Feature: [Linkgraph] Prioritize faster routes for passengers, mail and express cargo

Passengers usually prefer fast paths to short paths.
Average travel times of links are updated in real-time for use in Dijkstra's algorithm,
and newer travel times weigh more, just like capacities.

9 files changed, 71 insertions, 24 deletions

diff --git a/src/linkgraph/linkgraph.cpp b/src/linkgraph/linkgraph.cpp
index 93af907fc..4c300b0d5 100644
--- a/src/linkgraph/linkgraph.cpp
+++ b/src/linkgraph/linkgraph.cpp
@@ -39,6 +39,7 @@ inline void LinkGraph::BaseEdge::Init()
 {
 	this->capacity = 0;
 	this->usage = 0;
+	this->travel_time_sum = 0;
 	this->last_unrestricted_update = INVALID_DATE;
 	this->last_restricted_update = INVALID_DATE;
 	this->next_edge = INVALID_NODE;
@@ -73,6 +74,7 @@ void LinkGraph::Compress()
 			if (edge.capacity > 0) {
 				edge.capacity = std::max(1U, edge.capacity / 2);
 				edge.usage /= 2;
+				edge.travel_time_sum = std::max(1ULL, edge.travel_time_sum / 2);
 			}
 		}
 	}
@@ -100,9 +102,11 @@ void LinkGraph::Merge(LinkGraph *other)
 			backward = other->edges[node2][node1];
 			forward.capacity = LinkGraph::Scale(forward.capacity, age, other_age);
 			forward.usage = LinkGraph::Scale(forward.usage, age, other_age);
+			forward.travel_time_sum = LinkGraph::Scale(forward.travel_time_sum, age, other_age);
 			if (forward.next_edge != INVALID_NODE) forward.next_edge += first;
 			backward.capacity = LinkGraph::Scale(backward.capacity, age, other_age);
 			backward.usage = LinkGraph::Scale(backward.usage, age, other_age);
+			backward.travel_time_sum = LinkGraph::Scale(backward.travel_time_sum, age, other_age);
 			if (backward.next_edge != INVALID_NODE) backward.next_edge += first;
 		}
 		BaseEdge &new_start = this->edges[new_node][new_node];
@@ -188,13 +192,14 @@ NodeID LinkGraph::AddNode(const Station *st)
  * @param usage Usage to be added.
  * @param mode Update mode to be used.
  */
-void LinkGraph::Node::AddEdge(NodeID to, uint capacity, uint usage, EdgeUpdateMode mode)
+void LinkGraph::Node::AddEdge(NodeID to, uint capacity, uint usage, uint32 travel_time, EdgeUpdateMode mode)
 {
 	assert(this->index != to);
 	BaseEdge &edge = this->edges[to];
 	BaseEdge &first = this->edges[this->index];
 	edge.capacity = capacity;
 	edge.usage = usage;
+	edge.travel_time_sum = travel_time * capacity;
 	edge.next_edge = first.next_edge;
 	first.next_edge = to;
 	if (mode & EUM_UNRESTRICTED)  edge.last_unrestricted_update = _date;
@@ -208,14 +213,14 @@ void LinkGraph::Node::AddEdge(NodeID to, uint capacity, uint usage, EdgeUpdateMo
  * @param usage Usage to be added.
  * @param mode Update mode to be used.
  */
-void LinkGraph::Node::UpdateEdge(NodeID to, uint capacity, uint usage, EdgeUpdateMode mode)
+void LinkGraph::Node::UpdateEdge(NodeID to, uint capacity, uint usage, uint32 travel_time, EdgeUpdateMode mode)
 {
 	assert(capacity > 0);
 	assert(usage <= capacity);
 	if (this->edges[to].capacity == 0) {
-		this->AddEdge(to, capacity, usage, mode);
+		this->AddEdge(to, capacity, usage, travel_time, mode);
 	} else {
-		(*this)[to].Update(capacity, usage, mode);
+		(*this)[to].Update(capacity, usage, travel_time, mode);
 	}
 }
 
