3 files changed, 97 insertions, 0 deletions
diff --git a/src/core-files.json b/src/core-files.json
index f4f2dd2c40..4867bd3dc4 100644
--- a/src/core-files.json
+++ b/src/core-files.json
@@ -134,6 +134,7 @@
         "src/mbgl/renderer/renderer.cpp",
         "src/mbgl/renderer/renderer_impl.cpp",
         "src/mbgl/renderer/renderer_state.cpp",
+        "src/mbgl/renderer/source_state.cpp",
         "src/mbgl/renderer/sources/render_custom_geometry_source.cpp",
         "src/mbgl/renderer/sources/render_geojson_source.cpp",
         "src/mbgl/renderer/sources/render_image_source.cpp",
@@ -656,6 +657,7 @@
         "mbgl/renderer/render_tile.hpp": "src/mbgl/renderer/render_tile.hpp",
         "mbgl/renderer/render_tree.hpp": "src/mbgl/renderer/render_tree.hpp",
         "mbgl/renderer/renderer_impl.hpp": "src/mbgl/renderer/renderer_impl.hpp",
+        "mbgl/renderer/source_state.hpp": "src/mbgl/renderer/source_state.hpp",
         "mbgl/renderer/sources/render_custom_geometry_source.hpp": "src/mbgl/renderer/sources/render_custom_geometry_source.hpp",
         "mbgl/renderer/sources/render_geojson_source.hpp": "src/mbgl/renderer/sources/render_geojson_source.hpp",
         "mbgl/renderer/sources/render_image_source.hpp": "src/mbgl/renderer/sources/render_image_source.hpp",
diff --git a/src/mbgl/renderer/source_state.cpp b/src/mbgl/renderer/source_state.cpp
new file mode 100644
index 0000000000..087e28b2bb
--- /dev/null
+++ b/src/mbgl/renderer/source_state.cpp
@@ -0,0 +1,69 @@
+#include <mbgl/renderer/source_state.hpp>
+#include <mbgl/style/conversion_impl.hpp>
+#include <mbgl/renderer/render_tile.hpp>
+#include <mbgl/util/logging.hpp>
+
+namespace mbgl {
+
+void SourceFeatureState::updateState(const optional<std::string>& sourceLayerID, const std::string& featureID, const FeatureState& newState) {
+    std::string sourceLayer = sourceLayerID.value_or(std::string());
+    for (const auto& state : newState) {
+        auto& layerStates = stateChanges[sourceLayer];
+        auto& featureStates = layerStates[featureID];
+        featureStates[state.first] = state.second;
+    }
+}
+
+void SourceFeatureState::getState(FeatureState& result, const optional<std::string>& sourceLayerID, const std::string& featureID) const {
+    std::string sourceLayer = sourceLayerID.value_or(std::string());
+    FeatureState current, changes;
+    auto layerStates = currentStates.find(sourceLayer);
+    if (layerStates != currentStates.end()) {
+        const auto currentStateEntry = layerStates->second.find(featureID);
+        if (currentStateEntry != layerStates->second.end()) {
+            current = currentStateEntry->second;
+        }
+    }
+
+    layerStates = stateChanges.find(sourceLayer);
+    if (layerStates != stateChanges.end()) {
+        const auto stateChangesEntry = layerStates->second.find(featureID);
+        if (stateChangesEntry != layerStates->second.end()) {
+            changes = stateChangesEntry->second;
+        }
+    }
+    result = std::move(changes);
+    result.insert(current.begin(), current.end());
+}
+
+void SourceFeatureState::coalesceChanges(std::vector<RenderTile>& tiles) {
+    LayerFeatureStates changes;
+    for (const auto& layerStatesEntry : stateChanges) {
+        const auto& sourceLayer = layerStatesEntry.first;
+        FeatureStates layerStates;
+        for (const auto& featureStatesEntry : stateChanges[sourceLayer]) {
+            const auto& featureID = featureStatesEntry.first;
+            for (const auto& stateEntry : stateChanges[sourceLayer][featureID]) {
+                const auto& stateKey = stateEntry.first;
+                const auto& stateVal = stateEntry.second;
+
+                auto currentState = currentStates[sourceLayer][featureID].find(stateKey);
+                if (currentState != currentStates[sourceLayer][featureID].end()) {
+                    currentState->second = stateVal;
+                } else {
+                    currentStates[sourceLayer][featureID].insert(std::make_pair(stateKey, stateVal));
+                }
+            }
+            layerStates[featureID] = currentStates[sourceLayer][featureID];
+        }
+        changes[sourceLayer] = std::move(layerStates);
+    }
+    stateChanges.clear();
+    if (changes.empty()) return;
+
+    for (auto& tile : tiles) {
+        tile.setFeatureState(changes);
+    }
+}
+
+} // namespace mbgl
diff --git a/src/mbgl/renderer/source_state.hpp b/src/mbgl/renderer/source_state.hpp
new file mode 100644
index 0000000000..9944709b0d
--- /dev/null
+++ b/src/mbgl/renderer/source_state.hpp
@@ -0,0 +1,26 @@
+#pragma once
+
+#include <mbgl/style/conversion.hpp>
+#include <mbgl/util/feature.hpp>
+
+namespace mbgl {
+
+class RenderTile;
+using namespace style::conversion;
+
+class SourceFeatureState {
+public:
+    SourceFeatureState() = default;
+    ~SourceFeatureState() = default;
+
+    void updateState(const optional<std::string>& sourceLayerID, const std::string& featureID, const FeatureState& newState);
+    void getState(FeatureState& result, const optional<std::string>& sourceLayerID, const std::string& featureID) const;
+
+    void coalesceChanges(std::vector<RenderTile>& tiles);
+
+private:
+    LayerFeatureStates currentStates;
+    LayerFeatureStates stateChanges;
+};
+
+} // namespace mbgl