--- a/projects/openttd.vcproj	Tue May 15 17:54:46 2007 +0000
+++ b/projects/openttd.vcproj	Tue May 15 21:36:58 2007 +0000
@@ -519,6 +519,9 @@
 				RelativePath=".\..\src\newgrf_cargo.h">
 			</File>
 			<File
+				RelativePath=".\..\src\newgrf_commons.h">
+			</File>
+			<File
 				RelativePath=".\..\src\newgrf_config.h">
 			</File>
 			<File
@@ -947,6 +950,9 @@
 				RelativePath=".\..\src\newgrf_cargo.cpp">
 			</File>
 			<File
+				RelativePath=".\..\src\newgrf_commons.cpp">
+			</File>
+			<File
 				RelativePath=".\..\src\newgrf_config.cpp">
 			</File>
 			<File

--- a/projects/openttd_vs80.vcproj	Tue May 15 17:54:46 2007 +0000
+++ b/projects/openttd_vs80.vcproj	Tue May 15 21:36:58 2007 +0000
@@ -920,6 +920,10 @@
 				>
 			</File>
 			<File
+				RelativePath=".\..\src\newgrf_commons.h"
+				>
+			</File>
+			<File
 				RelativePath=".\..\src\newgrf_config.h"
 				>
 			</File>
@@ -1484,6 +1488,10 @@
 				>
 			</File>
 			<File
+				RelativePath=".\..\src\newgrf_commons.cpp"
+				>
+			</File>
+			<File
 				RelativePath=".\..\src\newgrf_config.cpp"
 				>
 			</File>

--- a/source.list	Tue May 15 17:54:46 2007 +0000
+++ b/source.list	Tue May 15 21:36:58 2007 +0000
@@ -140,6 +140,7 @@
 newgrf_callbacks.h
 newgrf_canal.h
 newgrf_cargo.h
+newgrf_commons.h
 newgrf_config.h
 newgrf_engine.h
 newgrf_house.h
@@ -286,6 +287,7 @@
 newgrf.cpp
 newgrf_canal.cpp
 newgrf_cargo.cpp
+newgrf_commons.cpp
 newgrf_config.cpp
 newgrf_engine.cpp
 newgrf_house.cpp

--- a/src/newgrf.cpp	Tue May 15 17:54:46 2007 +0000
+++ b/src/newgrf.cpp	Tue May 15 21:36:58 2007 +0000
@@ -40,6 +40,7 @@
 #include "cargotype.h"
 #include "industry.h"
 #include "newgrf_canal.h"
+#include "newgrf_commons.h"
 
 /* TTDPatch extended GRF format codec
  * (c) Petr Baudis 2004 (GPL'd)
@@ -1246,7 +1247,7 @@
 		_cur_grffile->housespec = CallocT<HouseSpec*>(HOUSE_MAX);
 
 		/* Reset any overrides that have been set. */
-		ResetHouseOverrides();
+		_house_mngr.ResetOverride();
 	}
 
 	housespec = &_cur_grffile->housespec[hid];
@@ -1372,7 +1373,7 @@
 					return false;
 				}
 
-				AddHouseOverride(hid, override);
+				_house_mngr.Add(hid, override);
 			}
 			break;
 
@@ -4591,7 +4592,7 @@
 		for (int i = 0; i < HOUSE_MAX; i++) {
 			HouseSpec *hs = file->housespec[i];
 			if (hs != NULL) {
-				SetHouseSpec(hs);
+				_house_mngr.SetEntitySpec(hs);
 				if (hs->min_date < 1930) reset_dates = false;
 			}
 		}

