--- a/projects/openttd_vs80.vcproj	Tue Feb 12 12:54:51 2008 +0000
+++ b/projects/openttd_vs80.vcproj	Tue Feb 12 13:23:57 2008 +0000
@@ -1072,6 +1072,10 @@
 				>
 			</File>
 			<File
+				RelativePath=".\..\src\newgrf_generic.h"
+				>
+			</File>
+			<File
 				RelativePath=".\..\src\newgrf_house.h"
 				>
 			</File>
@@ -1948,6 +1952,10 @@
 				>
 			</File>
 			<File
+				RelativePath=".\..\src\newgrf_generic.cpp"
+				>
+			</File>
+			<File
 				RelativePath=".\..\src\newgrf_house.cpp"
 				>
 			</File>

--- a/projects/openttd_vs90.vcproj	Tue Feb 12 12:54:51 2008 +0000
+++ b/projects/openttd_vs90.vcproj	Tue Feb 12 13:23:57 2008 +0000
@@ -1069,6 +1069,10 @@
 				>
 			</File>
 			<File
+				RelativePath=".\..\src\newgrf_generic.h"
+				>
+			</File>
+			<File
 				RelativePath=".\..\src\newgrf_house.h"
 				>
 			</File>
@@ -1945,6 +1949,10 @@
 				>
 			</File>
 			<File
+				RelativePath=".\..\src\newgrf_generic.cpp"
+				>
+			</File>
+			<File
 				RelativePath=".\..\src\newgrf_house.cpp"
 				>
 			</File>

--- a/source.list	Tue Feb 12 12:54:51 2008 +0000
+++ b/source.list	Tue Feb 12 13:23:57 2008 +0000
@@ -176,6 +176,7 @@
 newgrf_commons.h
 newgrf_config.h
 newgrf_engine.h
+newgrf_generic.h
 newgrf_house.h
 newgrf_industries.h
 newgrf_industrytiles.h
@@ -405,6 +406,7 @@
 newgrf_commons.cpp
 newgrf_config.cpp
 newgrf_engine.cpp
+newgrf_generic.cpp
 newgrf_house.cpp
 newgrf_industries.cpp
 newgrf_industrytiles.cpp

--- a/src/newgrf.cpp	Tue Feb 12 12:54:51 2008 +0000
+++ b/src/newgrf.cpp	Tue Feb 12 13:23:57 2008 +0000
@@ -3089,6 +3089,11 @@
 	 * W cid           cargo ID (sprite group ID) for this type of cargo
 	 * W def-cid       default cargo ID (sprite group ID) */
 
+	if (_cur_grffile->spritegroups == 0) {
+		grfmsg(1, "FeatureMapSpriteGroup: No sprite groups to work on! Skipping");
+		return;
+	}
+
 	if (!check_length(len, 6, "FeatureMapSpriteGroup")) return;
 
 	uint8 feature = buf[1];
@@ -3099,7 +3104,12 @@
 
 	/* If idcount is zero, this is a feature callback */
 	if (idcount == 0) {
-		grfmsg(2, "FeatureMapSpriteGroup: Feature callbacks not implemented yet");
+		byte *bp = &buf[4];
+		uint16 groupid = grf_load_word(&bp);
+
+		grfmsg(6, "FeatureMapSpriteGroup: Adding generic feature callback for feature %d", feature);
+
+		AddGenericCallback(feature, _cur_grffile, _cur_grffile->spritegroups[groupid]);
 		return;
 	}
 
@@ -3109,11 +3119,6 @@
 	grfmsg(6, "FeatureMapSpriteGroup: Feature %d, %d ids, %d cids, wagon override %d",
 			feature, idcount, cidcount, wagover);
 
-	if (_cur_grffile->spritegroups == 0) {
-		grfmsg(1, "FeatureMapSpriteGroup: No sprite groups to work on! Skipping");
-		return;
-	}
-
 	switch (feature) {
 		case GSF_TRAIN:
 		case GSF_ROAD:
@@ -5101,6 +5106,9 @@
 	UnloadCustomEngineSprites();
 	ResetEngineListOrder();
 
+	/* Reset generic feature callback lists */
+	ResetGenericCallbacks();
+
 	/* Reset price base data */
 	ResetPriceBaseMultipliers();
 

