(svn r26388) -Codechange: Move resolving of Action 3 into ResolverObject constructor.

17 files changed, 143 insertions, 184 deletions

diff --git a/src/newgrf_airport.cpp b/src/newgrf_airport.cpp
index 4c5b21a6b..4201fc622 100644
--- a/src/newgrf_airport.cpp
+++ b/src/newgrf_airport.cpp
@@ -237,6 +237,7 @@ AirportResolverObject::AirportResolverObject(TileIndex tile, Station *st, byte a
 		CallbackID callback, uint32 param1, uint32 param2)
 	: ResolverObject(AirportSpec::Get(airport_id)->grf_prop.grffile, callback, param1, param2), airport_scope(*this, tile, st, airport_id, layout)
 {
+	this->root_spritegroup = AirportSpec::Get(airport_id)->grf_prop.spritegroup[0];
 }
 
 /**
@@ -258,7 +259,7 @@ AirportScopeResolver::AirportScopeResolver(ResolverObject &ro, TileIndex tile, S
 SpriteID GetCustomAirportSprite(const AirportSpec *as, byte layout)
 {
 	AirportResolverObject object(INVALID_TILE, NULL, as->GetIndex(), layout);
-	const SpriteGroup *group = SpriteGroup::Resolve(as->grf_prop.spritegroup[0], object);
+	const SpriteGroup *group = object.Resolve();
 	if (group == NULL) return as->preview_sprite;
 
 	return group->GetResult();
@@ -267,10 +268,7 @@ SpriteID GetCustomAirportSprite(const AirportSpec *as, byte layout)
 uint16 GetAirportCallback(CallbackID callback, uint32 param1, uint32 param2, Station *st, TileIndex tile)
 {
 	AirportResolverObject object(tile, st, st->airport.type, st->airport.layout, callback, param1, param2);
-	const SpriteGroup *group = SpriteGroup::Resolve(st->airport.GetSpec()->grf_prop.spritegroup[0], object);
-	if (group == NULL) return CALLBACK_FAILED;
-
-	return group->GetCallbackResult();
+	return object.ResolveCallback();
 }
 
 /**
@@ -283,8 +281,7 @@ uint16 GetAirportCallback(CallbackID callback, uint32 param1, uint32 param2, Sta
 StringID GetAirportTextCallback(const AirportSpec *as, byte layout, uint16 callback)
 {
 	AirportResolverObject object(INVALID_TILE, NULL, as->GetIndex(), layout, (CallbackID)callback);
-	const SpriteGroup *group = SpriteGroup::Resolve(as->grf_prop.spritegroup[0], object);
-	uint16 cb_res = (group != NULL) ? group->GetCallbackResult() : CALLBACK_FAILED;
+	uint16 cb_res = object.ResolveCallback();
 	if (cb_res == CALLBACK_FAILED || cb_res == 0x400) return STR_UNDEFINED;
 	if (cb_res > 0x400) {
 		ErrorUnknownCallbackResult(as->grf_prop.grffile->grfid, callback, cb_res);
diff --git a/src/newgrf_airporttiles.cpp b/src/newgrf_airporttiles.cpp
index cc9471c80..323fb6cc1 100644
--- a/src/newgrf_airporttiles.cpp
+++ b/src/newgrf_airporttiles.cpp
@@ -217,6 +217,7 @@ AirportTileResolverObject::AirportTileResolverObject(const AirportTileSpec *ats,
 		CallbackID callback, uint32 callback_param1, uint32 callback_param2)
 	: ResolverObject(ats->grf_prop.grffile, callback, callback_param1, callback_param2), tiles_scope(*this, ats, tile, st)
 {
+	this->root_spritegroup = ats->grf_prop.spritegroup[0];
 }
 
 /**
@@ -237,10 +238,7 @@ AirportTileScopeResolver::AirportTileScopeResolver(ResolverObject &ro, const Air
 uint16 GetAirportTileCallback(CallbackID callback, uint32 param1, uint32 param2, const AirportTileSpec *ats, Station *st, TileIndex tile, int extra_data = 0)
 {
 	AirportTileResolverObject object(ats, tile, st, callback, param1, param2);
-	const SpriteGroup *group = SpriteGroup::Resolve(ats->grf_prop.spritegroup[0], object);
-	if (group == NULL) return CALLBACK_FAILED;
-
-	return group->GetCallbackResult();
+	return object.ResolveCallback();
 }
 
 static void AirportDrawTileLayout(const TileInfo *ti, const TileLayoutSpriteGroup *group, byte colour, StationGfx gfx)
@@ -275,7 +273,7 @@ bool DrawNewAirportTile(TileInfo *ti, Station *st, StationGfx gfx, const Airport
 	}
 
 	AirportTileResolverObject object(airts, ti->tile, st);
-	const SpriteGroup *group = SpriteGroup::Resolve(airts->grf_prop.spritegroup[0], object);
+	const SpriteGroup *group = object.Resolve();
 	if (group == NULL || group->type != SGT_TILELAYOUT) {
 		return false;
 	}
diff --git a/src/newgrf_canal.cpp b/src/newgrf_canal.cpp
index 7310186c0..8f81fd0d8 100644
--- a/src/newgrf_canal.cpp
+++ b/src/newgrf_canal.cpp
@@ -33,7 +33,7 @@ struct CanalScopeResolver : public ScopeResolver {
 struct CanalResolverObject : public ResolverObject {
 	CanalScopeResolver canal_scope;
 
-	CanalResolverObject(const GRFFile *grffile, TileIndex tile,
+	CanalResolverObject(CanalFeature feature, TileIndex tile,
 			CallbackID callback = CBID_NO_CALLBACK, uint32 callback_param1 = 0, uint32 callback_param2 = 0);
 
