From 5718730d685c3057afba777521b8953c5c3fc528 Mon Sep 17 00:00:00 2001
From: Jonathan G Rennison <j.g.rennison@gmail.com>
Date: Tue, 14 Mar 2023 17:57:30 +0000
Subject: [PATCH] VarAction2: Add support for more varaction2 types

Add CB failure and deterministic relative types
---
 docs/newgrf-additions-nml.html |  16 +++++
 docs/newgrf-additions.html     |  54 +++++++++++++++
 src/newgrf.cpp                 | 120 ++++++++++++++++++++++++++++++---
 src/newgrf_airport.cpp         |   2 +-
 src/newgrf_airporttiles.h      |   2 +-
 src/newgrf_canal.cpp           |   2 +-
 src/newgrf_engine.cpp          |  19 +++---
 src/newgrf_engine.h            |   4 +-
 src/newgrf_extension.cpp       |   1 +
 src/newgrf_extension.h         |   1 +
 src/newgrf_generic.cpp         |   2 +-
 src/newgrf_house.h             |   4 +-
 src/newgrf_industries.h        |   2 +-
 src/newgrf_industrytiles.h     |   2 +-
 src/newgrf_newlandscape.h      |   2 +-
 src/newgrf_newsignals.h        |   2 +-
 src/newgrf_object.h            |   2 +-
 src/newgrf_railtype.h          |   2 +-
 src/newgrf_roadstop.h          |   2 +-
 src/newgrf_roadtype.h          |   2 +-
 src/newgrf_spritegroup.cpp     |  64 +++++++++++++++---
 src/newgrf_spritegroup.h       |  21 +++++-
 src/newgrf_station.h           |   2 +-
 src/newgrf_town.h              |   2 +-
 24 files changed, 282 insertions(+), 50 deletions(-)

diff --git a/docs/newgrf-additions-nml.html b/docs/newgrf-additions-nml.html
index 581990b10e..93f5e4d315 100644
--- a/docs/newgrf-additions-nml.html
+++ b/docs/newgrf-additions-nml.html
@@ -36,6 +36,7 @@
 	<h3 id="sections">Sections</h3>
 	<ul>
 	<li><a href="#builtin-functions">Builtin functions</a></li>
+	<li><a href="#switch-types">Additional switch types</a></li>
 	<li><a href="#railtype-properties">Railtype properties</a></li>
 	<li><a href="#railtype-variables">Railtype variables</a></li>
 	<li><a href="#roadtype-properties">Roadtype properties</a></li>
@@ -58,6 +59,21 @@
 		In most cases it is not necessary to use this function, as extended properties (listed below) which are not supported are simply skipped/ignored.
 	</p>
 