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/newgrf_generic.cpp	Tue Feb 12 13:23:57 2008 +0000
@@ -0,0 +1,179 @@
+/* $Id$ */
+
+#include "stdafx.h"
+#include "openttd.h"
+#include "variables.h"
+#include "landscape.h"
+#include "debug.h"
+#include "newgrf.h"
+#include "newgrf_callbacks.h"
+#include "newgrf_commons.h"
+#include "newgrf_spritegroup.h"
+#include "newgrf_generic.h"
+#include "tile_map.h"
+#include <list>
+
+
+struct GenericCallback {
+	const GRFFile *file;
+	const SpriteGroup *group;
+
+	GenericCallback(const GRFFile *file, const SpriteGroup *group) :
+		file(file),
+		group(group)
+	{ }
+};
+
+typedef std::list<GenericCallback> GenericCallbackList;
+
+static GenericCallbackList _gcl[GSF_END];
+
+
+/**
+ * Reset all generic feature callback sprite groups.
+ */
+void ResetGenericCallbacks()
+{
+	for (uint8 feature = 0; feature < lengthof(_gcl); feature++) {
+		_gcl[feature].clear();
+	}
+}
+
+
+/**
+ * Add a generic feature callback sprite group to the appropriate feature list.
+ * @param feature
+ * @param file
+ * @param group
+ */
+void AddGenericCallback(uint8 feature, const GRFFile *file, const SpriteGroup *group)
+{
+	if (feature >= lengthof(_gcl)) {
+		grfmsg(5, "AddGenericCallback: Unsupported feature 0x%02X", feature);
+		return;
+	}
+
+	/* Generic feature callbacks are evaluated in reverse (i.e. the last group
+	 * to be added is evaluated first, etc) thus we push the group to the
+	 * beginning of the list so a standard iterator will do the right thing. */
+	_gcl[feature].push_front(GenericCallback(file, group));
+}
+
+
+static uint32 GenericCallbackGetRandomBits(const ResolverObject *object)
+{
+	return 0;
+}
+
+
+static uint32 GenericCallbackGetTriggers(const ResolverObject *object)
+{
+	return 0;
+}
+
+
+static void GenericCallbackSetTriggers(const ResolverObject *object, int triggers)
+{
+	return;
+}
+
+
+static uint32 GenericCallbackGetVariable(const ResolverObject *object, byte variable, byte parameter, bool *available)
+{
+	switch (variable) {
+		case 0x40: return object->u.generic.cargo_type;
+
+		case 0x80: return object->u.generic.cargo_type;
+		case 0x81: return object->u.generic.cargo_type;
+		case 0x82: return object->u.generic.default_selection;
+		case 0x83: return object->u.generic.src_industry;
+		case 0x84: return object->u.generic.dst_industry;
+		case 0x85: return object->u.generic.distance;
+		case 0x86: return object->u.generic.event;
+		case 0x87: return object->u.generic.count;
+		case 0x88: return object->u.generic.station_size;
+
+		default: break;
+	}
+
+	DEBUG(grf, 1, "Unhandled generic feature property 0x%02X", variable);
+
+	*available = false;
+	return 0;
+}
+
+
+static const SpriteGroup *GenericCallbackResolveReal(const ResolverObject *object, const SpriteGroup *group)
+{
+	if (group->g.real.num_loaded == 0) return NULL;
+
+	return group->g.real.loaded[0];
+}
+
+
+static inline void NewGenericResolver(ResolverObject *res)
+{
+	res->GetRandomBits = &GenericCallbackGetRandomBits;
+	res->GetTriggers   = &GenericCallbackGetTriggers;
+	res->SetTriggers   = &GenericCallbackSetTriggers;
+	res->GetVariable   = &GenericCallbackGetVariable;
+	res->ResolveReal   = &GenericCallbackResolveReal;
+
+	res->callback        = CBID_NO_CALLBACK;
+	res->callback_param1 = 0;
+	res->callback_param2 = 0;
+	res->last_value      = 0;
+	res->trigger         = 0;
+	res->reseed          = 0;
+}
+
+
+/** Follow a generic feature callback list and return the first successful
+ * answer
+ * @param feature GRF Feature of callback
+ * @param object  pre-populated resolver object
+ * @param file    address of GRFFile object if file reference is needed, NULL is valid
+ * @return callback value if successful or CALLBACK_FAILED
+ */
+static uint16 GetGenericCallbackResult(uint8 feature, ResolverObject *object, const GRFFile **file)
+{
+	assert(feature < lengthof(_gcl));
+
+	/* Test each feature callback sprite group. */
+	for (GenericCallbackList::const_iterator it = _gcl[feature].begin(); it != _gcl[feature].end(); ++it) {
+		const SpriteGroup *group = it->group;
+		group = Resolve(group, object);
+		if (group == NULL || group->type != SGT_CALLBACK) continue;
+
+		/* Return NewGRF file if necessary */
+		if (file != NULL) *file = it->file;
+
+		return group->g.callback.result;
+	}
+
+	/* No callback returned a valid result, so we've failed. */
+	return CALLBACK_FAILED;
+}
+
+
+/**
+ * 'Execute' an AI purchase selection callback
+ */
+uint16 GetAiPurchaseCallbackResult(uint8 feature, CargoID cargo_type, uint8 default_selection, IndustryType src_industry, IndustryType dst_industry, uint8 distance, AIConstructionEvent event, uint8 count, uint8 station_size, const GRFFile **file)
+{
+	ResolverObject object;
+
+	NewGenericResolver(&object);
+
+	object.callback = CBID_GENERIC_AI_PURCHASE_SELECTION;
+	object.u.generic.cargo_type        = cargo_type;
+	object.u.generic.default_selection = default_selection;
+	object.u.generic.src_industry      = src_industry;
+	object.u.generic.dst_industry      = dst_industry;
+	object.u.generic.distance          = distance;
+	object.u.generic.event             = event;
+	object.u.generic.count             = count;
+	object.u.generic.station_size      = station_size;
+
+	return GetGenericCallbackResult(feature, &object, file);
+}

