Saber: handwriting notes and local-first files

Handwriting apps are RenderObject-deep problems: stroke input, highlighter blend, export, and file format choices all matter.

Lessons

1. Local files first; sync second. Notes must open offline.
2. Model strokes as data (points/pressure), not screenshots.
3. Dual-layer highlighter compositing is a classic graphics lesson in a product.

Pitfalls

• Stylus latency is perceptible at ~1 frame.
• File format lock-in will anger users more than missing cloud features.

Study Saber when building canvas-centric Flutter tools.