feat: implement efficient(-ish) change detection for PolygonLayer &…

… `PolylineLayer` (fleaflet#1904)

example/lib/pages/polygon_perf_stress.dart

@@ -19,7 +19,7 @@ class PolygonPerfStressPage extends StatefulWidget {
 }
 
 class _PolygonPerfStressPageState extends State<PolygonPerfStressPage> {
-  double simplificationTolerance = 0.5;
+  double simplificationTolerance = 0.3;
   bool useAltRendering = true;
   double borderThickness = 1;
 
@@ -63,15 +63,13 @@ class _PolygonPerfStressPageState extends State<PolygonPerfStressPage> {
               openStreetMapTileLayer,
               FutureBuilder(
                 future: geoJsonParser,
-                builder: (context, geoJsonParser) =>
-                    geoJsonParser.connectionState != ConnectionState.done ||
-                            geoJsonParser.data == null
-                        ? const SizedBox.shrink()
-                        : PolygonLayer(
-                            polygons: geoJsonParser.data!.polygons,
-                            useAltRendering: useAltRendering,
-                            simplificationTolerance: simplificationTolerance,
-                          ),
+                builder: (context, geoJsonParser) => geoJsonParser.data == null
+                    ? const SizedBox.shrink()
+                    : PolygonLayer(
+                        polygons: geoJsonParser.data!.polygons,
+                        useAltRendering: useAltRendering,
+                        simplificationTolerance: simplificationTolerance,
+                      ),
               ),
             ],
           ),

example/lib/pages/polyline_perf_stress.dart

@@ -19,7 +19,7 @@ class PolylinePerfStressPage extends StatefulWidget {
 }
 
 class _PolylinePerfStressPageState extends State<PolylinePerfStressPage> {
-  double simplificationTolerance = 0.5;
+  double simplificationTolerance = 0.3;
 
   final _randomWalk = [const LatLng(44.861294, 13.845086)];
 

lib/src/layer/circle_layer/circle_marker.dart

@@ -3,7 +3,7 @@ part of 'circle_layer.dart';
 /// Immutable marker options for [CircleMarker]. Circle markers are a more
 /// simple and performant way to draw markers as the regular [Marker]
 @immutable
-base class CircleMarker<R extends Object> extends HitDetectableElement<R> {
+class CircleMarker<R extends Object> with HitDetectableElement<R> {
   /// An optional [Key] for the [CircleMarker].
   /// This key is not used internally.
   final Key? key;
@@ -27,6 +27,9 @@ base class CircleMarker<R extends Object> extends HitDetectableElement<R> {
   /// Set to true if the radius should use the unit meters.
   final bool useRadiusInMeter;
 
+  @override
+  final R? hitValue;
+
   /// Constructor to create a new [CircleMarker] object
   const CircleMarker({
     required this.point,
@@ -36,6 +39,6 @@ base class CircleMarker<R extends Object> extends HitDetectableElement<R> {
     this.color = const Color(0xFF00FF00),
     this.borderStrokeWidth = 0.0,
     this.borderColor = const Color(0xFFFFFF00),
-    super.hitValue,
+    this.hitValue,
   });
 }

lib/src/layer/polygon_layer/polygon_layer.dart

@@ -7,6 +7,8 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_map/flutter_map.dart';
 import 'package:flutter_map/src/layer/shared/layer_interactivity/internal_hit_detectable.dart';
+import 'package:flutter_map/src/layer/shared/layer_projection_simplification/state.dart';
+import 'package:flutter_map/src/layer/shared/layer_projection_simplification/widget.dart';
 import 'package:flutter_map/src/layer/shared/line_patterns/pixel_hiker.dart';
 import 'package:flutter_map/src/misc/offsets.dart';
 import 'package:flutter_map/src/misc/point_in_polygon.dart';
@@ -21,7 +23,8 @@ part 'projected_polygon.dart';
 
 /// A polygon layer for [FlutterMap].
 @immutable
-class PolygonLayer<R extends Object> extends StatefulWidget {
+base class PolygonLayer<R extends Object>
+    extends ProjectionSimplificationManagementSupportedWidget {
   /// [Polygon]s to draw
   final List<Polygon<R>> polygons;
 
@@ -52,16 +55,6 @@ class PolygonLayer<R extends Object> extends StatefulWidget {
   /// Defaults to `true`. Disabling is not recommended.
   final bool polygonCulling;
 
-  /// Distance between two neighboring polygon points, in logical pixels scaled
-  /// to floored zoom
-  ///
-  /// Increasing this value results in points further apart being collapsed and
-  /// thus more simplified polygons. Higher values improve performance at the
-  /// cost of visual fidelity and vice versa.
-  ///
-  /// Defaults to 0.5. Set to 0 to disable simplification.
-  final double simplificationTolerance;
-
   /// Whether to draw per-polygon labels
   ///
   /// Defaults to `true`.
@@ -82,79 +75,63 @@ class PolygonLayer<R extends Object> extends StatefulWidget {
     this.useAltRendering = false,
     this.debugAltRenderer = false,
     this.polygonCulling = true,
-    this.simplificationTolerance = 0.5,
     this.polygonLabels = true,
     this.drawLabelsLast = false,
     this.hitNotifier,
-  }) : assert(
-          simplificationTolerance >= 0,
-          'simplificationTolerance cannot be negative: $simplificationTolerance',
-        );
+    super.simplificationTolerance,
+    super.useDynamicUpdate,
+  }) : super();
 