 	/* virtual */ ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, byte relative = 0)
@@ -115,16 +115,17 @@ CanalScopeResolver::CanalScopeResolver(ResolverObject &ro, TileIndex tile) : Sco
 
 /**
  * Canal resolver constructor.
- * @param grffile Grf file.
+ * @param feature Which canal feature we want.
  * @param tile Tile index of canal.
  * @param callback Callback ID.
  * @param callback_param1 First parameter (var 10) of the callback.
  * @param callback_param2 Second parameter (var 18) of the callback.
  */
-CanalResolverObject::CanalResolverObject(const GRFFile *grffile, TileIndex tile,
+CanalResolverObject::CanalResolverObject(CanalFeature feature, TileIndex tile,
 		CallbackID callback, uint32 callback_param1, uint32 callback_param2)
-		: ResolverObject(grffile, callback, callback_param1, callback_param2), canal_scope(*this, tile)
+		: ResolverObject(_water_feature[feature].grffile, callback, callback_param1, callback_param2), canal_scope(*this, tile)
 {
+	this->root_spritegroup = _water_feature[feature].group;
 }
 
 /**
@@ -135,8 +136,8 @@ CanalResolverObject::CanalResolverObject(const GRFFile *grffile, TileIndex tile,
  */
 SpriteID GetCanalSprite(CanalFeature feature, TileIndex tile)
 {
-	CanalResolverObject object(_water_feature[feature].grffile, tile);
-	const SpriteGroup *group = SpriteGroup::Resolve(_water_feature[feature].group, object);
+	CanalResolverObject object(feature, tile);
+	const SpriteGroup *group = object.Resolve();
 	if (group == NULL) return 0;
 
 	return group->GetResult();
@@ -153,11 +154,8 @@ SpriteID GetCanalSprite(CanalFeature feature, TileIndex tile)
  */
 static uint16 GetCanalCallback(CallbackID callback, uint32 param1, uint32 param2, CanalFeature feature, TileIndex tile)
 {
-	CanalResolverObject object(_water_feature[feature].grffile, tile, callback, param1, param2);
-	const SpriteGroup *group = SpriteGroup::Resolve(_water_feature[feature].group, object);
-	if (group == NULL) return CALLBACK_FAILED;
-
-	return group->GetCallbackResult();
+	CanalResolverObject object(feature, tile, callback, param1, param2);
+	return object.ResolveCallback();
 }
 
 /**
diff --git a/src/newgrf_cargo.cpp b/src/newgrf_cargo.cpp
index 4186b53f6..016698523 100644
--- a/src/newgrf_cargo.cpp
+++ b/src/newgrf_cargo.cpp
@@ -40,6 +40,7 @@ struct CargoResolverObject : public ResolverObject {
 CargoResolverObject::CargoResolverObject(const CargoSpec *cs, CallbackID callback, uint32 callback_param1, uint32 callback_param2)
 		: ResolverObject(cs->grffile, callback, callback_param1, callback_param2)
 {
+	this->root_spritegroup = cs->group;
 }
 
 /**
@@ -50,7 +51,7 @@ CargoResolverObject::CargoResolverObject(const CargoSpec *cs, CallbackID callbac
 SpriteID GetCustomCargoSprite(const CargoSpec *cs)
 {
 	CargoResolverObject object(cs);
-	const SpriteGroup *group = SpriteGroup::Resolve(cs->group, object);
+	const SpriteGroup *group = object.Resolve();
 	if (group == NULL) return 0;
 
 	return group->GetResult();
@@ -60,10 +61,7 @@ SpriteID GetCustomCargoSprite(const CargoSpec *cs)
 uint16 GetCargoCallback(CallbackID callback, uint32 param1, uint32 param2, const CargoSpec *cs)
 {
 	CargoResolverObject object(cs, callback, param1, param2);
-	const SpriteGroup *group = SpriteGroup::Resolve(cs->group, object);
-	if (group == NULL) return CALLBACK_FAILED;
-
-	return group->GetCallbackResult();
+	return object.ResolveCallback();
 }
 
 /**
diff --git a/src/newgrf_engine.cpp b/src/newgrf_engine.cpp
index 309decb72..5d3af4105 100644
--- a/src/newgrf_engine.cpp
+++ b/src/newgrf_engine.cpp
@@ -973,12 +973,13 @@ static const GRFFile *GetEngineGrfFile(EngineID engine_type)
  * Resolver of a vehicle (chain).
  * @param engine_type Engine type
  * @param v %Vehicle being resolved.
+ * @param wagon_override Application of wagon overrides.
  * @param info_view Indicates if the item is being drawn in an info window.
  * @param callback Callback ID.
  * @param callback_param1 First parameter (var 10) of the callback.
  * @param callback_param2 Second parameter (var 18) of the callback.
  */
-VehicleResolverObject::VehicleResolverObject(EngineID engine_type, const Vehicle *v, bool info_view,
+VehicleResolverObject::VehicleResolverObject(EngineID engine_type, const Vehicle *v, WagonOverride wagon_override, bool info_view,
 		CallbackID callback, uint32 callback_param1, uint32 callback_param2)
 	: ResolverObject(GetEngineGrfFile(engine_type), callback, callback_param1, callback_param2),
 	self_scope(*this, engine_type, v, info_view),
@@ -986,55 +987,37 @@ VehicleResolverObject::VehicleResolverObject(EngineID engine_type, const Vehicle
 	relative_scope(*this, engine_type, v, info_view),
 	cached_relative_count(0)
 {
-}
-
-/**
- * Retrieve the SpriteGroup for the specified vehicle.
- * If the vehicle is not specified, the purchase list group for the engine is
- * chosen. For trains, an additional engine override lookup is performed.
- * @param engine    Engine type of the vehicle.
- * @param v         The vehicle itself.
- * @param use_cache Use cached override
- * @returns         The selected SpriteGroup for the vehicle.
- */
-static const SpriteGroup *GetVehicleSpriteGroup(EngineID engine, const Vehicle *v, bool use_cache = true)
-{
-	const SpriteGroup *group;
-	CargoID cargo;
-
-	if (v == NULL) {
-		cargo = CT_PURCHASE;
+	if (wagon_override == WO_SELF) {
+		this->root_spritegroup = GetWagonOverrideSpriteSet(engine_type, CT_DEFAULT, engine_type);
 	} else {
-		cargo = v->cargo_type;
+		if (wagon_override != WO_NONE && v != NULL && v->IsGroundVehicle()) {
+			assert(v->engine_type == engine_type); // overrides make little sense with fake scopes
 