+	<h3 id="switch-types"><a href="https://newgrf-specs.tt-wiki.net/wiki/NML:Switch">Additional switch types</a></h3>
+	<p>
+		In addition to SELF and PARENT, switches for vehicle features may use one of the following types below.<br />
+		(These are mostly the same as in <a href="https://newgrf-specs.tt-wiki.net/wiki/NML:Random_switch">random_switch</a>).<br />
+		The 'x' parameter (count x vehicles in given direction) is currently required to be a compile-time constant between 0 and 255.
+		<table>
+		<tr><th>Type</th><th>Meaning</th></tr>
+		<tr><td>BACKWARD_SELF(x)</td><td>Count x vehicles backward (away from the engine), starting at the vehicle itself</td></tr>
+		<tr><td>FORWARD_SELF(x)</td><td>Count x vehicles forward (towards the engine), starting at the vehicle itself</td></tr>
+		<tr><td>BACKWARD_ENGINE(x)</td><td>Count x vehicles backward, starting at the leading engine</td></tr>
+		<tr><td>BACKWARD_SAMEID(x)</td><td>Count x vehicles backward, starting at the first vehicle in the chain with the same ID</td></tr>
+		</table>
+		<p>These require the <span class="code">more_varaction2_types</span> feature. If this feature is not present, switches of these types will produce a CB_FAILED result.</p>
+	</p>
+
 	<h3 id="railtype-properties"><a href="https://newgrf-specs.tt-wiki.net/wiki/NML:Railtypes#Railtype_properties">Railtype properties</a></h3>
 	<table>
 	<tr><th>Property</th><th>Value range</th><th>Comment</th></tr>
diff --git a/docs/newgrf-additions.html b/docs/newgrf-additions.html
index eaf354397f..f029e4c0d6 100644
--- a/docs/newgrf-additions.html
+++ b/docs/newgrf-additions.html
@@ -47,6 +47,7 @@
 	<li><a href="#a0signals">Action 0 - Signals (Feature 0E)</a></li>
 	<li><a href="#a0objects">Action 0 - Objects</a></li>
 	<li><a href="#variable-mapping">Action 14 - Variable Mapping for Variational Action 2</a></li>
+	<li><a href="#varaction2_additional_types">Variational Action 2 - Additional Types</a></li>
 	<li><a href="#varaction2_station">Variational Action 2 - Stations</a></li>
 	<li><a href="#varaction2_railtypes">Variational Action 2 - Railtypes</a></li>
 	<li><a href="#varaction2_object">Variational Action 2 - Objects</a></li>
@@ -724,6 +725,59 @@
                    01 00          // default:       link to action2ID 01
 	</pre>
 	<br />
+	<h3 id="varaction2_additional_types">Variational Action 2 - Additional Types</h3>
+	<p>Additional variational action 2 types are indicated by the feature name: <font face="monospace">more_varaction2_types</font>, this document describes version 1.<br />
+	This feature name must be tested for to enable this feature.</p>
+	<p>See the <a href="https://newgrf-specs.tt-wiki.net/wiki/VariationalAction2#Type">Variational Action 2 Specification (types)</a> for background information.</p>
+	<p>This feature adds the type value 87, for additional variation action 2 modes/scopes. (This is used instead of the standard values: 81, 82, 85, 86, 89 or 8A).<br />
+	An additional byte follows to specify which sub-type.</p>
+	<p>
+	<pre>&lt;Sprite-number&gt; * &lt;Length&gt; 02 &lt;feature&gt; &lt;set-id&gt; 87 &lt;sub-type&gt; ...</pre>
+	The following sub-types are defined:
+	<table>
+	<tr><th>Sub-type</th><th>Meaning</th></tr>
+	<tr><td>00</td><td>Callback failure group</td></tr>
+	<tr><td>01</td><td>Relative scope for vehicles (same syntax as <a href="https://newgrf-specs.tt-wiki.net/wiki/RandomAction2#80.2F83.2F84">random action 2 type 84</a>)</td></tr>
+	<tr><td>02</td><td>Relative scope for vehicles (longer syntax)</td></tr>
+	</table>
+	<p>If an unknown sub-type is used, or if subsequent sub-type bytes are invalid, a callback failure group is created, the same as sub-type 00.</p>
+	<h4 id="varaction2_additional_type_00">Sub-type 00: Callback failure</h4>
+	<pre>&lt;Sprite-number&gt; * &lt;Length&gt; 02 &lt;feature&gt; &lt;set-id&gt; <b>87 00</b></pre>
+	This produces a callback failed result in all cases (appropriate whether or not variable 0C is currently 0).<br />
+	This can be used to avoiding needing to branch on variable 0C or create empty (feature-dependant) real sprite/sprite layout/industry production groups.
+	</p>
+	<h4 id="varaction2_additional_type_01">Sub-type 01: Relative scope for vehicles (random action 2 type 84 syntax)</h4>
+	<pre>&lt;Sprite-number&gt; * &lt;Length&gt; 02 &lt;feature&gt; &lt;set-id&gt; <b>87 01 &lt;count&gt;</b> &lt;variable&gt; &lt;varadjust&gt; [&lt;operator&gt; &lt;variable&gt; &lt;varadjust&gt;]... &lt;nvar&gt; (&lt;set-id&gt; &lt;low-range&gt; &lt;high-range&gt;){n} &lt;default&gt;</pre>
+	<p>This sub-type is only valid for vehicles.</p>
+	<p>The vehicle which is accessed can be any in the vehicle consist. The <font face="monospace">count</font> byte selects which, this has the same syntax and functionality
+	as the <a href="https://newgrf-specs.tt-wiki.net/wiki/RandomAction2#count"><font face="monospace">count</font> byte in random action 2 type 84</a>.</p>
+	<p>Note: The count byte mode where temporary variable 0x100 is used should be used with caution.</p>
+	<h4 id="varaction2_additional_type_02">Sub-type 02: Relative scope for vehicles (longer syntax)</h4>
+	<pre>&lt;Sprite-number&gt; * &lt;Length&gt; 02 &lt;feature&gt; &lt;set-id&gt; <b>87 02 &lt;mode&gt; &lt;offset&gt;</b> &lt;variable&gt; &lt;varadjust&gt; [&lt;operator&gt; &lt;variable&gt; &lt;varadjust&gt;]... &lt;nvar&gt; (&lt;set-id&gt; &lt;low-range&gt; &lt;high-range&gt;){n} &lt;default&gt;</pre>
+	<p>This sub-type is only valid for vehicles.</p>
+	<p>The vehicle which is accessed can be any in the vehicle consist. The <font face="monospace">mode</font> and <font face="monospace">offset</font> bytes select which.</p>
+	<p>The <font face="monospace">mode</font> byte has the following syntax:
+	<table>
+	<tr><th>Bits</th><th>Meaning</th></tr>
+	<tr><td>0 - 1</td><td>
+		Selection mode:<br/>
+		These values are the same as bits 6 - 7 of the <a href="https://newgrf-specs.tt-wiki.net/wiki/RandomAction2#count"><font face="monospace">count</font> byte in random action 2 type 84</a>.
+		<table>
+		<tr><th>Value</th><th>Meaning</th></tr>
+		<tr><td>0</td><td>Count back (away from the engine), starting at this vehicle</td></tr>
+		<tr><td>1</td><td>Count forward (toward the engine), starting at this vehicle</td></tr>
+		<tr><td>2</td><td>Count back, starting at the engine</td></tr>
+		<tr><td>3</td><td>Count back, starting at the first vehicle in this chain of vehicles with the same ID, as for vehicle variable 41</td></tr>
+		</table>
+	</td></tr>
+	<tr><td>7</td><td>If set, use variable 0x100 for the offset. The offset byte must be 0.</td></tr>
+	</table>
+	The remaining bits are reserved for future used and must be set to 0.
+	</p>
+	<p>The <font face="monospace">offset</font> byte specifies how far to count from the starting vehicle. A value of 0 is not special.<br />
+	Bit 7 of the <font face="monospace">mode</font> byte must be set to use temporary variable 0x100 instead.</p>
+	<p>Note: Using temporary variable 0x100 as the offset should be used with caution.</p>
+	<br />
 	<h3 id="varaction2_station"><a href="https://newgrf-specs.tt-wiki.net/wiki/VariationalAction2/Stations">Variational Action 2 - Stations</a></h3>
 	<h4 id="varaction2_station_var42">Track type in purchase list (42)</h4>
 	<p>This is indicated by the feature name: <font face="monospace">varaction2_station_var42</font>, version 1</p>
diff --git a/src/newgrf.cpp b/src/newgrf.cpp
index f927760b09..ffd06b55d0 100644
--- a/src/newgrf.cpp
+++ b/src/newgrf.cpp
@@ -5789,6 +5789,17 @@ static void ProcessDeterministicSpriteGroupRanges(const std::vector<Deterministi
 	}
 }
 