   @override
   State<PolygonLayer<R>> createState() => _PolygonLayerState<R>();
 }
 
-class _PolygonLayerState<R extends Object> extends State<PolygonLayer<R>> {
-  List<_ProjectedPolygon<R>>? _cachedProjectedPolygons;
-  final _cachedSimplifiedPolygons = <int, List<_ProjectedPolygon<R>>>{};
-
-  double? _devicePixelRatio;
+class _PolygonLayerState<R extends Object> extends State<PolygonLayer<R>>
+    with
+        ProjectionSimplificationManagement<_ProjectedPolygon<R>, Polygon<R>,
+            PolygonLayer<R>> {
+  @override
+  _ProjectedPolygon<R> projectElement({
+    required Projection projection,
+    required Polygon<R> element,
+  }) =>
+      _ProjectedPolygon._fromPolygon(projection, element);
 
   @override
-  void didUpdateWidget(PolygonLayer<R> oldWidget) {
-    super.didUpdateWidget(oldWidget);
+  _ProjectedPolygon<R> simplifyProjectedElement({
+    required _ProjectedPolygon<R> projectedElement,
+    required double tolerance,
+  }) =>
+      _ProjectedPolygon._(
+        polygon: projectedElement.polygon,
+        points: simplifyPoints(
+          points: projectedElement.points,
+          tolerance: tolerance,
+          highQuality: true,
+        ),
+        holePoints: List.generate(
+          projectedElement.holePoints.length,
+          (j) => simplifyPoints(
+            points: projectedElement.holePoints[j],
+            tolerance: tolerance,
+            highQuality: true,
+          ),
+          growable: false,
+        ),
+      );
 
-    if (!listEquals(oldWidget.polygons, widget.polygons)) {
-      // If the polylines have changed, then both the projections and the
-      // projection-dependendent simplifications must be invalidated
-      _cachedProjectedPolygons = null;
-      _cachedSimplifiedPolygons.clear();
-    } else if (oldWidget.simplificationTolerance !=
-        widget.simplificationTolerance) {
-      // If only the simplification tolerance has changed, this does not affect
-      // the projections (as that is done before simplification), so only
-      // invalidate the simplifications
-      _cachedSimplifiedPolygons.clear();
-    }
-  }
+  @override
+  Iterable<Polygon<R>> getElements(PolygonLayer<R> widget) => widget.polygons;
 
   @override
   Widget build(BuildContext context) {
-    final camera = MapCamera.of(context);
+    super.build(context);
 
-    final projected = _cachedProjectedPolygons ??= List.generate(
-      widget.polygons.length,
-      (i) => _ProjectedPolygon._fromPolygon(
-        camera.crs.projection,
-        widget.polygons[i],
-      ),
-      growable: false,
-    );
-
-    late final List<_ProjectedPolygon<R>> simplified;
-    if (widget.simplificationTolerance == 0) {
-      simplified = projected;
-    } else {
-      // If the DPR has changed, invalidate the simplification cache
-      final newDPR = MediaQuery.devicePixelRatioOf(context);
-      if (newDPR != _devicePixelRatio) {
-        _devicePixelRatio = newDPR;
-        _cachedSimplifiedPolygons.clear();
-      }
-
-      simplified = _cachedSimplifiedPolygons[camera.zoom.floor()] ??=
-          _computeZoomLevelSimplification(
-        camera: camera,
-        polygons: projected,
-        pixelTolerance: widget.simplificationTolerance,
-        devicePixelRatio: newDPR,
-      );
-    }
+    final camera = MapCamera.of(context);
 
     final culled = !widget.polygonCulling
-        ? simplified
-        : simplified
+        ? simplifiedElements.toList()
+        : simplifiedElements
             .where(
               (p) => p.polygon.boundingBox.isOverlapping(camera.visibleBounds),
             )
@@ -213,45 +190,4 @@ class _PolygonLayerState<R extends Object> extends State<PolygonLayer<R>> {
       yield prevValue += polygon.holePoints[i].length;
     }
   }
-
-  List<_ProjectedPolygon<R>> _computeZoomLevelSimplification({
-    required MapCamera camera,
-    required List<_ProjectedPolygon<R>> polygons,
-    required double pixelTolerance,
-    required double devicePixelRatio,
-  }) {
-    final tolerance = getEffectiveSimplificationTolerance(
-      crs: camera.crs,
-      zoom: camera.zoom.floor(),
-      pixelTolerance: pixelTolerance,
-      devicePixelRatio: devicePixelRatio,
-    );
-
-    return List<_ProjectedPolygon<R>>.generate(
-      polygons.length,
-      (i) {
-        final polygon = polygons[i];
-        final holes = polygon.holePoints;
-
-        return _ProjectedPolygon._(
-          polygon: polygon.polygon,
-          points: simplifyPoints(
-            points: polygon.points,
-            tolerance: tolerance,
-            highQuality: true,
-          ),
-          holePoints: List.generate(
-            holes.length,
-            (j) => simplifyPoints(
-              points: holes[j],
-              tolerance: tolerance,
-              highQuality: true,
-            ),
-            growable: false,
-          ),
-        );
-      },
-      growable: false,
-    );
-  }
 }

lib/src/layer/polygon_layer/projected_polygon.dart

@@ -1,7 +1,7 @@
 part of 'polygon_layer.dart';
 
 @immutable
-base class _ProjectedPolygon<R extends Object> extends HitDetectableElement<R> {
+class _ProjectedPolygon<R extends Object> with HitDetectableElement<R> {
   final Polygon<R> polygon;
   final List<DoublePoint> points;
   final List<List<DoublePoint>> holePoints;