-		if (v->IsGroundVehicle()) {
 			/* For trains we always use cached value, except for callbacks because the override spriteset
 			 * to use may be different than the one cached. It happens for callback 0x15 (refit engine),
 			 * as v->cargo_type is temporary changed to the new type */
-			if (use_cache && v->type == VEH_TRAIN) {
-				group = Train::From(v)->tcache.cached_override;
+			if (wagon_override == WO_CACHED && v->type == VEH_TRAIN) {
+				this->root_spritegroup = Train::From(v)->tcache.cached_override;
 			} else {
-				group = GetWagonOverrideSpriteSet(v->engine_type, v->cargo_type, v->GetGroundVehicleCache()->first_engine);
+				this->root_spritegroup = GetWagonOverrideSpriteSet(v->engine_type, v->cargo_type, v->GetGroundVehicleCache()->first_engine);
 			}
-			if (group != NULL) return group;
 		}
-	}
 
-	const Engine *e = Engine::Get(engine);
-
-	assert(cargo < lengthof(e->grf_prop.spritegroup));
-	group = e->grf_prop.spritegroup[cargo];
-	if (group != NULL) return group;
-
-	/* Fall back to the default set if the selected cargo type is not defined */
-	return e->grf_prop.spritegroup[CT_DEFAULT];
+		if (this->root_spritegroup == NULL) {
+			const Engine *e = Engine::Get(engine_type);
+			CargoID cargo = v != NULL ? v->cargo_type : CT_PURCHASE;
+			assert(cargo < lengthof(e->grf_prop.spritegroup));
+			this->root_spritegroup = e->grf_prop.spritegroup[cargo] != NULL ? e->grf_prop.spritegroup[cargo] : e->grf_prop.spritegroup[CT_DEFAULT];
+		}
+	}
 }
 
 
+
 SpriteID GetCustomEngineSprite(EngineID engine, const Vehicle *v, Direction direction, EngineImageType image_type)
 {
-	VehicleResolverObject object(engine, v, false, CBID_NO_CALLBACK, image_type);
-	const SpriteGroup *group = SpriteGroup::Resolve(GetVehicleSpriteGroup(engine, v), object);
+	VehicleResolverObject object(engine, v, VehicleResolverObject::WO_CACHED, false, CBID_NO_CALLBACK, image_type);
+	const SpriteGroup *group = object.Resolve();
 	if (group == NULL || group->GetNumResults() == 0) return 0;
 
 	return group->GetResult() + (direction % group->GetNumResults());
@@ -1049,15 +1032,14 @@ SpriteID GetRotorOverrideSprite(EngineID engine, const Aircraft *v, bool info_vi
 	assert(e->type == VEH_AIRCRAFT);
 	assert(!(e->u.air.subtype & AIR_CTOL));
 
-	VehicleResolverObject object(engine, v, info_view, CBID_NO_CALLBACK, image_type);
-	const SpriteGroup *group = GetWagonOverrideSpriteSet(engine, CT_DEFAULT, engine);
-	group = SpriteGroup::Resolve(group, object);
+	VehicleResolverObject object(engine, v, VehicleResolverObject::WO_SELF, info_view, CBID_NO_CALLBACK, image_type);
+	const SpriteGroup *group = object.Resolve();
 
 	if (group == NULL || group->GetNumResults() == 0) return 0;
 
-	if (v == NULL) return group->GetResult();
+	if (v == NULL || info_view) return group->GetResult();
 
-	return group->GetResult() + (info_view ? 0 : (v->Next()->Next()->state % group->GetNumResults()));
+	return group->GetResult() + (v->Next()->Next()->state % group->GetNumResults());
 }
 
 
@@ -1083,11 +1065,8 @@ bool UsesWagonOverride(const Vehicle *v)
  */
 uint16 GetVehicleCallback(CallbackID callback, uint32 param1, uint32 param2, EngineID engine, const Vehicle *v)
 {
-	VehicleResolverObject object(engine, v, false, callback, param1, param2);
-	const SpriteGroup *group = SpriteGroup::Resolve(GetVehicleSpriteGroup(engine, v, false), object);
-	if (group == NULL) return CALLBACK_FAILED;
-
-	return group->GetCallbackResult();
+	VehicleResolverObject object(engine, v, VehicleResolverObject::WO_UNCACHED, false, callback, param1, param2);
+	return object.ResolveCallback();
 }
 
 /**
@@ -1102,13 +1081,9 @@ uint16 GetVehicleCallback(CallbackID callback, uint32 param1, uint32 param2, Eng
  */
 uint16 GetVehicleCallbackParent(CallbackID callback, uint32 param1, uint32 param2, EngineID engine, const Vehicle *v, const Vehicle *parent)
 {
-	VehicleResolverObject object(engine, v, false, callback, param1, param2);
+	VehicleResolverObject object(engine, v, VehicleResolverObject::WO_NONE, false, callback, param1, param2);
 	object.parent_scope.SetVehicle(parent);
-
-	const SpriteGroup *group = SpriteGroup::Resolve(GetVehicleSpriteGroup(engine, v, false), object);
-	if (group == NULL) return CALLBACK_FAILED;
-
-	return group->GetCallbackResult();
+	return object.ResolveCallback();
 }
 
