[core] only render tiles that have data

src/mbgl/source/source.cpp

@@ -179,8 +179,9 @@ std::forward_list<Tile*> Source::getLoadedTiles() const {
     std::forward_list<Tile*> ptrs;
     auto it = ptrs.before_begin();
     for (const auto& pair : tiles) {
-        if (pair.second->data->isReady()) {
-            it = ptrs.insert_after(it, pair.second.get());
+        auto tile = pair.second.get();
+        if (tile->data->isReady() && tile->data->hasData()) {
+            it = ptrs.insert_after(it, tile);
         }
     }
     return ptrs;

src/mbgl/tile/raster_tile_data.cpp

@@ -81,3 +81,7 @@ void RasterTileData::cancel() {
     req = nullptr;
     workRequest.reset();
 }
+
+bool RasterTileData::hasData() const {
+    return bucket.get() != nullptr;
+}

src/mbgl/tile/raster_tile_data.hpp

@@ -24,6 +24,7 @@ public:
 
     void cancel() override;
     Bucket* getBucket(StyleLayer const &layer_desc) override;
+    bool hasData() const override;
 
 private:
     gl::TexturePool& texturePool;

src/mbgl/tile/tile_data.hpp

@@ -86,6 +86,9 @@ public:
         return isReadyState(state);
     }
 
+    // Returns true when there's at least some data that we can render.
+    virtual bool hasData() const = 0;
+
     State getState() const {
         return state;
     }

src/mbgl/tile/vector_tile_data.cpp

@@ -180,4 +180,8 @@ void VectorTileData::cancel() {
     workRequest.reset();
 }
 
+bool VectorTileData::hasData() const {
+    return !buckets.empty();
+}
+
 } // namespace mbgl

src/mbgl/tile/vector_tile_data.hpp

@@ -33,6 +33,8 @@ public:
     void redoPlacement(PlacementConfig config, const std::function<void()>&) override;
     void redoPlacement(const std::function<void()>&) override;
 
+    bool hasData() const override;
+
     void cancel() override;
 
 private: