vehicle_base.h

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/*
 * This file is part of OpenTTD.
 * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
 * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <https://www.gnu.org/licenses/old-licenses/gpl-2.0>.
 */

 
#ifndef VEHICLE_BASE_H
#define VEHICLE_BASE_H
 
#include "sprite.h"
#include "track_type.h"
#include "command_type.h"
#include "order_base.h"
#include "cargopacket.h"
#include "texteff.hpp"
#include "engine_type.h"
#include "order_func.h"
#include "transport_type.h"
#include "group_type.h"
#include "base_consist.h"
#include "network/network.h"
#include "saveload/saveload.h"
#include "timer/timer_game_calendar.h"
 
const uint TILE_AXIAL_DISTANCE = 192;  // Logical length of the tile in any DiagDirection used in vehicle movement.
const uint TILE_CORNER_DISTANCE = 128;  // Logical length of the tile corner crossing in any non-diagonal direction used in vehicle movement.

enum class VehState : uint8_t {
  Hidden         = 0, 
  Stopped        = 1, 
  Unclickable    = 2, 
  DefaultPalette = 3, 
  TrainSlowing   = 4, 
  Shadow         = 5, 
  AircraftBroken = 6, 
  Crashed        = 7, 
};
using VehStates = EnumBitSet<VehState, uint8_t>;

enum NewGRFCacheValidValues : uint8_t {
  NCVV_POSITION_CONSIST_LENGTH   = 0, 
  NCVV_POSITION_SAME_ID_LENGTH   = 1, 
  NCVV_CONSIST_CARGO_INFORMATION = 2, 
  NCVV_COMPANY_INFORMATION       = 3, 
  NCVV_POSITION_IN_VEHICLE       = 4, 
  NCVV_END,                           
};

struct NewGRFCache {
  /* Values calculated when they are requested for the first time after invalidating the NewGRF cache. */
  uint32_t position_consist_length = 0; 
  uint32_t position_same_id_length = 0; 
  uint32_t consist_cargo_information = 0; 
  uint32_t company_information = 0; 
  uint32_t position_in_vehicle = 0; 
  uint8_t  cache_valid = 0; 
 
  auto operator<=>(const NewGRFCache &) const = default;
};

enum VisualEffectSpawnModel : uint8_t {
  VESM_NONE              = 0, 
  VESM_STEAM,                 
  VESM_DIESEL,                
  VESM_ELECTRIC,              
 
  VESM_END
};

enum GroundVehicleSubtypeFlags : uint8_t {
  GVSF_FRONT            = 0, 
  GVSF_ARTICULATED_PART = 1, 
  GVSF_WAGON            = 2, 
  GVSF_ENGINE           = 3, 
  GVSF_FREE_WAGON       = 4, 
  GVSF_MULTIHEADED      = 5, 
};

struct VehicleCache {
  uint16_t cached_max_speed = 0; 
  uint16_t cached_cargo_age_period = 0; 
 
  uint8_t cached_vis_effect = 0;  
 
  auto operator<=>(const VehicleCache &) const = default;
};

struct VehicleSpriteSeq {
  std::array<PalSpriteID, 8> seq;
  uint count;
 
  bool operator==(const VehicleSpriteSeq &other) const
  {
    return std::ranges::equal(std::span(this->seq.data(), this->count), std::span(other.seq.data(), other.count));
  }

  bool IsValid() const
  {
    return this->count != 0;
  }

  void Clear()
  {
    this->count = 0;
  }

  void Set(SpriteID sprite)
  {
    this->count = 1;
    this->seq[0].sprite = sprite;
    this->seq[0].pal = 0;
  }

  void CopyWithoutPalette(const VehicleSpriteSeq &src)
  {
    this->count = src.count;
    for (uint i = 0; i < src.count; ++i) {
      this->seq[i].sprite = src.seq[i].sprite;
      this->seq[i].pal = 0;
    }
  }
 
  void GetBounds(Rect *bounds) const;
  void Draw(int x, int y, PaletteID default_pal, bool force_pal) const;
};

struct MutableSpriteCache {
  Direction last_direction = INVALID_DIR; 
  bool revalidate_before_draw = false; 
  bool is_viewport_candidate = false; 
  Rect old_coord{}; 
  VehicleSpriteSeq sprite_seq{}; 
};

typedef Pool<Vehicle, VehicleID, 512> VehiclePool;
extern VehiclePool _vehicle_pool;
 
