v1.3.0 — Ribbon mesh with arrowed β-sheets

What changed

The Ribbon render mode now produces a proper extruded mesh with shape-distinguished secondary structure, instead of width-modulated cylinders:

• α-helices — wide flat ribbon (red-tinted)
• β-sheets — wide flat ribbon (yellow-tinted) with a C-terminal arrowhead: the last residue of every sheet run tapers from a wider arrow base to a point, producing the canonical flanged arrow shape
• Loops / coil — thin near-square tube in chain color

Implementation: one extruded mesh per chain. The rectangular cross-section is swept along a Catmull-Rom spline through the Cα atoms using a parallel-transport frame (avoids ribbon-plane flips at curve inflections). Per-vertex color via an SCNGeometrySource(.color) keeps it to one SCNGeometry per chain. Chains are split at Cα–Cα gaps > 12 Å so the spline doesn't jump across the molecule.

Install

1. Download Structure-v1.3.0.zip, unzip.
2. Double-click Structure.saver. System Settings will offer to install it.
3. First launch may warn "unidentified developer" (ad-hoc signed) — right-click → Open to bypass once.

System Settings → Screen Saver → select Structure.

Notes

• Modes (cycle with the 3 key during preview): Ribbon (default), Backbone trace, Ball and stick, Spacefill (CPK).
• The ribbon plane orientation comes from a parallel-transported frame, not from peptide-plane / C=O direction. Helix and sheet rotation may differ from PyMOL but is stable and non-flipping across the molecule.