How to use

• Pen: Click to add points. Enter confirms as a closed polygon. Esc confirms as an open polyline.
• Rectangle / Regular polygon: Drag to create.
• Select: Click a shape to select. Drag vertices to edit. Drag inside to move.
• Run: Computes Straight Skeleton from the selected closed shape (auto-detects “outer boundary + holes” if needed), then draws demo mountain/valley creases and the one-cut line.

Note: This is a learning demo to explore the “fold-and-cut” idea. It does not fully reproduce the complete Demaine-style construction steps (e.g., final reflection stacking) with strict correctness. But it lets you see the straight-skeleton-based crease generation feel.