/* Some declarations of functions, so we can make them friendly */
struct GroundVehicleCache;
struct LoadgameState;
struct GRFFile;

struct RefitDesc {
  CargoType cargo;    
  uint16_t capacity;  
  uint16_t remaining; 
  RefitDesc(CargoType cargo, uint16_t capacity, uint16_t remaining) :
      cargo(cargo), capacity(capacity), remaining(remaining) {}
};

struct ClosestDepot {
  TileIndex location = INVALID_TILE;
  DestinationID destination{}; 
  bool reverse = false;
  bool found = false;
 
  ClosestDepot() = default;
 
  ClosestDepot(TileIndex location, DestinationID destination, bool reverse = false) :
    location(location), destination(destination), reverse(reverse), found(true) {}
};

struct Vehicle : VehiclePool::PoolItem<&_vehicle_pool>, BaseVehicle, BaseConsist {
private:
  typedef std::list<RefitDesc> RefitList;
 
  Vehicle *next = nullptr; 
  Vehicle *previous = nullptr; 
  Vehicle *first = nullptr; 
 
  Vehicle *next_shared = nullptr; 
  Vehicle *previous_shared = nullptr; 
 
public:
  friend void FixOldVehicles(LoadgameState &ls);
  friend void AfterLoadVehiclesPhase1(bool part_of_load);       
  friend bool LoadOldVehicle(LoadgameState &ls, int num);       
  /* So we can use private/protected variables in the saveload code */
  friend class SlVehicleCommon;
  friend class SlVehicleDisaster;
  friend void Ptrs_VEHS();
 
  TileIndex tile = INVALID_TILE; 

  TileIndex dest_tile = INVALID_TILE;
 
  Money profit_this_year = 0; 
  Money profit_last_year = 0; 
  Money value = 0; 
 
  CargoPayment *cargo_payment = nullptr; 
 
  mutable Rect coord{}; 
 
  Vehicle *hash_viewport_next = nullptr; 
  Vehicle **hash_viewport_prev = nullptr; 
 
  Vehicle *hash_tile_next = nullptr; 
  Vehicle **hash_tile_prev = nullptr; 
  Vehicle **hash_tile_current = nullptr; 
 
  SpriteID colourmap{}; 
 
  /* Related to age and service time */
  TimerGameCalendar::Year build_year{}; 
  TimerGameCalendar::Date age{}; 
  TimerGameEconomy::Date economy_age{}; 
  TimerGameCalendar::Date max_age{}; 
  TimerGameEconomy::Date date_of_last_service{}; 
  TimerGameCalendar::Date date_of_last_service_newgrf{}; 
  uint16_t reliability = 0; 
  uint16_t reliability_spd_dec = 0; 
  uint8_t breakdown_ctr = 0; 
  uint8_t breakdown_delay = 0; 
  uint8_t breakdowns_since_last_service = 0; 
  uint8_t breakdown_chance = 0; 
 
  int32_t x_pos = 0; 
  int32_t y_pos = 0; 
  int32_t z_pos = 0; 
  Direction direction = INVALID_DIR; 
 
  Owner owner = INVALID_OWNER; 
  uint8_t spritenum = 0;
  SpriteBounds bounds{}; 
  EngineID engine_type = EngineID::Invalid(); 
 
  TextEffectID fill_percent_te_id = INVALID_TE_ID; 
  UnitID unitnumber{}; 
 
  uint16_t cur_speed = 0; 
  uint8_t subspeed = 0; 
  uint8_t acceleration = 0; 
  uint32_t motion_counter = 0; 
  uint8_t progress = 0; 
 
  VehicleRandomTriggers waiting_random_triggers; 
  uint16_t random_bits = 0; 
 
  StationID last_station_visited = StationID::Invalid(); 
  StationID last_loading_station = StationID::Invalid(); 
  TimerGameTick::TickCounter last_loading_tick{}; 
 
  VehicleCargoList cargo{}; 
  CargoType cargo_type{}; 
  uint8_t cargo_subtype = 0; 
  uint16_t cargo_cap = 0; 
  uint16_t refit_cap = 0; 
  uint16_t cargo_age_counter = 0; 
  int8_t trip_occupancy = 0; 
 
  uint8_t day_counter = 0; 
  uint8_t tick_counter = 0; 
  uint8_t running_ticks = 0; 
  uint16_t load_unload_ticks = 0; 
 
