Fix a regression that broke handling of mouse clicks on some Linux Wayland systems with a touchpad

Basically, in Qt 6 Wayland, Qt reports the device for mouse events
as finger when they come from a touchpad instead of a mouse. This caused
them to be swallowed by the gesture recognizer as being synthesized
mouse events.

Fixes #1981629 [Viewer TOC and search results  are not clickable](https://bugs.launchpad.net/calibre/+bug/1981629)

manual/customize.rst

@@ -49,7 +49,7 @@ Environment variables
       the system theme -- beware of crashes and hangs.
     * ``CALIBRE_SHOW_DEPRECATION_WARNINGS`` - causes calibre to print deprecation warnings to stdout. Useful for calibre developers.
     * ``CALIBRE_NO_DEFAULT_PROGRAMS`` - prevent calibre from automatically registering the filetypes it is capable of handling with Windows.
-    * ``QT_QPA_PLATFORM`` - On Linux set this to ``wayland`` to force calibre to use Wayland. Note however that Qt + Wayland is extremely buggy.
+    * ``QT_QPA_PLATFORM`` - On Linux set this to ``wayland`` to force calibre to use Wayland and ``xcb`` to force use of X11.
     * ``SYSFS_PATH`` - Use if sysfs is mounted somewhere other than /sys
     * ``http_proxy``, ``https_proxy`` - used on Linux to specify an HTTP(S) proxy
 

src/calibre/gui2/__init__.py

@@ -1076,15 +1076,6 @@ class Application(QApplication):
                     args.extend(['-platform', 'windows:darkmode=2'])
                 else:
                     args.extend(['-platform', 'windows:darkmode=1'])
-            if not iswindows and not ismacos and not os.environ.get('QT_QPA_PLATFORM'):
-                # Various issues in Wayland make it unuseable so prevent Qt from
-                # using Wayland unless the user asks for it explicitly.
-                # In KDE right clicking on the book list causes left clicks on it
-                # to stop working till kwin is restarted. On GNOME there are no
-                # native window decorations. There have been reports of left clicks
-                # not working in GNOME though I cannot reproduce. So force use of
-                # XWayland.
-                args.extend(['-platform', 'xcb'])
 
         self.headless = headless
         from calibre_extensions import progress_indicator

src/calibre/gui2/gestures.py

@@ -5,14 +5,13 @@
 import os
 from functools import lru_cache
 from qt.core import (
-    QApplication, QEvent, QInputDevice, QMouseEvent, QObject, QPointF,
-    QPointingDevice, QScroller, Qt, pyqtSignal
+    QApplication, QEvent, QInputDevice, QMouseEvent, QObject, QPointF, QScroller, Qt,
+    pyqtSignal
 )
 
 from calibre.utils.monotonic import monotonic
 from polyglot.builtins import itervalues
 
-
 HOLD_THRESHOLD = 1.0  # seconds
 TAP_THRESHOLD  = 50   # manhattan pixels
 
@@ -160,6 +159,7 @@ class GestureManager(QObject):
         if touch_supported():
             view.viewport().setAttribute(Qt.WidgetAttribute.WA_AcceptTouchEvents)
         self.state = State()
+        self.last_touch_event_device_id = None
         self.state.tapped.connect(
             self.handle_tap,
             type=Qt.ConnectionType.QueuedConnection)  # has to be queued otherwise QApplication.keyboardModifiers() does not work
@@ -177,8 +177,8 @@ class GestureManager(QObject):
             return
         etype = ev.type()
         if etype in (QEvent.Type.MouseButtonPress, QEvent.Type.MouseMove, QEvent.Type.MouseButtonRelease, QEvent.Type.MouseButtonDblClick):
-            if ev.pointingDevice().pointerType() is QPointingDevice.PointerType.Finger:
-                # swallow fake mouse events generated from touch events
+            if self.last_touch_event_device_id is not None and self.last_touch_event_device_id == ev.pointingDevice().uniqueId():
+                # swallow fake mouse events generated by the same device as the last touch event
                 ev.ignore()
                 return False
             self.scroller.stop()
@@ -189,6 +189,7 @@ class GestureManager(QObject):
         boundary = self.evmap.get(etype)
         if boundary is None or ev.deviceType() != QInputDevice.DeviceType.TouchScreen:
             return
+        self.last_touch_event_device_id = ev.pointingDevice().uniqueId()
         self.state.update(ev, boundary=boundary)
         ev.accept()
         return True