Line-dasharray Impl.

lib/src/features/fill_renderer.dart

@@ -31,7 +31,7 @@ class FillRenderer extends FeatureRenderer {
     final fillPaint = style.fillPaint?.evaluate(evaluationContext);
     final outlinePaint = style.outlinePaint?.evaluate(evaluationContext);
 
-    final polygons = feature.paths;
+    final polygons = feature.getPaths();
 
     for (final polygon in polygons) {
       if (!context.optimizations.skipInBoundsChecks &&

lib/src/features/line_renderer.dart

@@ -47,7 +47,11 @@ class LineRenderer extends FeatureRenderer {
     effectivePaint.strokeWidth =
         context.tileSpaceMapper.widthFromPixelToTile(strokeWidth);
 
-    final lines = feature.paths;
+    final dashLengths = effectivePaint.strokeDashPattern
+        .map((e) => context.tileSpaceMapper.widthFromPixelToTile(e))
+        .toList(growable: false);
+
+    final lines = feature.getPaths(dashLengths: dashLengths);
 
     for (final line in lines) {
       if (!context.optimizations.skipInBoundsChecks &&

lib/src/features/symbol_line_renderer.dart

@@ -29,7 +29,7 @@ class SymbolLineRenderer extends FeatureRenderer {
       return;
     }
 
-    final lines = feature.paths;
+    final lines = feature.getPaths();
     if (lines.isEmpty) {
       return;
     }

lib/src/model/path_utils.dart

@@ -0,0 +1,25 @@
+import 'dart:ui';
+
+import 'ring_number_provider.dart';
+
+extension DashPath on Path {
+  // convert a path into a dashed path with given intervals
+  Path dashPath(RingNumberProvider dashArray) {
+    final Path dest = Path();
+    for (final PathMetric metric in this.computeMetrics()) {
+      double distance = .0;
+      bool draw = true;
+      while (distance < metric.length) {
+        final double len = dashArray.next;
+        if (draw) {
+          dest.addPath(
+              metric.extractPath(distance, distance + len), Offset.zero);
+        }
+        distance += len;
+        draw = !draw;
+      }
+    }
+
+    return dest;
+  }
+}

lib/src/model/ring_number_provider.dart

@@ -0,0 +1,13 @@
+class RingNumberProvider {
+  RingNumberProvider(this._vals);
+
+  final List<double> _vals;
+  int _idx = 0;
+
+  double get next {
+    if (_idx >= _vals.length) {
+      _idx = 0;
+    }
+    return _vals[_idx++];
+  }
+}

lib/src/model/tile_model.dart

@@ -1,5 +1,7 @@
 import 'dart:ui';
 
+import 'ring_number_provider.dart';
+import 'path_utils.dart';
 import 'geometry_model.dart';
 import 'geometry_model_ui.dart';
 
@@ -56,7 +58,7 @@ class TileFeature {
 
   bool get hasPoints => type == TileFeatureType.point;
 
-  List<Path> get paths {
+  List<Path> getPaths({List<double> dashLengths = const []}) {
     if (type == TileFeatureType.point) {
       throw StateError('Cannot get paths from a point feature');
     }
@@ -78,7 +80,12 @@ class TileFeature {
           .toList(growable: false);
       _modelPolygons = null;
     }
-    return _paths;
+
+    if (dashLengths.length >= 2) {
+      return _paths.map((e) => e.dashPath(RingNumberProvider(dashLengths))).toList();
+    } else {
+      return _paths;
+    }
   }
 }
 

lib/src/themes/paint_factory.dart

@@ -6,14 +6,14 @@ import 'expression/expression.dart';
 import 'expression/literal_expression.dart';
 import 'expression/numeric_expression.dart';
 
-class PaintExpression extends Expression<Paint> {
+class PaintExpression extends Expression<PaintModel> {
   final PaintStyle _delegate;
 
   PaintExpression(this._delegate)
       : super(_cacheKey(_delegate), _properties(_delegate));
 
   @override
-  Paint? evaluate(EvaluationContext context) => _delegate.paint(context);
+  PaintModel? evaluate(EvaluationContext context) => _delegate.paint(context);
 
