VibeCoding/.agents/skills/camerax/references/foldables.md

Foldable devices introduce unique challenges for camera applications, including dynamic layout changes, multiple display orientations, and physical device postures, such as tabletop and book modes.

Manage fold states and postures

State	Posture	User interaction	Implementation goal
FLAT	Standard	Full screen preview	Conventional mobile phone layout.
HALF_OPENED	Tabletop	Lower half for controls	Split-screen layout, viewfinder on top, controls on bottom.
HALF_OPENED	Book	Side-by-side	Viewfinder on one panel, gallery and controls on the other.

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Follow the implementation guide

Detect posture changes

Use the Jetpack WindowManager library to observe the device's hinge state and fold layout.

lifecycleScope.launch {
    lifecycle.repeatOnLifecycle(Lifecycle.State.STARTED) {
        windowInfoTracker.windowLayoutInfo(activity)
            .collect { layoutInfo ->
                val displayFeature = layoutInfo.displayFeatures
                    .filterIsInstance<FoldingFeature>()
                    .firstOrNull()

                updateCameraLayout(displayFeature)
            }
    }
}

Handle tabletop mode

In Tabletop mode, horizontal fold, you should move the viewfinder to the top half of the screen and the controls to the bottom half to prevent the user from seeing a "bent" image.

• Identify orientation: Check FoldingFeature.orientation.
• Calculate geometry: Use FoldingFeature.bounds to identify the hinge's physical location on the screen.
• Update UI: Apply padding or constraints to move the PreviewView above the hinge.

Coordinate mapping and Viewport

When the UI layout changes due to a fold, you must update the Viewport to ensure that tap-to-focus and image capture coordinates remain accurate.

val viewport = ViewPort.Builder(Rational(viewfinder.width, viewfinder.height), display.rotation)
    .setScaleType(ViewPort.FILL_CENTER)
    .build()

val useCaseGroup = UseCaseGroup.Builder()
    .addUseCase(preview)
    .setViewPort(viewport)
    .build()

Rear display mode

Some foldables allow using the rear camera with the cover display while the device is unfolded.

• Verification: If available through OEM SDKs or Android 14 (API level 34) or higher, check DeviceState.REAR_DISPLAY_STATE.
• Logic: Handle preview detachment and reattachment on different display surfaces with varying aspect ratios.

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Foldable pitfalls

• Hinge distortion: Don't span the camera preview across a hinge in HALF_OPENED state.
• Physical orientation: The camera sensor's physical orientation relative to the screen often changes when you fold or unfold the device. Always rely on CameraInfo.getSensorRotationDegrees.
• Latency: Rebinding UseCase objects during a fold event is expensive. Use the internal scaling of PreviewView before performing a full bindToLifecycle reconfiguration.