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/newgrf_generic.h	Tue Feb 12 13:23:57 2008 +0000
@@ -0,0 +1,35 @@
+/* $Id$ */
+
+#ifndef NEWGRF_GENERIC_H
+#define NEWGRF_GENERIC_H
+
+enum AIConstructionEvent {
+	AICE_TRAIN_CHECK_RAIL_ENGINE     = 0x00, ///< Check if we should build an engine
+	AICE_TRAIN_CHECK_ELRAIL_ENGINE   = 0x01,
+	AICE_TRAIN_CHECK_MONORAIL_ENGINE = 0x02,
+	AICE_TRAIN_CHECK_MAGLEV_ENGINE   = 0x03,
+	AICE_TRAIN_GET_RAIL_WAGON        = 0x08,
+	AICE_TRAIN_GET_ELRAIL_WAGON      = 0x09,
+	AICE_TRAIN_GET_MONORAIL_WAGON    = 0x0A,
+	AICE_TRAIN_GET_MAGLEV_WAGON      = 0x0B,
+	AICE_TRAIN_GET_RAILTYPE          = 0x0F,
+
+	AICE_ROAD_CHECK_ENGINE           = 0x00, ///< Check if we should build an engine
+	AICE_ROAD_GET_FIRST_ENGINE       = 0x01, ///< Unused, we check all
+	AICE_ROAD_GET_NUMBER_ENGINES     = 0x02, ///< Unused, we check all
+
+	AICE_SHIP_CHECK_ENGINE           = 0x00, ///< Check if we should build an engine
+	AICE_SHIP_GET_FIRST_ENGINE       = 0x01, ///< Unused, we check all
+	AICE_SHIP_GET_NUMBER_ENGINES     = 0x02, ///< Unused, we check all
+
+	AICE_AIRCRAFT_CHECK_ENGINE       = 0x00, ///< Check if we should build an engine
+
+	AICE_STATION_GET_STATION_ID      = 0x00, ///< Get a station ID to build
+};
+
+void ResetGenericCallbacks();
+void AddGenericCallback(uint8 feature, const struct GRFFile *file, const struct SpriteGroup *group);
+
+uint16 GetAiPurchaseCallbackResult(uint8 feature, CargoID cargo_type, uint8 default_selection, IndustryType src_industry, IndustryType dst_industry, uint8 distance, AIConstructionEvent event, uint8 count, uint8 station_size, const struct GRFFile **file);
+
+#endif /* NEWGRF_GENERIC_H */

--- a/src/newgrf_spritegroup.h	Tue Feb 12 12:54:51 2008 +0000
+++ b/src/newgrf_spritegroup.h	Tue Feb 12 13:23:57 2008 +0000
@@ -10,6 +10,7 @@
 #include "newgrf_storage.h"
 #include "core/bitmath_func.hpp"
 #include "gfx_type.h"
+#include "newgrf_generic.h"
 
 /**
  * Gets the value of a so-called newgrf "register".
@@ -236,6 +237,16 @@
 		struct {
 			const struct CargoSpec *cs;
 		} cargo;
+		struct {
+			CargoID cargo_type;
+			uint8 default_selection;
+			IndustryType src_industry;
+			IndustryType dst_industry;
+			uint8 distance;
+			AIConstructionEvent event;
+			uint8 count;
+			uint8 station_size;
+		} generic;
 	} u;
 
 	uint32 (*GetRandomBits)(const struct ResolverObject*);