Pen tool p95 hits 406ms at 50K points

[kostyafarber]

Problem

Pen tool point placement at 50K-point scale takes 82ms p50, 406ms p95 — far over the 16.6ms frame budget. The p95 spike to ~400ms likely comes from GC pressure and full snapshot rebuilds on every click.

Measured via Playwright E2E perf tests (perf.spec.ts) on the real Electron app.

Perf Report (50K points)

Operation	p50 (ms)	p95 (ms)	p99 (ms)
translate-drag (all pts)	2.40	7.90	12.70
pen-tool (100 clicks)	81.90	405.70	407.30

For comparison, draft translate at 50K all-points is 2.4ms p50 — ~34x faster.

Likely Causes

Each pen click at 50K points:

1. Adds a point to the active contour via the bridge (NAPI call)
2. Rebuilds the glyph snapshot from Rust
3. Fires glyph identity signal → triggers React re-renders for sidebar, handles, segments
4. Records an undo entry with the full command
5. The p95 spike to ~400ms suggests GC pressure from allocations (50K-point snapshot copies)

Investigation Areas

• Profile the pen click path to isolate which step dominates
• Consider batching snapshot rebuilds (dirty flag + next-frame sync instead of immediate)
• Check if the sidebar/glyph-info components are re-rendering on every point add
• The ~400ms p95 spike happening consistently suggests a specific expensive operation (full snapshot JSON serialization?) rather than random GC

Files

• src/renderer/src/lib/tools/pen/ — pen tool behaviors
• src/renderer/src/bridge/NativeBridge.ts — addPointToContour, snapshot sync
• src/renderer/src/lib/model/Glyph.ts — reactive model updates

Related

• Nudge is 14x slower than draft translate at 50K points #36 — Nudge is 14x slower than draft translate (similar sync-every-frame pattern)