Linkgraph overlay: Skip refresh if periodic cache rebuild has no changes

src/linkgraph/linkgraph_gui.cpp

@@ -106,6 +106,30 @@ void LinkGraphOverlay::MarkStationViewportLinksDirty(const Station *st)
 	}
 }
 
+/**
+ * Rebuild the cache using RebuildCache, and return whether a re-draw is required.
+ */
+bool LinkGraphOverlay::RebuildCacheCheckCahnged()
+{
+	static LinkList prev_cached_links;
+	static StationSupplyList prev_cached_stations;
+
+	uint64_t prev_rebuild_counter = this->rebuild_counter;
+
+	prev_cached_links.swap(this->cached_links);
+	prev_cached_stations.swap(this->cached_stations);
+
+	this->RebuildCache(false);
+
+	if (prev_cached_links == this->cached_links && prev_cached_stations == this->cached_stations) {
+		/* No change */
+		this->rebuild_counter = prev_rebuild_counter;
+		return false;
+	}
+
+	return true;
+}
+
 /**
  * Rebuild the cache and recalculate which links and stations to be shown.
  */

src/linkgraph/linkgraph_gui.h

@@ -34,6 +34,8 @@ struct LinkProperties {
 	CargoID cargo; ///< Cargo type of the link.
 	uint32_t time; ///< Travel time of the link.
 	bool shared;   ///< If this is a shared link to be drawn dashed.
+
+	bool operator==(const LinkProperties&) const = default;
 };
 
 /**
@@ -46,6 +48,8 @@ public:
 		StationID id;
 		uint quantity;
 		Point pt;
+
+		bool operator==(const StationSupplyInfo&) const = default;
 	};
 
 	struct LinkInfo {
@@ -54,6 +58,8 @@ public:
 		Point from_pt;
 		Point to_pt;
 		LinkProperties prop;
+
+		bool operator==(const LinkInfo&) const = default;
 	};
 
 	typedef std::vector<StationSupplyInfo> StationSupplyList;
@@ -73,6 +79,7 @@ public:
 			window(w), widget_id(wid), cargo_mask(cargo_mask), company_mask(company_mask), scale(scale), dirty(true)
 	{}
 
+	bool RebuildCacheCheckCahnged();
 	void RebuildCache(bool incremental = false);
 	bool CacheStillValid() const;
 	void MarkStationViewportLinksDirty(const Station *st);

src/main_gui.cpp

@@ -271,9 +271,10 @@ struct MainWindow : Window
 			return;
 		}
 
-		this->viewport->overlay->SetDirty();
+		if (this->viewport->overlay->RebuildCacheCheckCahnged()) {
 			this->GetWidget<NWidgetBase>(WID_M_VIEWPORT)->SetDirty(this);
 		}
+	}
 
 	void OnPaint() override
 	{