[core] Prepare Filter and FilterEvaluator for extraction (#5366)

8 files changed, 74 insertions, 98 deletions

diff --git a/benchmark/parse/filter.cpp b/benchmark/parse/filter.cpp
index 7450fc7804..8beff3b308 100644
--- a/benchmark/parse/filter.cpp
+++ b/benchmark/parse/filter.cpp
@@ -13,32 +13,6 @@ using namespace mbgl;
 
 typedef std::multimap<std::string, Value> Properties;
 
-class StubFeature : public GeometryTileFeature {
-public:
-    inline StubFeature(const Properties& properties_, FeatureType type_)
-        : properties(properties_), type(type_) {
-    }
-
-    optional<Value> getValue(const std::string& key) const override {
-        auto it = properties.find(key);
-        if (it == properties.end())
-            return optional<Value>();
-        return it->second;
-    }
-
-    FeatureType getType() const override {
-        return type;
-    }
-
-    GeometryCollection getGeometries() const override {
-        return GeometryCollection();
-    }
-
-private:
-    const Properties properties;
-    FeatureType type;
-};
-
 style::Filter parse(const char* expression) {
     rapidjson::GenericDocument<rapidjson::UTF8<>, rapidjson::CrtAllocator> doc;
     doc.Parse<0>(expression);
@@ -54,10 +28,14 @@ static void Parse_Filter(benchmark::State& state) {
 static void Parse_EvaluateFilter(benchmark::State& state) {
     const style::Filter filter = parse(R"FILTER(["==", "foo", "bar"])FILTER");
     const Properties properties = { { "foo", std::string("bar") } };
-    const StubFeature feature(properties, FeatureType::Unknown);
 
     while (state.KeepRunning()) {
-        style::Filter::visit(filter, style::FilterEvaluator{ feature });
+        filter(FeatureType::Unknown, [&] (const std::string& key) -> optional<Value> {
+            auto it = properties.find(key);
+            if (it == properties.end())
+                return {};
+            return it->second;
+        });
     }
 }
 
diff --git a/include/mbgl/style/filter.hpp b/include/mbgl/style/filter.hpp
index 9cf84f5e1d..6a5afb7b47 100644
--- a/include/mbgl/style/filter.hpp
+++ b/include/mbgl/style/filter.hpp
@@ -2,6 +2,7 @@
 
 #include <mbgl/util/variant.hpp>
 #include <mbgl/util/feature.hpp>
+#include <mbgl/util/geometry.hpp>
 
 #include <string>
 #include <vector>
@@ -9,22 +10,7 @@
 namespace mbgl {
 namespace style {
 
-typedef variant<
-    class NullFilter,
-    class EqualsFilter,
-    class NotEqualsFilter,
-    class LessThanFilter,
-    class LessThanEqualsFilter,
-    class GreaterThanFilter,
-    class GreaterThanEqualsFilter,
-    class InFilter,
-    class NotInFilter,
-    class AnyFilter,
-    class AllFilter,
-    class NoneFilter,
-    class HasFilter,
-    class NotHasFilter
-    > Filter;
+class Filter;
 
 class NullFilter {};
 
@@ -101,5 +87,29 @@ public:
     std::string key;
 };
 
+using FilterBase = variant<
+    class NullFilter,
+    class EqualsFilter,
+    class NotEqualsFilter,
+    class LessThanFilter,
+    class LessThanEqualsFilter,
+    class GreaterThanFilter,
+    class GreaterThanEqualsFilter,
+    class InFilter,
+    class NotInFilter,
+    class AnyFilter,
+    class AllFilter,
+    class NoneFilter,
+    class HasFilter,
+    class NotHasFilter>;
+
+class Filter : public FilterBase {
+public:
+    using FilterBase::FilterBase;
+
+    template <class PropertyAccessor>
+    bool operator()(FeatureType type, PropertyAccessor accessor) const;
+};
+
 } // namespace style
 } // namespace mbgl
diff --git a/src/mbgl/style/filter_evaluator.hpp b/include/mbgl/style/filter_evaluator.hpp
index 9d5919ced1..a458a2807b 100644
--- a/src/mbgl/style/filter_evaluator.hpp
+++ b/include/mbgl/style/filter_evaluator.hpp
@@ -1,17 +1,32 @@
 #pragma once
 
 #include <mbgl/style/filter.hpp>
-#include <mbgl/tile/geometry_tile_data.hpp>
+#include <mbgl/util/geometry.hpp>
 
 #include <type_traits>
 
 namespace mbgl {
 namespace style {
 
+/*
+   A visitor that evaluates a `Filter` for a given feature type and properties. For maximum
+   flexibility, it is templated on the PropertyAccessor type, which must be a callable type with
+   function signature `optional<Value> (const std::string&)`, returning the value for the given
+   key, if it exists.
+
+   Use via `Filter::operator()`. For example:
+
+       if (filter(feature.getType(), [&] (const std::string& key) { return feature.getValue(key); })) {
+           // matches the filter
+       } else {
+           // does not match
+       }
+*/
+template <class PropertyAccessor>
 class FilterEvaluator {
 public:
-    FilterEvaluator(const GeometryTileFeature& feature_)
-        : feature(feature_) {}
+    const FeatureType featureType;
+    const PropertyAccessor propertyAccessor;
 
     bool operator()(const NullFilter&) const {
         return true;
@@ -107,10 +122,10 @@ public:
     }
 
 private:
-    optional<Value> getValue(const std::string& key) const {
-        return key == "$type"
-            ? optional<Value>(uint64_t(feature.getType()))
-            : feature.getValue(key);
+    optional<Value> getValue(const std::string& key_) const {
+        return key_ == "$type"
+            ? optional<Value>(uint64_t(featureType))
+            : propertyAccessor(key_);
     }
 
     template <class Op>
@@ -155,9 +170,12 @@ private:
     bool equal(const Value& lhs, const Value& rhs) const {
         return compare(lhs, rhs, [] (const auto& lhs_, const auto& rhs_) { return lhs_ == rhs_; });
     }
-
-    const GeometryTileFeature& feature;
 };
 