  VehStates vehstatus{}; 
  uint8_t subtype = 0; 
  Order current_order{}; 
 
  union {
    OrderList *orders = nullptr; 
    uint32_t old_orders; 
  };
 
  NewGRFCache grf_cache{}; 
  VehicleCache vcache{}; 
 
  GroupID group_id = GroupID::Invalid(); 
 
  mutable MutableSpriteCache sprite_cache{}; 

  virtual uint16_t GetMaxWeight() const
  {
    return 0;
  }
 
  Vehicle(VehicleID index, VehicleType type = VEH_INVALID);
 
  void PreDestructor();
  ~Vehicle() override;
 
  void BeginLoading();
  void CancelReservation(StationID next, Station *st);
  void LeaveStation();
 
  GroundVehicleCache *GetGroundVehicleCache();
  const GroundVehicleCache *GetGroundVehicleCache() const;
 
  uint16_t &GetGroundVehicleFlags();
  const uint16_t &GetGroundVehicleFlags() const;
 
  void DeleteUnreachedImplicitOrders();
 
  void HandleLoading(bool mode = false);

  virtual void MarkDirty() {}

  virtual void UpdateDeltaXY() {}

  inline uint GetOldAdvanceSpeed(uint speed)
  {
    return (this->direction & 1) ? speed : speed * 3 / 4;
  }

  static inline uint GetAdvanceSpeed(uint speed)
  {
    return speed * 3 / 4;
  }

  inline uint GetAdvanceDistance()
  {
    return (this->direction & 1) ? TILE_AXIAL_DISTANCE : TILE_CORNER_DISTANCE * 2;
  }

  virtual ExpensesType GetExpenseType([[maybe_unused]] bool income) const { return EXPENSES_OTHER; }

  virtual void PlayLeaveStationSound([[maybe_unused]] bool force = false) const {}

  virtual bool IsPrimaryVehicle() const { return false; }
 
  const Engine *GetEngine() const;

  virtual void GetImage([[maybe_unused]] Direction direction, [[maybe_unused]] EngineImageType image_type, [[maybe_unused]] VehicleSpriteSeq *result) const { result->Clear(); }
 
  const GRFFile *GetGRF() const;
  uint32_t GetGRFID() const;

  inline void InvalidateNewGRFCache()
  {
    this->grf_cache.cache_valid = 0;
  }

  inline void InvalidateNewGRFCacheOfChain()
  {
    for (Vehicle *u = this; u != nullptr; u = u->Next()) {
      u->InvalidateNewGRFCache();
    }
  }

  [[debug_inline]] inline bool IsGroundVehicle() const
  {
    return this->type == VEH_TRAIN || this->type == VEH_ROAD;
  }

  virtual int GetDisplaySpeed() const { return 0; }

  virtual int GetDisplayMaxSpeed() const { return 0; }

  virtual int GetCurrentMaxSpeed() const { return 0; }

  virtual Money GetRunningCost() const { return 0; }

  virtual bool IsInDepot() const { return false; }

  virtual bool IsChainInDepot() const { return this->IsInDepot(); }

  bool IsStoppedInDepot() const
  {
    assert(this == this->First());
    /* Free wagons have no VehState::Stopped state */
    if (this->IsPrimaryVehicle() && !this->vehstatus.Test(VehState::Stopped)) return false;
    return this->IsChainInDepot();
  }

  virtual bool Tick() { return true; };

  virtual void OnNewCalendarDay() {};

  virtual void OnNewEconomyDay() {};
 
  void ShiftDates(TimerGameEconomy::Date interval);

  virtual uint Crash(bool flooded = false);

  virtual Trackdir GetVehicleTrackdir() const { return INVALID_TRACKDIR; }

  Money GetDisplayRunningCost() const { return (this->GetRunningCost() >> 8); }

  Money GetDisplayProfitThisYear() const { return (this->profit_this_year >> 8); }

  Money GetDisplayProfitLastYear() const { return (this->profit_last_year >> 8); }
 
  void SetNext(Vehicle *next);

  inline Vehicle *Next() const { return this->next; }

  inline Vehicle *Previous() const { return this->previous; }

  inline Vehicle *First() const { return this->first; }

  inline Vehicle *Last()
  {
    Vehicle *v = this;
    while (v->Next() != nullptr) v = v->Next();
    return v;
  }

  inline const Vehicle *Last() const
  {
    const Vehicle *v = this;
    while (v->Next() != nullptr) v = v->Next();
    return v;
  }

