name: canvas-drawing-patterns description: Canvas/ink-editor architecture checklist (manager lifecycle, API design, geometry perf) adapted for iinkTS from tldraw/excalidraw conventions. Invoke when adding or reviewing managers, renderer code, or hit-testing/geometry logic. metadata: version: "1.0.0"

Canvas/Drawing-App Patterns

Manager lifecycle

A manager that adds an event listener or holds a resource (timer, subscription) MUST implement destroy() and get called on editor teardown.

Verify before adding a new listener: grep -rl "addEventListener\|addListener" src/manager then confirm each hit overrides destroy() from IIAbstractManager. Managers currently holding listeners: IIOverlayManager, IDebugSVGManager, IIKeyboardManager, IISelectionManager — check their cleanup coverage before extending them.

API design

Avoid boolean or ambiguous positional params on new public methods — use a named options object. A bare true/false at a call site forces the reader to check the signature to know what it means.

// bad
resize(el, true, false)
// good
resize(el, { preserveAspectRatio: true, animate: false })

Geometry / perf

• Use computeDistanceSquared (no sqrt), not computeDistance, when only comparing against a threshold — already in src/utils/geometry.ts.
• Cache bounding boxes when queried repeatedly per frame/gesture instead of recomputing from raw points each time.

Per-symbol-type encapsulation

Keep type-specific logic in the matching *Ops object (StrokeOps, TextOps, MathOps, ShapeOps, EdgeOps, DecoratorOps — co-located with the type in src/symbol/{type}/), and rendering/registry glue in the matching *Util adapter (src/symbol-utils/{type}/), dispatched via symbolRegistry.getUtil(symbol.type). Don't branch on SymbolType inline in managers or renderers. src/symbol/SymbolHelpers.ts is unrelated (just cloneSymbol()), not a dispatcher.

Testing

Prefer asserting whole objects (toEqual(fullObject)) over field-by-field checks when it gives a clearer failure diff.