fix: calculate LayerHitResult.coordinate correctly (#2093)

Author: JaffaKetchup

example/lib/pages/polygon.dart

@@ -437,6 +437,42 @@ class _PolygonPageState extends State<PolygonPage> {
                   ),
                 ],
               ),
+              IgnorePointer(
+                // Ignore the marker so it doesn't capture the pointer
+                // (as the marker is over the pointer)
+                child: ValueListenableBuilder(
+                  valueListenable: _hitNotifier,
+                  builder: (context, value, _) => MarkerLayer(
+                    rotate: true,
+                    markers: [
+                      if (value != null)
+                        Marker(
+                          height: 22,
+                          width: 24,
+                          alignment: Alignment.topCenter,
+                          point: value.coordinate,
+                          child: DecoratedBox(
+                            decoration: BoxDecoration(
+                              shape: BoxShape.circle,
+                              boxShadow: [
+                                BoxShadow(
+                                  blurRadius: 15,
+                                  spreadRadius: 5,
+                                  color: Colors.black.withAlpha(255 ~/ 3),
+                                  offset: const Offset(0, 11),
+                                ),
+                              ],
+                            ),
+                            child: const Icon(
+                              Icons.location_on,
+                              color: Colors.green,
+                            ),
+                          ),
+                        ),
+                    ],
+                  ),
+                ),
+              ),
             ],
           ),
           Positioned(

lib/src/layer/polygon_layer/painter.dart

@@ -62,10 +62,7 @@ class _PolygonPainter<R extends Object> extends CustomPainter
     required this.invertedFill,
     required this.hitNotifier,
   }) : bounds = camera.visibleBounds {
-    _helper = OffsetHelper(
-      camera: camera,
-      origin: origin,
-    );
+    _helper = OffsetHelper(camera: camera);
   }
 
   late final OffsetHelper _helper;
@@ -255,7 +252,7 @@ class _PolygonPainter<R extends Object> extends CustomPainter
           polygon.labelPosition,
           shift: shift,
         ),
-        bounds: _getBounds(origin, polygon),
+        bounds: _getBounds(camera.pixelOrigin, polygon),
         textPainter: polygon.textPainter!,
         rotationRad: camera.rotationRad,
         rotate: polygon.rotateLabel,

lib/src/layer/polyline_layer/painter.dart

@@ -21,10 +21,7 @@ class _PolylinePainter<R extends Object> extends CustomPainter
     required this.camera,
     required this.hitNotifier,
   }) {
-    _helper = OffsetHelper(
-      camera: camera,
-      origin: origin,
-    );
+    _helper = OffsetHelper(camera: camera);
   }
 
   late final OffsetHelper _helper;

lib/src/layer/shared/feature_layer_utils.dart

@@ -102,10 +102,6 @@ mixin FeatureLayerUtils on CustomPainter {
     }
   }
 
-  /// Returns the origin of the camera.
-  Offset get origin =>
-      camera.projectAtZoom(camera.center) - camera.size.center(Offset.zero);
-
   /// Returns the world size in pixels.
   ///
   /// Equivalent to [MapCamera.getWorldWidthAtZoom].

lib/src/layer/shared/layer_interactivity/internal_hit_detectable.dart

@@ -1,6 +1,5 @@
 import 'package:flutter/widgets.dart';
 import 'package:flutter_map/flutter_map.dart';
-import 'package:flutter_map/src/layer/shared/feature_layer_utils.dart';
 import 'package:latlong2/latlong.dart';
 import 'package:meta/meta.dart';
 
@@ -42,8 +41,7 @@ mixin HitDetectablePainter<R extends Object, E extends HitDetectableElement<R>>
   /// Avoid performing calculations that are not dependent on [element]. Instead,
   /// override [hitTest], store the necessary calculation results in
   /// (`late` non-`null`able) members, and call `super.hitTest(position)` at the
-  /// end. To calculate the camera origin in this way, instead mix in and use
-  /// [FeatureLayerUtils.origin].
+  /// end. The camera origin may be retrieved with [MapCamera.pixelOrigin].
   ///
   /// Should return whether an element has been hit.
   bool elementHitTest(
@@ -60,13 +58,12 @@ mixin HitDetectablePainter<R extends Object, E extends HitDetectableElement<R>>
     _hits.clear();
     bool hasHit = false;
 