 
@@ -1133,10 +1108,10 @@ static void DoTriggerVehicle(Vehicle *v, VehicleTrigger trigger, byte base_rando
 	/* We can't trigger a non-existent vehicle... */
 	assert(v != NULL);
 
-	VehicleResolverObject object(v->engine_type, v, false, CBID_RANDOM_TRIGGER);
+	VehicleResolverObject object(v->engine_type, v, VehicleResolverObject::WO_CACHED, false, CBID_RANDOM_TRIGGER);
 	object.trigger = trigger;
 
-	const SpriteGroup *group = SpriteGroup::Resolve(GetVehicleSpriteGroup(v->engine_type, v), object);
+	const SpriteGroup *group = object.Resolve();
 	if (group == NULL) return;
 
 	byte new_random_bits = Random();
@@ -1300,7 +1275,7 @@ void CommitVehicleListOrderChanges()
  */
 void FillNewGRFVehicleCache(const Vehicle *v)
 {
-	VehicleResolverObject ro(v->engine_type, v);
+	VehicleResolverObject ro(v->engine_type, v, VehicleResolverObject::WO_NONE);
 
 	/* These variables we have to check; these are the ones with a cache. */
 	static const int cache_entries[][2] = {
diff --git a/src/newgrf_engine.h b/src/newgrf_engine.h
index 5e1661cca..4a6f211c4 100644
--- a/src/newgrf_engine.h
+++ b/src/newgrf_engine.h
@@ -38,13 +38,21 @@ struct VehicleScopeResolver : public ScopeResolver {
 
 /** Resolver for a vehicle (chain) */
 struct VehicleResolverObject : public ResolverObject {
+	/** Application of 'wagon overrides'. */
+	enum WagonOverride {
+		WO_NONE,     //!< Resolve no wagon overrides.
+		WO_UNCACHED, //!< Resolve wagon overrides.
+		WO_CACHED,   //!< Resolve wagon overrides using TrainCache::cached_override.
+		WO_SELF,     //!< Resolve self-override (helicopter rotors and such).
+	};
+
 	VehicleScopeResolver self_scope;     ///< Scope resolver for the indicated vehicle.
 	VehicleScopeResolver parent_scope;   ///< Scope resolver for its parent vehicle.
 
 	VehicleScopeResolver relative_scope; ///< Scope resolver for an other vehicle in the chain.
 	byte cached_relative_count;          ///< Relative position of the other vehicle.
 
-	VehicleResolverObject(EngineID engine_type, const Vehicle *v, bool info_view = false,
+	VehicleResolverObject(EngineID engine_type, const Vehicle *v, WagonOverride wagon_override, bool info_view = false,
 			CallbackID callback = CBID_NO_CALLBACK, uint32 callback_param1 = 0, uint32 callback_param2 = 0);
 
 	/* virtual */ ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, byte relative = 0);
diff --git a/src/newgrf_generic.cpp b/src/newgrf_generic.cpp
index f1305636d..55eee6d23 100644
--- a/src/newgrf_generic.cpp
+++ b/src/newgrf_generic.cpp
@@ -179,17 +179,17 @@ static uint16 GetGenericCallbackResult(uint8 feature, ResolverObject &object, ui
 
 	/* Test each feature callback sprite group. */
 	for (GenericCallbackList::const_iterator it = _gcl[feature].begin(); it != _gcl[feature].end(); ++it) {
-		const SpriteGroup *group = it->group;
 		object.grffile = it->file;
+		object.root_spritegroup = it->group;
 		/* Set callback param based on GRF version. */
 		object.callback_param1 = it->file->grf_version >= 8 ? param1_grfv8 : param1_grfv7;
-		group = SpriteGroup::Resolve(group, object);
-		if (group == NULL || group->GetCallbackResult() == CALLBACK_FAILED) continue;
+		uint16 result = object.ResolveCallback();
+		if (result == CALLBACK_FAILED) continue;
 
 		/* Return NewGRF file if necessary */
 		if (file != NULL) *file = it->file;
 
-		return group->GetCallbackResult();
+		return result;
 	}
 
 	/* No callback returned a valid result, so we've failed. */
diff --git a/src/newgrf_house.cpp b/src/newgrf_house.cpp
index a31ac4bc4..c660fe3ab 100644
--- a/src/newgrf_house.cpp
+++ b/src/newgrf_house.cpp
@@ -81,6 +81,7 @@ HouseResolverObject::HouseResolverObject(HouseID house_id, TileIndex tile, Town
 	house_scope(*this, house_id, tile, town, not_yet_constructed, initial_random_bits, watched_cargo_triggers),
 	town_scope(*this, town, not_yet_constructed) // Don't access StorePSA if house is not yet constructed.
 {
+	this->root_spritegroup = HouseSpec::Get(house_id)->grf_prop.spritegroup[0];
 }
 
 HouseClassID AllocateHouseClassID(byte grf_class_id, uint32 grfid)
@@ -439,11 +440,7 @@ uint16 GetHouseCallback(CallbackID callback, uint32 param1, uint32 param2, House
 
 	HouseResolverObject object(house_id, tile, town, callback, param1, param2,
 			not_yet_constructed, initial_random_bits, watched_cargo_triggers);
-
-	const SpriteGroup *group = SpriteGroup::Resolve(HouseSpec::Get(house_id)->grf_prop.spritegroup[0], object);
-	if (group == NULL) return CALLBACK_FAILED;
-
-	return group->GetCallbackResult();
+	return object.ResolveCallback();
 }
 
 static void DrawTileLayout(const TileInfo *ti, const TileLayoutSpriteGroup *group, byte stage, HouseID house_id)
@@ -490,7 +487,7 @@ void DrawNewHouseTile(TileInfo *ti, HouseID house_id)
 
 	HouseResolverObject object(house_id, ti->tile, Town::GetByTile(ti->tile));
 
