map_utils_core 0.0.2

Platform-agnostic geometry algorithms, shape models, drawing state, snapping, undo/redo, and GeoJSON utilities. No map-SDK dependency — works with any map engine.

map_utils_core

Platform-agnostic geometry algorithms, shape models, drawing state, snapping, undo/redo, GeoJSON utilities, and shared UI widgets. Zero map-SDK dependency — works with any map engine.

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What is this?

map_utils_core is the shared foundation of the map-utils ecosystem. It provides all geometry, state management, snapping, and serialization logic with zero dependency on any map SDK.

                  map_utils_core
                   ╱           ╲
        flutter_map_utils    google_map_utils
        (flutter_map)        (google_maps_flutter)

Most users should depend on flutter_map_utils or google_map_utils instead — they re-export everything from this package automatically.

Use map_utils_core directly if:

• You need geometry algorithms without any Flutter/map dependency
• You're building a custom map engine integration
• You want pure-Dart shape manipulation for a server or CLI

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Modules

Module	Contents
Drawing State	DrawingState, DrawingMode, UndoRedoManager
Shape Models	DrawablePolygon, DrawablePolyline, DrawableCircle, DrawableRectangle (sealed)
Shape Styles	ShapeStyle, StrokeType, resolved/default/selected style cascading, presets
Geometry	Area, perimeter, distance, centroid, midpoint, simplification, smoothing, point-in-polygon, self-intersection, bounding-box
GeoJSON	Import/export via GeoJsonUtils (Feature, FeatureCollection, string, Map)
Snapping	SnappingEngine with vertex, midpoint, edge, intersection, grid, perpendicular
Selection	SelectionUtils.findClosestShape() with configurable tolerance
UI Widgets	DrawingToolbar, ShapeInfoPanel — shared across map providers

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Installation

dependencies:
  map_utils_core: ^0.2.0

Tip: If you use flutter_map_utils or google_map_utils, this package is already included.

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Drawing State

DrawingState is the central ChangeNotifier that drives all drawing, editing, selection, and undo.

Lifecycle

import 'package:map_utils_core/map_utils_core.dart';

final state = DrawingState();

// 1. Set mode
state.setMode(DrawingMode.polygon);

// 2. Add points (from map taps)
state.addDrawingPoint(LatLng(51.5, -0.1));
state.addDrawingPoint(LatLng(51.6, -0.1));
state.addDrawingPoint(LatLng(51.6, 0.0));

// 3. Finish → produces a DrawablePolygon
final shape = state.finishDrawing();

// 4. Select & edit
state.setMode(DrawingMode.select);
state.selectShape(shape!.id);
state.updateVertexPosition(shape.id, 0, LatLng(51.51, -0.09));

// 5. Undo / redo
state.undo();
state.redo();

Key properties

Property	Type	Description
shapes	List<DrawableShape>	All committed shapes
activeMode	DrawingMode	Current mode (polygon, polyline, select, etc.)
currentPoints	List<LatLng>	Points being drawn (in-progress)
selectedShape	DrawableShape?	Currently selected shape
selectedShapeId	String?	ID of the selected shape
isDrawing	bool	Whether actively drawing
canUndo / canRedo	bool	Whether undo/redo is available
shouldAbsorbMapGestures	bool	Whether the map should disable pan/zoom (true during drawing)

Shape operations

// Delete
state.removeShape(shapeId);

// Duplicate
state.duplicateSelected();

// Clear all
state.clearAll();

// Deselect
state.deselectAll();

// Update a vertex
state.updateVertexPosition(shapeId, vertexIndex, newLatLng);

Circles

state.setMode(DrawingMode.circle);
state.setCircleCenter(LatLng(51.5, -0.1));
state.setCircleRadius(500.0); // meters
state.finishCircleDrawing();

Holes

state.selectShape(polygonId);
state.setMode(DrawingMode.hole);
state.selectShape(polygonId); // re-select after mode change
state.addDrawingPoint(...); // hole vertices
state.finishHoleDrawing();

