feat: add Ribbon descriptor (1D touch-strip gestures)

[edumeneses]

Summary

Adds puara_gestures::Ribbon for a 1D touch strip (ribbon / SoftPot / linear position sensor). It turns a position + touched pair into playable gestures: absolute position, slide velocity/direction (glissando), touch-down/up events, and a quick tap (a brief touch that barely moves).

It handles the awkward parts: velocity is not computed across a lift-and-retouch (so moving your finger to a new spot does not produce a spurious jump), and it resets cleanly on release.

API

puara_gestures::Ribbon ribbon;

bool touched = ribbonTouched();
double pos = ribbonPosition(); // e.g. 0..1
ribbon.update(pos, touched);

double pitch = ribbon.position;
double slide = ribbon.velocity;
if (ribbon.tap) triggerNote();

Outputs: position, velocity, direction, touched, onset/release, tap. tapMaxTime/tapMaxTravel define what counts as a tap.

Design note

Timing uses the monotonic clock (update(pos, touched)) or an explicit step (update(pos, touched, dt)) for reproducible results. Identical in Arduino loop(), thread, or ossia process.

Conventions kept

• Header-only, #pragma once, puara_gestures namespace
• update(...) overloads, current_value() (position), reset()
• Doubles only, no STL/Boost/allocation → Arduino-friendly

Files

• include/puara/descriptors/ribbon.h
• registered in include/puara/gestures.h
• examples/arduino/descriptors/ribbon/ribbon.ino
• Catch2 tests in tests/test_descriptors.cpp ([descriptors][ribbon])
• README entry + quick example

Testing

• Ribbon: 17 assertions / 3 cases pass (position/velocity/direction, re-touch jump suppression, tap vs long/large touch)
• Full descriptor suite: 272 assertions / 10 cases pass (no regressions)

🤖 Generated with Claude Code

https://claude.ai/code/session_0163cH7Znu2oYvnaP7fTEQMN