perf!: cache projection of polygon points & CRS improvements (#1801)

lib/flutter_map.dart

@@ -16,7 +16,7 @@
 /// * discord.gg: <https://discord.gg/BwpEsjqMAH>
 library flutter_map;
 
-export 'package:flutter_map/src/geo/crs.dart';
+export 'package:flutter_map/src/geo/crs.dart' hide CrsWithStaticTransformation;
 export 'package:flutter_map/src/geo/latlng_bounds.dart';
 export 'package:flutter_map/src/gestures/interactive_flag.dart';
 export 'package:flutter_map/src/gestures/latlng_tween.dart';

lib/src/geo/crs.dart

@@ -29,10 +29,15 @@ abstract class Crs {
     this.wrapLat,
   });
 
+  /// Project a spherical LatLng coordinate into planar space (unscaled).
   Projection get projection;
 
-  /// Converts a point on the sphere surface (with a certain zoom) in a
-  /// map point.
+  /// Scale planar coordinate to scaled map point.
+  (double, double) transform(double x, double y, double scale);
+  (double, double) untransform(double x, double y, double scale);
+
+  /// Converts a point on the sphere surface (with a certain zoom) to a
+  /// scaled map point.
   (double, double) latLngToXY(LatLng latlng, double scale);
 
   Point<double> latLngToPoint(LatLng latlng, double zoom) {
@@ -53,33 +58,42 @@ abstract class Crs {
   Bounds<double>? getProjectedBounds(double zoom);
 }
 
+/// Internal base class for CRS with a single zoom-level independent transformation.
 @immutable
-abstract class _CrsWithStaticTransformation extends Crs {
+@internal
+abstract class CrsWithStaticTransformation extends Crs {
   @nonVirtual
   @protected
-  final _Transformation transformation;
+  final _Transformation _transformation;
 
   @override
   final Projection projection;
 
-  const _CrsWithStaticTransformation({
-    required this.transformation,
+  const CrsWithStaticTransformation._({
+    required _Transformation transformation,
     required this.projection,
     required super.code,
     required super.infinite,
     super.wrapLng,
     super.wrapLat,
-  });
+  }) : _transformation = transformation;
+
+  @override
+  (double, double) transform(double x, double y, double scale) =>
+      _transformation.transform(x, y, scale);
+  @override
+  (double, double) untransform(double x, double y, double scale) =>
+      _transformation.untransform(x, y, scale);
 
   @override
   (double, double) latLngToXY(LatLng latlng, double scale) {
     final (x, y) = projection.projectXY(latlng);
-    return transformation.transform(x, y, scale);
+    return _transformation.transform(x, y, scale);
   }
 
   @override
   LatLng pointToLatLng(Point point, double zoom) {
-    final (x, y) = transformation.untransform(
+    final (x, y) = _transformation.untransform(
       point.x.toDouble(),
       point.y.toDouble(),
       scale(zoom),
@@ -93,8 +107,8 @@ abstract class _CrsWithStaticTransformation extends Crs {
 
     final b = projection.bounds!;
     final s = scale(zoom);
-    final (minx, miny) = transformation.transform(b.min.x, b.min.y, s);
-    final (maxx, maxy) = transformation.transform(b.max.x, b.max.y, s);
+    final (minx, miny) = _transformation.transform(b.min.x, b.min.y, s);
+    final (maxx, maxy) = _transformation.transform(b.max.x, b.max.y, s);
     return Bounds<double>(
       Point<double>(minx, miny),
       Point<double>(maxx, maxy),
@@ -104,9 +118,9 @@ abstract class _CrsWithStaticTransformation extends Crs {
 
 // Custom CRS for non geographical maps
 @immutable
-class CrsSimple extends _CrsWithStaticTransformation {
+class CrsSimple extends CrsWithStaticTransformation {
   const CrsSimple()
-      : super(
+      : super._(
           code: 'CRS.SIMPLE',
           transformation: const _Transformation(1, 0, -1, 0),
           projection: const _LonLat(),
@@ -118,11 +132,11 @@ class CrsSimple extends _CrsWithStaticTransformation {
 