  inline Vehicle *Move(int n)
  {
    Vehicle *v = this;
    if (n < 0) {
      for (int i = 0; i != n && v != nullptr; i--) v = v->Previous();
    } else {
      for (int i = 0; i != n && v != nullptr; i++) v = v->Next();
    }
    return v;
  }

  inline const Vehicle *Move(int n) const
  {
    const Vehicle *v = this;
    if (n < 0) {
      for (int i = 0; i != n && v != nullptr; i--) v = v->Previous();
    } else {
      for (int i = 0; i != n && v != nullptr; i++) v = v->Next();
    }
    return v;
  }

  inline const Order *GetFirstOrder() const { return (this->orders == nullptr) ? nullptr : this->GetOrder(this->orders->GetFirstOrder()); }
 
  inline std::span<const Order> Orders() const
  {
    if (this->orders == nullptr) return {};
    return this->orders->GetOrders();
  }
 
  inline std::span<Order> Orders()
  {
    if (this->orders == nullptr) return {};
    return this->orders->GetOrders();
  }
 
  void AddToShared(Vehicle *shared_chain);
  void RemoveFromShared();

  inline Vehicle *NextShared() const { return this->next_shared; }

  inline Vehicle *PreviousShared() const { return this->previous_shared; }

  inline Vehicle *FirstShared() const { return (this->orders == nullptr) ? this->First() : this->orders->GetFirstSharedVehicle(); }

  inline bool IsOrderListShared() const { return this->orders != nullptr && this->orders->IsShared(); }

  inline VehicleOrderID GetNumOrders() const { return (this->orders == nullptr) ? 0 : this->orders->GetNumOrders(); }

  inline VehicleOrderID GetNumManualOrders() const { return (this->orders == nullptr) ? 0 : this->orders->GetNumManualOrders(); }

  inline void GetNextStoppingStation(std::vector<StationID> &next_station) const
  {
    if (this->orders == nullptr) return;
    this->orders->GetNextStoppingStation(next_station, this);
  }
 
  void ResetRefitCaps();
 
  void ReleaseUnitNumber();

  inline void CopyVehicleConfigAndStatistics(Vehicle *src)
  {
    this->CopyConsistPropertiesFrom(src);
 
    this->ReleaseUnitNumber();
    this->unitnumber = src->unitnumber;
 
    this->current_order = src->current_order;
    this->dest_tile  = src->dest_tile;
 
    this->profit_this_year = src->profit_this_year;
    this->profit_last_year = src->profit_last_year;
 
    src->unitnumber = 0;
  }
 
 
  bool HandleBreakdown();
 
  bool NeedsAutorenewing(const Company *c, bool use_renew_setting = true) const;
 
  bool NeedsServicing() const;
  bool NeedsAutomaticServicing() const;

  virtual TileIndex GetOrderStationLocation([[maybe_unused]] StationID station) { return INVALID_TILE; }

  virtual TileIndex GetCargoTile() const { return this->tile; }

  virtual ClosestDepot FindClosestDepot() { return {}; }

  virtual void SetDestTile(TileIndex tile) { this->dest_tile = tile; }
 
  CommandCost SendToDepot(DoCommandFlags flags, DepotCommandFlags command);
 
  void UpdateVisualEffect(bool allow_power_change = true);
  void ShowVisualEffect() const;
 
  void UpdatePosition();
  void UpdateViewport(bool dirty);
  void UpdateBoundingBoxCoordinates(bool update_cache) const;
  void UpdatePositionAndViewport();
  bool MarkAllViewportsDirty() const;
 
  inline uint16_t GetServiceInterval() const { return this->service_interval; }
 
  inline void SetServiceInterval(uint16_t interval) { this->service_interval = interval; }
 
  inline bool ServiceIntervalIsCustom() const { return this->vehicle_flags.Test(VehicleFlag::ServiceIntervalIsCustom); }
 
  inline bool ServiceIntervalIsPercent() const { return this->vehicle_flags.Test(VehicleFlag::ServiceIntervalIsPercent); }
 
  inline void SetServiceIntervalIsCustom(bool on) { this->vehicle_flags.Set(VehicleFlag::ServiceIntervalIsCustom, on); }
 
  inline void SetServiceIntervalIsPercent(bool on) { this->vehicle_flags.Set(VehicleFlag::ServiceIntervalIsPercent, on); }
 
