OpenNoodl/dev-docs/tasks/phase-4-canvas-visualisation-views/PREREQ-003-canvas-overlay-pattern/CHANGELOG.md

PREREQ-003: Document Canvas Overlay Pattern - CHANGELOG

Status: ✅ COMPLETED

Started: January 3, 2026
Completed: January 3, 2026
Time Spent: ~8 hours

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Overview

Successfully documented the Canvas Overlay Pattern by studying CommentLayer implementation and extracting reusable patterns for future Phase 4 visualization overlays (Data Lineage, Impact Radar, Semantic Layers).

The pattern is now comprehensively documented across five modular documentation files with practical examples, code snippets, and best practices.

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Deliverables Completed

📚 Documentation Created

Five comprehensive documentation files in dev-docs/reference/:

1. CANVAS-OVERLAY-PATTERN.md (Overview)

   • Main entry point with quick start example
   • Key concepts and architecture overview
   • Links to all specialized docs
   • Common gotchas and best practices

2. CANVAS-OVERLAY-ARCHITECTURE.md (Integration)

   • How overlays integrate with NodeGraphEditor
   • DOM structure and z-index layering
   • Two-layer system (background + foreground)
   • EventDispatcher subscription patterns
   • Complete lifecycle (creation → disposal)
   • Full example overlay implementation

3. CANVAS-OVERLAY-COORDINATES.md (Coordinate Systems)

   • Canvas space vs Screen space transformations
   • Transform math (canvasToScreen/screenToCanvas)
   • React component positioning via parent container transform
   • Scale-dependent vs scale-independent sizing
   • Common patterns (badges, highlights, hit testing)

4. CANVAS-OVERLAY-EVENTS.md (Mouse Event Handling)

   • Event handling when overlay sits in front of canvas
   • Three-step mouse event forwarding solution
   • Event flow diagrams
   • Preventing infinite loops
   • Pointer events CSS strategies
   • Special cases (wheel, drag, multi-select)

5. CANVAS-OVERLAY-REACT.md (React 19 Patterns)

   • React root management with createRoot API
   • Root reuse pattern (create once, render many)
   • State management approaches
   • Scale prop special handling for react-rnd
   • Async rendering workarounds
   • Performance optimizations
   • Common React-specific gotchas

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Key Technical Discoveries

🎯 CSS Transform Strategy

The most elegant solution for coordinate transformation:

• Parent container uses transform: scale() translate()
• React children automatically positioned in canvas coordinates
• No manual recalculation needed for each element

.overlay-container {
  transform: scale(${scale}) translate(${pan.x}px, ${pan.y}px);
}

🔄 React 19 Root Reuse Pattern

Critical pattern for performance:

// ✅ CORRECT - Create once, reuse
this.root = createRoot(container);
this.root.render(<Component />); // Update many times

// ❌ WRONG - Creates new root each render
createRoot(container).render(<Component />);

🎭 Two-Layer System

CommentLayer uses two overlay layers:

• Background Layer - Behind canvas for comment boxes with shadows
• Foreground Layer - In front of canvas for interactive controls

This allows sophisticated layering without z-index conflicts.

🖱️ Smart Mouse Event Forwarding

Three-step solution for click-through:

1. Capture all mouse events on overlay
2. Check if event target is interactive UI (has pointer-events: auto)
3. If not, forward event to canvas

Prevents infinite loops while maintaining both overlay and canvas interactivity.

📐 EventDispatcher Context Pattern

Must use context object for proper cleanup:

const context = {};
editor.on('viewportChanged', handler, context);
return () => editor.off(context);  // Cleanup all listeners

React hook wrappers handle this automatically.

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Files Analyzed

Primary Source

• packages/noodl-editor/src/editor/src/views/nodegrapheditor/commentlayer.ts (~500 lines)
  • Production-ready overlay implementation
  • All patterns extracted from this working example

Related Files

• packages/noodl-editor/src/editor/src/views/CommentLayer/CommentLayerView.tsx
• packages/noodl-editor/src/editor/src/views/CommentLayer/CommentForeground.tsx
• packages/noodl-editor/src/editor/src/views/CommentLayer/CommentBackground.tsx

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Design Decisions

Modular Documentation Structure

Decision: Split documentation into 5 focused files instead of one large file.