@@ -231,6 +236,7 @@ void LinkGraph::Node::RemoveEdge(NodeID to)
 	edge.last_unrestricted_update = INVALID_DATE;
 	edge.last_restricted_update = INVALID_DATE;
 	edge.usage = 0;
+	edge.travel_time_sum = 0;
 
 	NodeID prev = this->index;
 	NodeID next = this->edges[this->index].next_edge;
@@ -249,23 +255,39 @@ void LinkGraph::Node::RemoveEdge(NodeID to)
 
 /**
  * Update an edge. If mode contains UM_REFRESH refresh the edge to have at
- * least the given capacity and usage, otherwise add the capacity and usage.
+ * least the given capacity and usage, otherwise add the capacity, usage and travel time.
  * In any case set the respective update timestamp(s), according to the given
  * mode.
  * @param capacity Capacity to be added/updated.
  * @param usage Usage to be added.
+ * @param travel_time Travel time to be added, in ticks.
  * @param mode Update mode to be applied.
  */
-void LinkGraph::Edge::Update(uint capacity, uint usage, EdgeUpdateMode mode)
+void LinkGraph::Edge::Update(uint capacity, uint usage, uint32 travel_time, EdgeUpdateMode mode)
 {
 	assert(this->edge.capacity > 0);
 	assert(capacity >= usage);
 
 	if (mode & EUM_INCREASE) {
+		if (this->edge.travel_time_sum == 0) {
+			this->edge.travel_time_sum = (this->edge.capacity + capacity) * travel_time;
+		} else if (travel_time == 0) {
+			this->edge.travel_time_sum += this->edge.travel_time_sum / this->edge.capacity * capacity;
+		} else {
+			this->edge.travel_time_sum += travel_time * capacity;
+		}
 		this->edge.capacity += capacity;
 		this->edge.usage += usage;
 	} else if (mode & EUM_REFRESH) {
-		this->edge.capacity = std::max(this->edge.capacity, capacity);
+		/* If travel time is not provided, we scale the stored time based on
+		 * the capacity increase. */
+		if (capacity > this->edge.capacity && travel_time == 0) {
+			this->edge.travel_time_sum = this->edge.travel_time_sum / this->edge.capacity * capacity;
+			this->edge.capacity = capacity;
+		} else {
+			this->edge.capacity = std::max(this->edge.capacity, capacity);
+			this->edge.travel_time_sum = std::max<uint64>(this->edge.travel_time_sum, travel_time * capacity);
+		}
 		this->edge.usage = std::max(this->edge.usage, usage);
 	}
 	if (mode & EUM_UNRESTRICTED) this->edge.last_unrestricted_update = _date;
diff --git a/src/linkgraph/linkgraph.h b/src/linkgraph/linkgraph.h
index a11b67a52..3a2c37977 100644
--- a/src/linkgraph/linkgraph.h
+++ b/src/linkgraph/linkgraph.h
@@ -62,6 +62,7 @@ public:
 	struct BaseEdge {
 		uint capacity;                 ///< Capacity of the link.
 		uint usage;                    ///< Usage of the link.
+		uint64 travel_time_sum;        ///< Sum of the travel times of the link, in ticks.
 		Date last_unrestricted_update; ///< When the unrestricted part of the link was last updated.
 		Date last_restricted_update;   ///< When the restricted part of the link was last updated.
 		NodeID next_edge;              ///< Destination of next valid edge starting at the same source node.
@@ -98,6 +99,12 @@ public:
 		uint Usage() const { return this->edge.usage; }
 
