeglis <gatis.paeglis@theqtcompany.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/src/plugins/platforms/xcb/qxcbconnection.cpp b/src/plugins/platforms/xcb/qxcbconnection.cpp
index edfaf2b015..669ef3a98e 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.cpp
+++ b/src/plugins/platforms/xcb/qxcbconnection.cpp
@@ -1626,8 +1626,13 @@ bool QXcbConnection::compressEvent(xcb_generic_event_t *event, int currentIndex,
         if (!m_xi2Enabled)
             return false;
 
-        // compress XI_Motion
+        // compress XI_Motion, but not from tablet devices
         if (isXIType(event, m_xiOpCode, XI_Motion)) {
+#ifndef QT_NO_TABLETEVENT
+            xXIDeviceEvent *xdev = reinterpret_cast<xXIDeviceEvent *>(event);
+            if (const_cast<QXcbConnection *>(this)->tabletDataForDevice(xdev->sourceid))
+                return false;
+#endif // QT_NO_TABLETEVENT
             for (int j = nextIndex; j < eventqueue->size(); ++j) {
                 xcb_generic_event_t *next = eventqueue->at(j);
                 if (!isValid(next))