Custom drawing implementation

lib/features/sheet_viewer/drawing/drawing_line.dart

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+import 'dart:ui';
+
+/// Represents a single stroke/line drawn on the canvas.
+///
+/// Points are stored in normalized coordinates (0.0 to 1.0) where:
+/// - (0, 0) is the top-left corner of the drawing area
+/// - (1, 1) is the bottom-right corner of the drawing area
+///
+/// This allows drawings to scale correctly when the canvas size changes.
+class DrawingLine {
+  /// Points in normalized coordinates (0.0 to 1.0)
+  final List<Offset> points;
+
+  /// Color of the line (stored as ARGB integer for JSON serialization)
+  final Color color;
+
+  /// Stroke width in normalized units (relative to canvas width)
+  /// A value of 0.01 means the stroke is 1% of the canvas width
+  final double strokeWidth;
+
+  const DrawingLine({
+    required this.points,
+    required this.color,
+    required this.strokeWidth,
+  });
+
+  /// Creates a DrawingLine from JSON data.
+  factory DrawingLine.fromJson(Map<String, dynamic> json) {
+    final pointsList = (json['points'] as List)
+        .map((p) => Offset(
+              (p['x'] as num).toDouble(),
+              (p['y'] as num).toDouble(),
+            ))
+        .toList();
+
+    return DrawingLine(
+      points: pointsList,
+      color: Color(json['color'] as int),
+      strokeWidth: (json['strokeWidth'] as num).toDouble(),
+    );
+  }
+
+  /// Converts this line to a JSON-serializable map.
+  Map<String, dynamic> toJson() {
+    return {
+      'points': points.map((p) => {'x': p.dx, 'y': p.dy}).toList(),
+      'color': color.toARGB32(),
+      'strokeWidth': strokeWidth,
+    };
+  }
+
+  /// Creates a copy of this line with an additional point.
+  DrawingLine addPoint(Offset normalizedPoint) {
+    return DrawingLine(
+      points: [...points, normalizedPoint],
+      color: color,
+      strokeWidth: strokeWidth,
+    );
+  }
+
+  /// Creates a copy with updated points.
+  DrawingLine copyWith({
+    List<Offset>? points,
+    Color? color,
+    double? strokeWidth,
+  }) {
+    return DrawingLine(
+      points: points ?? this.points,
+      color: color ?? this.color,
+      strokeWidth: strokeWidth ?? this.strokeWidth,
+    );
+  }
+
+  @override
+  bool operator ==(Object other) {
+    if (identical(this, other)) return true;
+    if (other is! DrawingLine) return false;
+    if (points.length != other.points.length) return false;
+    if (color != other.color) return false;
+    if (strokeWidth != other.strokeWidth) return false;
+    for (int i = 0; i < points.length; i++) {
+      if (points[i] != other.points[i]) return false;
+    }
+    return true;
+  }
+
+  @override
+  int get hashCode => Object.hash(
+        Object.hashAll(points),
+        color,
+        strokeWidth,
+      );
+}