map_viewport_bloc 0.4.9

Declarative camera state machine (follow / free look / route overview) for navigation maps with six-layer composition.

map_viewport_bloc

Camera follow, free look, route overview — without reinventing viewport logic. Declarative state machine for navigation map cameras and layer composition.

Use map_viewport_bloc when you need stable camera rules (follow, free look, overview) and a six-layer composition contract, but want freedom to choose your own map renderer.

Features

• MapBloc with three camera modes: follow, freeLook, overview.
• Six-layer composition contract: base tile, route, fleet, hazard, weather, safety.
• Pure Dart _core exports for CameraMode, MapLayerType, and MapLayerZ.
• Free-look auto-return timer with a default 10 second idle threshold.
• Safety-compatible follow override path for alert-driven recentering.

Install

dependencies:
  map_viewport_bloc: ^0.4.3

Quick Start

import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:latlong2/latlong.dart';
import 'package:map_viewport_bloc/map_viewport_bloc.dart';

class MapViewportExample extends StatelessWidget {
  const MapViewportExample({super.key});

  @override
  Widget build(BuildContext context) {
    return BlocProvider(
      create: (_) => MapBloc()
        ..add(const MapInitialized(
          center: LatLng(35.1709, 136.8815),
          zoom: 15,
        )),
      child: BlocBuilder<MapBloc, MapState>(
        builder: (context, state) {
          return Text(
            'Camera: ${state.cameraMode.name} | '
            'Layers: ${state.visibleLayers.map((layer) => layer.name).join(', ')}',
          );
        },
      ),
    );
  }
}

Camera Modes

Mode	Purpose	Trigger	Auto-return
follow	Keeps the driver centered during active guidance	Startup, return button, safety override	—
freeLook	Gives the user direct viewport control	User pan or pinch gesture	After 10 seconds idle by default
overview	Fits the route into frame	Route preview or fit-to-bounds request	Ends on user pan or explicit follow

Z-Layer Contract

Z	Layer	Type	Visibility rule
0	Base tile	Raster	Always on
1	Route	Vector	Toggleable
2	Fleet	Icons	Toggleable
3	Hazard	Filled polygon / clusters	Toggleable
4	Weather	Semi-transparent overlay	Toggleable
5	Safety	Full-screen alert plane	Not user-toggleable

User toggles are intentionally restricted to Z1 through Z4. Z0 is foundational and Z5 is safety-critical.

Design Principles

• Camera modes are explicit enum values, not boolean flags — testable by default.
• The Z-layer contract is fixed so safety (Z5) is never displaced by application code.
• The state machine owns no renderer code — swap flutter_map, Mapbox, or anything else without touching the bloc.
• Free-look and overview transitions are fully reversible and deterministic.

Pure Dart Core

Use the _core barrel when you only need model access.

import 'package:map_viewport_bloc/map_viewport_bloc_core.dart';

final weatherZ = MapLayerType.weather.zIndex;
final safetyToggleable = MapLayerType.safety.isUserToggleable;

API Overview

Type	Purpose
MapBloc	Viewport state machine for camera mode, bounds fitting, and layer visibility.
MapState	Current center, zoom, camera mode, visible layers, and fit-bounds state.
MapEvent	Inputs for initialization, camera changes, pans, bounds fitting, and layer toggles.
CameraMode	Canonical follow, freeLook, and overview camera states.
MapLayerType	Six-layer contract for route, fleet, hazard, weather, and safety rendering.
MapLayerZ	Stable Z-order constants for renderer integrations.

Example

The included example app shows camera mode buttons, user-toggleable layers, and live state updates without requiring a specific renderer.

flutter run -d linux -t example/lib/main.dart

Works With

Package	How
flutter_map	Drive flutter_map's camera from MapBloc state
navigation_safety	Safety overlay occupies Z5 — always on top, never user-toggleable
offline_tiles	Base tile layer (Z0) resolves through offline tile manager

See Also

• routing_bloc — Route lifecycle state machine
• kalman_dr — Dead reckoning through GPS loss
• offline_tiles — Offline tile management with MBTiles

Part of SNGNav — 11 packages for offline-first navigation on Flutter.

License

BSD-3-Clause — see LICENSE.