 /// The most common CRS used for rendering maps.
 @immutable
-class Epsg3857 extends _CrsWithStaticTransformation {
+class Epsg3857 extends CrsWithStaticTransformation {
   static const double _scale = 0.5 / (math.pi * SphericalMercator.r);
 
   const Epsg3857()
-      : super(
+      : super._(
           code: 'EPSG:3857',
           transformation: const _Transformation(_scale, 0.5, -_scale, 0.5),
           projection: const SphericalMercator(),
@@ -132,12 +146,15 @@ class Epsg3857 extends _CrsWithStaticTransformation {
 
   @override
   (double, double) latLngToXY(LatLng latlng, double scale) =>
-      transformation.transform(SphericalMercator.projectLng(latlng.longitude),
-          SphericalMercator.projectLat(latlng.latitude), scale);
+      _transformation.transform(
+        SphericalMercator.projectLng(latlng.longitude),
+        SphericalMercator.projectLat(latlng.latitude),
+        scale,
+      );
 
   @override
   Point<double> latLngToPoint(LatLng latlng, double zoom) {
-    final (x, y) = transformation.transform(
+    final (x, y) = _transformation.transform(
       SphericalMercator.projectLng(latlng.longitude),
       SphericalMercator.projectLat(latlng.latitude),
       scale(zoom),
@@ -148,9 +165,9 @@ class Epsg3857 extends _CrsWithStaticTransformation {
 
 /// A common CRS among GIS enthusiasts. Uses simple Equirectangular projection.
 @immutable
-class Epsg4326 extends _CrsWithStaticTransformation {
+class Epsg4326 extends CrsWithStaticTransformation {
   const Epsg4326()
-      : super(
+      : super._(
           projection: const _LonLat(),
           transformation: const _Transformation(1 / 180, 1, -1 / 180, 0.5),
           code: 'EPSG:4326',
@@ -222,6 +239,13 @@ class Proj4Crs extends Crs {
     );
   }
 
+  @override
+  (double, double) transform(double x, double y, double scale) =>
+      _getTransformationByZoom(zoom(scale)).transform(x, y, scale);
+  @override
+  (double, double) untransform(double x, double y, double scale) =>
+      _getTransformationByZoom(zoom(scale)).untransform(x, y, scale);
+
   /// Converts a point on the sphere surface (with a certain zoom) in a
   /// map point.
   @override

lib/src/layer/polygon_layer/painter.dart

@@ -1,13 +1,13 @@
 part of 'polygon_layer.dart';
 
-class PolygonPainter extends CustomPainter {
-  final List<Polygon> polygons;
+class _PolygonPainter extends CustomPainter {
+  final List<_ProjectedPolygon> polygons;
   final MapCamera camera;
   final LatLngBounds bounds;
   final bool polygonLabels;
   final bool drawLabelsLast;
 
-  PolygonPainter({
+  _PolygonPainter({
     required this.polygons,
     required this.camera,
     required this.polygonLabels,
@@ -17,23 +17,11 @@ class PolygonPainter extends CustomPainter {
   ({Offset min, Offset max}) getBounds(Offset origin, Polygon polygon) {
     final bbox = polygon.boundingBox;
     return (
-      min: getOffset(origin, bbox.southWest),
-      max: getOffset(origin, bbox.northEast),
+      min: getOffset(camera, origin, bbox.southWest),
+      max: getOffset(camera, origin, bbox.northEast),
     );
   }
 
-  Offset getOffset(Offset origin, LatLng point) {
-    // Critically create as little garbage as possible. This is called on every frame.
-    final projected = camera.project(point);
-    return Offset(projected.x - origin.dx, projected.y - origin.dy);
-  }
-
-  List<Offset> getOffsets(Offset origin, List<LatLng> points) => List.generate(
-        points.length,
-        (index) => getOffset(origin, points[index]),
-        growable: false,
-      );
-
   @override
   void paint(Canvas canvas, Size size) {
     var filledPath = ui.Path();
@@ -73,11 +61,12 @@ class PolygonPainter extends CustomPainter {
     final origin = (camera.project(camera.center) - camera.size / 2).toOffset();
 
     // Main loop constructing batched fill and border paths from given polygons.
-    for (final polygon in polygons) {
-      if (polygon.points.isEmpty) {
+    for (final projectedPolygon in polygons) {
+      if (projectedPolygon.points.isEmpty) {
         continue;
       }
-      final offsets = getOffsets(origin, polygon.points);
+      final polygon = projectedPolygon.polygon;
+      final offsets = getOffsetsXY(camera, origin, projectedPolygon.points);
 
       // The hash is based on the polygons visual properties. If the hash from
       // the current and the previous polygon no longer match, we need to flush
@@ -110,7 +99,7 @@ class PolygonPainter extends CustomPainter {
 
         final holeOffsetsList = List<List<Offset>>.generate(
           holePointsList.length,
-          (i) => getOffsets(origin, holePointsList[i]),
+          (i) => getOffsets(camera, origin, holePointsList[i]),
           growable: false,
         );
 
@@ -155,10 +144,11 @@ class PolygonPainter extends CustomPainter {
     drawPaths();
 
     if (polygonLabels && drawLabelsLast) {
-      for (final polygon in polygons) {
-        if (polygon.points.isEmpty) {
+      for (final projectedPolygon in polygons) {
+        if (projectedPolygon.points.isEmpty) {
           continue;
         }
+        final polygon = projectedPolygon.polygon;
         final textPainter = polygon.textPainter;
         if (textPainter != null) {
           final painter = _buildLabelTextPainter(
@@ -221,26 +211,32 @@ class PolygonPainter extends CustomPainter {
   }
 
   void _addDottedLineToPath(
-      ui.Path path, List<Offset> offsets, double radius, double stepLength) {
+    ui.Path path,
+    List<Offset> offsets,
+    double radius,
+    double stepLength,
+  ) {
     if (offsets.isEmpty) {
       return;
     }
 
     double startDistance = 0;
-    for (var i = 0; i < offsets.length; i++) {
+    for (int i = 0; i < offsets.length; i++) {
       final o0 = offsets[i % offsets.length];
       final o1 = offsets[(i + 1) % offsets.length];
       final totalDistance = (o0 - o1).distance;
 
       double distance = startDistance;
-      for (; distance < totalDistance; distance += stepLength) {
+      while (distance < totalDistance) {
         final done = distance / totalDistance;
         final remain = 1.0 - done;
         final offset = Offset(
           o0.dx * remain + o1.dx * done,
           o0.dy * remain + o1.dy * done,
         );
         path.addOval(Rect.fromCircle(center: offset, radius: radius));
+
+        distance += stepLength;
       }
 
       startDistance = distance < totalDistance
@@ -256,5 +252,5 @@ class PolygonPainter extends CustomPainter {
   }
 
   @override
-  bool shouldRepaint(PolygonPainter oldDelegate) => false;
+  bool shouldRepaint(_PolygonPainter oldDelegate) => false;
 }

lib/src/layer/polygon_layer/polygon.dart

@@ -77,24 +77,6 @@ class Polygon {
   }) : _filledAndClockwise =
             (isFilled ?? (color != null)) && isClockwise(points);
 
-  Polygon copyWithNewPoints(List<LatLng> points) => Polygon(
-        points: points,
-        holePointsList: holePointsList,
-        color: color,
-        borderStrokeWidth: borderStrokeWidth,
-        borderColor: borderColor,
-        disableHolesBorder: disableHolesBorder,
-        isDotted: isDotted,
-        // ignore: deprecated_member_use_from_same_package
-        isFilled: isFilled,
-        strokeCap: strokeCap,
-        strokeJoin: strokeJoin,
-        label: label,
-        labelStyle: labelStyle,
-        labelPlacement: labelPlacement,
-        rotateLabel: rotateLabel,
-      );
-
   static bool isClockwise(List<LatLng> points) {
     double sum = 0;
     for (int i = 0; i < points.length; ++i) {