feat: add option to draw labels on top of all Polygons (#1707)

Remove weird left-side label pruning and add an option to draw labels last on top of all the polygons.

lib/src/layer/polygon_layer/label.dart

@@ -6,57 +6,46 @@ import 'package:flutter_map/src/layer/polygon_layer/polygon_layer.dart';
 import 'package:latlong2/latlong.dart';
 import 'package:polylabel/polylabel.dart';
 
-void Function(Canvas canvas)? buildLabelTextPainter(
-  List<LatLng> locs,
-  LatLng labelLoc, {
+void Function(Canvas canvas)? buildLabelTextPainter({
   required Offset placementPoint,
   required List<Offset> points,
   required String labelText,
   required double rotationRad,
-  bool rotate = false,
-  TextStyle? labelStyle,
-  double padding = 0,
+  required bool rotate,
+  required TextStyle labelStyle,
+  required double padding,
 }) {
-  double dx = placementPoint.dx;
-  double dy = placementPoint.dy;
+  final textSpan = TextSpan(text: labelText, style: labelStyle);
+  final textPainter = TextPainter(
+    text: textSpan,
+    textAlign: TextAlign.center,
+    textDirection: TextDirection.ltr,
+  )..layout();
 
-  if (dx > 0) {
-    final textSpan = TextSpan(text: labelText, style: labelStyle);
-    final textPainter = TextPainter(
-      text: textSpan,
-      textAlign: TextAlign.center,
-      textDirection: TextDirection.ltr,
-      maxLines: 1,
-    );
+  final dx = placementPoint.dx - textPainter.width / 2;
+  final dy = placementPoint.dy - textPainter.height / 2;
 
-    textPainter.layout();
-    dx -= textPainter.width / 2;
-    dy -= textPainter.height / 2;
+  double maxDx = 0;
+  var minDx = double.infinity;
+  for (final point in points) {
+    maxDx = math.max(maxDx, point.dx);
+    minDx = math.min(minDx, point.dx);
+  }
 
-    var maxDx = 0.0;
-    var minDx = double.infinity;
-    for (final point in points) {
-      maxDx = math.max(maxDx, point.dx);
-      minDx = math.min(minDx, point.dx);
-    }
+  if (maxDx - minDx - padding > textPainter.width) {
+    return (canvas) {
+      if (rotate) {
+        canvas.save();
+        canvas.translate(placementPoint.dx, placementPoint.dy);
+        canvas.rotate(-rotationRad);
+        canvas.translate(-placementPoint.dx, -placementPoint.dy);
+      }
 
-    if (maxDx - minDx - padding > textPainter.width) {
-      return (canvas) {
-        if (rotate) {
-          canvas.save();
-          canvas.translate(placementPoint.dx, placementPoint.dy);
-          canvas.rotate(-rotationRad);
-          canvas.translate(-placementPoint.dx, -placementPoint.dy);
-        }
-        textPainter.paint(
-          canvas,
-          Offset(dx, dy),
-        );
-        if (rotate) {
-          canvas.restore();
-        }
-      };
-    }
+      textPainter.paint(canvas, Offset(dx, dy));
+      if (rotate) {
+        canvas.restore();
+      }
+    };
   }
   return null;
 }
@@ -89,9 +78,8 @@ LatLng _computePolylabel(List<LatLng> points) {
     // i.e. cheaper at the expense off less optimal label placement.
     precision: 0.000001,
   );
-  final latlng = LatLng(
+  return LatLng(
     labelPosition.point.y.toDouble(),
     labelPosition.point.x.toDouble(),
   );
-  return latlng;
 }

lib/src/layer/polygon_layer/polygon_layer.dart

@@ -98,11 +98,15 @@ class PolygonLayer extends StatelessWidget {
   // Turn on/off per-polygon label drawing on the layer-level.
   final bool polygonLabels;
 
+  // Whether to draw labels last and thus over all the polygons.
+  final bool drawLabelsLast;
+
   const PolygonLayer({
     super.key,
     required this.polygons,
     this.polygonCulling = false,
     this.polygonLabels = true,
+    this.drawLabelsLast = false,
   });
 
   @override
@@ -118,7 +122,7 @@ class PolygonLayer extends StatelessWidget {
 
     return MobileLayerTransformer(
       child: CustomPaint(
-        painter: PolygonPainter(pgons, map, polygonLabels),
+        painter: PolygonPainter(pgons, map, polygonLabels, drawLabelsLast),
         size: size,
         isComplex: true,
       ),
@@ -131,8 +135,10 @@ class PolygonPainter extends CustomPainter {
   final MapCamera map;
   final LatLngBounds bounds;
   final bool polygonLabels;
+  final bool drawLabelsLast;
 
-  PolygonPainter(this.polygons, this.map, this.polygonLabels)
+  PolygonPainter(
+      this.polygons, this.map, this.polygonLabels, this.drawLabelsLast)
       : bounds = map.visibleBounds;
 
   int get hash {
@@ -189,10 +195,10 @@ class PolygonPainter extends CustomPainter {
 
     // Main loop constructing batched fill and border paths from given polygons.
     for (final polygon in polygons) {
-      final offsets = getOffsets(polygon.points);
-      if (offsets.isEmpty) {
+      if (polygon.points.isEmpty) {
         continue;
       }
+      final offsets = getOffsets(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
@@ -235,7 +241,7 @@ class PolygonPainter extends CustomPainter {
         }
       }
 
-      if (polygonLabels && polygon.label != null) {
+      if (polygonLabels && !drawLabelsLast && polygon.label != null) {
         // Labels are expensive because:
         //  * they themselves cannot easily be pulled into our batched path
         //    painting with the given text APIs
@@ -246,15 +252,13 @@ class PolygonPainter extends CustomPainter {
         // The painter will be null if the layouting algorithm determined that
         // there isn't enough space.
         final painter = buildLabelTextPainter(
-          polygon.points,
-          polygon.labelPosition,
           placementPoint: map.getOffsetFromOrigin(polygon.labelPosition),
           points: offsets,
           labelText: polygon.label!,
           labelStyle: polygon.labelStyle,
           rotationRad: map.rotationRad,
           rotate: polygon.rotateLabel,
-          padding: 10,
+          padding: 20,
         );
 
         if (painter != null) {
@@ -267,6 +271,29 @@ class PolygonPainter extends CustomPainter {
     }
 
     drawPaths();
+
+    if (polygonLabels && drawLabelsLast) {
+      for (final polygon in polygons) {
+        if (polygon.points.isEmpty) {
+          continue;
+        }
+        final offsets = getOffsets(polygon.points);
+
+        if (polygon.label != null) {
+          final painter = buildLabelTextPainter(
+            placementPoint: map.getOffsetFromOrigin(polygon.labelPosition),
+            points: offsets,
+            labelText: polygon.label!,
+            labelStyle: polygon.labelStyle,
+            rotationRad: map.rotationRad,
+            rotate: polygon.rotateLabel,
+            padding: 20,
+          );
+
+          painter?.call(canvas);
+        }
+      }
+    }
   }
 
   Paint _getBorderPaint(Polygon polygon) {