Pattern layout performance improvement (#3495)

src/mbgl/layout/pattern_layout.hpp

@@ -1,5 +1,4 @@
 #pragma once
-#include <list>
 #include <mbgl/geometry/feature_index.hpp>
 #include <mbgl/layout/layout.hpp>
 #include <mbgl/renderer/bucket_parameters.hpp>
@@ -18,25 +17,33 @@ public:
     std::string max;
 };
 
-using PatternLayerMap = std::map<std::string, PatternDependency>;
+using PatternLayerMap = mbgl::unordered_map<std::string, PatternDependency>;
 
 class PatternFeature {
 public:
     PatternFeature(std::size_t i_,
-                   std::unique_ptr<GeometryTileFeature> feature_,
-                   PatternLayerMap patterns_,
+                   std::unique_ptr<GeometryTileFeature>&& feature_,
+                   PatternLayerMap&& patterns_,
                    float sortKey_ = 0.0f)
         : i(i_),
           feature(std::move(feature_)),
-          patterns(std::move(patterns_)),
-          sortKey(sortKey_) {}
+          sortKey(sortKey_),
+          patterns(std::make_unique<PatternLayerMap>(std::move(patterns_))) {}
+    PatternFeature(const PatternFeature&) = delete;
+    PatternFeature(PatternFeature&&) = default;
+    PatternFeature& operator=(const PatternFeature&) = delete;
+    PatternFeature& operator=(PatternFeature&&) = default;
+
+    const PatternLayerMap& getPatterns() const { return *patterns; }
 
     friend bool operator<(const PatternFeature& lhs, const PatternFeature& rhs) { return lhs.sortKey < rhs.sortKey; }
 
     std::size_t i;
     std::unique_ptr<GeometryTileFeature> feature;
-    PatternLayerMap patterns;
     float sortKey;
+
+protected:
+    std::unique_ptr<PatternLayerMap> patterns;
 };
 
 template <typename SortKeyPropertyType>
@@ -182,7 +189,7 @@ public:
         for (auto& patternFeature : features) {
             const auto i = patternFeature.i;
             std::unique_ptr<GeometryTileFeature> feature = std::move(patternFeature.feature);
-            const PatternLayerMap& patterns = patternFeature.patterns;
+            const PatternLayerMap& patterns = patternFeature.getPatterns();
             const GeometryCollection& geometries = feature->getGeometries();
 
             bucket->addFeature(*feature, geometries, patternPositions, patterns, i, canonical);

src/mbgl/renderer/bucket.hpp

@@ -19,7 +19,7 @@ class RenderLayer;
 class CrossTileSymbolLayerIndex;
 class OverscaledTileID;
 class PatternDependency;
-using PatternLayerMap = std::map<std::string, PatternDependency>;
+using PatternLayerMap = mbgl::unordered_map<std::string, PatternDependency>;
 class Placement;
 class TransformState;
 class BucketPlacementData;