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macOS: cached CGMainDisplayID goes stale after display re-enumeration; all mouse input collapses to (0,0)

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Valutazione

Difficoltà
3/5
Tempo stimato
1-2 giorni
Idoneità per principianti
68/100
Tipo di issue
Bug
Chiarezza
Abbastanza chiara
Stato di attività
Attiva
Stack tecnologico
cpp, macos
Ambito
desktop, operating-systems

Direzione di ricerca

Start in macos_backend.cpp around line 387 and trace MacosInputState, submit_absolute_motion(), and post_mouse(), focusing on how the cached display ID is used after display re-enumeration. Reproduce the monitor reconnect scenario and verify that both absolute and relative mouse input continue to map to the current display rather than a zero-sized bounds rectangle.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

Bug

On macOS, MacosInputState caches CGMainDisplayID() once at construction (macos_backend.cpp:387). When the display later re-enumerates (monitor power cycle, DisplayPort link renegotiation), macOS assigns a new display ID and the cached ID becomes invalid. From that point on:

  • submit_absolute_motion() calls CGDisplayBounds(state_->display) on the stale ID, which returns a zero rect. scale_absolute_axis() then returns 0 for display_size <= 0, so every absolute mouse event is mapped to (0,0) — the cursor is pinned to the top-left corner.
  • post_mouse() clamps the target location into that same zero rect (std::clamp(raw, origin, origin + size - 1)), so relative motion is also trapped — observed cursor positions oscillate only between (0,0) and (-1,-1).

Restarting the consumer process (re-creating the state, hence re-caching the current display ID) restores input until the next display re-enumeration.

Evidence (observed via Sunshine v2026.914.233613 on Mac mini M4, macOS arm64)

  • Main display ID changes across monitor reconnects: 10 → 12 → 1 over consecutive days.
  • While the bug is active:
    • CGDisplayBounds(staleId 12) → (0,0,0,0)
    • CGDisplayBounds(CGMainDisplayID() = 1) → (0,0,1920,1080)
    • Client input packets arrive (UDP control channel has traffic), video capture is unaffected (capture re-enumerates per session), but the cursor never leaves the origin.
  • After restarting Sunshine, input works again — until the display ID changes once more.

Reproduction

  1. Start a libvirtualhid consumer (e.g. Sunshine) and note the main display ID.
  2. Force the display to re-enumerate: power-cycle the monitor, or unplug/replug it (many DP/USB-C monitors do this on their own when entering deep sleep).
  3. Send absolute or relative mouse input — cursor stays pinned at (0,0).

Suggested fix

Either:

  • Resolve the display at event time (CGMainDisplayID() in submit_absolute_motion / post_mouse instead of the cached value), or
  • Register CGDisplayRegisterReconfigurationCallback and update the cached display / display_scaling on reconfiguration events.

Additionally, guard against zero-sized CGDisplayBounds results (invalid/offline display) instead of clamping into a degenerate rect — e.g. fall back to CGMainDisplayID() bounds.

Happy to provide more diagnostics if needed.

Lingua principale
C++
Stelle
66
Fork
18
Merge medio
14h 20m
PR unite (30g)
40

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