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jcsteh
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Wait for sent keys to be picked up by the keyboard hook. (nvaccess#15957)
Fixes nvaccess#15822. Summary of the issue: With "Handle keys from other applications" enabled, NVDA interferes with certain software which intercepts and re-transmits keyboard commands such as Nudi6.1. For example, this makes it impossible to use backspace while this software is running. Description of user facing changes Backspace now works correctly when using Nudi6.1 with NVDA's "Handle keys from other applications" setting enabled. Description of development approach Before nvaccess#14708, we delayed slightly when sending keys, which would mean that any keys sent by an app which captured a key sent by NVDA would be ignored during that period. After nvaccess#14708, we only ignore any keys received while NVDA is sending keys, but that doesn't include any keys captured and sent afterward by, for example, Nudi6.1. This could result in a loop where NVDA kept receiving the key it sent (re-transmitted by the other app) and sending it again. To fix this, we now explicitly wait for the key sent by NVDA (e.g. backspace) to be received by the keyboard hook before we stop ignoring keys and thus return from KeyboardInputGesture.send(). This means that if another application intercepts this key and re-transmits it, we will wait for that re-transmission and ignore it. We use a kernel event so that the notification from the keyboard hook can be handled as quickly as possible without being dependent on the system timer resolution. There is a chance that a key will be intercepted and never re-sent. To deal with this, we wait for a maximum timeout of 10 ms. This means that in the best case scenario, nothing intercepts a key sent by NVDA and we return almost immediately. In the worst case scenario, we wait between 10 and 30 ms (depending on the system timer resolution), which is no worse than the situation before nvaccess#14708.
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2 files changed

Lines changed: 28 additions & 4 deletions

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‎source/keyboardHandler.py‎

Lines changed: 26 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -35,13 +35,16 @@
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import NVDAState
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from contextlib import contextmanager
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import threading
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import winKernel
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if typing.TYPE_CHECKING:
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from NVDAObjects import NVDAObject # noqa: F401
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from watchdog import WatchdogObserver
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_watchdogObserver: typing.Optional["WatchdogObserver"] = None
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ignoreInjected=False
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_lastInjectedKeyUp: tuple[int, int] | None = None
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_injectionDoneEvent: int | None = None
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# Fake vk codes.
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# These constants should be assigned to the name that NVDA will use for the key.
@@ -285,11 +288,15 @@ def internal_keyUpEvent(vkCode,scanCode,extended,injected):
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"""
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try:
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global lastNVDAModifier, lastNVDAModifierReleaseTime, bypassNVDAModifier, passKeyThroughCount, lastPassThroughKeyDown, currentModifiers
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# Injected keys should be ignored in some cases.
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if injected and (ignoreInjected or not config.conf['keyboard']['handleInjectedKeys']):
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return True
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keyCode = (vkCode, extended)
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# Injected keys should be ignored in some cases.
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if injected:
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if not config.conf['keyboard']['handleInjectedKeys']:
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return True
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if ignoreInjected:
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if keyCode == _lastInjectedKeyUp:
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winKernel.kernel32.SetEvent(_injectionDoneEvent)
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return True
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if passKeyThroughCount >= 1:
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if lastPassThroughKeyDown == keyCode:
@@ -567,7 +574,12 @@ def executeScript(self, script):
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# Now actually execute the script.
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super().executeScript(script)
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#: The maximum amount of time (in ms) to wait for keys injected by NVDA to be
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#: received by NVDA.
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_INJECTION_WAIT_TIMEOUT: int = 10
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def send(self):
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global _lastInjectedKeyUp, _injectionDoneEvent
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keys = []
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for vk, ext in self.generalizedModifiers:
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if vk == VK_WIN:
@@ -582,6 +594,11 @@ def send(self):
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keys.append((self.vkCode, self.scanCode, self.isExtended))
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with ignoreInjection():
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handleInjectedKeys = config.conf['keyboard']['handleInjectedKeys']
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if handleInjectedKeys:
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_lastInjectedKeyUp = (keys[0][0], keys[0][2])
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if not _injectionDoneEvent:
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_injectionDoneEvent = winKernel.createEvent()
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if winUser.getKeyState(self.vkCode) & 32768:
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# This key is already down, so send a key up for it first.
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winUser.keybd_event(self.vkCode, self.scanCode, self.isExtended + 2, 0)
@@ -592,6 +609,11 @@ def send(self):
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# Send key up events for the keys in reverse order.
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for vk, scan, ext in reversed(keys):
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winUser.keybd_event(vk, scan, ext + 2, 0)
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if handleInjectedKeys:
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# Wait for the keys to be received by NVDA. We don't do this if
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# handleInjectedKeys is disabled because we just ignore all injected keys
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# in that case.
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winKernel.waitForSingleObject(_injectionDoneEvent, self._INJECTION_WAIT_TIMEOUT)
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@classmethod
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def fromName(cls, name):

‎user_docs/en/changes.t2t‎

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Original file line numberDiff line numberDiff line change
@@ -13,6 +13,8 @@ What's New in NVDA
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== Bug Fixes ==
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- Backspace now works correctly when using Nudi 6.1 with NVDA's "Handle keys from other applications" setting enabled. (#15822, @jcsteh)
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-
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== Changes for Developers ==

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