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/newgrf_commons.cpp	Tue May 15 21:36:58 2007 +0000
@@ -0,0 +1,150 @@
+/* $Id$ */
+
+/** @file newgrf_commons.cpp Implementation of the class OverrideManagerBase
+ * and its descendance, present and futur
+ */
+
+#include "stdafx.h"
+#include "openttd.h"
+#include "town.h"
+#include "industry.h"
+#include "newgrf.h"
+#include "newgrf_commons.h"
+
+/** Constructor of generic class
+ * @param offset end of original data for this entity. i.e: houses = 110
+ * @param maximum of entities this manager can deal with. i.e: houses = 512
+ * @param invalid is the ID used to identify an invalid entity id
+ */
+OverrideManagerBase::OverrideManagerBase(uint16 offset, uint16 maximum, uint16 invalid)
+{
+	max_offset = offset;
+	max_new_entities = maximum;
+	invalid_ID = invalid;
+
+	mapping_ID = CallocT<EntityIDMapping>(max_new_entities);
+	entity_overrides = MallocT<uint16>(max_offset);
+	memset(entity_overrides, invalid, sizeof(entity_overrides));
+}
+
+/** Destructor of the generic class.
+ * Frees allocated memory of constructor
+ */
+OverrideManagerBase::~OverrideManagerBase()
+{
+	free(mapping_ID);
+	free(entity_overrides);
+}
+
+/** Since the entity IDs defined by the GRF file does not necessarily correlate
+ * to those used by the game, the IDs used for overriding old entities must be
+ * translated when the entity spec is set.
+ * @param local_id id in grf file
+ * @param entity_type original entity type
+ */
+void OverrideManagerBase::Add(uint8 local_id, uint entity_type)
+{
+	assert(entity_type < max_offset);
+	entity_overrides[entity_type] = local_id;
+}
+
+/** Resets the mapping, which is used while initializing game */
+void OverrideManagerBase::ResetMapping()
+{
+	memset(mapping_ID, 0, (max_new_entities - 1) * sizeof(EntityIDMapping));
+}
+
+/** Resets the override, which is used while initializing game */
+void OverrideManagerBase::ResetOverride()
+{
+	for (uint16 i = 0; i < max_offset; i++) {
+		entity_overrides[i] = invalid_ID;
+	}
+}
+
+/** Return the ID (if ever available) of a previously inserted entity.
+ * @param grf_local_id ID of this enity withing the grfID
+ * @param grfid ID of the grf file
+ * @return the ID of the candidate, of the Invalid flag item ID
+ */
+uint16 OverrideManagerBase::GetID(uint8 grf_local_id, uint32 grfid)
+{
+	const EntityIDMapping *map;
+
+	for (uint16 id = max_offset; id < max_new_entities; id++) {
+		map = &mapping_ID[id];
+		if (map->entity_id == grf_local_id && map->grfid == grfid) {
+			return id;
+		}
+	}
+	return invalid_ID;
+}
+
+/** Reserves a place in the mapping array for an entity to be installed
+ * @param grf_local_id is an arbitrary id given by the grf's author.  Also known as setid
+ * @param grfid is the id of the grf file itself
+ * @param substitute_id is the original entity from which data is copied for the new one
+ * @return the proper usable slot id, or invalid marker if none is found
+ */
+uint16 OverrideManagerBase::AddEntityID(byte grf_local_id, uint32 grfid, byte substitute_id)
+{
+	uint16 id = this->GetID(grf_local_id, grfid);
+	EntityIDMapping *map;
+
+	/* Look to see if this entity has already been added. This is done
+	 * separately from the loop below in case a GRF has been deleted, and there
+	 * are any gaps in the array.
+	 */
+	if (id != invalid_ID) {
+		return id;
+	}
+
+	/* This entity hasn't been defined before, so give it an ID now. */
+	for (id = max_offset; id < max_new_entities; id++) {
+		map = &mapping_ID[id];
+
+		if (map->entity_id == 0 && map->grfid == 0) {
+			map->entity_id     = grf_local_id;
+			map->grfid         = grfid;
+			map->substitute_id = substitute_id;
+			return id;
+		}
+	}
+
+	return invalid_ID;
+}
+
+/** Gives the substitute of the entity, as specified by the grf file
+ * @param entity_id of the entity being queried
+ * @return mapped id
+ */
+uint16 OverrideManagerBase::GetSubstituteID(byte entity_id)
+{
+	return mapping_ID[entity_id].substitute_id;
+}
+
+/** Install the specs into the HouseSpecs array
+ * It will find itself the proper slot onwhich it will go
+ * @param hs HouseSpec read from the grf file, ready for inclusion
+ */
+void HouseOverrideManager::SetEntitySpec(const HouseSpec *hs)
+{
+	HouseID house_id = this->AddEntityID(hs->local_id, hs->grffile->grfid, hs->substitute_id);
+
+	if (house_id == invalid_ID) {
+		grfmsg(1, "House.SetEntitySpec: Too many houses allocated. Ignoring.");
+		return;
+	}
+
+	memcpy(&_house_specs[house_id], hs, sizeof(*hs));
+
+	/* Now add the overrides. */
+	for (int i = 0; i != max_offset; i++) {
+		HouseSpec *overridden_hs = GetHouseSpecs(i);
+
+		if (entity_overrides[i] != hs->local_id) continue;
+
+		overridden_hs->override = house_id;
+		entity_overrides[i] = invalid_ID;
+	}
+}

