support caching of VectorTileFeatures resolved for a ThemeLayer

lib/src/themes/feature_resolver.dart

@@ -0,0 +1,52 @@
+import 'package:vector_tile_renderer/src/themes/selector.dart';
+
+import '../../vector_tile_renderer.dart';
+
+/// Resolver for resolving the features, that are selected by a
+/// [TileLayerSelector].
+abstract class LayerFeatureResolver {
+  /// Resolves and returns the features that the given [selector] selects.
+  Iterable<LayerFeature> resolveFeatures(TileLayerSelector selector);
+}
+
+/// Default implementation of [LayerFeatureResolver] that resolves
+/// features from a [tileset].
+class DefaultThemeLayerFeatureResolver implements LayerFeatureResolver {
+  DefaultThemeLayerFeatureResolver(this.tileset);
+
+  /// The [Tileset] from which to resolves features.
+  final Tileset tileset;
+
+  @override
+  Iterable<LayerFeature> resolveFeatures(TileLayerSelector selector) sync* {
+    for (final layer in selector.select(tileset)) {
+      for (final feature in selector.layerSelector.features(layer.features)) {
+        yield LayerFeature(layer, feature);
+      }
+    }
+  }
+}
+
+/// A [LayerFeatureResolver] that uses another resolver and caches its results.
+class CachingThemeLayerFeatureResolver implements LayerFeatureResolver {
+  CachingThemeLayerFeatureResolver(this._resolver);
+
+  final LayerFeatureResolver _resolver;
+
+  final _cache = <TileLayerSelector, List<LayerFeature>>{};
+
+  @override
+  Iterable<LayerFeature> resolveFeatures(TileLayerSelector selector) {
+    return _cache.putIfAbsent(
+      selector,
+      () => _resolver.resolveFeatures(selector).toList(),
+    );
+  }
+}
+
+class LayerFeature {
+  LayerFeature(this.layer, this.feature);
+
+  final VectorTileLayer layer;
+  final VectorTileFeature feature;
+}

lib/src/themes/theme_layers.dart

@@ -3,6 +3,7 @@ import 'dart:ui';
 import 'package:vector_tile/vector_tile_feature.dart';
 
 import '../context.dart';
+import '../tileset.dart';
 import 'selector.dart';
 import 'style.dart';
 import 'theme.dart';
@@ -11,23 +12,25 @@ class DefaultLayer extends ThemeLayer {
   final TileLayerSelector selector;
   final Style style;
 
-  DefaultLayer(String id, ThemeLayerType type,
-      {required this.selector,
-      required this.style,
-      required double? minzoom,
-      required double? maxzoom})
-      : super(id, type, minzoom: minzoom, maxzoom: maxzoom);
+  DefaultLayer(
+    String id,
+    ThemeLayerType type, {
+    required this.selector,
+    required this.style,
+    required double? minzoom,
+    required double? maxzoom,
+  }) : super(id, type, minzoom: minzoom, maxzoom: maxzoom);
 
   @override
   void render(Context context) {
-    selector.select(context.tileset).forEach((layer) {
-      selector.layerSelector.features(layer.features).forEach((feature) {
-        context.featureRenderer.render(context, type, style, layer, feature);
-        if (!context.tileset.preprocessed) {
-          _releaseMemory(feature);
-        }
-      });
-    });
+    for (final feature
+        in context.tileset.resolver.resolveFeatures(this.selector)) {
+      context.featureRenderer
+          .render(context, type, style, feature.layer, feature.feature);
+      if (!context.tileset.preprocessed) {
+        _releaseMemory(feature.feature);
+      }
+    }
   }
 
   void _releaseMemory(VectorTileFeature feature) {

lib/src/tileset.dart

@@ -1,5 +1,6 @@
 import 'package:vector_tile/vector_tile.dart';
 
+import 'themes/feature_resolver.dart';
 import 'themes/theme.dart';
 import 'themes/theme_layers.dart';
 
@@ -8,16 +9,23 @@ import 'themes/theme_layers.dart';
 class Tileset {
   final bool preprocessed;
   final Map<String, VectorTile> tiles;
+  late final LayerFeatureResolver _resolver;
 
-  Tileset(this.tiles) : this.preprocessed = false;
+  Tileset(this.tiles) : this.preprocessed = false {
+    _resolver = DefaultThemeLayerFeatureResolver(this);
+  }
 
-  Tileset._preprocessed(Tileset original)
+  Tileset._preprocessed(Tileset original, this._resolver)
       : this.tiles = original.tiles,
         this.preprocessed = true;
 
