Block touch input while the magnifier is running

source/_magnifier/magnifier.py

@@ -12,10 +12,14 @@
 from comtypes import COMError
 from logHandler import log
 import wx
+import gui
 import ui
 import speech
 import screenCurtain
+import touchHandler
 from winAPI import _displayTracking
+from winAPI.winUser.constants import SystemMetrics
+from winBindings import user32
 from winAPI._displayTracking import OrientationState, getPrimaryDisplayOrientation
 from .utils.types import (
 	MagnifierParameters,
@@ -184,6 +188,39 @@ def _startMagnifier(self) -> None:
 
 		self._isActive = True
 		self.currentCoordinates = self._focusManager.getCurrentFocusCoordinates()
+		if touchHandler.handler is not None:
+			# Touch events are already intercepted by NVDA; block gesture execution
+			# to prevent incorrect coordinates from the magnified view reaching the system.
+			touchHandler.blockTouchInput = True
+		elif user32.GetSystemMetrics(SystemMetrics.MAXIMUM_TOUCHES) > 0:
+			# The user has a touchscreen but NVDA cannot intercept inputs; warn them.
+			if touchHandler.touchSupported():
+				reason = pgettext(
+					"magnifier",
+					# Translators: Warning when magnifier is started on a device with a touch screen but NVDA's touch support is disabled.
+					"Touch screen input cannot be used because NVDA touch support is disabled. ",
+				)
+			else:
+				reason = pgettext(
+					"magnifier",
+					# Translators: Warning when the magnifier starts on a portable/source copy with a touchscreen.
+					"Touch screen input cannot be used because NVDA is not installed. ",
+				)
+			wx.CallAfter(
+				gui.messageBox,
+				reason
+				+ pgettext(
+					"magnifier",
+					# Translators: Suffix appended to touch warning when touch inputs cannot be blocked by the magnifier.
+					"Touch inputs may not behave as expected while the magnifier is running.",
+				),
+				pgettext(
+					"magnifier",
+					# Translators: Title of the warning dialog shown when touch cannot be intercepted while the magnifier is running.
+					"Touch Screen Warning",
+				),
+				wx.OK | wx.ICON_WARNING,
+			)
 
 	def _updateMagnifier(self) -> None:
 		"""
@@ -254,6 +291,8 @@ def _stopMagnifier(self) -> None:
 			return
 		self._stopTimer()
 		self._isActive = False
+		if touchHandler.handler is not None:
+			touchHandler.blockTouchInput = False
 		# Unregister from display changes
 		_displayTracking.displayChanged.unregister(self._onDisplayChanged)
 

source/touchHandler.py

@@ -9,6 +9,7 @@
 """
 
 import threading
+import winsound
 from functools import cached_property
 from typing import (
 	TYPE_CHECKING,
@@ -189,6 +190,7 @@ class POINTER_TOUCH_INFO(Structure):
 
 touchWindow = None
 touchThread = None
+blockTouchInput: bool = False
 
 
 class TouchInputGesture(inputCore.InputGesture):
@@ -391,6 +393,9 @@ def setMode(self, mode):
 
 	def pump(self):
 		for preheldTracker, tracker in self.trackerManager.emitTrackers():
+			if blockTouchInput:
+				winsound.MessageBeep(winsound.MB_ICONASTERISK)
+				continue
 			gesture = TouchInputGesture(preheldTracker, tracker, self._curTouchMode.value)
 			try:
 				inputCore.manager.executeGesture(gesture)

tests/unit/test_magnifier/test_magnifierTouchscreen.py

@@ -0,0 +1,86 @@
+# A part of NonVisual Desktop Access (NVDA)
+# Copyright (C) 2025-2026 NV Access Limited, Antoine Haffreingue
+# This file may be used under the terms of the GNU General Public License, version 2 or later, as modified by the NVDA license.
+# For full terms and any additional permissions, see the NVDA license file: https://github.com/nvaccess/nvda/blob/master/copying.txt
+
+from _magnifier.magnifier import Magnifier
+from _magnifier.utils.types import Coordinates
+from tests.unit.test_magnifier.test_magnifier import _TestMagnifier
+import touchHandler
+from winAPI._displayTracking import getPrimaryDisplayOrientation
+from unittest.mock import MagicMock, patch
+
+
+class TestMagnifierTouchscreen(_TestMagnifier):
+	"""Tests for touchscreen blocking/warning behaviour when the magnifier starts and stops."""
+
+	def setUp(self):
+		super().setUp()
+		self.magnifier = Magnifier()
+		screenDimensions = getPrimaryDisplayOrientation()
+		self.focusCoords = Coordinates(screenDimensions.width // 2, screenDimensions.height // 2)
+		self.magnifier._focusManager.getCurrentFocusCoordinates = MagicMock(return_value=self.focusCoords)
+
+	def tearDown(self):
+		if hasattr(self.magnifier, "_timer") and self.magnifier._timer:
+			self.magnifier._timer.Stop()
+			self.magnifier._timer = None
+		if hasattr(self.magnifier, "_isActive") and self.magnifier._isActive:
+			self.magnifier._isActive = False
+		super().tearDown()
+
+	def testStartMagnifierBlocksTouchWhenHandlerActive(self):
+		"""blockTouchInput is set when the magnifier starts with the touch handler running."""
+		with (
+			patch("touchHandler.handler", new=MagicMock()),
+			patch("touchHandler.blockTouchInput", False),
+		):
+			self.magnifier._startMagnifier()
+			self.assertTrue(touchHandler.blockTouchInput)
+
+	def testStartMagnifierWarnsWhenTouchSupportDisabled(self):
+		"""Dialog shown when device has a touchscreen but NVDA touch support is disabled."""
+		with (
+			patch("touchHandler.handler", new=None),
+			patch("winBindings.user32.GetSystemMetrics", return_value=5),
+			patch("touchHandler.touchSupported", return_value=True),
+			patch("_magnifier.magnifier.wx.CallAfter") as mock_call_after,
+		):
+			self.magnifier._startMagnifier()
+
+		mock_call_after.assert_called_once()
+
+	def testStartMagnifierWarnsOnPortableOrNoUIAccess(self):
+		"""Dialog shown when device has a touchscreen but NVDA cannot intercept (portable/no UI access)."""
+		with (
+			patch("touchHandler.handler", new=None),
+			patch("winBindings.user32.GetSystemMetrics", return_value=5),
+			patch("touchHandler.touchSupported", return_value=False),
+			patch("_magnifier.magnifier.wx.CallAfter") as mock_call_after,
+		):
+			self.magnifier._startMagnifier()
+
+		mock_call_after.assert_called_once()
+
+	def testStartMagnifierNoActionWithoutTouchscreen(self):
+		"""No dialog and no blocking when the device has no touchscreen."""
+		with (
+			patch("touchHandler.handler", new=None),
+			patch("winBindings.user32.GetSystemMetrics", return_value=0),
+			patch("_magnifier.magnifier.wx.CallAfter") as mock_call_after,
+		):
+			self.magnifier._startMagnifier()
+
+		mock_call_after.assert_not_called()
+
+	def testStopMagnifierUnblocksTouchInput(self):
+		"""blockTouchInput is reset to False when the magnifier stops with the touch handler active."""
+		self.magnifier._stopTimer = MagicMock()
+		self.magnifier._isActive = True
+		touchHandler.blockTouchInput = True
+		self.addCleanup(setattr, touchHandler, "blockTouchInput", False)
+
+		with patch("touchHandler.handler", new=MagicMock()):
+			self.magnifier._stopMagnifier()
+
+		self.assertFalse(touchHandler.blockTouchInput)