2D Accordion Paper Fold Crease Pattern

This 2D companion to the 3D origami paper fold simulation draws the same accordion mechanism from directly above as an exact kinematic chain: each paper strip is a rigid link, each crease is a hinge, and every strip's direction is computed as the cumulative sum of all the hinge rotations before it, alternating sign so the chain closes into a flat bellows rather than spiraling away. Drag the strip-count slider to rebuild the chain with 4 to 16 segments, use the fold slider or the Fold/Unfold button to drive the crease angle from a flat sheet to a fully closed accordion, or switch on auto-folding to watch the bellows breathe in and out on its own, with mountain and valley creases marked in the standard origami-diagram convention.