+static VarSpriteGroupScopeOffset ParseRelativeScopeByte(byte relative)
+{
+	VarSpriteGroupScopeOffset var_scope_count = (GB(relative, 6, 2) << 8);
+	if ((relative & 0xF) == 0) {
+		SetBit(var_scope_count, 15);
+	} else {
+		var_scope_count |= (relative & 0xF);
+	}
+	return var_scope_count;
+}
+
 /* Action 0x02 */
 static void NewSpriteGroup(ByteReader *buf)
 {
@@ -5819,6 +5830,16 @@ static void NewSpriteGroup(ByteReader *buf)
 	 * we do not need to delete anything if there is an exception from the
 	 * ByteReader. */
 
+	/* Decoded sprite type */
+	enum SpriteType {
+		STYPE_NORMAL,
+		STYPE_DETERMINISTIC,
+		STYPE_DETERMINISTIC_RELATIVE,
+		STYPE_DETERMINISTIC_RELATIVE_2,
+		STYPE_RANDOMIZED,
+		STYPE_CB_FAILURE,
+	};
+	SpriteType stype = STYPE_NORMAL;
 	switch (type) {
 		/* Deterministic Sprite Group */
 		case 0x81: // Self scope, byte
@@ -5827,7 +5848,73 @@ static void NewSpriteGroup(ByteReader *buf)
 		case 0x86: // Parent scope, word
 		case 0x89: // Self scope, dword
 		case 0x8A: // Parent scope, dword
+			stype = STYPE_DETERMINISTIC;
+			break;
+
+		/* Randomized Sprite Group */
+		case 0x80: // Self scope
+		case 0x83: // Parent scope
+		case 0x84: // Relative scope
+			stype = STYPE_RANDOMIZED;
+			break;
+
+		/* Extension type */
+		case 0x87:
+			if (HasBit(_cur.grffile->observed_feature_tests, GFTOF_MORE_VARACTION2_TYPES)) {
+				byte subtype = buf->ReadByte();
+				switch (subtype) {
+					case 0:
+						stype = STYPE_CB_FAILURE;
+						break;
+
+					case 1:
+						stype = STYPE_DETERMINISTIC_RELATIVE;
+						break;
+
+					case 2:
+						stype = STYPE_DETERMINISTIC_RELATIVE_2;
+						break;
+
+					default:
+						grfmsg(1, "NewSpriteGroup: Unknown 0x87 extension subtype %02X for feature %s, handling as CB failure", subtype, GetFeatureString(feature));
+						stype = STYPE_CB_FAILURE;
+						break;
+				}
+			}
+			break;
+
+		default:
+			break;
+	}
+
+	switch (stype) {
+		/* Deterministic Sprite Group */
+		case STYPE_DETERMINISTIC:
+		case STYPE_DETERMINISTIC_RELATIVE:
+		case STYPE_DETERMINISTIC_RELATIVE_2:
 		{
+			VarSpriteGroupScopeOffset var_scope_count = 0;
+			if (stype == STYPE_DETERMINISTIC_RELATIVE) {
+				var_scope_count = ParseRelativeScopeByte(buf->ReadByte());
+			} else if (stype == STYPE_DETERMINISTIC_RELATIVE_2) {
+				uint8 mode = buf->ReadByte();
+				uint8 offset = buf->ReadByte();
+				bool invalid = false;
+				if ((mode & 0x7F) >= VSGSRM_END) {
+					invalid = true;
+				}
+				if (HasBit(mode, 7)) {
+					/* Use variable 0x100 */
+					if (offset != 0) invalid = true;
+				}
+				if (invalid) {
+					grfmsg(1, "NewSpriteGroup: Unknown 0x87 extension subtype 2 relative mode: %02X %02X for feature %s, handling as CB failure", mode, offset, GetFeatureString(feature));
+					act_group = NewCallbackResultSpriteGroupNoTransform(CALLBACK_FAILED);
+					break;
+				}
+				var_scope_count = (mode << 8) | offset;
+			}
+
 			byte varadjust;
 			byte varsize;
 
@@ -5839,13 +5926,22 @@ static void NewSpriteGroup(ByteReader *buf)
 			group->feature = feature;
 			if (_action6_override_active) group->sg_flags |= SGF_ACTION6;
 			act_group = group;
-			group->var_scope = HasBit(type, 1) ? VSG_SCOPE_PARENT : VSG_SCOPE_SELF;
 
-			switch (GB(type, 2, 2)) {
-				default: NOT_REACHED();
-				case 0: group->size = DSG_SIZE_BYTE;  varsize = 1; break;
-				case 1: group->size = DSG_SIZE_WORD;  varsize = 2; break;
-				case 2: group->size = DSG_SIZE_DWORD; varsize = 4; break;
+			if (stype == STYPE_DETERMINISTIC_RELATIVE || stype == STYPE_DETERMINISTIC_RELATIVE_2) {
+				group->var_scope = (feature <= GSF_AIRCRAFT) ? VSG_SCOPE_RELATIVE : VSG_SCOPE_SELF;
+				group->var_scope_count = var_scope_count;
+
+				group->size = DSG_SIZE_DWORD;
+				varsize = 4;
+			} else {
+				group->var_scope = HasBit(type, 1) ? VSG_SCOPE_PARENT : VSG_SCOPE_SELF;
+
+				switch (GB(type, 2, 2)) {
+					default: NOT_REACHED();
+					case 0: group->size = DSG_SIZE_BYTE;  varsize = 1; break;
+					case 1: group->size = DSG_SIZE_WORD;  varsize = 2; break;
+					case 2: group->size = DSG_SIZE_DWORD; varsize = 4; break;
+				}
 			}
 
 			const VarAction2AdjustInfo info = { feature, GetGrfSpecFeatureForScope(feature, group->var_scope), varsize };
@@ -5962,9 +6058,7 @@ static void NewSpriteGroup(ByteReader *buf)
 		}
 