-	const SpriteGroup *group = SpriteGroup::Resolve(hs->grf_prop.spritegroup[0], object);
+	const SpriteGroup *group = object.Resolve();
 	if (group != NULL && group->type == SGT_TILELAYOUT) {
 		/* Limit the building stage to the number of stages supplied. */
 		const TileLayoutSpriteGroup *tlgroup = (const TileLayoutSpriteGroup *)group;
@@ -615,7 +612,7 @@ static void DoTriggerHouse(TileIndex tile, HouseTrigger trigger, byte base_rando
 	HouseResolverObject object(hid, tile, Town::GetByTile(tile), CBID_RANDOM_TRIGGER);
 	object.trigger = trigger;
 
-	const SpriteGroup *group = SpriteGroup::Resolve(hs->grf_prop.spritegroup[0], object);
+	const SpriteGroup *group = object.Resolve();
 	if (group == NULL) return;
 
 	byte new_random_bits = Random();
diff --git a/src/newgrf_industries.cpp b/src/newgrf_industries.cpp
index dfc615b29..725373d10 100644
--- a/src/newgrf_industries.cpp
+++ b/src/newgrf_industries.cpp
@@ -432,6 +432,7 @@ IndustriesResolverObject::IndustriesResolverObject(TileIndex tile, Industry *ind
 	industries_scope(*this, tile, indus, type, random_bits),
 	town_scope(NULL)
 {
+	this->root_spritegroup = GetIndustrySpec(type)->grf_prop.spritegroup[0];
 }
 
 IndustriesResolverObject::~IndustriesResolverObject()
@@ -490,10 +491,7 @@ IndustriesScopeResolver::IndustriesScopeResolver(ResolverObject &ro, TileIndex t
 uint16 GetIndustryCallback(CallbackID callback, uint32 param1, uint32 param2, Industry *industry, IndustryType type, TileIndex tile)
 {
 	IndustriesResolverObject object(tile, industry, type, 0, callback, param1, param2);
-	const SpriteGroup *group = SpriteGroup::Resolve(GetIndustrySpec(type)->grf_prop.spritegroup[0], object);
-	if (group == NULL) return CALLBACK_FAILED;
-
-	return group->GetCallbackResult();
+	return object.ResolveCallback();
 }
 
 /**
@@ -523,12 +521,10 @@ CommandCost CheckIfCallBackAllowsCreation(TileIndex tile, IndustryType type, uin
 	ind.psa = NULL;
 
 	IndustriesResolverObject object(tile, &ind, type, seed, CBID_INDUSTRY_LOCATION, 0, creation_type);
-	const SpriteGroup *group = SpriteGroup::Resolve(GetIndustrySpec(type)->grf_prop.spritegroup[0], object);
+	uint16 result = object.ResolveCallback();
 
 	/* Unlike the "normal" cases, not having a valid result means we allow
 	 * the building of the industry, as that's how it's done in TTDP. */
-	if (group == NULL) return CommandCost();
-	uint16 result = group->GetCallbackResult();
 	if (result == CALLBACK_FAILED) return CommandCost();
 
 	return GetErrorMessageFromLocationCallbackResult(result, indspec->grf_prop.grffile, STR_ERROR_SITE_UNSUITABLE);
@@ -596,7 +592,7 @@ void IndustryProductionCallback(Industry *ind, int reason)
 		}
 
 		SB(object.callback_param2, 8, 16, loop);
-		const SpriteGroup *tgroup = SpriteGroup::Resolve(spec->grf_prop.spritegroup[0], object);
+		const SpriteGroup *tgroup = object.Resolve();
 		if (tgroup == NULL || tgroup->type != SGT_INDUSTRY_PRODUCTION) break;
 		const IndustryProductionSpriteGroup *group = (const IndustryProductionSpriteGroup *)tgroup;
 
diff --git a/src/newgrf_industrytiles.cpp b/src/newgrf_industrytiles.cpp
index 7e31c1bc4..f22514a03 100644
--- a/src/newgrf_industrytiles.cpp
+++ b/src/newgrf_industrytiles.cpp
@@ -147,6 +147,7 @@ IndustryTileResolverObject::IndustryTileResolverObject(IndustryGfx gfx, TileInde
 	indtile_scope(*this, indus, tile),
 	ind_scope(*this, tile, indus, indus->type)
 {
+	this->root_spritegroup = GetIndustryTileSpec(gfx)->grf_prop.spritegroup[0];
 }
 
 /**
@@ -190,10 +191,7 @@ uint16 GetIndustryTileCallback(CallbackID callback, uint32 param1, uint32 param2
 	assert(industry->index == INVALID_INDUSTRY || IsTileType(tile, MP_INDUSTRY));
 
 	IndustryTileResolverObject object(gfx_id, tile, industry, callback, param1, param2);
-	const SpriteGroup *group = SpriteGroup::Resolve(GetIndustryTileSpec(gfx_id)->grf_prop.spritegroup[0], object);
-	if (group == NULL || group->type != SGT_CALLBACK) return CALLBACK_FAILED;
-
-	return group->GetCallbackResult();
+	return object.ResolveCallback();
 }
 
 bool DrawNewIndustryTile(TileInfo *ti, Industry *i, IndustryGfx gfx, const IndustryTileSpec *inds)
@@ -211,7 +209,7 @@ bool DrawNewIndustryTile(TileInfo *ti, Industry *i, IndustryGfx gfx, const Indus
 
 	IndustryTileResolverObject object(gfx, ti->tile, i);
 
-	const SpriteGroup *group = SpriteGroup::Resolve(inds->grf_prop.spritegroup[0], object);
+	const SpriteGroup *group = object.Resolve();
 	if (group == NULL || group->type != SGT_TILELAYOUT) return false;
 
