pointer_lock 0.4.0

Locks the mouse pointer in place and reports its motion as relative deltas, which Flutter offers on no desktop platform and does not surface in a browser.

pointer_lock

Locks the mouse pointer in place and reports its motion as relative deltas.

Flutter exposes no pointer lock on any desktop platform, and does not surface the browser's either, which makes a first-person camera impossible out of the box: the cursor reaches the edge of the window and the view stops turning. This plugin is the missing piece on both.

final capture = MouseCapture.instance;

if (capture.isSupported) {
  await capture.capture();
}

// Once per simulation step:
final delta = capture.takeDelta();
yaw   += delta.dx * sensitivity;
pitch += delta.dy * sensitivity;

Pull, not push

The delta is drained with takeDelta rather than delivered by a stream, because that is the shape a game wants. A simulation running on a fixed timestep asks "how far did the mouse move since the last step" once per step; handing it a stream of individual mouse events only moves the accumulation into every caller, and each of them has to get it right.

takeDelta is synchronous for the same reason — it is called from inside the step, where awaiting anything would mean the step no longer sees a consistent snapshot of its inputs.

Releasing

Losing window focus drops the capture and announces it on onStateChanged. Anything else would leave a hidden cursor over another application, which the user cannot recover from. Treat an unrequested CaptureState.released as a reason to pause.

The plugin does not watch for Escape. Key handling belongs to the application, which calls release() itself.

Platforms

Platform	Status	How
macOS	supported	CGAssociateMouseAndMouseCursorPosition(0), NSCursor.hide(), a local NSEvent monitor
Web, desktop browser	supported	document.requestPointerLock through package:web. Pure Dart, so nothing is registered and flutter test --platform chrome reaches it
Web, phone or tablet	not applicable	reported by (pointer: coarse); isSupported is false so the game shows its touch controls
Windows	not yet	Raw Input plus ClipCursor
Linux	not yet	gdk_seat_grab, or XI2 raw events
iOS, Android	not applicable	no pointer to capture; isSupported is false

isSupported is answered by the backend rather than guessed by the caller, so an application can offer another control scheme instead of discovering the gap at the first call. The engine above this reads exactly that: a build where it is false turns the camera by dragging.

What a browser does that a desktop does not

A capture must come out of a user gesture. requestPointerLock called from a timer, a future or a frame callback is refused — ask inside the handler of the press that prompted it.

A refusal is an event, not an exception. It arrives as pointerlockerror, and on browsers that return a promise as a rejected promise as well; both are handled here, and a refused capture leaves the state released rather than pretending.

The player can leave without asking. Escape releases the lock, as does switching tab, and both arrive as an unrequested CaptureState.released — the signal to pause.

In an iframe the parent decides. A page embedding the game needs allow="pointer-lock" on the iframe, or every capture is refused with nothing in the console to say why.

Hot restart

The native side outlives the Dart isolate. A hot restart while the pointer is captured would otherwise leave the cursor hidden with nothing left that remembers to ask for it back, so construction always issues a reset first.

Prior art

helgoboss/pointer_lock (MIT) solves the same problem across more platforms and is where the macOS technique here came from. It is not published on pub.dev. This plugin exists because three things it does not do matter to a game:

• no observer for focus loss, so Cmd+Tab strands the cursor system-wide;
• one channel message per mouse event, at a 1000 Hz polling rate;
• no isSupported, which a build targeting mobile needs.

Cost

One platform-channel message per mouse event, carrying a two-element Float64List. Whether that shows up in a frame profile at a 1000 Hz polling rate has not been measured yet; if it does, the fix is to accumulate natively and flush once per frame.

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Part of flutter3d, an independent implementation of a 3D engine for Flutter — not a fork or a binding of another engine, and not affiliated with the Flutter team. Three switchable rendering backends: Impeller via Flutter GPU, WebGL2, and a software rasteriser. glTF, OBJ and .f3d loading, six lighting models, shadows, bloom, skinning, animation, BVH culling and picking; a deterministic fixed-step game layer with collision, navigation, positional audio, and gamepad and touch input. Three example games — shooter, platformer, racing — each built on its genre package: flutter3d_game_shooter, flutter3d_game_platformer, flutter3d_game_racing. A new game starts from apps/flutter3d_template_app. Documentation: https://flutter3d.pleion.dev.