nvda

7f2d68f4 - handle conflicts between Windows magnifier and NVDA magnifier (#20025)

handle conflicts between Windows magnifier and NVDA magnifier (#20025) fix #20012 Summary of the issue: When Windows Magnifier was already running, NVDA Magnifier could still start because MagInitialize() succeeds even when the API is held by another process. Only MagSetFullscreenTransform() would fail, triggering the recovery loop — which itself only tested MagInitialize() and MagSetFullscreenColorEffect(), both of which succeed, causing it to falsely declare victory and restart the timer indefinitely. Description of user facing changes: NVDA now shows a clear message ("Cannot start magnifier: the magnification API is unavailable. Windows Magnifier may already be running.") when the magnification API cannot be fully initialized at startup. If the conflict occurs after startup, the recovery mechanism is now capped at 3 attempts before stopping the magnifier and notifying the user, preventing log spam. Description of developer facing changes: _initializeNativeMagnification() no longer uses @trackNativeMagnifierErrors — it now raises OSError on failure (including a MagSetFullscreenTransform probe that detects the Windows Magnifier conflict). _startMagnifier() catches this error, calls _stopMagnifier() to properly unregister the display change handler, and returns early. _attemptRecovery() reuses _initializeNativeMagnification() to avoid duplicating the probe logic, and is now capped by _MAX_RECOVERY_ATTEMPTS = 3. Description of development approach: The fix centers on making _initializeNativeMagnification() a reliable gate: it probes MagSetFullscreenTransform (the actual failing call) as part of initialization and raises on failure rather than silently returning. This single change fixes both the startup path and the recovery path, since _attemptRecovery() can delegate to the same method. A _recoveryAttempts counter (capped at _MAX_RECOVERY_ATTEMPTS) prevents the infinite restart loop when the API remains permanently unavailable.