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/newgrf_commons.h	Tue May 15 21:36:58 2007 +0000
@@ -0,0 +1,69 @@
+/* $Id$ */
+
+/** @file newgrf_commons.h This file simplyfies and embeds a common mechanism of
+ * loading/saving and mapping of grf entities.
+ */
+
+#ifndef NEWGRF_COMMONS_H
+#define NEWGRF_COMMONS_H
+
+/**
+ * Maps an entity id stored on the map to a GRF file.
+ * Entities are objects used ingame (houses, industries, industry tiles) for
+ * which we need to correlate the ids from the grf files with the ones in the
+ * the savegames themselves.
+ * An array of EntityIDMapping structs is saved with the savegame so
+ * that those GRFs can be loaded in a different order, or removed safely. The
+ * index in the array is the entity's ID stored on the map.
+ *
+ * The substitute ID is the ID of an original entity that should be used instead
+ * if the GRF containing the new entity is not available.
+ */
+struct EntityIDMapping {
+	uint32 grfid;          ///< The GRF ID of the file the entity belongs to
+	uint8  entity_id;      ///< The entity ID within the GRF file
+	uint8  substitute_id;  ///< The (original) entity ID to use if this GRF is not available
+};
+
+class OverrideManagerBase
+{
+protected:
+	uint16 *entity_overrides;
+
+	uint16 max_offset;       ///< what is the length of the original entity's array of specs
+	uint16 max_new_entities; ///< what is the amount of entities, old and new summed
+
+	uint16 invalid_ID;       ///< ID used to dected invalid entities;
+
+	virtual uint16 AddEntityID(byte grf_local_id, uint32 grfid, byte substitute_id);
+public:
+	EntityIDMapping *mapping_ID; ///< mapping of ids from grf files.  Public out of convenience
+
+	OverrideManagerBase(uint16 offset, uint16 maximum, uint16 invalid);
+	virtual ~OverrideManagerBase();
+
+	void ResetOverride();
+	void ResetMapping();
+
+	void Add(uint8 local_id, uint entity_type);
+
+	uint16 GetSubstituteID(byte entity_id);
+	uint16 GetID(uint8 grf_local_id, uint32 grfid);
+
+	inline uint16 GetMaxMapping() { return max_new_entities; };
+	inline uint16 GetMaxOffset() { return max_offset; };
+};
+
+
+struct HouseSpec;
+class HouseOverrideManager : public OverrideManagerBase
+{
+public:
+	HouseOverrideManager(uint16 offset, uint16 maximum, uint16 invalid) : OverrideManagerBase(offset, maximum, invalid) {};
+	void SetEntitySpec(const HouseSpec *hs);
+};
+
+
+extern HouseOverrideManager _house_mngr;
+
+#endif /* NEWGRF_COMMONS_H */

--- a/src/newgrf_house.cpp	Tue May 15 17:54:46 2007 +0000
+++ b/src/newgrf_house.cpp	Tue May 15 21:36:58 2007 +0000
@@ -24,92 +24,12 @@
 #include "newgrf_callbacks.h"
 #include "newgrf_town.h"
 #include "newgrf_sound.h"
+#include "newgrf_commons.h"
 