 		/* Randomized Sprite Group */
-		case 0x80: // Self scope
-		case 0x83: // Parent scope
-		case 0x84: // Relative scope
+		case STYPE_RANDOMIZED:
 		{
 			assert(RandomizedSpriteGroup::CanAllocateItem());
 			RandomizedSpriteGroup *group = new RandomizedSpriteGroup();
@@ -5975,7 +6069,7 @@ static void NewSpriteGroup(ByteReader *buf)
 
 			if (HasBit(type, 2)) {
 				if (feature <= GSF_AIRCRAFT) group->var_scope = VSG_SCOPE_RELATIVE;
-				group->count = buf->ReadByte();
+				group->var_scope_count = ParseRelativeScopeByte(buf->ReadByte());
 			}
 
 			uint8 triggers = buf->ReadByte();
@@ -6005,8 +6099,12 @@ static void NewSpriteGroup(ByteReader *buf)
 			break;
 		}
 
+		case STYPE_CB_FAILURE:
+			act_group = NewCallbackResultSpriteGroupNoTransform(CALLBACK_FAILED);
+			break;
+
 		/* Neither a variable or randomized sprite group... must be a real group */
-		default:
+		case STYPE_NORMAL:
 		{
 			switch (feature) {
 				case GSF_TRAINS:
diff --git a/src/newgrf_airport.cpp b/src/newgrf_airport.cpp
index 7e11b9be99..1e3031601e 100644
--- a/src/newgrf_airport.cpp
+++ b/src/newgrf_airport.cpp
@@ -49,7 +49,7 @@ struct AirportResolverObject : public ResolverObject {
 	AirportResolverObject(TileIndex tile, Station *st, byte airport_id, byte layout,
 			CallbackID callback = CBID_NO_CALLBACK, uint32 callback_param1 = 0, uint32 callback_param2 = 0);
 
-	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, byte relative = 0) override
+	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, VarSpriteGroupScopeOffset relative = 0) override
 	{
 		switch (scope) {
 			case VSG_SCOPE_SELF: return &this->airport_scope;
diff --git a/src/newgrf_airporttiles.h b/src/newgrf_airporttiles.h
index f95a88023b..dff59e1375 100644
--- a/src/newgrf_airporttiles.h
+++ b/src/newgrf_airporttiles.h
@@ -48,7 +48,7 @@ struct AirportTileResolverObject : public ResolverObject {
 	AirportTileResolverObject(const AirportTileSpec *ats, TileIndex tile, Station *st,
 			CallbackID callback = CBID_NO_CALLBACK, uint32 callback_param1 = 0, uint32 callback_param2 = 0);
 
-	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, byte relative = 0) override
+	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, VarSpriteGroupScopeOffset relative = 0) override
 	{
 		switch (scope) {
 			case VSG_SCOPE_SELF: return &tiles_scope;
diff --git a/src/newgrf_canal.cpp b/src/newgrf_canal.cpp
index 2ebecf59fd..71668b67d4 100644
--- a/src/newgrf_canal.cpp
+++ b/src/newgrf_canal.cpp
@@ -41,7 +41,7 @@ struct CanalResolverObject : public ResolverObject {
 	CanalResolverObject(CanalFeature feature, TileIndex tile,
 			CallbackID callback = CBID_NO_CALLBACK, uint32 callback_param1 = 0, uint32 callback_param2 = 0);
 
-	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, byte relative = 0) override
+	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, VarSpriteGroupScopeOffset relative = 0) override
 	{
 		switch (scope) {
 			case VSG_SCOPE_SELF: return &this->canal_scope;
diff --git a/src/newgrf_engine.cpp b/src/newgrf_engine.cpp
index b587ae2d33..f3687c303a 100644
--- a/src/newgrf_engine.cpp
+++ b/src/newgrf_engine.cpp
@@ -329,32 +329,33 @@ static byte MapAircraftMovementAction(const Aircraft *v)
 }
 
 
-/* virtual */ ScopeResolver *VehicleResolverObject::GetScope(VarSpriteGroupScope scope, byte relative)
+/* virtual */ ScopeResolver *VehicleResolverObject::GetScope(VarSpriteGroupScope scope, VarSpriteGroupScopeOffset relative)
 {
 	switch (scope) {
 		case VSG_SCOPE_SELF:   return &this->self_scope;
 		case VSG_SCOPE_PARENT: return &this->parent_scope;
 		case VSG_SCOPE_RELATIVE: {
-			int32 count = GB(relative, 0, 4);
-			if (this->self_scope.v != nullptr && (relative != this->cached_relative_count || count == 0)) {
+			int32 count = GB(relative, 0, 8);
+			if (this->self_scope.v != nullptr && (relative != this->cached_relative_count || HasBit(relative, 15))) {
 				/* Note: This caching only works as long as the VSG_SCOPE_RELATIVE cannot be used in
 				 *       VarAct2 with procedure calls. */
-				if (count == 0) count = GetRegister(0x100);
+				/* Therefore procedure calls made from within a relative scope must save and restore the cached relative scope */
+				if (HasBit(relative, 15)) count = GetRegister(0x100);
 