 		/**
+		 * Get edge's average travel time.
+		 * @return Travel time, in ticks.
+		 */
+		uint32 TravelTime() const { return this->edge.travel_time_sum / this->edge.capacity; }
+
+		/**
 		 * Get the date of the last update to the edge's unrestricted capacity.
 		 * @return Last update.
 		 */
@@ -296,7 +303,7 @@ public:
 		 * @param edge Edge to be wrapped.
 		 */
 		Edge(BaseEdge &edge) : EdgeWrapper<BaseEdge>(edge) {}
-		void Update(uint capacity, uint usage, EdgeUpdateMode mode);
+		void Update(uint capacity, uint usage, uint32 time, EdgeUpdateMode mode);
 		void Restrict() { this->edge.last_unrestricted_update = INVALID_DATE; }
 		void Release() { this->edge.last_restricted_update = INVALID_DATE; }
 	};
@@ -429,8 +436,8 @@ public:
 			this->node.demand = demand;
 		}
 
-		void AddEdge(NodeID to, uint capacity, uint usage, EdgeUpdateMode mode);
-		void UpdateEdge(NodeID to, uint capacity, uint usage, EdgeUpdateMode mode);
+		void AddEdge(NodeID to, uint capacity, uint usage, uint32 time, EdgeUpdateMode mode);
+		void UpdateEdge(NodeID to, uint capacity, uint usage, uint32 time, EdgeUpdateMode mode);
 		void RemoveEdge(NodeID to);
 	};
 
diff --git a/src/linkgraph/mcf.cpp b/src/linkgraph/mcf.cpp
index f24a8e028..8cd73cb91 100644
--- a/src/linkgraph/mcf.cpp
+++ b/src/linkgraph/mcf.cpp
@@ -284,12 +284,21 @@ void MultiCommodityFlow::Dijkstra(NodeID source_node, PathVector &paths)
 				capacity /= 100;
 				if (capacity == 0) capacity = 1;
 			}
-			/* punish in-between stops a little */
+			/* Prioritize the fastest route for passengers, mail and express cargo,
+			 * and the shortest route for other classes of cargo.
+			 * In-between stops are punished with a 1 tile or 1 day penalty. */
+			bool express = IsCargoInClass(this->job.Cargo(), CC_PASSENGERS) ||
+				IsCargoInClass(this->job.Cargo(), CC_MAIL) ||
+				IsCargoInClass(this->job.Cargo(), CC_EXPRESS);
 			uint distance = DistanceMaxPlusManhattan(this->job[from].XY(), this->job[to].XY()) + 1;
+			/* Compute a default travel time from the distance and an average speed of 1 tile/day. */
+			uint time = (edge.TravelTime() != 0) ? edge.TravelTime() + DAY_TICKS : distance * DAY_TICKS;
+			uint distance_anno = express ? time : distance;
+
 			Tannotation *dest = static_cast<Tannotation *>(paths[to]);
-			if (dest->IsBetter(source, capacity, capacity - edge.Flow(), distance)) {
+			if (dest->IsBetter(source, capacity, capacity - edge.Flow(), distance_anno)) {
 				annos.erase(dest);
-				dest->Fork(source, capacity, capacity - edge.Flow(), distance);
+				dest->Fork(source, capacity, capacity - edge.Flow(), distance_anno);
 				dest->UpdateAnnotation();
 				annos.insert(dest);
 			}
diff --git a/src/linkgraph/refresh.cpp b/src/linkgraph/refresh.cpp
index 430e29072..78fdd1643 100644
--- a/src/linkgraph/refresh.cpp
+++ b/src/linkgraph/refresh.cpp
@@ -218,6 +218,12 @@ void LinkRefresher::RefreshStats(const Order *cur, const Order *next)
 			/* A link is at least partly restricted if a vehicle can't load at its source. */
 			EdgeUpdateMode restricted_mode = (cur->GetLoadType() & OLFB_NO_LOAD) == 0 ?
 						EUM_UNRESTRICTED : EUM_RESTRICTED;
+			Station *st_to = Station::GetIfValid(next_station);
+			/* This estimates the travel time of the link as the time needed
+			 * to travel between the stations at half the max speed of the consist.
+			 * The result is in tiles/tick (= 2048 km-ish/h). */
+			uint32 time_estimate = (st_to != nullptr) ?
+				DistanceManhattan(st->xy, st_to->xy) * 4096U / this->vehicle->GetDisplayMaxSpeed() : 0;
 
