Feature: mouse capture to main Window (disable/enable with mouse middle button)

[maximilien-noal]

Description of Changes

Enables mouse capture to the mainWindow edges.

Rationale behind Changes

A lot of games use edge scrolling (Dune 2, Transarctica)

Dune has controls on the edges of the screen that are easier to target with this feature.

Suggested Testing Steps

Tested on Windows succesfully.
Other platforms are fully implemented, but if it doesn't work there is no issue (no exceptions) anyway.

[github-advanced-security]

CodeQL found more than 20 potential problems in the proposed changes. Check the Files changed tab for more details.

[Copilot]

Pull request overview

Adds an initial “mouse capture” feature to the Avalonia game window so the cursor can be constrained to the emulator display area (useful for edge-scrolling games).

Changes:

• Introduces a new NativeMouseCapture helper (Windows ClipCursor, macOS CoreGraphics calls, Linux X11 grab).
• Moves mouse input wiring into MainWindow and adds middle-click toggling + periodic recapture logic.
• Appends a capture status hint to the main window title.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
src/Spice86/Views/MainWindow.axaml.cs	Hooks pointer events, toggles capture via middle-click, and manages capture lifecycle on window events.
src/Spice86/Views/MainWindow.axaml	Adds a Name to the Viewbox hosting the display.
src/Spice86/ViewModels/MainWindowViewModel.cs	Adds MouseCaptureHint and includes it in the window title.
src/Spice86/Native/NativeMouseCapture.cs	New cross-platform native mouse capture implementation (Win/macOS/Linux).
src/Spice86/App.axaml.cs	Removes now-relocated pointer-event wiring from App startup.

[maximilien-noal]

@copilot open a new pull request to apply changes based on the comments in this thread

[Copilot]

@maximilien-noal I've opened a new pull request, #1962, to work on those changes. Once the pull request is ready, I'll request review from you.

In general terms, since we cannot reasonably replace CoreGraphics mouse APIs with fully managed alternatives, the best practical fix is to minimize and encapsulate calls to unmanaged code. For this class, that means calling CGMainDisplayID() only once, caching its result in a managed field, and reusing that cached value in both EnableCapture and DisableCapture. This reduces unmanaged interop calls and keeps the managed interface unchanged.

Concretely, in src/Spice86/Native/MacOsMouseCaptureBackend.cs:

1. Add a private static uint field (e.g., _mainDisplayId) initialized to 0 to cache the main display ID.
2. Add a private helper method (e.g., TryEnsureMainDisplayId(out uint mainDisplay)) that:
   • If _mainDisplayId is 0, calls NativeMouseCaptureInterop.CGMainDisplayID() once, stores it in _mainDisplayId, and returns true only if it is non‑zero.
   • If _mainDisplayId is already set, just returns it without another unmanaged call.
3. In EnableCapture, replace the direct call to CGMainDisplayID() with a call to TryEnsureMainDisplayId and use the resulting mainDisplay value.
4. In DisableCapture, similarly replace the direct call to CGMainDisplayID() with the helper, again using the cached value.

This keeps all external behavior the same (same success/failure conditions and error handling) but reduces unmanaged calls and centralizes the interop usage.

General approach: We cannot replace XSync with a pure managed alternative, but we can reduce the number of unmanaged transitions by avoiding redundant calls. That lessens overhead and slightly reduces the surface area of unmanaged interaction, aligning with the spirit of the recommendation without changing behavior.

Best concrete fix in this snippet: In DisableCapture, after a successful XUngrabPointer, we call NativeMouseCaptureInterop.XSync(_display, 0); on line 76. EnableCapture already performs a sync after attempting the grab, and Cleanup will close the display and free resources. For most X11 patterns, an explicit XSync after XUngrabPointer is not strictly required for correctness in this high‑level managed wrapper, whereas each XSync forces a roundtrip to the X server. Removing this specific XSync reduces calls to unmanaged code without altering the public API or observable behavior in typical usage (the ungrab still occurs; the X server will process it as part of its normal request handling).

Changes needed:

• File: src/Spice86/Native/X11MouseCaptureBackend.cs
• In method DisableCapture, remove the line that calls NativeMouseCaptureInterop.XSync(_display, 0);.
• No new methods, imports, or type definitions are required.