The unfold, as code.
An open reconstruction of the iPhone Duo hand-off. The cover screen blurs and stretches away from the hinge while the inner screen resolves from the fold out. Each screen renders the result of a function of the hinge angle.
What each screen actually draws
Run these two renderers on the two displays and feed them the same hinge angle.
One layout, every posture
classify() turns Viewport Segments, Device Posture, and screen shape into one state object.
<DuoSplit> and duo.css then put each pane on its own side of the fold.