Rationale:

• Initial attempt at single file exceeded API size limits
• Modular structure easier to navigate
• Each file covers one concern (SRP)
• Cross-referenced with links for discoverability

Files:

• Pattern overview (entry point)
• Architecture (integration)
• Coordinates (math)
• Events (interaction)
• React (rendering)

Documentation Approach

Decision: Document existing patterns rather than create new infrastructure.

Rationale:

• CommentLayer already provides production-ready examples
• Phase 4 can use CommentLayer as reference implementation
• Premature abstraction avoided
• Future overlays will reveal common needs organically

Next Steps:

• VIEW-005, 006, 007 implementations will identify reusable utilities
• Extract shared code when patterns become clear (not before)

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Impact on Phase 4

Unblocks

This prerequisite fully unblocks:

• ✅ VIEW-005: Data Lineage - Can implement path highlighting overlay
• ✅ VIEW-006: Impact Radar - Can implement dependency highlighting
• ✅ VIEW-007: Semantic Layers - Can implement visibility filtering UI

Provides Foundation

Each visualization view can now:

1. Reference CANVAS-OVERLAY-PATTERN.md for quick start
2. Copy CommentLayer patterns for specific needs
3. Follow React 19 best practices from documentation
4. Avoid common gotchas documented in each guide

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Testing Approach

Validation Method: Documentation verified against working CommentLayer implementation.

All patterns documented are:

• Currently in production
• Battle-tested in real usage
• Verified to work with React 19
• Compatible with existing NodeGraphEditor

No new code created = no new bugs introduced.

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Lessons Learned

What Worked Well

1. Studying Production Code

   • CommentLayer provided real-world patterns
   • No guessing about what actually works
   • Edge cases already handled

2. Modular Documentation

   • Splitting into 5 files prevented API size issues
   • Easier to find specific information
   • Better for future maintenance

3. Code Examples

   • Every concept backed by working code
   • Practical not theoretical
   • Copy-paste friendly snippets

Challenges Overcome

1. API Size Limits

   • Initial comprehensive doc too large
   • Solution: Modular structure with cross-references

2. Complex Coordinate Math

   • Transform math can be confusing
   • Solution: Visual diagrams and step-by-step examples

3. React 19 Specifics

   • New API patterns not well documented elsewhere
   • Solution: Dedicated React patterns guide

For Future Tasks

• Start with modular structure for large documentation
• Include visual diagrams for spatial concepts
• Balance theory with practical examples
• Cross-reference between related docs

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Success Metrics

✅ Completeness

• All CommentLayer patterns documented
• All coordinate transformation cases covered
• All event handling scenarios explained
• All React 19 patterns captured

✅ Clarity

• Each doc has clear scope and purpose
• Code examples for every pattern
• Common gotchas highlighted
• Cross-references for navigation

✅ Usability

• Quick start example provided
• Copy-paste friendly code snippets
• Practical not academic tone
• Real-world examples from CommentLayer

✅ Future-Proof

• Foundation for VIEW-005, 006, 007
• Patterns generalizable to other overlays
• Follows React 19 best practices
• Compatible with existing architecture

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Next Steps

Immediate

• Create CHANGELOG.md (this file)
• Update LEARNINGS.md with key discoveries
• Task marked as complete

Future (Phase 4 Views)

• Implement VIEW-005 (Data Lineage) using these patterns
• Implement VIEW-006 (Impact Radar) using these patterns
• Implement VIEW-007 (Semantic Layers) using these patterns
• Extract shared utilities if patterns emerge across views

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References

Documentation Created

• dev-docs/reference/CANVAS-OVERLAY-PATTERN.md
• dev-docs/reference/CANVAS-OVERLAY-ARCHITECTURE.md
• dev-docs/reference/CANVAS-OVERLAY-COORDINATES.md
• dev-docs/reference/CANVAS-OVERLAY-EVENTS.md
• dev-docs/reference/CANVAS-OVERLAY-REACT.md

Source Files Analyzed

• packages/noodl-editor/src/editor/src/views/nodegrapheditor/commentlayer.ts
• packages/noodl-editor/src/editor/src/views/CommentLayer/ (React components)

Related Tasks

• PREREQ-001: Webpack Caching (prerequisite, completed)
• PREREQ-002: React 19 Debug Fixes (parallel, completed)
• VIEW-005: Data Lineage (unblocked by this task)
• VIEW-006: Impact Radar (unblocked by this task)
• VIEW-007: Semantic Layers (unblocked by this task)

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Task completed: January 3, 2026