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Migration from zigzag_gap_line.dart to flutter_ecg_monitor package

What Was Moved

The heartbeat monitor display logic was extracted from lib/screens/zigzag_gap_line.dart into a standalone Flutter package at packages/flutter_ecg_monitor/.

Code Removed from zigzag_gap_line.dart

Total lines deleted: ~450

  1. _StaticBackgroundPainter class (lines 38-114)

    • Static ECG-paper grid background
    • Now: EcgGridPainter in package

  2. Heartbeat-specific static members in _GapLinePainter:

    • _heartbeatLUT + _precomputeHeartbeat() — PQRST waveform lookup table
    • _trailBuffer — ring buffer for trail storage
    • _distanceToPaintLUT — pre-baked distance-to-paint-index mapping
    • _corePaints, _glowPaints — pre-built paint lists
    • _lastCursorX, _lastIntCursorX — cursor tracking state

  3. _drawHeartbeatMonitor() method (~260 lines)

    • Entire heartbeat rendering logic
    • Now: EcgTrailPainter.paint() in package

  4. Unused imports:

    • dart:typed_data (only used by deleted heartbeat code)

  5. Removed constructor parameters:

    • tipColor from _GapLinePainter (only used by heartbeat)

Code Added to Package

New package structure:

packages/flutter_ecg_monitor/
├── lib/
│   ├── flutter_ecg_monitor.dart          — barrel export
│   └── src/
│       ├── ecg_monitor_config.dart       — all tunable params
│       ├── ecg_monitor.dart              — EcgMonitor widget
│       ├── ecg_grid_painter.dart         — static grid (was _StaticBackgroundPainter)
│       └── ecg_trail_painter.dart        — trail + cursor (was _drawHeartbeatMonitor)
├── example/lib/main.dart                 — demo app
├── pubspec.yaml
├── README.md
└── ARCHITECTURE.md                       — optimization techniques documentation

How zigzag_gap_line.dart Now Uses the Package

Before (inline implementation)

// build() method created _GapLinePainter which called _drawHeartbeatMonitor()
return Stack([
  RepaintBoundary(child: CustomPaint(painter: _StaticBackgroundPainter(...))),
  CustomPaint(painter: _GapLinePainter(...)), // calls _drawHeartbeatMonitor
]);

After (package delegation)

@override
Widget build(BuildContext context) {
  // Short-circuit for heartbeat style
  if (widget.style == GapVisualizationStyle.heartbeatMonitor) {
    return EcgMonitor(
      height: widget.height,
      config: EcgMonitorConfig(
        heartRateBPM: 27.0,
        beatDurationSeconds: 0.8,
        cursorSpeedPixelsPerSecond: 40.0,
        color: widget.color ?? CalendarGridTheme.subtleGrid(context),
      ),
    );
  }
  
  // Other styles still use _GapLinePainter
  return SizedBox(
    child: AnimatedBuilder(
      builder: (context, child) => CustomPaint(painter: _GapLinePainter(...)),
    ),
  );
}

The case GapVisualizationStyle.heartbeatMonitor: in _GapLinePainter.paint() is now unreachable (the build method returns early), but left as a comment for clarity.

Benefits of Extraction

  1. Reusability — EcgMonitor can be used in any Flutter app, not just where_when
  2. Separation of concerns — Gap visualization styles vs ECG rendering are now independent
  3. Cleaner codebase — Removed ~450 lines from zigzag_gap_line.dart
  4. Better documentation — Package has dedicated README + ARCHITECTURE.md
  5. Independent versioning — Package can be published to pub.dev separately
  6. Testability — Package can have its own unit/widget tests

Files Modified in where_when

  • lib/screens/zigzag_gap_line.dart — removed heartbeat code, added package import + short-circuit
  • pubspec.yaml — added flutter_ecg_monitor: path: packages/flutter_ecg_monitor

Verification

Run flutter pub get to resolve the package dependency. The heartbeat monitor style should work identically to before the migration.