  bool HasFullLoadOrder() const;
  bool HasConditionalOrder() const;
  bool HasUnbunchingOrder() const;
  void LeaveUnbunchingDepot();
  bool IsWaitingForUnbunching() const;
 
private:
  void SkipToNextRealOrderIndex()
  {
    if (this->GetNumManualOrders() > 0) {
      /* Advance to next real order */
      do {
        this->cur_real_order_index++;
        if (this->cur_real_order_index >= this->GetNumOrders()) this->cur_real_order_index = 0;
      } while (this->GetOrder(this->cur_real_order_index)->IsType(OT_IMPLICIT));
    } else {
      this->cur_real_order_index = 0;
    }
  }
 
public:
  void IncrementImplicitOrderIndex()
  {
    if (this->cur_implicit_order_index == this->cur_real_order_index) {
      /* Increment real order index as well */
      this->SkipToNextRealOrderIndex();
    }
 
    assert(this->cur_real_order_index == 0 || this->cur_real_order_index < this->GetNumOrders());
 
    /* Advance to next implicit order */
    do {
      this->cur_implicit_order_index++;
      if (this->cur_implicit_order_index >= this->GetNumOrders()) this->cur_implicit_order_index = 0;
    } while (this->cur_implicit_order_index != this->cur_real_order_index && !this->GetOrder(this->cur_implicit_order_index)->IsType(OT_IMPLICIT));
 
    InvalidateVehicleOrder(this, 0);
  }

  void IncrementRealOrderIndex()
  {
    if (this->cur_implicit_order_index == this->cur_real_order_index) {
      /* Increment both real and implicit order */
      this->IncrementImplicitOrderIndex();
    } else {
      /* Increment real order only */
      this->SkipToNextRealOrderIndex();
      InvalidateVehicleOrder(this, 0);
    }
  }

  void UpdateRealOrderIndex()
  {
    /* Make sure the index is valid */
    if (this->cur_real_order_index >= this->GetNumOrders()) this->cur_real_order_index = 0;
 
    if (this->GetNumManualOrders() > 0) {
      /* Advance to next real order */
      while (this->GetOrder(this->cur_real_order_index)->IsType(OT_IMPLICIT)) {
        this->cur_real_order_index++;
        if (this->cur_real_order_index >= this->GetNumOrders()) this->cur_real_order_index = 0;
      }
    } else {
      this->cur_real_order_index = 0;
    }
  }

  inline Order *GetOrder(int index) const
  {
    return (this->orders == nullptr) ? nullptr : this->orders->GetOrderAt(index);
  }

  inline const Order *GetLastOrder() const
  {
    return (this->orders == nullptr) ? nullptr : this->orders->GetOrderAt(this->orders->GetLastOrder());
  }
 
  bool IsEngineCountable() const;
  bool HasEngineType() const;
  bool HasDepotOrder() const;
  void HandlePathfindingResult(bool path_found);

  [[debug_inline]] inline bool IsFrontEngine() const
  {
    return this->IsGroundVehicle() && HasBit(this->subtype, GVSF_FRONT);
  }

  inline bool IsArticulatedPart() const
  {
    return this->IsGroundVehicle() && HasBit(this->subtype, GVSF_ARTICULATED_PART);
  }

  inline bool HasArticulatedPart() const
  {
    return this->Next() != nullptr && this->Next()->IsArticulatedPart();
  }

  inline Vehicle *GetNextArticulatedPart() const
  {
    assert(this->HasArticulatedPart());
    return this->Next();
  }

  inline Vehicle *GetFirstEnginePart()
  {
    Vehicle *v = this;
    while (v->IsArticulatedPart()) v = v->Previous();
    return v;
  }

  inline const Vehicle *GetFirstEnginePart() const
  {
    const Vehicle *v = this;
    while (v->IsArticulatedPart()) v = v->Previous();
    return v;
  }

  inline Vehicle *GetLastEnginePart()
  {
    Vehicle *v = this;
    while (v->HasArticulatedPart()) v = v->GetNextArticulatedPart();
    return v;
  }

  inline Vehicle *GetNextVehicle() const
  {
    const Vehicle *v = this;
    while (v->HasArticulatedPart()) v = v->GetNextArticulatedPart();
 
