Performance Profiling

Performance profiling

Do not ask the user to open DevTools. Run the matching script, then read the JSON or the diff. Phase names and console commands: PERFORMANCE_PROFILING.md.

Which command

These are not interchangeable. Match the command to the change. The ZIP pair is not a substitute for profile:app, and profile:load is not a substitute for either (Vite serve pretty-prints metadata; window.profiler starts after catalog import). Layout shift during load is cls, not a row on this table.

Before any of them: npx playwright install once. ZIP scripts need dist/*-metadata.js (npm run dev or npm run build once) and use npx serve. profile:app starts Vite serve on 127.0.0.1:5178 (override APP_PROFILE_PORT) unless you pass --url http://127.0.0.1:5173. profile:load runs vite build then vite preview on 127.0.0.1:4178 unless you pass --url.

A full ZIP run can take several minutes (up to 10). App profile with both recolor modes is usually 2–4 minutes. profile:load is a production build plus five homepage navigations. Request full permissions; Playwright needs a real browser. If PLAYWRIGHT_BROWSERS_PATH points at a Cursor sandbox cache, the script unsets it.

Workflow

If the change is not yet made, take a baseline first. Use the matching pair (:quick with :quick, profile:app with profile:app).

npm run profile:app:baseline
# …make the change…
npm run profile:app
npm run diff:app-profile -- tmp/baseline-app-profile.json tmp/app-profile.json

Catalog bootstrap / metadata payload:

npm run profile:load:baseline
# …make the change…
npm run profile:load
npm run diff:app-load-profile -- tmp/baseline-app-load-profile.json tmp/app-load-profile.json

A few milliseconds on indexReadyMs / liteReadyMs is noise; 50 ms+ median is worth a second look (first-paint gates). A 50 ms+ move on catalogReadyMs alone can be the credits/palette tail. diff:app-load-profile always exits 0.

diff:app-profile prints two sections when both files contain both modes: ======== webgl ======== and ======== cpu ========. Compare like-with-like. One mode only: --recolor webgl or --recolor cpu.

npm run profile:zip:baseline:quick
npm run profile:zip:quick
npm run diff:zip-profile -- tmp/baseline-zip-export-profile-quick.json tmp/zip-export-profile-quick.json

If the change is already made and tmp/baseline-*.json exists from this machine, diff against it. If there is no baseline, report the absolute numbers and flag outliers. Do not invent a baseline after the fact.

JSON lands under tmp/ (gitignored) and is also printed on stdout.

Interpreting

A positive Δ means the after run was slower. Compare on the same machine. A few milliseconds is noise. renderCharacter can swing tens of ms between two runs; repeat once if a single Δ is the only evidence.

Confirm activeMode and recolorStats in each section: CPU must show activeMode: cpu and cpu > 0 if the outfit recolours. WebGL should show webgl > 0 (or cpu if this Chromium has no GL). Confirm renderer (unmaskedRenderer): SwiftShader / llvmpipe is software GL, not the user's GPU. Hardware looks like ANGLE (Apple, … Metal …) or an NVIDIA/AMD name. --headed --channel chrome fails the run if the renderer is still software.

App profile (profiler.snapshot(), same buckets as profiler.report()):

• renderCharacter — compositing only (not dynamic-import wait)
• snapshot().renderCharacter.calls[] — per-step phasesMs / counters for each completed render (mithrilRedrawStart, buildDrawCalls, sizeCanvas, loadImages, recolor, draw, customLoad, customRecolor, customDraw, mithrilRedrawEnd)
• image-load:<path> — one span per network load
• hash-loadSelectionsFromHash — URL hash hydration
• Category totals: imageLoads, draws, previews, domUpdates
• Slow-operation threshold is 50ms (slowThresholdMs)
• diff:app-profile prints ── renderCharacter phases ── (call 0 vs call 0, call 1 vs call 1)

Catalog load profile (profile:load, production vite preview):

• indexReadyMs — navigation time origin to __LPC_waitCatalogIndexReady()
• liteReadyMs — navigation time origin to __LPC_waitCatalogLiteReady() (hash / initCanvas wait on index+lite)
• catalogReadyMs — navigation time origin to __LPC_waitCatalogAllReady() (credits, palette, layers too)
• catalog-load / catalog-chunk:* — User Timing around each metadata import
• metadata *-metadata* resources — transferSize, decodedBodySize, duration
• A few milliseconds is noise; 50 ms+ on indexReadyMs or liteReadyMs median is worth a second look

ZIP profile (phasesMs / metadata):

• render_imageLoadDecode_* / render_composite_*
• drawAndSlice, pngEncode, zipFile, staticFiles
• generateZip — only meaningful on the real-JSZip run

The default character is the full outfit in zip-profile-default-hash.ts, not whatever was last open in a browser. profile:app then deselects the layered gear (body + head + expression only).

Limit one ZIP export: npm run profile:zip -- --only splitAnimations (also splitItemSheets, splitItemAnimations, individualFrames). Custom app hashes: npm run profile:app -- --hash '…' --hash2 '…'. Real GPU: npm run profile:app -- --headed --channel chrome (and the same flags on profile:app:baseline). Compare GPU baselines only to GPU runs.

Still ask the user

WebGL vs CPU visual correctness is not this skill: canvas-render. Timing both recolor paths is.