+template <class PropertyAccessor>
+inline bool Filter::operator()(FeatureType type, PropertyAccessor accessor) const {
+    return FilterBase::visit(*this, FilterEvaluator<PropertyAccessor> { type, accessor });
+}
+
 } // namespace style
 } // namespace mbgl
diff --git a/include/mbgl/util/geometry.hpp b/include/mbgl/util/geometry.hpp
index 6b9c332bf2..7fc2668c2c 100644
--- a/include/mbgl/util/geometry.hpp
+++ b/include/mbgl/util/geometry.hpp
@@ -5,6 +5,13 @@
 
 namespace mbgl {
 
+enum class FeatureType : uint8_t {
+    Unknown = 0,
+    Point = 1,
+    LineString = 2,
+    Polygon = 3
+};
+
 template <class T>
 using Point = mapbox::geometry::point<T>;
 
diff --git a/src/mbgl/renderer/symbol_bucket.cpp b/src/mbgl/renderer/symbol_bucket.cpp
index e34aedb47e..496745dda1 100644
--- a/src/mbgl/renderer/symbol_bucket.cpp
+++ b/src/mbgl/renderer/symbol_bucket.cpp
@@ -119,9 +119,7 @@ void SymbolBucket::parseFeatures(const GeometryTileLayer& layer, const Filter& f
     const GLsizei featureCount = static_cast<GLsizei>(layer.featureCount());
     for (GLsizei i = 0; i < featureCount; i++) {
         auto feature = layer.getFeature(i);
-
-        FilterEvaluator evaluator(*feature);
-        if (!Filter::visit(filter, evaluator))
+        if (!filter(feature->getType(), [&] (const auto& key) { return feature->getValue(key); }))
             continue;
 
         SymbolFeature ft;
diff --git a/src/mbgl/style/bucket_parameters.cpp b/src/mbgl/style/bucket_parameters.cpp
index 1a928dcecc..5bb08af873 100644
--- a/src/mbgl/style/bucket_parameters.cpp
+++ b/src/mbgl/style/bucket_parameters.cpp
@@ -10,11 +10,8 @@ void BucketParameters::eachFilteredFeature(const Filter& filter,
     auto name = layer.getName();
     for (std::size_t i = 0; !cancelled() && i < layer.featureCount(); i++) {
         auto feature = layer.getFeature(i);
-
-        FilterEvaluator evaluator(*feature);
-        if (!Filter::visit(filter, evaluator))
+        if (!filter(feature->getType(), [&] (const auto& key) { return feature->getValue(key); }))
             continue;
-
         function(*feature, i, name);
     }
 }
diff --git a/src/mbgl/tile/geometry_tile_data.hpp b/src/mbgl/tile/geometry_tile_data.hpp
index 753ba6b8a2..1dc22e0c55 100644
--- a/src/mbgl/tile/geometry_tile_data.hpp
+++ b/src/mbgl/tile/geometry_tile_data.hpp
@@ -17,13 +17,6 @@
 
 namespace mbgl {
 
-enum class FeatureType : uint8_t {
-    Unknown = 0,
-    Point = 1,
-    LineString = 2,
-    Polygon = 3
-};
-
 class CanonicalTileID;
 
 // Normalized vector tile coordinates.
diff --git a/test/style/filter.cpp b/test/style/filter.cpp
index d28ee4a357..4a1010445e 100644
--- a/test/style/filter.cpp
+++ b/test/style/filter.cpp
@@ -3,7 +3,6 @@
 #include <mbgl/style/filter.hpp>
 #include <mbgl/style/filter_evaluator.hpp>
 #include <mbgl/style/parser.hpp>
-#include <mbgl/tile/geometry_tile_data.hpp>
 
 #include <rapidjson/document.h>
 
@@ -14,33 +13,6 @@ using namespace mbgl::style;
 
 typedef std::multimap<std::string, mbgl::Value> Properties;
 
-class StubFeature : public GeometryTileFeature {
-public:
-    inline StubFeature(Properties properties_, FeatureType type_)
-        : properties(std::move(properties_))
-        , type(type_)
-    {}
-
-    optional<Value> getValue(const std::string &key) const override {
-        auto it = properties.find(key);
-        if (it == properties.end())
-            return optional<Value>();
-        return it->second;
-    }
-
-    FeatureType getType() const override {
-        return type;
-    }
-
-    GeometryCollection getGeometries() const override {
-        return GeometryCollection();
-    }
-
-private:
-    const Properties properties;
-    FeatureType type;
-};
-
 Filter parse(const char * expression) {
     rapidjson::GenericDocument<rapidjson::UTF8<>, rapidjson::CrtAllocator> doc;
     doc.Parse<0>(expression);
@@ -48,9 +20,12 @@ Filter parse(const char * expression) {
 }
 
 bool evaluate(const Filter& filter, const Properties& properties, FeatureType type = FeatureType::Unknown) {
-    StubFeature feature(properties, type);
-    FilterEvaluator evaluator(feature);
-    return Filter::visit(filter, evaluator);
+    return filter(type, [&] (const std::string& key) -> optional<Value> {
+        auto it = properties.find(key);
+        if (it == properties.end())
+            return {};
+        return it->second;
+    });
 }
 
 TEST(Filter, EqualsString) {