   @override
   bool get isConstant => false;
@@ -28,21 +28,27 @@ class PaintExpression extends Expression<Paint> {
       };
 }
 
+class PaintModel extends Paint {
+  List<double> strokeDashPattern = [];
+}
+
 class PaintStyle {
   final String id;
   final PaintingStyle paintingStyle;
   final Expression<double> opacity;
   final Expression<double> strokeWidth;
   final Expression<Color> color;
+  final List<double> strokeDashPattern;
 
   PaintStyle(
       {required this.id,
       required this.paintingStyle,
       required this.opacity,
       required this.strokeWidth,
-      required this.color});
+      required this.color,
+      required this.strokeDashPattern});
 
-  Paint? paint(EvaluationContext context) {
+  PaintModel? paint(EvaluationContext context) {
     final opacity = this.opacity.evaluate(context);
     if (opacity != null && opacity <= 0) {
       return null;
@@ -51,7 +57,9 @@ class PaintStyle {
     if (color == null) {
       return null;
     }
-    final paint = Paint()..style = paintingStyle;
+    final paint = PaintModel()
+      ..style = paintingStyle
+      ..strokeDashPattern = strokeDashPattern;
     if (opacity != null && opacity < 1.0) {
       paint.color = color.withOpacity(opacity);
     } else {
@@ -73,7 +81,7 @@ class PaintFactory {
   final ExpressionParser expressionParser;
   PaintFactory(this.logger) : expressionParser = ExpressionParser(logger);
 
-  Expression<Paint>? create(
+  Expression<PaintModel>? create(
       String id, PaintingStyle style, String prefix, paint,
       {double? defaultStrokeWidth = 1.0}) {
     if (paint == null) {
@@ -87,11 +95,23 @@ class PaintFactory {
         whenNull: () => LiteralExpression(1.0));
     final strokeWidth = expressionParser.parse(paint['$prefix-width'],
         whenNull: () => LiteralExpression(defaultStrokeWidth));
+
+    List<double> dashArray = [];
+    final dashJson = paint['$prefix-dasharray'];
+    if (dashJson != null && dashJson is List<num> && dashJson.length >= 2) {
+      if (dashJson.any((element) => element < .0)) {
+        logger.warn(() => '$prefix-dasharray contains value < 0');
+      } else {
+        dashArray = dashJson.map((e) => e.toDouble()).toList(growable: false);
+      }
+    }
+
     return PaintExpression(PaintStyle(
         id: id,
         paintingStyle: style,
         opacity: opacity.asDoubleExpression(),
         strokeWidth: strokeWidth.asDoubleExpression(),
-        color: color.asColorExpression()));
+        color: color.asColorExpression(),
+        strokeDashPattern: dashArray));
   }
 }

lib/src/themes/style.dart

@@ -4,6 +4,7 @@ import 'dart:math';
 import 'dart:ui';
 
 import 'package:flutter/widgets.dart';
+import 'package:vector_tile_renderer/src/themes/paint_factory.dart';
 import 'expression/expression.dart';
 
 import '../extensions.dart';
@@ -12,14 +13,14 @@ typedef ColorZoomFunction = Color? Function(double zoom);
 typedef TextTransformFunction = String? Function(String? text);
 
 class Style {
-  final Expression<Paint>? fillPaint;
+  final Expression<PaintModel>? fillPaint;
   final Extrusion? fillExtrusion;
-  final Expression<Paint>? linePaint;
+  final Expression<PaintModel>? linePaint;
   final LineLayout? lineLayout;
-  final Expression<Paint>? textPaint;
+  final Expression<PaintModel>? textPaint;
   final TextLayout? textLayout;
   final Expression<List<Shadow>>? textHalo;
-  final Expression<Paint>? outlinePaint;
+  final Expression<PaintModel>? outlinePaint;
 
   Style(
       {this.fillPaint,

lib/src/tileset.dart

@@ -59,7 +59,7 @@ class TilesetPreprocessor {
         if (_initializeGeometry) {
           for (final feature in features) {
             if (feature.feature.hasPaths) {
-              feature.feature.paths;
+              feature.feature.getPaths();
             } else if (feature.feature.hasPoints) {
               feature.feature.points;
             }