 			/* If the vehicle is currently full loading, increase the capacities at the station
 			 * where it is loading by an estimate of what it would have transported if it wasn't
@@ -231,15 +237,15 @@ void LinkRefresher::RefreshStats(const Order *cur, const Order *next)
 				uint effective_capacity = cargo_quantity * this->vehicle->load_unload_ticks;
 				if (effective_capacity > (uint)this->vehicle->orders.list->GetTotalDuration()) {
 					IncreaseStats(st, c, next_station, effective_capacity /
-							this->vehicle->orders.list->GetTotalDuration(), 0,
+							this->vehicle->orders.list->GetTotalDuration(), 0, 0,
 							EUM_INCREASE | restricted_mode);
 				} else if (RandomRange(this->vehicle->orders.list->GetTotalDuration()) < effective_capacity) {
-					IncreaseStats(st, c, next_station, 1, 0, EUM_INCREASE | restricted_mode);
+					IncreaseStats(st, c, next_station, 1, 0, 0, EUM_INCREASE | restricted_mode);
 				} else {
-					IncreaseStats(st, c, next_station, cargo_quantity, 0, EUM_REFRESH | restricted_mode);
+					IncreaseStats(st, c, next_station, cargo_quantity, 0, time_estimate, EUM_REFRESH | restricted_mode);
 				}
 			} else {
-				IncreaseStats(st, c, next_station, cargo_quantity, 0, EUM_REFRESH | restricted_mode);
+				IncreaseStats(st, c, next_station, cargo_quantity, 0, time_estimate, EUM_REFRESH | restricted_mode);
 			}
 		}
 	}
diff --git a/src/saveload/linkgraph_sl.cpp b/src/saveload/linkgraph_sl.cpp
index ae21de4c7..9ff7e130a 100644
--- a/src/saveload/linkgraph_sl.cpp
+++ b/src/saveload/linkgraph_sl.cpp
@@ -33,6 +33,7 @@ public:
 	inline static const SaveLoad description[] = {
 		    SLE_VAR(Edge, capacity,                 SLE_UINT32),
 		    SLE_VAR(Edge, usage,                    SLE_UINT32),
+		SLE_CONDVAR(Edge, travel_time_sum,          SLE_UINT64, SLV_LINKGRAPH_TRAVEL_TIME, SL_MAX_VERSION),
 		    SLE_VAR(Edge, last_unrestricted_update, SLE_INT32),
 		SLE_CONDVAR(Edge, last_restricted_update,   SLE_INT32, SLV_187, SL_MAX_VERSION),
 		    SLE_VAR(Edge, next_edge,                SLE_UINT16),
diff --git a/src/saveload/saveload.h b/src/saveload/saveload.h
index 3047cbfd8..ad8b368c8 100644
--- a/src/saveload/saveload.h
+++ b/src/saveload/saveload.h
@@ -337,6 +337,7 @@ enum SaveLoadVersion : uint16 {
 
 	SLV_TABLE_CHUNKS,                       ///< 295  PR#9322 Introduction of CH_TABLE and CH_SPARSE_TABLE.
 	SLV_SCRIPT_INT64,                       ///< 296  PR#9415 SQInteger is 64bit but was saved as 32bit.
+	SLV_LINKGRAPH_TRAVEL_TIME,              ///< 297  PR#9457 Store travel time in the linkgraph.
 