 	/* Limit the building stage to the number of stages supplied. */
@@ -328,7 +326,7 @@ static void DoTriggerIndustryTile(TileIndex tile, IndustryTileTrigger trigger, I
 	IndustryTileResolverObject object(gfx, tile, ind, CBID_RANDOM_TRIGGER);
 	object.trigger = trigger;
 
-	const SpriteGroup *group = SpriteGroup::Resolve(itspec->grf_prop.spritegroup[0], object);
+	const SpriteGroup *group = object.Resolve();
 	if (group == NULL) return;
 
 	byte new_random_bits = Random();
diff --git a/src/newgrf_object.cpp b/src/newgrf_object.cpp
index 3917b6510..6f7e3f0ff 100644
--- a/src/newgrf_object.cpp
+++ b/src/newgrf_object.cpp
@@ -356,24 +356,6 @@ unhandled:
 }
 
 /**
- * Get the object's sprite group.
- * @param spec The specification to get the sprite group from.
- * @param o    The object to get he sprite group for.
- * @return The resolved sprite group.
- */
-static const SpriteGroup *GetObjectSpriteGroup(const ObjectSpec *spec, const Object *o)
-{
-	const SpriteGroup *group = NULL;
-
-	if (o == NULL) group = spec->grf_prop.spritegroup[CT_PURCHASE_OBJECT];
-	if (group != NULL) return group;
-
-	/* Fall back to the default set if the selected cargo type is not defined */
-	return spec->grf_prop.spritegroup[0];
-
-}
-
-/**
  * Constructor of the object resolver.
  * @param obj Object being resolved.
  * @param tile %Tile of the object.
@@ -387,6 +369,8 @@ ObjectResolverObject::ObjectResolverObject(const ObjectSpec *spec, Object *obj,
 	: ResolverObject(spec->grf_prop.grffile, callback, param1, param2), object_scope(*this, obj, tile, view)
 {
 	this->town_scope = NULL;
+	this->root_spritegroup = (obj == NULL && spec->grf_prop.spritegroup[CT_PURCHASE_OBJECT] != NULL) ?
+			spec->grf_prop.spritegroup[CT_PURCHASE_OBJECT] : spec->grf_prop.spritegroup[0];
 }
 
 ObjectResolverObject::~ObjectResolverObject()
@@ -428,10 +412,7 @@ TownScopeResolver *ObjectResolverObject::GetTown()
 uint16 GetObjectCallback(CallbackID callback, uint32 param1, uint32 param2, const ObjectSpec *spec, Object *o, TileIndex tile, uint8 view)
 {
 	ObjectResolverObject object(spec, o, tile, view, callback, param1, param2);
-	const SpriteGroup *group = SpriteGroup::Resolve(GetObjectSpriteGroup(spec, o), object);
-	if (group == NULL) return CALLBACK_FAILED;
-
-	return group->GetCallbackResult();
+	return object.ResolveCallback();
 }
 
 /**
@@ -471,7 +452,7 @@ void DrawNewObjectTile(TileInfo *ti, const ObjectSpec *spec)
 	Object *o = Object::GetByTile(ti->tile);
 	ObjectResolverObject object(spec, o, ti->tile);
 
-	const SpriteGroup *group = SpriteGroup::Resolve(GetObjectSpriteGroup(spec, o), object);
+	const SpriteGroup *group = object.Resolve();
 	if (group == NULL || group->type != SGT_TILELAYOUT) return;
 
 	DrawTileLayout(ti, (const TileLayoutSpriteGroup *)group, spec);
@@ -487,7 +468,7 @@ void DrawNewObjectTile(TileInfo *ti, const ObjectSpec *spec)
 void DrawNewObjectTileInGUI(int x, int y, const ObjectSpec *spec, uint8 view)
 {
 	ObjectResolverObject object(spec, NULL, INVALID_TILE, view);
-	const SpriteGroup *group = SpriteGroup::Resolve(GetObjectSpriteGroup(spec, NULL), object);
+	const SpriteGroup *group = object.Resolve();
 	if (group == NULL || group->type != SGT_TILELAYOUT) return;
 
 	const DrawTileSprites *dts = ((const TileLayoutSpriteGroup *)group)->ProcessRegisters(NULL);
diff --git a/src/newgrf_railtype.cpp b/src/newgrf_railtype.cpp
index de735193f..f43689698 100644
--- a/src/newgrf_railtype.cpp
+++ b/src/newgrf_railtype.cpp
@@ -79,15 +79,17 @@ RailTypeScopeResolver::RailTypeScopeResolver(ResolverObject &ro, TileIndex tile,
 
 /**
  * Resolver object for rail types.
+ * @param rti Railtype. NULL in NewGRF Inspect window.
  * @param tile %Tile containing the track. For track on a bridge this is the southern bridgehead.
  * @param context Are we resolving sprites for the upper halftile, or on a bridge?
- * @param grffile The GRF to do the lookup for.
+ * @param rtsg Railpart of interest
  * @param param1 Extra parameter (first parameter of the callback, except railtypes do not have callbacks).
  * @param param2 Extra parameter (second parameter of the callback, except railtypes do not have callbacks).
  */
-RailTypeResolverObject::RailTypeResolverObject(TileIndex tile, TileContext context, const GRFFile *grffile, uint32 param1, uint32 param2)
-	: ResolverObject(grffile, CBID_NO_CALLBACK, param1, param2), railtype_scope(*this, tile, context)
+RailTypeResolverObject::RailTypeResolverObject(const RailtypeInfo *rti, TileIndex tile, TileContext context, RailTypeSpriteGroup rtsg, uint32 param1, uint32 param2)
+	: ResolverObject(rti != NULL ? rti->grffile[rtsg] : NULL, CBID_NO_CALLBACK, param1, param2), railtype_scope(*this, tile, context)
 {
+	this->root_spritegroup = rti != NULL ? rti->group[rtsg] : NULL;
 }
 