 				const Vehicle *v = nullptr;
-				switch (GB(relative, 6, 2)) {
+				switch (GB(relative, 8, 2)) {
 					default: NOT_REACHED();
-					case 0x00: // count back (away from the engine), starting at this vehicle
+					case VSGSRM_BACKWARD_SELF: // count back (away from the engine), starting at this vehicle
 						v = this->self_scope.v;
 						break;
-					case 0x01: // count forward (toward the engine), starting at this vehicle
+					case VSGSRM_FORWARD_SELF: // count forward (toward the engine), starting at this vehicle
 						v = this->self_scope.v;
 						count = -count;
 						break;
-					case 0x02: // count back, starting at the engine
+					case VSGSRM_BACKWARD_ENGINE: // count back, starting at the engine
 						v = this->parent_scope.v;
 						break;
-					case 0x03: { // count back, starting at the first vehicle in this chain of vehicles with the same ID, as for vehicle variable 41
+					case VSGSRM_BACKWARD_SAMEID: { // count back, starting at the first vehicle in this chain of vehicles with the same ID, as for vehicle variable 41
 						const Vehicle *self = this->self_scope.v;
 						for (const Vehicle *u = self->First(); u != self; u = u->Next()) {
 							if (u->engine_type != self->engine_type) {
diff --git a/src/newgrf_engine.h b/src/newgrf_engine.h
index 7364b58d58..dfe2d2ffc8 100644
--- a/src/newgrf_engine.h
+++ b/src/newgrf_engine.h
@@ -57,12 +57,12 @@ struct VehicleResolverObject : public ResolverObject {
 	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.
+	VarSpriteGroupScopeOffset cached_relative_count; ///< Relative position of the other vehicle.
 
 	VehicleResolverObject(EngineID engine_type, const Vehicle *v, WagonOverride wagon_override, bool rotor_in_gui = false,
 			CallbackID callback = CBID_NO_CALLBACK, uint32 callback_param1 = 0, uint32 callback_param2 = 0);
 
-	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, byte relative = 0) override;
+	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, VarSpriteGroupScopeOffset relative = 0) override;
 
 	const SpriteGroup *ResolveReal(const RealSpriteGroup *group) const override;
 
diff --git a/src/newgrf_extension.cpp b/src/newgrf_extension.cpp
index 6be3e8570d..93a5ef2da9 100644
--- a/src/newgrf_extension.cpp
+++ b/src/newgrf_extension.cpp
@@ -65,6 +65,7 @@ extern const GRFFeatureInfo _grf_feature_list[] = {
 	GRFFeatureInfo("town_feature", 1),
 	GRFFeatureInfo("town_uncapped_variables", 1),
 	GRFFeatureInfo("town_zone_callback", 1, GFTOF_TOWN_ZONE_CALLBACK),
+	GRFFeatureInfo("more_varaction2_types", 1, GFTOF_MORE_VARACTION2_TYPES),
 	GRFFeatureInfo(),
 };
 
diff --git a/src/newgrf_extension.h b/src/newgrf_extension.h
index a1e94a3d0e..d3e06548cb 100644
--- a/src/newgrf_extension.h
+++ b/src/newgrf_extension.h
@@ -100,6 +100,7 @@ enum GRFFeatureTestObservationFlag : uint8 {
 	GFTOF_MORE_OBJECTS_PER_GRF = 0,
 	GFTOF_MORE_ACTION2_IDS,
 	GFTOF_TOWN_ZONE_CALLBACK,
+	GFTOF_MORE_VARACTION2_TYPES,
 
 	GFTOF_INVALID = 0xFF,
 };
diff --git a/src/newgrf_generic.cpp b/src/newgrf_generic.cpp
index 8dd96cbc6f..54ec4067ba 100644
--- a/src/newgrf_generic.cpp
+++ b/src/newgrf_generic.cpp
@@ -58,7 +58,7 @@ struct GenericResolverObject : public ResolverObject {
 
 	GenericResolverObject(bool ai_callback, CallbackID callback = CBID_NO_CALLBACK);
 
-	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, byte relative = 0) override
+	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, VarSpriteGroupScopeOffset relative = 0) override
 	{
 		switch (scope) {
 			case VSG_SCOPE_SELF: return &this->generic_scope;
diff --git a/src/newgrf_house.h b/src/newgrf_house.h
index 6f01a8d373..7adea9ca6c 100644
--- a/src/newgrf_house.h
+++ b/src/newgrf_house.h
@@ -82,7 +82,7 @@ struct HouseResolverObject : public ResolverObject {
 			CallbackID callback = CBID_NO_CALLBACK, uint32 param1 = 0, uint32 param2 = 0,
 			bool not_yet_constructed = false, uint8 initial_random_bits = 0, CargoTypes watched_cargo_triggers = 0);
 
-	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, byte relative = 0) override
+	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, VarSpriteGroupScopeOffset relative = 0) override
 	{
 		switch (scope) {
 			case VSG_SCOPE_SELF:   return &this->house_scope;
@@ -103,7 +103,7 @@ struct FakeHouseResolverObject : public ResolverObject {
 	FakeHouseResolverObject(HouseID house_id,
 			CallbackID callback = CBID_NO_CALLBACK, uint32 param1 = 0, uint32 param2 = 0);
 
-	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, byte relative = 0) override
+	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, VarSpriteGroupScopeOffset relative = 0) override
 	{
 		switch (scope) {
 			case VSG_SCOPE_SELF:   return &this->house_scope;
diff --git a/src/newgrf_industries.h b/src/newgrf_industries.h
index 6fc0c3f770..6c0cd4ba2b 100644
--- a/src/newgrf_industries.h
+++ b/src/newgrf_industries.h
@@ -49,7 +49,7 @@ struct IndustriesResolverObject : public ResolverObject {
 
