Maintain map of targeted road vehicles to small UFO disaster vehicle

src/disaster_vehicle.cpp

@@ -48,6 +48,7 @@
 #include "core/backup_type.hpp"
 #include "core/checksum_func.hpp"
 #include "event_logs.h"
+#include "3rdparty/cpp-btree/btree_map.h"
 
 #include "table/strings.h"
 
@@ -57,6 +58,7 @@
 uint16_t _disaster_delay;
 
 static uint32_t _disaster_vehicle_count = 0;
+static btree::btree_map<VehicleID, VehicleID> _disaster_ufo_target_map;
 
 static void DisasterClearSquare(TileIndex tile)
 {
@@ -369,6 +371,11 @@ static bool DisasterTick_Ufo(DisasterVehicle *v)
 		for (const RoadVehicle *u : RoadVehicle::Iterate()) {
 			/* Find (n+1)-th road vehicle. */
 			if (u->IsFrontEngine() && (n-- == 0)) {
+				if (u->crashed_ctr != 0 || !SetDisasterVehicleTargetingVehicle(u->index, v->index)) {
+					/* Targetted vehicle is crashed or already a target, destroy the UFO. */
+					delete v;
+					return false;
+				}
 				/* Target it. */
 				v->dest_tile = u->index;
 				v->age = 0;
@@ -1010,22 +1017,43 @@ void ReleaseDisastersTargetingIndustry(IndustryID i)
  * Notify disasters that we are about to delete a vehicle. So make them head elsewhere.
  * @param vehicle deleted vehicle
  */
-void ReleaseDisastersTargetingVehicle(VehicleID vehicle)
+void ReleaseDisasterVehicleTargetingVehicle(VehicleID vehicle)
 {
 	if (!_disaster_vehicle_count) return;
 
-	for (DisasterVehicle *v : DisasterVehicle::Iterate()) {
+	auto iter = _disaster_ufo_target_map.find(vehicle);
+	if (iter == _disaster_ufo_target_map.end()) return;
+
+	DisasterVehicle *v = DisasterVehicle::GetIfValid(iter->second);
+	_disaster_ufo_target_map.erase(iter);
+
+	if (v == nullptr) return;
+
 	/* primary disaster vehicles that have chosen target */
-		if (v->subtype == ST_SMALL_UFO) {
+	assert(v->subtype == ST_SMALL_UFO);
-			if (v->state != 0 && v->dest_tile == vehicle) {
+	assert(v->state != 0);
+
 	/* Revert to target-searching */
 	v->state = 0;
 	v->dest_tile = RandomTile();
 	GetAircraftFlightLevelBounds(v, &v->z_pos, nullptr);
 	v->age = 0;
 }
+
+void ResetDisasterVehicleTargeting()
+{
+	_disaster_ufo_target_map.clear();
 }
+
+bool SetDisasterVehicleTargetingVehicle(VehicleID vehicle, VehicleID disaster_vehicle)
+{
+	auto insert_result = _disaster_ufo_target_map.insert(std::make_pair(vehicle, disaster_vehicle));
+	if (!insert_result.second) {
+		/* Vehicle already has an associated disaster vehicle, return failure if that isn't this disaster vehicle */
+		if (insert_result.first->second != disaster_vehicle) return false;
 	}
+
+	return true;
 }
 
 void DisasterVehicle::UpdateDeltaXY()

src/misc.cpp

@@ -120,6 +120,7 @@ void InitializeGame(uint size_x, uint size_y, bool reset_date, bool reset_settin
 	AllocateMap(size_x, size_y);
 
 	ViewportMapClearTunnelCache();
+	ResetDisasterVehicleTargeting();
 	ClearCommandLog();
 	ClearCommandQueue();
 	ClearSpecialEventsLog();

src/openttd.cpp

@@ -520,6 +520,7 @@ static void ShutdownGame()
 	InvalidateVehicleTickCaches();
 	ClearVehicleTickCaches();
 	InvalidateTemplateReplacementImages();
+	ResetDisasterVehicleTargeting();
 	ClearCommandLog();
 	ClearCommandQueue();
 	ClearSpecialEventsLog();

src/sl/vehicle_sl.cpp

@@ -507,6 +507,8 @@ void AfterLoadVehicles(bool part_of_load)
 		}
 	}
 
+	ResetDisasterVehicleTargeting();
+
 	for (Vehicle *v : Vehicle::Iterate()) {
 		si_v = v;
 		switch (v->type) {
@@ -539,6 +541,22 @@ void AfterLoadVehicles(bool part_of_load)
 					UpdateAircraftCache(Aircraft::From(v), true);
 				}
 				break;
+
+			case VEH_DISASTER: {
+				auto *dv = DisasterVehicle::From(v);
+				if (dv->subtype == ST_SMALL_UFO && dv->state != 0) {
+					RoadVehicle *u = RoadVehicle::GetIfValid(v->dest_tile);
+					if (u != nullptr && u->IsFrontEngine()) {
+						/* Delete UFO targeting a vehicle which is already a target. */
+						if (!SetDisasterVehicleTargetingVehicle(u->index, dv->index)) {
+							delete v;
+							continue;
+						}
+					}
+				}
+				break;
+			}
+
 			default: break;
 		}
 

src/vehicle.cpp

@@ -1030,6 +1030,7 @@ void InitializeVehicles()
 {
 	_vehicles_to_autoreplace.clear();
 	ResetVehicleHash();
+	ResetDisasterVehicleTargeting();
 }
 
 uint CountVehiclesInChain(const Vehicle *v)
@@ -1202,6 +1203,8 @@ void Vehicle::PreDestructor()
 			/* Leave the drive through roadstop, when you have not already left it. */
 			RoadStop::GetByTile(v->tile, GetRoadStopType(v->tile))->Leave(v);
 		}
+
+		ReleaseDisasterVehicleTargetingVehicle(this->index);
 	}
 
 	if (HasBit(this->vehicle_flags, VF_HAVE_SLOT)) {
@@ -1238,8 +1241,6 @@ void Vehicle::PreDestructor()
 
 	StopGlobalFollowVehicle(this);
 
-	ReleaseDisastersTargetingVehicle(this->index);
-
 	/* sometimes, eg. for disaster vehicles, when company bankrupts, when removing crashed/flooded vehicles,
 	 * it may happen that vehicle chain is deleted when visible */
 	if (this->IsDrawn()) this->MarkAllViewportsDirty();

src/vehicle_func.h

@@ -258,7 +258,9 @@ bool CanVehicleUseStation(EngineID engine_type, const struct Station *st);
 bool CanVehicleUseStation(const Vehicle *v, const struct Station *st);
 StringID GetVehicleCannotUseStationReason(const Vehicle *v, const Station *st);
 
-void ReleaseDisastersTargetingVehicle(VehicleID vehicle);
+void ResetDisasterVehicleTargeting();
+void ReleaseDisasterVehicleTargetingVehicle(VehicleID vehicle);
+bool SetDisasterVehicleTargetingVehicle(VehicleID vehicle, VehicleID disaster_vehicle);
 
 typedef std::vector<VehicleID> VehicleSet;
 void GetVehicleSet(VehicleSet &set, Vehicle *v, uint8_t num_vehicles);