 /**
@@ -104,8 +106,8 @@ SpriteID GetCustomRailSprite(const RailtypeInfo *rti, TileIndex tile, RailTypeSp
 
 	if (rti->group[rtsg] == NULL) return 0;
 
-	RailTypeResolverObject object(tile, context, rti->grffile[rtsg]);
-	const SpriteGroup *group = SpriteGroup::Resolve(rti->group[rtsg], object);
+	RailTypeResolverObject object(rti, tile, context, rtsg);
+	const SpriteGroup *group = object.Resolve();
 	if (group == NULL || group->GetNumResults() == 0) return 0;
 
 	return group->GetResult();
@@ -127,9 +129,9 @@ SpriteID GetCustomSignalSprite(const RailtypeInfo *rti, TileIndex tile, SignalTy
 
 	uint32 param1 = gui ? 0x10 : 0x00;
 	uint32 param2 = (type << 16) | (var << 8) | state;
-	RailTypeResolverObject object(tile, TCX_NORMAL, rti->grffile[RTSG_SIGNALS], param1, param2);
+	RailTypeResolverObject object(rti, tile, TCX_NORMAL, RTSG_SIGNALS, param1, param2);
 
-	const SpriteGroup *group = SpriteGroup::Resolve(rti->group[RTSG_SIGNALS], object);
+	const SpriteGroup *group = object.Resolve();
 	if (group == NULL || group->GetNumResults() == 0) return 0;
 
 	return group->GetResult();
diff --git a/src/newgrf_railtype.h b/src/newgrf_railtype.h
index 8c5bce843..9b00bf5bf 100644
--- a/src/newgrf_railtype.h
+++ b/src/newgrf_railtype.h
@@ -31,7 +31,7 @@ struct RailTypeScopeResolver : public ScopeResolver {
 struct RailTypeResolverObject : public ResolverObject {
 	RailTypeScopeResolver railtype_scope; ///< Resolver for the railtype scope.
 
-	RailTypeResolverObject(TileIndex tile, TileContext context, const GRFFile *grffile, uint32 param1 = 0, uint32 param2 = 0);
+	RailTypeResolverObject(const RailtypeInfo *rti, TileIndex tile, TileContext context, RailTypeSpriteGroup rtsg, uint32 param1 = 0, uint32 param2 = 0);
 
 	/* virtual */ ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, byte relative = 0)
 	{
diff --git a/src/newgrf_spritegroup.cpp b/src/newgrf_spritegroup.cpp
index b3a0a829f..59fc70fe4 100644
--- a/src/newgrf_spritegroup.cpp
+++ b/src/newgrf_spritegroup.cpp
@@ -150,6 +150,7 @@ ResolverObject::ResolverObject(const GRFFile *grffile, CallbackID callback, uint
 	this->ResetState();
 
 	this->grffile = grffile;
+	this->root_spritegroup = NULL;
 }
 
 ResolverObject::~ResolverObject() {}
diff --git a/src/newgrf_spritegroup.h b/src/newgrf_spritegroup.h
index c3753dcfd..0a7705d66 100644
--- a/src/newgrf_spritegroup.h
+++ b/src/newgrf_spritegroup.h
@@ -321,6 +321,26 @@ struct ResolverObject {
 	uint32 reseed[VSG_END];     ///< Collects bits to rerandomise while triggering triggers.
 
 	const GRFFile *grffile;     ///< GRFFile the resolved SpriteGroup belongs to
+	const SpriteGroup *root_spritegroup; ///< Root SpriteGroup to use for resolving
+
+	/**
+	 * Resolve SpriteGroup.
+	 * @return Result spritegroup.
+	 */
+	const SpriteGroup *Resolve()
+	{
+		return SpriteGroup::Resolve(this->root_spritegroup, *this);
+	}
+
+	/**
+	 * Resolve callback.
+	 * @return Callback result.
+	 */
+	uint16 ResolveCallback()
+	{
+		const SpriteGroup *result = Resolve();
+		return result != NULL ? result->GetCallbackResult() : CALLBACK_FAILED;
+	}
 
 	virtual const SpriteGroup *ResolveReal(const RealSpriteGroup *group) const;
 
diff --git a/src/newgrf_station.cpp b/src/newgrf_station.cpp
index 85277337d..647e8781a 100644
--- a/src/newgrf_station.cpp
+++ b/src/newgrf_station.cpp
@@ -550,6 +550,32 @@ StationResolverObject::StationResolverObject(const StationSpec *statspec, BaseSt
 {
 	/* Invalidate all cached vars */
 	_svc.valid = 0;
+
+	CargoID ctype = CT_DEFAULT_NA;
+
+	if (this->station_scope.st == NULL) {
+		/* No station, so we are in a purchase list */
+		ctype = CT_PURCHASE;
+	} else if (Station::IsExpected(this->station_scope.st)) {
+		const Station *st = Station::From(this->station_scope.st);
+		/* Pick the first cargo that we have waiting */
+		const CargoSpec *cs;
+		FOR_ALL_CARGOSPECS(cs) {
+			if (this->station_scope.statspec->grf_prop.spritegroup[cs->Index()] != NULL &&
+					st->goods[cs->Index()].cargo.TotalCount() > 0) {
+				ctype = cs->Index();
+				break;
+			}
+		}
+	}
+
+	if (this->station_scope.statspec->grf_prop.spritegroup[ctype] == NULL) {
+		ctype = CT_DEFAULT;
+	}
+
+	/* Remember the cargo type we've picked */
+	this->station_scope.cargo_type = ctype;
+	this->root_spritegroup = this->station_scope.statspec->grf_prop.spritegroup[this->station_scope.cargo_type];
 }
 
 StationResolverObject::~StationResolverObject()
@@ -574,39 +600,6 @@ StationScopeResolver::StationScopeResolver(ResolverObject &ro, const StationSpec
 	this->axis = INVALID_AXIS;
 }
 