---

Shape Styles

Custom style

final style = ShapeStyle(
  fillColor: Color(0x554285F4),
  borderColor: Color(0xFF4285F4),
  borderWidth: 2.0,
  fillOpacity: 0.3,
  strokeType: StrokeType.dashed,
  selectedOverride: ShapeStyle(
    borderColor: Color(0xFFFF0000),
    borderWidth: 4.0,
  ),
  hoverOverride: ShapeStyle(
    borderColor: Color(0xFFFFAA00),
  ),
);

Style resolution

resolve() cascades overrides based on shape state:

final resolved = style.resolve(isSelected: true, isHovered: false);
// resolved.borderColor == Color(0xFFFF0000)  (from selectedOverride)
// resolved.fillColor == Color(0x554285F4)    (from base)

Presets

ShapeStylePresets.zone;               // blue translucent fill
ShapeStylePresets.warning;            // red translucent fill
ShapeStylePresets.route;              // line-only, no fill
ShapeStylePresets.selected;           // selection highlight
ShapeStylePresets.hover;              // hover highlight
ShapeStylePresets.defaultWithStates;  // sensible defaults with selected/hover

JSON serialization

final json = style.toJson();
final restored = ShapeStyle.fromJson(json);

---

Geometry Utilities

All methods are static on GeometryUtils:

Point-in-polygon

final inside = GeometryUtils.pointInPolygon(
  LatLng(51.5, -0.1),
  polygonPoints,
);

Area & perimeter

final areaM2 = GeometryUtils.polygonArea(points);        // square meters
final areaFt2 = GeometryUtils.areaInSquareFeet(areaM2);  // square feet
final acres = GeometryUtils.areaInAcres(areaM2);         // acres
final lengthM = GeometryUtils.polylineLength(points);     // meters

Shape-level (works with any DrawableShape)

final area = GeometryUtils.shapeArea(someShape);          // square meters
final perimeter = GeometryUtils.shapePerimeter(someShape); // meters

Centroid & midpoint

final center = GeometryUtils.centroid(points);
final mid = GeometryUtils.midpoint(pointA, pointB);

Distance

final meters = GeometryUtils.distanceBetween(pointA, pointB);

Nearest point on segment

final (:point, :t) = GeometryUtils.nearestPointOnSegment(
  cursor, segmentStart, segmentEnd,
);
// point = closest LatLng on the segment
// t = 0..1 parameter along the segment

Self-intersection detection

final selfIntersects = GeometryUtils.isSelfIntersecting(points);

Winding order

final cw = GeometryUtils.isClockwise(points);
final ordered = GeometryUtils.ensureClockwise(points);

Path simplification & smoothing

// Douglas-Peucker simplification
final simplified = GeometryUtils.simplifyPath(points, tolerance: 0.0001);

// Catmull-Rom smoothing
final smooth = GeometryUtils.smoothPath(points, segments: 8);

---

GeoJSON

Export

// All shapes → GeoJSON string
final geojsonStr = GeoJsonUtils.toGeoJsonString(state.shapes);

// All shapes → Map (FeatureCollection)
final featureCollection = GeoJsonUtils.toFeatureCollection(state.shapes);

// Single shape → Feature map
final feature = GeoJsonUtils.toGeoJson(oneShape);

Import

// From string
final shapes = GeoJsonUtils.fromGeoJsonString(geojsonStr);

// From Map
final shapes = GeoJsonUtils.fromGeoJson(featureCollectionMap);

Round-trip fidelity

final exported = GeoJsonUtils.toGeoJsonString(state.shapes);
final reimported = GeoJsonUtils.fromGeoJsonString(exported);
// reimported is identical to the original shapes

---

Snapping

Configuration

final snapEngine = SnappingEngine(
  config: SnapConfig(
    enabled: true,
    toleranceMeters: 15.0,
    priorities: [
      SnapType.vertex,       // snap to existing vertices first
      SnapType.midpoint,     // then to edge midpoints
      SnapType.edge,         // then to nearest point on edge
      SnapType.intersection, // then to edge intersections
      SnapType.grid,         // then to grid
    ],
    gridSpacing: 0.0001,     // ~11m grid at equator
  ),
);

