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## Summary of the Pull Request Scrolling the mouse wheel over the Power Display tray icon adjusts brightness, without opening the flyout. - New **Tray icon mouse wheel** setting: `Off` / `Primary display` / `All displays`, defaulting to **`Off`**. It is scoped to the tray icon — the flyout sliders accept wheel input regardless, as they always have. The existing **Mouse wheel increment** setting supplies the per-notch step. - **Off by default.** The gesture consumes a wheel notch that would otherwise reach the window under the pointer, and acting on it installs a system-wide `WH_MOUSE_LL` hook. Neither is something an existing installation should acquire silently on upgrade. With the setting `Off` no hook is ever installed and no notch is ever consumed, so this PR changes no existing behaviour until the user opts in: 1958 insertions, 2 deletions, and both deletions are refactors of lines this feature reuses. - **No feedback UI.** Brightness is self-evidencing — you scroll and the screen changes — so the display itself is the feedback. The notification icon is untouched: same tooltip, same text, same legacy notification-icon protocol. ## PR Checklist - [x] Closes: #49410 - [ ] **Communication:** I've discussed this with core contributors already. If the work hasn't been agreed, this work might be rejected - [x] **Tests:** Added/updated and all pass - [x] **Localization:** All end-user-facing strings can be localized - [x] **Dev docs:** Added/updated - [ ] **New binaries:** Added on the required places - [ ] [JSON for signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json) for new binaries - [ ] [WXS for installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs) for new binaries and localization folder - [ ] [YML for CI pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml) for new test projects - [ ] [YML for signed pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml) - [ ] **Documentation updated:** If checked, please file a pull request on [our docs repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys) and link it here: #xxx No new binaries or projects — everything lands in existing assemblies. Communication is unchecked because #49410 is still Needs-Triage. ## Detailed Description of the Pull Request / Additional comments ### Why a low-level hook The Shell does not forward `WM_MOUSEWHEEL` to a notification icon's callback window under any `NOTIFYICON_VERSION`, and a click-through overlay placed over the icon cannot receive wheel input either. `TrayIconMouseWheelListener` therefore installs a `WH_MOUSE_LL` hook — but only transiently, and only when it will act on the result: - Nothing is installed at all while the setting is `Off`, which is the default. - Installed in `EnsureHook()` when the UI thread confirms the pointer is inside the rectangle from `Shell_NotifyIconGetRect` **and** `CanAdjustBrightnessFromTrayWheel` says some monitor can accept a brightness write. - Removed in `DisarmCore()` as soon as either condition stops holding, the pointer leaves the rectangle, or the mode changes. - A notch is consumed (the hook proc returns non-zero) only while armed and only for points inside the armed rectangle, so a wheel event Power Display will not act on still reaches the window under the cursor. The hook runs on a dedicated background thread with its own message loop; the proc itself only enqueues a sample and posts a drain request. Deltas are marshalled to the UI thread in batches, and `WheelDeltaAccumulator` folds high-resolution deltas (precision wheels, touchpads) into whole notches. Each sample carries the hover generation it was captured under, so samples from a hover the UI thread has already retired are discarded rather than applied late. ### Hover detection The Shell sends `WM_MOUSEMOVE` to the icon's callback window while the pointer is over it. `TrayIconService.HandleTrayMouseMove` resolves the rectangle with `Shell_NotifyIconGetRect` and caches it for a second, because that message repeats for every pixel of travel. `TrayIconService` gains nothing else: no protocol change, no new hover UI, no polling. The rest of the file — and `MainWindow.xaml` — is untouched. ### Linked brightness While linked brightness is on, a notch has to move the whole group, so it goes through `MainViewModel.LinkedBrightness` rather than the individual monitor setters. The new master value is taken from the planner's value for the monitor the wheel named, **not** from the current master. The master is positional only — `SeedInitialLinkedBrightness` takes it from the lowest-numbered linked monitor and never writes hardware, and every monitor-list rebuild re-seeds it — so it can sit arbitrarily far from the monitor the wheel is aimed at. Stepping it relative to itself would apply a wrong-sized or wrong-signed change, and a master already clamped at 0/100 would swallow the notch while writing nothing at all. The setting description calls out that linked brightness widens the scope, so `Primary display` is not literally a single display while it is on. ### What is deliberately not here An earlier revision of this PR showed the target and percentage in a custom overlay as you scrolled. Doing that meant the standard Shell tooltip would not do (it cannot be shown on demand), which meant an own window, which meant suppressing the Shell tooltip so the two did not collide, which meant `NOTIFYICON_VERSION_4`, which changed the callback packing and made the app responsible for all hover text — including for keyboard and touch users, who never reach a cursor-anchored overlay and would have been left with no visible tooltip at all. That chain was about half the diff, for a readout that adds little on top of watching the screen change. It is gone. If a readout is wanted later it can be argued on its own merits, separately from this feature. The same revision also gated the flyout sliders on this setting. That bundled two unrelated things behind one switch — turning off tray scrolling would also have stopped the contrast and volume sliders responding to the wheel — so the setting is now scoped to the tray icon and named accordingly. An earlier revision also routed the tray **Exit** action through `Shutdown()`. That fixes a pre-existing teardown leak which has nothing to do with this feature, so it now lives in #49580 and is out of scope here. This branch does not depend on it: the hook thread is a background thread and the process is ending either way. ## Validation Steps Performed - Unit tests: `PowerDisplay.Lib.UnitTests` 215 passed, `Settings.UI.UnitTests` 165 passed. - Builds: `PowerDisplay` and Settings UI, x64 Debug, no warnings. - Automated coverage is in `PowerDisplay.Lib.UnitTests`: target selection per mode, wheel accumulation including negative deltas, partial notches and direction reversal, half-open rectangle containment, and settings serialization and round-trip for the new mode, including that a settings file predating the feature loads as `Off`. `Settings.UI.UnitTests` covers the view-model index mapping and pins the enum values to the ComboBox item order. - The Win32 glue in `TrayIconService` and `TrayIconMouseWheelListener` is not unit tested. Manual passes performed: scrolling over the icon in both modes, the icon parked in the notification overflow, high-resolution wheel input, brightness boundaries, live monitor refresh while hovering, tray icon hidden and re-enabled, Explorer restart, the context menu and left-click, `Off` stopping tray scrolling while the flyout sliders keep working, and confirming a notch that Power Display will not act on still reaches the window under the cursor. Not verified, needing hardware this branch has not been run on: - Multiple taskbars, where the tray icon is on a secondary display and `Primary display` mode adjusts a monitor the user may not be looking at. - Mixed-DPI setups, for the `Shell_NotifyIconGetRect` rectangle and the hook's physical-pixel hit test. --------- Co-authored-by: Yu Leng <yuleng@microsoft.com> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com> Copilot-Session: 5d7f36fe-d175-4aa9-a3c7-b370d952d1d3