 	SL_MAX_VERSION,                         ///< Highest possible saveload version
 };
diff --git a/src/station_cmd.cpp b/src/station_cmd.cpp
index 6a5cabc8d..05e837287 100644
--- a/src/station_cmd.cpp
+++ b/src/station_cmd.cpp
@@ -3737,7 +3737,7 @@ void DeleteStaleLinks(Station *from)
  * @param usage Usage to add to link stat.
  * @param mode Update mode to be applied.
  */
-void IncreaseStats(Station *st, CargoID cargo, StationID next_station_id, uint capacity, uint usage, EdgeUpdateMode mode)
+void IncreaseStats(Station *st, CargoID cargo, StationID next_station_id, uint capacity, uint usage, uint32 time, EdgeUpdateMode mode)
 {
 	GoodsEntry &ge1 = st->goods[cargo];
 	Station *st2 = Station::Get(next_station_id);
@@ -3779,7 +3779,7 @@ void IncreaseStats(Station *st, CargoID cargo, StationID next_station_id, uint c
 		}
 	}
 	if (lg != nullptr) {
-		(*lg)[ge1.node].UpdateEdge(ge2.node, capacity, usage, mode);
+		(*lg)[ge1.node].UpdateEdge(ge2.node, capacity, usage, time, mode);
 	}
 }
 
@@ -3789,7 +3789,7 @@ void IncreaseStats(Station *st, CargoID cargo, StationID next_station_id, uint c
  * @param front First vehicle in the consist.
  * @param next_station_id Station the consist will be travelling to next.
  */
-void IncreaseStats(Station *st, const Vehicle *front, StationID next_station_id)
+void IncreaseStats(Station *st, const Vehicle *front, StationID next_station_id, uint32 time)
 {
 	for (const Vehicle *v = front; v != nullptr; v = v->Next()) {
 		if (v->refit_cap > 0) {
@@ -3800,7 +3800,7 @@ void IncreaseStats(Station *st, const Vehicle *front, StationID next_station_id)
 			 * As usage is not such an important figure anyway we just
 			 * ignore the additional cargo then.*/
 			IncreaseStats(st, v->cargo_type, next_station_id, v->refit_cap,
-					std::min<uint>(v->refit_cap, v->cargo.StoredCount()), EUM_INCREASE);
+					std::min<uint>(v->refit_cap, v->cargo.StoredCount()), time, EUM_INCREASE);
 		}
 	}
 }
diff --git a/src/station_func.h b/src/station_func.h
index dc8942841..65b9ac5e6 100644
--- a/src/station_func.h
+++ b/src/station_func.h
@@ -52,8 +52,8 @@ void UpdateAirportsNoise();
 
 bool SplitGroundSpriteForOverlay(const TileInfo *ti, SpriteID *ground, RailTrackOffset *overlay_offset);
 
-void IncreaseStats(Station *st, const Vehicle *v, StationID next_station_id);
-void IncreaseStats(Station *st, CargoID cargo, StationID next_station_id, uint capacity, uint usage, EdgeUpdateMode mode);
+void IncreaseStats(Station *st, const Vehicle *v, StationID next_station_id, uint32 time);
+void IncreaseStats(Station *st, CargoID cargo, StationID next_station_id, uint capacity, uint usage, uint32 time, EdgeUpdateMode mode);
 void RerouteCargo(Station *st, CargoID c, StationID avoid, StationID avoid2);
 
 /**
diff --git a/src/vehicle.cpp b/src/vehicle.cpp
index 955f9bde0..6df16caf6 100644
--- a/src/vehicle.cpp
+++ b/src/vehicle.cpp
@@ -2100,6 +2100,7 @@ void Vehicle::BeginLoading()
 {
 	assert(IsTileType(this->tile, MP_STATION) || this->type == VEH_SHIP);
 
+	uint32 travel_time = this->current_order_time;
 	if (this->current_order.IsType(OT_GOTO_STATION) &&
 			this->current_order.GetDestination() == this->last_station_visited) {
 		this->DeleteUnreachedImplicitOrders();
@@ -2206,7 +2207,7 @@ void Vehicle::BeginLoading()
 			this->last_loading_station != this->last_station_visited &&
 			((this->current_order.GetLoadType() & OLFB_NO_LOAD) == 0 ||
 			(this->current_order.GetUnloadType() & OUFB_NO_UNLOAD) == 0)) {
-		IncreaseStats(Station::Get(this->last_loading_station), this, this->last_station_visited);
+		IncreaseStats(Station::Get(this->last_loading_station), this, this->last_station_visited, travel_time);
 	}
 
 	PrepareUnload(this);