 	TownScopeResolver *GetTown();
 
-	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, byte relative = 0) override
+	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, VarSpriteGroupScopeOffset relative = 0) override
 	{
 		switch (scope) {
 			case VSG_SCOPE_SELF: return &industries_scope;
diff --git a/src/newgrf_industrytiles.h b/src/newgrf_industrytiles.h
index ba5752cd13..68a1fd9ad6 100644
--- a/src/newgrf_industrytiles.h
+++ b/src/newgrf_industrytiles.h
@@ -44,7 +44,7 @@ struct IndustryTileResolverObject : public ResolverObject {
 	IndustryTileResolverObject(IndustryGfx gfx, TileIndex tile, Industry *indus,
 			CallbackID callback = CBID_NO_CALLBACK, uint32 callback_param1 = 0, uint32 callback_param2 = 0);
 
-	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, byte relative = 0) override
+	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, VarSpriteGroupScopeOffset relative = 0) override
 	{
 		switch (scope) {
 			case VSG_SCOPE_SELF: return &indtile_scope;
diff --git a/src/newgrf_newlandscape.h b/src/newgrf_newlandscape.h
index 307b88986e..105e6ce1a8 100644
--- a/src/newgrf_newlandscape.h
+++ b/src/newgrf_newlandscape.h
@@ -39,7 +39,7 @@ struct NewLandscapeResolverObject : public ResolverObject {
 
 	NewLandscapeResolverObject(const GRFFile *grffile, const TileInfo *ti, NewLandscapeType landscape_type, uint32 param1 = 0, uint32 param2 = 0);
 
-	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, byte relative = 0) override
+	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, VarSpriteGroupScopeOffset relative = 0) override
 	{
 		switch (scope) {
 			case VSG_SCOPE_SELF: return &this->newlandscape_scope;
diff --git a/src/newgrf_newsignals.h b/src/newgrf_newsignals.h
index d32e5850e4..1c72edd875 100644
--- a/src/newgrf_newsignals.h
+++ b/src/newgrf_newsignals.h
@@ -89,7 +89,7 @@ struct NewSignalsResolverObject : public ResolverObject {
 
 	NewSignalsResolverObject(const GRFFile *grffile, TileIndex tile, TileContext context, uint32 param1, uint32 param2, CustomSignalSpriteContext signal_context, uint8 signal_style, const TraceRestrictProgram *prog = nullptr);
 
-	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, byte relative = 0) override
+	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, VarSpriteGroupScopeOffset relative = 0) override
 	{
 		switch (scope) {
 			case VSG_SCOPE_SELF: return &this->newsignals_scope;
diff --git a/src/newgrf_object.h b/src/newgrf_object.h
index 5b6da81c19..ef6b3763ea 100644
--- a/src/newgrf_object.h
+++ b/src/newgrf_object.h
@@ -174,7 +174,7 @@ struct ObjectResolverObject : public ResolverObject {
 			CallbackID callback = CBID_NO_CALLBACK, uint32 param1 = 0, uint32 param2 = 0);
 	~ObjectResolverObject();
 
-	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, byte relative = 0) override
+	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, VarSpriteGroupScopeOffset relative = 0) override
 	{
 		switch (scope) {
 			case VSG_SCOPE_SELF:
diff --git a/src/newgrf_railtype.h b/src/newgrf_railtype.h
index 8764efcef4..a4dc0f43e0 100644
--- a/src/newgrf_railtype.h
+++ b/src/newgrf_railtype.h
@@ -46,7 +46,7 @@ struct RailTypeResolverObject : public ResolverObject {
 
 	RailTypeResolverObject(const RailtypeInfo *rti, TileIndex tile, TileContext context, RailTypeSpriteGroup rtsg, uint32 param1 = 0, uint32 param2 = 0, CustomSignalSpriteContext signal_context = CSSC_GUI, const TraceRestrictProgram *prog = nullptr);
 
-	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, byte relative = 0) override
+	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, VarSpriteGroupScopeOffset relative = 0) override
 	{
 		switch (scope) {
 			case VSG_SCOPE_SELF: return &this->railtype_scope;
diff --git a/src/newgrf_roadstop.h b/src/newgrf_roadstop.h
index 1adc150fd1..90bb1bc15d 100644
--- a/src/newgrf_roadstop.h
+++ b/src/newgrf_roadstop.h
@@ -111,7 +111,7 @@ struct RoadStopResolverObject : public ResolverObject {
 	RoadStopResolverObject(const RoadStopSpec* roadstopspec, BaseStation* st, TileIndex tile, RoadType roadtype, StationType type, uint8 view, CallbackID callback = CBID_NO_CALLBACK, uint32 param1 = 0, uint32 param2 = 0);
 	~RoadStopResolverObject();
 
-	ScopeResolver* GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, byte relative = 0) override {
+	ScopeResolver* GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, VarSpriteGroupScopeOffset relative = 0) override {
 		switch (scope) {
 			case VSG_SCOPE_SELF: return &this->roadstop_scope;
 			case VSG_SCOPE_PARENT: {
diff --git a/src/newgrf_roadtype.h b/src/newgrf_roadtype.h
index 4c29d47178..b18c243a33 100644
--- a/src/newgrf_roadtype.h
+++ b/src/newgrf_roadtype.h
@@ -42,7 +42,7 @@ struct RoadTypeResolverObject : public ResolverObject {
 
 	RoadTypeResolverObject(const RoadTypeInfo *rti, TileIndex tile, TileContext context, RoadTypeSpriteGroup rtsg, uint32 param1 = 0, uint32 param2 = 0);
 
