Cache grouped sparse buffers (#15594)

continuation of #15531

src/client/clientmap.h

@@ -36,6 +36,16 @@ namespace irr::video
 	class IVideoDriver;
 }
 
+struct CachedMeshBuffer {
+	std::vector<scene::IMeshBuffer*> buf;
+	u8 age = 0;
+
+	void drop();
+};
+
+using CachedMeshBuffers = std::unordered_map<std::string, CachedMeshBuffer>;
+
+
 /*
 	ClientMap
 
@@ -95,6 +105,8 @@ public:
 
 	void renderPostFx(CameraMode cam_mode);
 
+	void invalidateMapBlockMesh(MapBlockMesh *mesh);
+
 	// For debug printing
 	void PrintInfo(std::ostream &out) override;
 
@@ -151,6 +163,7 @@ private:
 	std::vector<MapBlock*> m_keeplist;
 	std::map<v3s16, MapBlock*> m_drawlist_shadow;
 	bool m_needs_update_drawlist;
+	CachedMeshBuffers m_dynamic_buffers;
 
 	bool m_cache_trilinear_filter;
 	bool m_cache_bilinear_filter;