Monomorphize projection call and avoid Num.clamp. Saves another 22% C…

…PU cycles on the UI thread for my test-case.

lib/src/geo/crs.dart

@@ -322,13 +322,15 @@ abstract class Projection {
 
   const Projection(this.bounds);
 
+  @nonVirtual
   Point<double> project(LatLng latlng) {
     final (x, y) = projectXY(latlng);
     return Point<double>(x, y);
   }
 
   (double, double) projectXY(LatLng latlng);
 
+  @nonVirtual
   LatLng unproject(Point point) =>
       unprojectXY(point.x.toDouble(), point.y.toDouble());
   LatLng unprojectXY(double x, double y);
@@ -365,7 +367,7 @@ class SphericalMercator extends Projection {
   const SphericalMercator() : super(_bounds);
 
   static double projectLat(double latitude) {
-    final lat = latitude.clamp(-maxLatitude, maxLatitude);
+    final lat = _clampSym(latitude, maxLatitude);
     final sin = math.sin(lat * math.pi / 180);
 
     return r / 2 * math.log((1 + sin) / (1 - sin));
@@ -445,5 +447,8 @@ class _Transformation {
       );
 }
 
-double _inclusiveLat(double value) => value.clamp(-90, 90);
-double _inclusiveLng(double value) => value.clamp(-180, 180);
+// Num.clamp is slow due to virtual function overhead.
+double _clampSym(double value, double limit) =>
+    value < -limit ? -limit : (value > limit ? limit : value);
+double _inclusiveLat(double value) => _clampSym(value, 90);
+double _inclusiveLng(double value) => _clampSym(value, 180);

lib/src/layer/polygon_layer/polygon_layer.dart

@@ -5,6 +5,7 @@ import 'package:flutter_map/src/geo/latlng_bounds.dart';
 import 'package:flutter_map/src/layer/general/mobile_layer_transformer.dart';
 import 'package:flutter_map/src/layer/polygon_layer/label.dart';
 import 'package:flutter_map/src/map/camera/camera.dart';
+import 'package:flutter_map/src/misc/offsets.dart';
 import 'package:flutter_map/src/misc/point_extensions.dart';
 import 'package:latlong2/latlong.dart' hide Path; // conflict with Path from UI
 
@@ -164,31 +165,8 @@ 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),
-    );
-  }
-
-  Offset getOffset(Offset origin, LatLng point) {
-    // Critically create as little garbage as possible. This is called on every frame.
-    final projected = map.project(point, map.zoom);
-    return Offset(projected.x - origin.dx, projected.y - origin.dy);
-  }
-
-  List<Offset> getOffsets(Offset origin, List<LatLng> points) {
-    final crs = map.crs;
-    final zoomScale = crs.scale(map.zoom);
-
-    final ox = -origin.dx;
-    final oy = -origin.dy;
-
-    return List<Offset>.generate(
-      points.length,
-      (index) {
-        final (x, y) = crs.latLngToXY(points[index], zoomScale);
-        return Offset(x + ox, y + oy);
-      },
-      growable: false,
+      min: getOffset(map, origin, bbox.southWest),
+      max: getOffset(map, origin, bbox.northEast),
     );
   }
 
@@ -234,7 +212,7 @@ class PolygonPainter extends CustomPainter {
       if (polygon.points.isEmpty) {
         continue;
       }
-      final offsets = getOffsets(origin, polygon.points);
+      final offsets = getOffsets(map, origin, polygon.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
@@ -264,7 +242,7 @@ class PolygonPainter extends CustomPainter {
 
         final holeOffsetsList = List<List<Offset>>.generate(
           holePointsList.length,
-          (i) => getOffsets(origin, holePointsList[i]),
+          (i) => getOffsets(map, origin, holePointsList[i]),
           growable: false,
         );
 

lib/src/layer/polyline_layer.dart

@@ -5,6 +5,7 @@ import 'package:flutter/widgets.dart';
 import 'package:flutter_map/src/geo/latlng_bounds.dart';
 import 'package:flutter_map/src/layer/general/mobile_layer_transformer.dart';
 import 'package:flutter_map/src/map/camera/camera.dart';
+import 'package:flutter_map/src/misc/offsets.dart';
 import 'package:flutter_map/src/misc/point_extensions.dart';
 import 'package:latlong2/latlong.dart';
 
@@ -98,29 +99,6 @@ class PolylinePainter extends CustomPainter {
 
   int? _hash;
 
-  Offset getOffset(Offset origin, LatLng point) {
-    // Critically create as little garbage as possible. This is called on every frame.
-    final projected = map.project(point, map.zoom);
-    return Offset(projected.x - origin.dx, projected.y - origin.dy);
-  }
-
-  List<Offset> getOffsets(Offset origin, List<LatLng> points) {
-    final crs = map.crs;
-    final zoomScale = crs.scale(map.zoom);
-
-    final ox = -origin.dx;
-    final oy = -origin.dy;
-
-    return List<Offset>.generate(
-      points.length,
-      (index) {
-        final (x, y) = crs.latLngToXY(points[index], zoomScale);
-        return Offset(x + ox, y + oy);
-      },
-      growable: false,
-    );
-  }
-
   @override
   void paint(Canvas canvas, Size size) {
     final rect = Offset.zero & size;
@@ -163,7 +141,7 @@ class PolylinePainter extends CustomPainter {
     final origin = map.project(map.center).toOffset() - map.size.toOffset() / 2;
 
     for (final polyline in polylines) {
-      final offsets = getOffsets(origin, polyline.points);
+      final offsets = getOffsets(map, origin, polyline.points);
       if (offsets.isEmpty) {
         continue;
       }
@@ -185,7 +163,7 @@ class PolylinePainter extends CustomPainter {
           polyline.strokeWidth,
           180,
         );
-        final delta = firstOffset - getOffset(origin, r);
+        final delta = firstOffset - getOffset(map, origin, r);
 
         strokeWidth = delta.distance;
       } else {

lib/src/misc/offsets.dart

@@ -0,0 +1,40 @@
+import 'dart:ui';
+
+import 'package:flutter_map/src/geo/crs.dart';
+import 'package:flutter_map/src/map/camera/camera.dart';
+import 'package:latlong2/latlong.dart';
+
+Offset getOffset(MapCamera camera, Offset origin, LatLng point) {
+  final crs = camera.crs;
+  final zoomScale = crs.scale(camera.zoom);
+  final (x, y) = crs.latLngToXY(point, zoomScale);
+  return Offset(x - origin.dx, y - origin.dy);
+}
+
+List<Offset> getOffsets(MapCamera camera, Offset origin, List<LatLng> points) {
+  // Critically create as little garbage as possible. This is called on every frame.
+  final crs = camera.crs;
+  final zoomScale = crs.scale(camera.zoom);
+
+  final ox = -origin.dx;
+  final oy = -origin.dy;
+  final len = points.length;
+
+  // Optimization: monomorphize the Epsg3857-case to save the virtual function overhead.
+  if (crs is Epsg3857) {
+    final Epsg3857 epsg3857 = crs;
+    final v = List<Offset>.filled(len, Offset.zero);
+    for (int i = 0; i < len; ++i) {
+      final (x, y) = epsg3857.latLngToXY(points[i], zoomScale);
+      v[i] = Offset(x + ox, y + oy);
+    }
+    return v;
+  }
+
+  final v = List<Offset>.filled(len, Offset.zero);
+  for (int i = 0; i < len; ++i) {
+    final (x, y) = crs.latLngToXY(points[i], zoomScale);
+    v[i] = Offset(x + ox, y + oy);
+  }
+  return v;
+}