-    final point = position;
-    final coordinate = camera.screenOffsetToLatLng(point);
+    final coordinate = camera.unprojectAtZoom(camera.pixelOrigin + position);
 
     for (int i = elements.length - 1; i >= 0; i--) {
       final element = elements.elementAt(i);
       if (hasHit && element.hitValue == null) continue;
-      if (elementHitTest(element, point: point, coordinate: coordinate)) {
+      if (elementHitTest(element, point: position, coordinate: coordinate)) {
         if (element.hitValue != null) _hits.add(element.hitValue!);
         hasHit = true;
       }
@@ -80,7 +77,7 @@ mixin HitDetectablePainter<R extends Object, E extends HitDetectableElement<R>>
     hitNotifier?.value = LayerHitResult(
       hitValues: _hits,
       coordinate: coordinate,
-      point: point,
+      point: position,
     );
     return true;
   }

lib/src/map/camera/camera.dart

@@ -88,6 +88,28 @@ class MapCamera {
   /// The offset of the top-left corner of the bounding rectangle of this
   /// camera. This will not equal the offset of the top-left visible pixel when
   /// the map is rotated.
+  /* (jaffaketchup) This is used for painters & hit testing extensively. We want
+     to convert [position], which is in the canvas' coordinate space to a
+     [coordinate]. See `screenOffsetToLatLng` - it uses `nonRotatedSize` then
+     does more rotations after. We don't want to do this. So we copy the
+     implementation, and replace/remove the necessary parts, resulting in the
+     code below.
+
+      final pointCenterDistance = camera.size.center(Offset.zero) - position;
+      final a = camera.crs.latLngToOffset(camera.center, camera.zoom);
+      final coordinate = camera.crs.offsetToLatLng(
+        a - pointCenterDistance,
+        camera.zoom,
+      );
+     
+     `camera.crs.latLngToOffset` is longhand for `projectAtZoom`. So we have
+     `a - (b - c)`, where `c` is [position]. This is equivalent to `(a - b) + c`.
+     `(a - b)` is this.
+
+     This was provided in [FeatureLayerUtils.origin] for a few versions. It has
+     been removed, because this exists, so I'm not sure why it needed to be
+     duplicated. See [HitDetectablePainter.hitTest] for an easy usage example.
+  */
   Offset get pixelOrigin =>
       _pixelOrigin ??= projectAtZoom(center, zoom) - size.center(Offset.zero);
 

lib/src/misc/offsets.dart

@@ -9,13 +9,12 @@ import 'package:meta/meta.dart';
 class OffsetHelper {
   OffsetHelper({
     required this.camera,
-    required this.origin,
-  }) : _replicatesWorldLongitude = camera.crs.replicatesWorldLongitude;
+  })  : _replicatesWorldLongitude = camera.crs.replicatesWorldLongitude,
+        _origin = camera.pixelOrigin;
 
   final MapCamera camera;
 
-  final Offset origin;
-
+  final Offset _origin;
   final bool _replicatesWorldLongitude;
 
   /// Calculate the [Offset] for the [LatLng] point.
@@ -26,18 +25,18 @@ class OffsetHelper {
     final crs = camera.crs;
     final zoomScale = crs.scale(camera.zoom);
     final (x, y) = crs.latLngToXY(point, zoomScale);
-    return Offset(x - origin.dx + shift, y - origin.dy);
+    return Offset(x - _origin.dx + shift, y - _origin.dy);
   }
 
-// TODO not sure if still relevant
+  // TODO not sure if still relevant
   /// Calculate the [Offset]s for the list of [LatLng] points.
   List<Offset> getOffsets(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 ox = -_origin.dx;
+    final oy = -_origin.dy;
     final len = points.length;
 
     // Optimization: monomorphize the Epsg3857-case to avoid the virtual function overhead.
@@ -74,8 +73,8 @@ class OffsetHelper {
         ? points
         : points.followedBy(holePoints.expand((e) => e));
 
-    final ox = -origin.dx;
-    final oy = -origin.dy;
+    final ox = -_origin.dx;
+    final oy = -_origin.dy;
     final len = realPoints.length;
 
     /// Returns additional world width in order to have visible points.