Add get_drape_folds — vertical fold rendering engine (Python port of robert-engine.ts)

[Copilot]

Ports the vertical fold simulation logic from robert-engine.ts into a new Python module api/robert_engine.py. The function computes per-fold position and opacity for fabric drape rendering, with sinusoidal animation driven by a timestamp.

Changes

api/robert_engine.py

• Adds get_drape_folds(fabric, garment_w, gravity_h, now_ms) — selects 3 or 5 folds based on drapeCoefficient threshold (< 0.5), applies per-fold sinusoidal X offset for motion simulation, and derives alpha from the drape coefficient
• Full docstring documenting required fabric['drapeCoefficient'] key and returned dict structure (x, width, height, alpha)

tests/test_robert_engine.py

• 13 unit tests covering fold count at and around the 0.5 boundary, dimension ratios (8% width / 70% height), opacity formula across the coefficient range, X position formula against manual calculation, and sinusoidal variation with now_ms

fabric = {"drapeCoefficient": 0.7}
folds = get_drape_folds(fabric, garment_w=100.0, gravity_h=200.0, now_ms=0.0)
# → 5 folds, each with x, width=8.0, height=140.0, alpha=0.12

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Project	Deployment	Actions	Updated (UTC)
tryonyou-pilot	Error		Apr 7, 2026 1:57pm