"Build a great camera experience for iPhone Duo" covers the device open and the device closed, including reconfiguring the session from AVCaptureDeviceDirectionCoordinator's change handler when the forward-facing camera changes. It does not cover the partially open pose, which "Leverage multiple displays and scenes on iPhone Duo" treats as a first-class hinge state with a continuous angle.
Consider a camera app that keeps a live preview on screen and adopts AVCaptureDevice.RotationCoordinator — the documented remedy for cases like the square front sensor on iPhone 17, where a hard-coded 90° leaves the preview tilted — applying videoRotationAngleForHorizonLevelPreview to both the preview and the capture connection.
In the partially open pose the two halves are at different physical attitudes: one stands up, the other lies flat.
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Which camera does AVCaptureDeviceDirectionCoordinator report as forward-facing while the hinge status is partially open? Does the hinge angle affect that decision?
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RotationCoordinator derives its angle from device attitude. With the two halves at different attitudes, which one does videoRotationAngleForHorizonLevelPreview reflect — the half carrying the active camera, the half hosting the preview layer, or a single device-level reference?
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If an app deliberately keeps the rear camera on the scene while its preview is drawn on the half facing the user, is that a supported configuration, or is the coordinator expected to override that choice?
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Is any of this modelled in the iPhone Duo simulator, or does the partially open pose require real hardware to test?
Question 4 matters for planning: building against a rotation value that only appears on device would be worth knowing about before the hardware ships.