-	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, byte relative = 0) override
+	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, VarSpriteGroupScopeOffset relative = 0) override
 	{
 		switch (scope) {
 			case VSG_SCOPE_SELF: return &this->roadtype_scope;
diff --git a/src/newgrf_spritegroup.cpp b/src/newgrf_spritegroup.cpp
index 62ac6a0f55..1868d3d35b 100644
--- a/src/newgrf_spritegroup.cpp
+++ b/src/newgrf_spritegroup.cpp
@@ -18,6 +18,7 @@
 #include "newgrf_extension.h"
 #include "scope.h"
 #include "debug_settings.h"
+#include "newgrf_engine.h"
 
 #include "safeguards.h"
 
@@ -165,7 +166,7 @@ static inline uint32 GetVariable(const ResolverObject &object, ScopeResolver *sc
  * @param relative Additional parameter for #VSG_SCOPE_RELATIVE.
  * @return The resolver for the requested scope.
  */
-/* virtual */ ScopeResolver *ResolverObject::GetScope(VarSpriteGroupScope scope, byte relative)
+/* virtual */ ScopeResolver *ResolverObject::GetScope(VarSpriteGroupScope scope, VarSpriteGroupScopeOffset relative)
 {
 	return &this->default_scope;
 }
@@ -259,7 +260,7 @@ const SpriteGroup *DeterministicSpriteGroup::Resolve(ResolverObject &object) con
 	uint32 last_value = 0;
 	uint32 value = 0;
 
-	ScopeResolver *scope = object.GetScope(this->var_scope);
+	ScopeResolver *scope = object.GetScope(this->var_scope, this->var_scope_count);
 
 	const DeterministicSpriteGroupAdjust *end = this->adjusts.data() + this->adjusts.size();
 	for (const DeterministicSpriteGroupAdjust *iter = this->adjusts.data(); iter != end; ++iter) {
@@ -271,6 +272,17 @@ const SpriteGroup *DeterministicSpriteGroup::Resolve(ResolverObject &object) con
 		/* Try to get the variable. We shall assume it is available, unless told otherwise. */
 		GetVariableExtra extra(adjust.and_mask << adjust.shift_num);
 		if (adjust.variable == 0x7E) {
+			const Vehicle *relative_scope_vehicle = nullptr;
+			VarSpriteGroupScopeOffset relative_scope_cached_count = 0;
+			if (this->var_scope == VSG_SCOPE_RELATIVE) {
+				/* Save relative scope vehicle in case it will be changed during the procedure */
+				VehicleResolverObject *veh_object = dynamic_cast<VehicleResolverObject *>(&object);
+				if (veh_object != nullptr) {
+					relative_scope_vehicle = veh_object->relative_scope.v;
+					relative_scope_cached_count = veh_object->cached_relative_count;
+				}
+			}
+
 			const SpriteGroup *subgroup = SpriteGroup::Resolve(adjust.subroutine, object, false);
 			if (subgroup == nullptr) {
 				value = CALLBACK_FAILED;
@@ -278,6 +290,13 @@ const SpriteGroup *DeterministicSpriteGroup::Resolve(ResolverObject &object) con
 				value = subgroup->GetCallbackResult();
 			}
 
+			if (relative_scope_vehicle != nullptr) {
+				/* Reset relative scope vehicle in case it was changed during the procedure */
+				VehicleResolverObject *veh_object = static_cast<VehicleResolverObject *>(&object);
+				veh_object->relative_scope.v = relative_scope_vehicle;
+				veh_object->cached_relative_count = relative_scope_cached_count;
+			}
+
 			/* Note: 'last_value' and 'reseed' are shared between the main chain and the procedure */
 		} else if (adjust.variable == 0x7B) {
 			_sprite_group_resolve_check_veh_check = false;
@@ -338,7 +357,7 @@ bool DeterministicSpriteGroup::GroupMayBeBypassed() const
 
 const SpriteGroup *RandomizedSpriteGroup::Resolve(ResolverObject &object) const
 {
-	ScopeResolver *scope = object.GetScope(this->var_scope, this->count);
+	ScopeResolver *scope = object.GetScope(this->var_scope, this->var_scope_count);
 	if (object.callback == CBID_RANDOM_TRIGGER) {
 		/* Handle triggers */
 		byte match = this->triggers & object.waiting_triggers;
@@ -445,6 +464,14 @@ static const char *_sg_size_names[] {
 	"DWORD",
 };
 
+static const char *_sg_relative_scope_modes[] {
+	"BACKWARD_SELF",
+	"FORWARD_SELF",
+	"BACKWARD_ENGINE",
+	"BACKWARD_SAMEID",
+};
+static_assert(lengthof(_sg_relative_scope_modes) == VSGSRM_END);
+
 static char *GetAdjustOperationName(char *str, const char *last, DeterministicSpriteGroupAdjustOperation operation)
 {
 	if (operation < DSGA_OP_END) return strecat(str, _dsg_op_names[operation], last);
@@ -601,6 +628,23 @@ void SpriteGroupDumper::DumpSpriteGroup(const SpriteGroup *sg, const char *paddi
 		if (sg->sg_flags & SGF_INLINING) strecat(extra_info, " (inlining)", lastof(extra_info));
 	}
 