 static BuildingCounts    _building_counts;
 static HouseClassMapping _class_mapping[HOUSE_CLASS_MAX];
-HouseIDMapping _house_id_mapping[HOUSE_MAX];
-
-/* Since the house IDs defined by the GRF file don't necessarily correlate
- * to those used by the game, the IDs used for overriding old houses must be
- * translated when the house spec is set. */
-static uint16 _house_overrides[NEW_HOUSE_OFFSET];
-
-void AddHouseOverride(uint8 local_id, uint house_type)
-{
-	assert(house_type < NEW_HOUSE_OFFSET);
-	_house_overrides[house_type] = local_id;
-}
-
-void ResetHouseOverrides()
-{
-	for (int i = 0; i != lengthof(_house_overrides); i++) {
-		_house_overrides[i] = INVALID_HOUSE_ID;
-	}
-}
-
-static HouseID GetHouseID(byte grf_local_id, uint32 grfid)
-{
-	const HouseIDMapping *map;
-
-	for (HouseID house_id = NEW_HOUSE_OFFSET; house_id != lengthof(_house_id_mapping); house_id++) {
-		map = &_house_id_mapping[house_id];
-		if (map->house_id == grf_local_id && map->grfid == grfid) return house_id;
-	}
-	return INVALID_HOUSE_ID;
-}
-
-static HouseID AddHouseID(byte grf_local_id, uint32 grfid, byte substitute_id)
-{
-	HouseID house_id;
-	HouseIDMapping *map;
 
-	/* Look to see if this house has already been added. This is done
-	 * separately from the loop below in case a GRF has been deleted, and there
-	 * are any gaps in the array. */
-	house_id = GetHouseID(grf_local_id, grfid);
-	if (house_id != INVALID_HOUSE_ID) return house_id;
-
-	/* This house hasn't been defined before, so give it an ID now. */
-	for (house_id = NEW_HOUSE_OFFSET; house_id != lengthof(_house_id_mapping); house_id++) {
-		map = &_house_id_mapping[house_id];
-
-		if (map->house_id == 0 && map->grfid == 0) {
-			map->house_id      = grf_local_id;
-			map->grfid         = grfid;
-			map->substitute_id = substitute_id;
-			return house_id;
-		}
-	}
-
-	return INVALID_HOUSE_ID;
-}
-
-void SetHouseSpec(const HouseSpec *hs)
-{
-	HouseID house_id = AddHouseID(hs->local_id, hs->grffile->grfid, hs->substitute_id);
-
-	if (house_id == INVALID_HOUSE_ID) {
-		grfmsg(1, "SetHouseSpec: Too many houses allocated. Ignoring.");
-		return;
-	}
-
-	memcpy(&_house_specs[house_id], hs, sizeof(*hs));
-
-	/* Now add the overrides. */
-	for (int i = 0; i != lengthof(_house_overrides); i++) {
-		HouseSpec *overridden_hs = GetHouseSpecs(i);
-
-		if (_house_overrides[i] != hs->local_id) continue;
-
-		overridden_hs->override = house_id;
-		_house_overrides[i] = INVALID_HOUSE_ID;
-	}
-}
-
-void ResetHouseIDMapping()
-{
-	memset(&_house_id_mapping, 0, sizeof(_house_id_mapping));
-}
+HouseOverrideManager _house_mngr(NEW_HOUSE_OFFSET, HOUSE_MAX, INVALID_HOUSE_ID);
 
 void CheckHouseIDs()
 {
@@ -122,7 +42,7 @@
 		if (!GetHouseSpecs(house_id)->enabled && house_id >= NEW_HOUSE_OFFSET) {
 			/* The specs for this type of house are not available any more, so
 			 * replace it with the substitute original house type. */
-			SetHouseType(t, _house_id_mapping[house_id].substitute_id);
+			SetHouseType(t, _house_mngr.GetSubstituteID(house_id));
 		}
 	}
 
@@ -313,7 +233,7 @@
 			const HouseSpec *hs = GetHouseSpecs(house_id);
 			if (hs->grffile == NULL) return 0;
 
-			HouseID new_house = GetHouseID(parameter, hs->grffile->grfid);
+			HouseID new_house = _house_mngr.GetID(parameter, hs->grffile->grfid);
 			return new_house == INVALID_HOUSE_ID ? 0 : GetNumHouses(new_house, town);
 		}
 