Snap a point

final result = snapEngine.snap(
  candidatePoint: cursorLatLng,
  shapes: state.shapes,
  excludeShapeId: state.selectedShapeId, // don't snap to itself
);

if (result != null) {
  print(result.type);          // e.g. SnapType.vertex
  print(result.point);         // snapped coordinate
  print(result.distance);      // meters from cursor to snap point
  print(result.sourceShapeId); // which shape it snapped to
}

Snap types

Type	Behavior
vertex	Snaps to existing shape vertices
midpoint	Snaps to the midpoint of each shape edge
edge	Snaps to the nearest point on any edge
intersection	Snaps to where two edges cross
grid	Snaps to a regular lat/lng grid
perpendicular	Snaps to perpendicular projection on nearby edges

---

Selection

Find closest shape

final shapeId = SelectionUtils.findClosestShape(
  LatLng(51.5, -0.1),
  state.shapes,
  toleranceMeters: 20.0,
);

if (shapeId != null) {
  state.selectShape(shapeId);
}

Distance to shape

final dist = SelectionUtils.distanceToShape(
  LatLng(51.5, -0.1),
  someShape,
);
// Returns 0.0 for point inside a polygon
// Returns distance to nearest edge/boundary otherwise

---

Undo / Redo

final state = DrawingState(maxHistoryDepth: 100);

// Every shape add/remove/update is tracked automatically.
state.undo();
state.redo();

print(state.canUndo); // true
print(state.canRedo); // false

---

Serialization

Shape JSON

// Save entire shape list to JSON (preserves styles, holes, all properties)
final json = state.shapesToJson();

// Restore
state.loadShapesFromJson(json);

Style JSON

final json = myStyle.toJson();
final restored = ShapeStyle.fromJson(json);

---

UI Widgets

DrawingToolbar

A mode-selector + action buttons widget. Map-engine agnostic — works with any map.

DrawingToolbar(
  drawingState: state,
  showUndoRedo: true,
  showDelete: true,
  // Customize button appearance:
  buttonBuilder: (context, mode, isActive, onTap) {
    return ElevatedButton(
      onPressed: onTap,
      style: ElevatedButton.styleFrom(
        backgroundColor: isActive ? Colors.blue : Colors.grey,
      ),
      child: Text(mode.name),
    );
  },
)

ShapeInfoPanel

Displays selected shape info: type, area, perimeter, vertex count.

ShapeInfoPanel(drawingState: state)

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API Reference

Class	Purpose
DrawingState	Central ChangeNotifier: shapes, selection, mode, drawing state, undo/redo
DrawingMode	Enum: none, polygon, polyline, rectangle, circle, freehand, select, measure, hole
DrawableShape	Sealed base — DrawablePolygon, DrawablePolyline, DrawableCircle, DrawableRectangle
ShapeStyle	Fill, stroke, opacity, selected/hover overrides, JSON serializable
ShapeStylePresets	Ready-to-use styles: zone, warning, route, selected, hover, defaultWithStates
StrokeType	Enum: solid, dashed, dotted
UndoRedoManager	Command-pattern history (AddShapeCommand, RemoveShapeCommand, UpdateShapeCommand)
GeometryUtils	20+ static methods for geometry calculations
GeoJsonUtils	GeoJSON import/export (string, Map, FeatureCollection)
SnappingEngine	Priority-based snapping with configurable tolerance and snap types
SnapConfig	Configuration: enabled, tolerance, priorities, grid spacing
SnapResult	Snap result: type, point, distance, source shape ID
SnapType	Enum: vertex, midpoint, edge, intersection, grid, perpendicular
SelectionUtils	Hit-testing: findClosestShape(), distanceToShape(), nearestEdgeDistance()
DrawingToolbar	Mode selector with undo/redo/delete — customizable via buttonBuilder
ShapeInfoPanel	Displays selected shape info

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Compatibility

Dependency	Version
Dart	>= 3.6.0
Flutter	>= 3.27.0 (for UI widgets only)
latlong2	^0.9.1

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About

Built and maintained by UBXTY Unboxing Technology.

Part of the flutter_map_utils monorepo.

License

MIT — see LICENSE for details.