dix: don't create core motion events for non-x/y valuators.

Devices that send motion events with valuators other than x/y get core
motion events with unchanged x/y coordinates. This confuses some
applications.

If the DeviceEvent does not have the x/y valuators set, return BadMatch on
core conversion, thus skipping the event altogether.

Reported-by: Bartosz Brachaczek <b.brachaczek@gmail.com>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Tested-by: Bartosz Brachaczek <b.brachaczek@gmail.com>

dix/eventconvert.c

@@ -102,6 +102,15 @@ EventToCore(InternalEvent *event, xEvent *core)
     switch(event->any.type)
     {
         case ET_Motion:
+            {
+                DeviceEvent *e = &event->device_event;
+                /* Don't create core motion event if neither x nor y are
+                 * present */
+                if (!BitIsOn(e->valuators.mask, 0) &&
+                    !BitIsOn(e->valuators.mask, 1))
+                    return BadMatch;
+            }
+            /* fallthrough */
         case ET_ButtonPress:
         case ET_ButtonRelease:
         case ET_KeyPress: