[core] Throttle tiles to redo symbol placement at most once every 300ms.

Fixes issue #8435 and prepares for pitch-scaling changes in issue #8967.

2 files changed, 14 insertions, 2 deletions

diff --git a/src/mbgl/tile/geometry_tile.cpp b/src/mbgl/tile/geometry_tile.cpp
index 3da429ddf6..8f14a9c8aa 100644
--- a/src/mbgl/tile/geometry_tile.cpp
+++ b/src/mbgl/tile/geometry_tile.cpp
@@ -18,6 +18,7 @@
 #include <mbgl/map/query.hpp>
 #include <mbgl/util/run_loop.hpp>
 #include <mbgl/style/filter_evaluator.hpp>
+#include <mbgl/util/chrono.hpp>
 #include <mbgl/util/logging.hpp>
 
 #include <iostream>
@@ -41,7 +42,8 @@ GeometryTile::GeometryTile(const OverscaledTileID& id_,
              obsolete,
              parameters.mode),
       glyphAtlas(glyphAtlas_),
-      spriteAtlas(spriteAtlas_) {
+      spriteAtlas(spriteAtlas_),
+      placementThrottler(Milliseconds(300), [this] { invokePlacement(); }) {
 }
 
 GeometryTile::~GeometryTile() {
@@ -85,7 +87,13 @@ void GeometryTile::setPlacementConfig(const PlacementConfig& desiredConfig) {
 
     ++correlationID;
     requestedConfig = desiredConfig;
-    worker.invoke(&GeometryTileWorker::setPlacementConfig, desiredConfig, correlationID);
+    placementThrottler.invoke();
+}
+
+void GeometryTile::invokePlacement() {
+    if (requestedConfig) {
+        worker.invoke(&GeometryTileWorker::setPlacementConfig, *requestedConfig, correlationID);
+    }
 }
 
 void GeometryTile::redoLayout() {
diff --git a/src/mbgl/tile/geometry_tile.hpp b/src/mbgl/tile/geometry_tile.hpp
index 7d275fc72c..6e4c29d723 100644
--- a/src/mbgl/tile/geometry_tile.hpp
+++ b/src/mbgl/tile/geometry_tile.hpp
@@ -6,6 +6,7 @@
 #include <mbgl/text/glyph_atlas.hpp>
 #include <mbgl/text/placement_config.hpp>
 #include <mbgl/util/feature.hpp>
+#include <mbgl/util/throttler.hpp>
 #include <mbgl/actor/actor.hpp>
 
 #include <atomic>
@@ -88,6 +89,7 @@ protected:
 
 private:
     void markObsolete();
+    void invokePlacement();
 
     const std::string sourceID;
     style::Style& style;
@@ -110,6 +112,8 @@ private:
 
     std::unordered_map<std::string, std::shared_ptr<Bucket>> symbolBuckets;
     std::unique_ptr<CollisionTile> collisionTile;
+    
+    util::Throttler placementThrottler;
 };
 
 } // namespace mbgl