   VectorTile? tile(String sourceId) => tiles[sourceId];
 }
 
+extension InternalTileset on Tileset {
+  LayerFeatureResolver get resolver => _resolver;
+}
+
 /// A pre-processor for [Tileset]s. A pre-processing is an optional step
 /// that can reduce CPU overhead during rendering at the cost of higher memory
 /// usage.
@@ -29,17 +37,19 @@ class TilesetPreprocessor {
   /// Pre-processes a tileset to eliminate some expensive processing from
   /// the rendering stage.
   ///
-  /// returns a pre-processed tileset
+  /// Returns a pre-processed tileset.
   Tileset preprocess(Tileset tileset) {
-    theme.layers.whereType<DefaultLayer>().forEach((themeLayer) {
-      themeLayer.selector.select(tileset).forEach((layer) {
-        themeLayer.selector.layerSelector
-            .features(layer.features)
-            .forEach((feature) {
-          feature.decodeGeometry();
-        });
-      });
-    });
-    return Tileset._preprocessed(tileset);
+    final featureResolver = tileset.resolver is CachingThemeLayerFeatureResolver
+        ? tileset.resolver
+        : CachingThemeLayerFeatureResolver(tileset.resolver);
+
+    for (final themeLayer in theme.layers.whereType<DefaultLayer>()) {
+      for (final feature
+          in featureResolver.resolveFeatures(themeLayer.selector)) {
+        feature.feature.decodeGeometry();
+      }
+    }
+
+    return Tileset._preprocessed(tileset, featureResolver);
   }
 }

lib/vector_tile_renderer.dart

@@ -9,5 +9,5 @@ export 'src/renderer.dart';
 export 'src/themes/provided_themes.dart';
 export 'src/themes/theme.dart';
 export 'src/themes/theme_reader.dart';
-export 'src/tileset.dart';
+export 'src/tileset.dart' hide InternalTileset;
 export 'src/vector_tile_reader.dart';

pubspec.lock

@@ -29,6 +29,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "2.7.0"
+  benchmark_harness:
+    dependency: "direct dev"
+    description:
+      name: benchmark_harness
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "2.0.0"
   boolean_selector:
     dependency: transitive
     description:

pubspec.yaml

@@ -13,4 +13,5 @@ dependencies:
   vector_tile: ^0.3.0
 
 dev_dependencies:
+  benchmark_harness: ^2.0.0
   test: ^1.17.5

test/benchmark/rendering_test.dart

@@ -0,0 +1,89 @@
+import 'dart:ui';
+
+import 'package:benchmark_harness/benchmark_harness.dart';
+import 'package:vector_tile_renderer/src/constants.dart';
+import 'package:vector_tile_renderer/src/themes/light_theme.dart';
+import 'package:vector_tile_renderer/vector_tile_renderer.dart';
+
+import '../src/test_tile.dart';
+
+Picture _renderPicture({
+  required Theme theme,
+  required double scale,
+  required Tileset tileset,
+  required double zoom,
+}) {
+  assert(scale >= 1 && scale <= 4);
+
+  double size = scale * tileSize;
+  final rect = Rect.fromLTRB(0, 0, size, size);
+
+  final recorder = PictureRecorder();
+  final canvas = Canvas(recorder, rect);
+  canvas.clipRect(rect);
+  canvas.scale(scale.toDouble(), scale.toDouble());
+
+  Renderer(theme: theme).render(
+    canvas,
+    tileset,
+    zoomScaleFactor: scale,
+    zoom: zoom,
+  );
+
+  return recorder.endRecording();
+}
+
+class RenderPicture extends BenchmarkBase {
+  RenderPicture({
+    required this.zoom,
+    required this.preprocessTile,
+  }) : super('RenderPicture('
+            'zoom: $zoom, '
+            'preprocessTile: $preprocessTile'
+            ')');
+
+  static Future<void> setupAll() async {
+    testTile = await readTestTile();
+  }
+
+  static late final VectorTile testTile;
+
+  final double zoom;
+  final bool preprocessTile;
+
+  late final Theme theme;
+  late final Tileset tileset;
+
+  @override
+  void setup() {
+    theme = ThemeReader().read(lightThemeData());
+    final tileset = Tileset({'openmaptiles': testTile});
+
+    this.tileset = preprocessTile
+        ? TilesetPreprocessor(theme).preprocess(tileset)
+        : tileset;
+  }
+
+  @override
+  void run() => _renderPicture(
+        theme: theme,
+        tileset: tileset,
+        scale: 1,
+        zoom: zoom,
+      );
+}
+
+Future<void> main() async {
+  await RenderPicture.setupAll();
+
+  final benchmarks = [
+    for (final zoom in <double>[0, 12, 24]) ...[
+      RenderPicture(zoom: zoom, preprocessTile: false),
+      RenderPicture(zoom: zoom, preprocessTile: true),
+    ]
+  ];
+
+  for (final benchmark in benchmarks) {
+    benchmark.report();
+  }
+}