@@ -577,7 +497,11 @@
 		return true;
 	}
 
-	/* @todo: Magic with triggers goes here.  Got to implement that, one day. .. */
+	/* @todo: Magic with triggers goes here.  Got to implement that, one day. ..
+	 * Process randomizing of tiles following specs.
+	 * Once done, redraw the house
+	 * MarkTileDirtyByTile(tile);
+	 */
 
 	if (HASBIT(hs->callback_mask, CBM_ANIMATION_START_STOP)) {
 		/* If this house is marked as having a synchronised callback, all the

--- a/src/newgrf_house.h	Tue May 15 17:54:46 2007 +0000
+++ b/src/newgrf_house.h	Tue May 15 21:36:58 2007 +0000
@@ -41,15 +41,7 @@
 	uint8  class_id;  ////< The class id within the grf file
 };
 
-extern HouseIDMapping _house_id_mapping[HOUSE_MAX]; ///< Declared in newgrf_house.cpp
-
-void AddHouseOverride(uint8 local_id, uint house_type);
-void ResetHouseOverrides();
-
-void SetHouseSpec(const HouseSpec *hs);
-
 void CheckHouseIDs();
-void ResetHouseIDMapping();
 
 HouseClassID AllocateHouseClassID(byte grf_class_id, uint32 grfid);
 

--- a/src/openttd.cpp	Tue May 15 17:54:46 2007 +0000
+++ b/src/openttd.cpp	Tue May 15 21:36:58 2007 +0000
@@ -61,6 +61,7 @@
 #include "newgrf.h"
 #include "newgrf_config.h"
 #include "newgrf_house.h"
+#include "newgrf_commons.h"
 #include "player_face.h"
 
 #include "bridge_map.h"
@@ -685,7 +686,7 @@
 	_game_mode = GM_NORMAL;
 
 	ResetGRFConfig(true);
-	ResetHouseIDMapping();
+	_house_mngr.ResetMapping();
 
 	GenerateWorldSetCallback(&MakeNewGameDone);
 	GenerateWorld(from_heightmap ? GW_HEIGHTMAP : GW_NEWGAME, 1 << _patches.map_x, 1 << _patches.map_y);

--- a/src/town_cmd.cpp	Tue May 15 17:54:46 2007 +0000
+++ b/src/town_cmd.cpp	Tue May 15 21:36:58 2007 +0000
@@ -38,6 +38,7 @@
 #include "newgrf.h"
 #include "newgrf_callbacks.h"
 #include "newgrf_house.h"
+#include "newgrf_commons.h"
 
 /**
  * Called if a new block is added to the town-pool
@@ -2371,19 +2372,19 @@
 /* Save and load the mapping between the house id on the map, and the grf file
  * it came from. */
 static const SaveLoad _house_id_mapping_desc[] = {
-	SLE_VAR(HouseIDMapping, grfid,         SLE_UINT32),
-	SLE_VAR(HouseIDMapping, house_id,      SLE_UINT8),
-	SLE_VAR(HouseIDMapping, substitute_id, SLE_UINT8),
+	SLE_VAR(EntityIDMapping, grfid,         SLE_UINT32),
+	SLE_VAR(EntityIDMapping, entity_id,     SLE_UINT8),
+	SLE_VAR(EntityIDMapping, substitute_id, SLE_UINT8),
 	SLE_END()
 };
 
 static void Save_HOUSEIDS()
 {
-	uint i;
-
-	for (i = 0; i != lengthof(_house_id_mapping); i++) {
+	uint j = _house_mngr.GetMaxMapping();
+
+	for (uint i = 0; i < j; i++) {
 		SlSetArrayIndex(i);
-		SlObject(&_house_id_mapping[i], _house_id_mapping_desc);
+		SlObject(&_house_mngr.mapping_ID[i], _house_id_mapping_desc);
 	}
 }
 
@@ -2391,11 +2392,12 @@
 {
 	int index;
 
-	ResetHouseIDMapping();
+	_house_mngr.ResetMapping();
+	uint max_id = _house_mngr.GetMaxMapping();
 
 	while ((index = SlIterateArray()) != -1) {
-		if ((uint)index >= lengthof(_house_id_mapping)) break;
-		SlObject(&_house_id_mapping[index], _house_id_mapping_desc);
+		if ((uint)index >= max_id) break;
+		SlObject(&_house_mngr.mapping_ID[index], _house_id_mapping_desc);
 	}
 }