    /* v now contains the last articulated part in the engine */
    return v->Next();
  }

  inline Vehicle *GetPrevVehicle() const
  {
    Vehicle *v = this->Previous();
    while (v != nullptr && v->IsArticulatedPart()) v = v->Previous();
 
    return v;
  }
 
  uint32_t GetDisplayMaxWeight() const;
  uint32_t GetDisplayMinPowerToWeight() const;
};

template <class T, VehicleType Type>
struct SpecializedVehicle : public Vehicle {
  static const VehicleType EXPECTED_TYPE = Type; 
 
  typedef SpecializedVehicle<T, Type> SpecializedVehicleBase; 

  inline SpecializedVehicle(VehicleID index) : Vehicle(index, Type)
  {
    this->sprite_cache.sprite_seq.count = 1;
  }

  inline T *First() const { return (T *)this->Vehicle::First(); }

  inline T *Last() { return (T *)this->Vehicle::Last(); }

  inline const T *Last() const { return (const T *)this->Vehicle::Last(); }

  inline T *Next() const { return (T *)this->Vehicle::Next(); }

  inline T *Previous() const { return (T *)this->Vehicle::Previous(); }

  inline T *GetNextArticulatedPart() { return (T *)this->Vehicle::GetNextArticulatedPart(); }

  inline T *GetNextArticulatedPart() const { return (T *)this->Vehicle::GetNextArticulatedPart(); }

  inline T *GetFirstEnginePart() { return (T *)this->Vehicle::GetFirstEnginePart(); }

  inline const T *GetFirstEnginePart() const { return (const T *)this->Vehicle::GetFirstEnginePart(); }

  inline T *GetLastEnginePart() { return (T *)this->Vehicle::GetLastEnginePart(); }

  inline T *GetNextVehicle() const { return (T *)this->Vehicle::GetNextVehicle(); }

  inline T *GetPrevVehicle() const { return (T *)this->Vehicle::GetPrevVehicle(); }

  static inline bool IsValidID(auto index)
  {
    return Vehicle::IsValidID(index) && Vehicle::Get(index)->type == Type;
  }

  static inline T *Get(auto index)
  {
    return (T *)Vehicle::Get(index);
  }

  static inline T *GetIfValid(auto index)
  {
    return IsValidID(index) ? Get(index) : nullptr;
  }

  template <typename... Targs>
  static inline T *Create(Targs &&... args)
  {
    return Vehicle::Create<T>(std::forward<Targs&&>(args)...);
  }

  template <typename... Targs>
  static inline T *CreateAtIndex(VehicleID index, Targs &&... args)
  {
    return Vehicle::CreateAtIndex<T>(index, std::forward<Targs&&>(args)...);
  }

  static inline T *From(Vehicle *v)
  {
    assert(v->type == Type);
    return (T *)v;
  }

  static inline const T *From(const Vehicle *v)
  {
    assert(v->type == Type);
    return (const T *)v;
  }

  inline void UpdateViewport(bool force_update, bool update_delta)
  {
    bool sprite_has_changed = false;
 
    /* Skip updating sprites on dedicated servers without screen */
    if (_network_dedicated) return;
 
    /* Explicitly choose method to call to prevent vtable dereference -
     * it gives ~3% runtime improvements in games with many vehicles */
    if (update_delta) ((T *)this)->T::UpdateDeltaXY();
 
    /*
     * Only check for a new sprite sequence if the vehicle direction
     * has changed since we last checked it, assuming that otherwise
     * there won't be enough change in bounding box or offsets to need
     * to resolve a new sprite.
     */
    if (this->direction != this->sprite_cache.last_direction || this->sprite_cache.is_viewport_candidate) {
      VehicleSpriteSeq seq;
 
      ((T*)this)->T::GetImage(this->direction, EIT_ON_MAP, &seq);
      if (this->sprite_cache.sprite_seq != seq) {
        sprite_has_changed = true;
        this->sprite_cache.sprite_seq = seq;
      }
 
      this->sprite_cache.last_direction = this->direction;
      this->sprite_cache.revalidate_before_draw = false;
    } else {
      /*
       * A change that could potentially invalidate the sprite has been
       * made, signal that we should still resolve it before drawing on a
       * viewport.
       */
      this->sprite_cache.revalidate_before_draw = true;
    }
 
    if (force_update || sprite_has_changed) {
      this->Vehicle::UpdateViewport(true);
    }
  }

  static Pool::IterateWrapper<T> Iterate(size_t from = 0) { return Pool::IterateWrapper<T>(from); }
};

static const int32_t INVALID_COORD = 0x7fffffff;
 
#endif /* VEHICLE_BASE_H */