-static const SpriteGroup *ResolveStation(StationResolverObject &object)
-{
-	CargoID ctype = CT_DEFAULT_NA;
-
-	if (object.station_scope.st == NULL) {
-		/* No station, so we are in a purchase list */
-		ctype = CT_PURCHASE;
-	} else if (Station::IsExpected(object.station_scope.st)) {
-		const Station *st = Station::From(object.station_scope.st);
-		/* Pick the first cargo that we have waiting */
-		const CargoSpec *cs;
-		FOR_ALL_CARGOSPECS(cs) {
-			if (object.station_scope.statspec->grf_prop.spritegroup[cs->Index()] != NULL &&
-					st->goods[cs->Index()].cargo.TotalCount() > 0) {
-				ctype = cs->Index();
-				break;
-			}
-		}
-	}
-
-	const SpriteGroup *group = object.station_scope.statspec->grf_prop.spritegroup[ctype];
-	if (group == NULL) {
-		ctype = CT_DEFAULT;
-		group = object.station_scope.statspec->grf_prop.spritegroup[ctype];
-		if (group == NULL) return NULL;
-	}
-
-	/* Remember the cargo type we've picked */
-	object.station_scope.cargo_type = ctype;
-
-	return SpriteGroup::Resolve(group, object);
-}
-
 /**
  * Resolve sprites for drawing a station tile.
  * @param statspec Station spec
@@ -618,7 +611,7 @@ static const SpriteGroup *ResolveStation(StationResolverObject &object)
 SpriteID GetCustomStationRelocation(const StationSpec *statspec, BaseStation *st, TileIndex tile, uint32 var10)
 {
 	StationResolverObject object(statspec, st, tile, CBID_NO_CALLBACK, var10);
-	const SpriteGroup *group = ResolveStation(object);
+	const SpriteGroup *group = object.Resolve();
 	if (group == NULL || group->type != SGT_RESULT) return 0;
 	return group->GetResult() - 0x42D;
 }
@@ -637,7 +630,7 @@ SpriteID GetCustomStationFoundationRelocation(const StationSpec *statspec, BaseS
 	/* callback_param1 == 2 means  we are resolving the foundation sprites. */
 	StationResolverObject object(statspec, st, tile, CBID_NO_CALLBACK, 2, layout | (edge_info << 16));
 
-	const SpriteGroup *group = ResolveStation(object);
+	const SpriteGroup *group = object.Resolve();
 	if (group == NULL || group->type != SGT_RESULT) return 0;
 
 	/* Note: SpriteGroup::Resolve zeroes all registers, so register 0x100 is initialised to 0. (compatibility) */
@@ -648,9 +641,7 @@ SpriteID GetCustomStationFoundationRelocation(const StationSpec *statspec, BaseS
 uint16 GetStationCallback(CallbackID callback, uint32 param1, uint32 param2, const StationSpec *statspec, BaseStation *st, TileIndex tile)
 {
 	StationResolverObject object(statspec, st, tile, callback, param1, param2);
-	const SpriteGroup *group = ResolveStation(object);
-	if (group == NULL) return CALLBACK_FAILED;
-	return group->GetCallbackResult();
+	return object.ResolveCallback();
 }
 
 /**
@@ -673,8 +664,7 @@ CommandCost PerformStationTileSlopeCheck(TileIndex north_tile, TileIndex cur_til
 			(numtracks << 24) | (plat_len << 16) | (axis == AXIS_Y ? TileX(diff) << 8 | TileY(diff) : TileY(diff) << 8 | TileX(diff)));
 	object.station_scope.axis = axis;
 
-	const SpriteGroup *group = ResolveStation(object);
-	uint16 cb_res = group != NULL ? group->GetCallbackResult() : CALLBACK_FAILED;
+	uint16 cb_res = object.ResolveCallback();
 
 	/* Failed callback means success. */
 	if (cb_res == CALLBACK_FAILED) return CommandCost();
@@ -1024,7 +1014,7 @@ void TriggerStationRandomisation(Station *st, TileIndex tile, StationRandomTrigg
 				StationResolverObject object(ss, st, tile, CBID_RANDOM_TRIGGER, 0);
 				object.trigger = trigger_bit;
 
-				const SpriteGroup *group = ResolveStation(object);
+				const SpriteGroup *group = object.Resolve();
 				if (group == NULL) continue;
 
 				uint32 reseed = object.GetReseedSum();
diff --git a/src/table/newgrf_debug_data.h b/src/table/newgrf_debug_data.h
index b4756882f..4814ae50c 100644
--- a/src/table/newgrf_debug_data.h
+++ b/src/table/newgrf_debug_data.h
@@ -79,7 +79,7 @@ class NIHVehicle : public NIHelper {
 	/* virtual */ uint Resolve(uint index, uint var, uint param, bool *avail) const
 	{
 		Vehicle *v = Vehicle::Get(index);
-		VehicleResolverObject ro(v->engine_type, v);
+		VehicleResolverObject ro(v->engine_type, v, VehicleResolverObject::WO_CACHED);
 		return ro.GetScope(VSG_SCOPE_SELF)->GetVariable(var, param, avail);
 	}
 };
@@ -429,7 +429,7 @@ class NIHRailType : public NIHelper {
 	{
 		/* There is no unique GRFFile for the tile. Multiple GRFs can define different parts of the railtype.
 		 * However, currently the NewGRF Debug GUI does not display variables depending on the GRF (like 0x7F) anyway. */
-		RailTypeResolverObject ro(index, TCX_NORMAL, NULL);
+		RailTypeResolverObject ro(NULL, index, TCX_NORMAL, RTSG_END);
 		return ro.GetScope(VSG_SCOPE_SELF)->GetVariable(var, param, avail);
 	}
 };