[Bug] Windows 10: transparent always-on-top window sporadically renders transparent areas / desktop wallpaper black (composition race when toggling cursor events or minimizing)

[wersling]

Describe the bug

We ship a desktop-pet style game (transparent always-on-top window is its core form factor): a large (1440×900) transparent: true, alwaysOnTop: true, decorations: false, shadow: false window rendering a WebGL (PixiJS) scene on a transparent canvas (backgroundAlpha: 0), with HTML div UI on top. Because it is a desktop pet, we frequently toggle set_ignore_cursor_events() as the cursor moves in/out of the interactive region (a "cursor event guard": transparent areas of the window are click-through, the canvas area is interactive).

Players on Windows 10 report two sporadic rendering failures, both observed in player-recorded videos:

1. Desktop wallpaper turns black while the app is minimized, and restores when the window is brought back. The wallpaper file itself is never modified — purely a display failure that self-recovers with the window state change.
2. The window's transparent areas turn black during normal interaction (e.g. opening a UI panel, entering item-placement mode, moving the cursor across the canvas boundary) — exactly the moments our app toggles set_ignore_cursor_events().

Both are low-probability events under high-frequency triggers: the vast majority of toggles/minimizes render correctly.

Expected behavior

Transparent regions and the desktop wallpaper should stay correctly composed on Windows 10 when toggling set_ignore_cursor_events or minimizing/restoring a transparent always-on-top window.

Analysis (from reading tao 0.34.8 sources)

• tao/src/platform_impl/windows/window.rs — when attributes.transparent && !pl_attribs.no_redirection_bitmap, tao enables the legacy DwmEnableBlurBehindWindow + empty-region (0, 0, -1, -1) hack for full-window transparency.
• tao/src/platform_impl/windows/window_state.rs — set_ignore_cursor_events toggles WS_EX_TRANSPARENT | WS_EX_LAYERED via SetWindowLongPtr, forcing DWM to rebuild the composition tree (layered ⇄ direct composition path).

Our working model: BlurBehind hack + frequent WS_EX_LAYERED toggles (cursor guard) + minimize/restore of a large always-on-top transparent window occasionally race with DWM's composition-tree rebuild on Windows 10, losing either the window's alpha or the wallpaper layer (WorkerW) for a moment — the "black" being an invalid/uninitialized surface. We are still correlating occurrences with dwm.exe events in the Windows Event Log to determine whether DWM actually restarts or this is a non-crash composition failure, so the model above is our best current hypothesis rather than a confirmed root cause.

Relation to #15410

noRedirectionBitmap (WS_EX_NOREDIRECTIONBITMAP / DirectComposition path) looks like the structural fix for this class of issue: it sidesteps the BlurBehind hack entirely. Questions for maintainers:

1. Which release will include feat(core): add no_redirection_bitmap API on Windows #15410 — a 2.12.0? Any chance of a backport to 2.11.x?
2. Are you aware of other Windows 10 reports where toggling set_ignore_cursor_events or minimizing transparent windows corrupts composition (black wallpaper / black transparent areas)? Possibly related: [bug] window effects leak out of the window on Windows 10 #12849, [bug] maximized window config causes black flash on launch #11284.

Platform and Versions

• tauri: 2.10.3 (tao 0.34.8, wry 0.48.0)
• OS: Windows 10 (player reports so far; exact builds + GPU/driver info being collected)
• WebView2 runtime: affected machines' versions being collected
• Frontend: PixiJS 8 WebGL canvas (backgroundAlpha: 0, preference: 'webgl'), HTML div UI coexisting in the same transparent window

Additional context

• App: "PicoCat", a Steam desktop-pet / idle game.
• We plan mitigations on our side (hide-to-tray instead of minimize; debouncing cursor-event toggles), but the underlying composition path seems worth flagging upstream.
• Happy to provide player videos / Windows Event Log data once collected.