+	char scope_buffer[64] = "";
+	auto get_scope_name = [&](VarSpriteGroupScope var_scope, VarSpriteGroupScopeOffset var_scope_count) -> const char * {
+		if (var_scope == VSG_SCOPE_RELATIVE) {
+			char *b = scope_buffer;
+			b += seprintf(b, lastof(scope_buffer), "%s[%s, ", _sg_scope_names[var_scope], _sg_relative_scope_modes[GB(var_scope_count, 8, 2)]);
+			byte offset = GB(var_scope_count, 0, 8);
+			if (HasBit(var_scope_count, 15)) {
+				b += seprintf(b, lastof(scope_buffer), "var 0x100]");
+			} else {
+				b += seprintf(b, lastof(scope_buffer), "%u]", offset);
+			}
+			return scope_buffer;
+		} else {
+			return _sg_scope_names[var_scope];
+		}
+	};
+
 	switch (sg->type) {
 		case SGT_REAL: {
 			const RealSpriteGroup *rsg = (const RealSpriteGroup*)sg;
@@ -660,26 +704,26 @@ void SpriteGroupDumper::DumpSpriteGroup(const SpriteGroup *sg, const char *paddi
 			}
 			if (dsg == this->top_default_group && !((flags & SGDF_DEFAULT) && strlen(padding) == 2)) {
 				seprintf(this->buffer, lastof(this->buffer), "%sTOP LEVEL DEFAULT GROUP: Deterministic (%s, %s), [%u]",
-						padding, _sg_scope_names[dsg->var_scope], _sg_size_names[dsg->size], dsg->nfo_line);
+						padding, get_scope_name(dsg->var_scope, dsg->var_scope_count), _sg_size_names[dsg->size], dsg->nfo_line);
 				print();
 				return;
 			}
 			if (dsg == this->top_graphics_group && !((flags & SGDF_RANGE) && strlen(padding) == 2)) {
 				seprintf(this->buffer, lastof(this->buffer), "%sTOP LEVEL GRAPHICS GROUP: Deterministic (%s, %s), [%u]",
-						padding, _sg_scope_names[dsg->var_scope], _sg_size_names[dsg->size], dsg->nfo_line);
+						padding, get_scope_name(dsg->var_scope, dsg->var_scope_count), _sg_size_names[dsg->size], dsg->nfo_line);
 				print();
 				return;
 			}
 			auto res = this->seen_dsgs.insert(dsg);
 			if (!res.second) {
 				seprintf(this->buffer, lastof(this->buffer), "%sGROUP SEEN ABOVE: Deterministic (%s, %s), [%u]",
-						padding, _sg_scope_names[dsg->var_scope], _sg_size_names[dsg->size], dsg->nfo_line);
+						padding, get_scope_name(dsg->var_scope, dsg->var_scope_count), _sg_size_names[dsg->size], dsg->nfo_line);
 				print();
 				return;
 			}
 			char *p = this->buffer;
 			p += seprintf(p, lastof(this->buffer), "%sDeterministic (%s, %s)%s [%u]",
-					padding, _sg_scope_names[dsg->var_scope], _sg_size_names[dsg->size], extra_info, dsg->nfo_line);
+					padding, get_scope_name(dsg->var_scope, dsg->var_scope_count), _sg_size_names[dsg->size], extra_info, dsg->nfo_line);
 			if (HasBit(_misc_debug_flags, MDF_NEWGRF_SG_DUMP_MORE_DETAIL)) {
 				if (dsg->dsg_flags & DSGF_NO_DSE) p += seprintf(p, lastof(this->buffer), ", NO_DSE");
 				if (dsg->dsg_flags & DSGF_VAR_TRACKING_PENDING) p += seprintf(p, lastof(this->buffer), ", VAR_PENDING");
@@ -752,9 +796,9 @@ void SpriteGroupDumper::DumpSpriteGroup(const SpriteGroup *sg, const char *paddi
 				}
 			}
 
-			seprintf(this->buffer, lastof(this->buffer), "%sRandom (%s, %s, triggers: %X, count: %X, lowest_randbit: %X, groups: %u)%s [%u]",
-					padding, _sg_scope_names[rsg->var_scope], rsg->cmp_mode == RSG_CMP_ANY ? "ANY" : "ALL",
-					rsg->triggers, rsg->count, rsg->lowest_randbit, (uint)rsg->groups.size(), extra_info, rsg->nfo_line);
+			seprintf(this->buffer, lastof(this->buffer), "%sRandom (%s, %s, triggers: %X, lowest_randbit: %X, groups: %u)%s [%u]",
+					padding, get_scope_name(rsg->var_scope, rsg->var_scope_count), rsg->cmp_mode == RSG_CMP_ANY ? "ANY" : "ALL",
+					rsg->triggers, rsg->lowest_randbit, (uint)rsg->groups.size(), extra_info, rsg->nfo_line);
 			print();
 			emit_start();
 			std::string sub_padding(padding);
diff --git a/src/newgrf_spritegroup.h b/src/newgrf_spritegroup.h
index 6ff3b399a4..adc7a57bb5 100644
--- a/src/newgrf_spritegroup.h
+++ b/src/newgrf_spritegroup.h
@@ -120,6 +120,22 @@ enum VarSpriteGroupScope : uint8 {
 };
 DECLARE_POSTFIX_INCREMENT(VarSpriteGroupScope)
 
+enum VarSpriteGroupScopeRelativeMode : uint8 {
+	VSGSRM_BACKWARD_SELF         = 0,
+	VSGSRM_FORWARD_SELF          = 1,
+	VSGSRM_BACKWARD_ENGINE       = 2,
+	VSGSRM_BACKWARD_SAMEID       = 3,
+	VSGSRM_END,
+};
+
+/*
+ * Decoded relative scope offset:
+ * Bits 0..7: offset
+ * Bits 8..9: mode (VarSpriteGroupScopeRelativeMode)
+ * Bit    15: use var 0x100
+ */
+typedef uint16 VarSpriteGroupScopeOffset;
+
 GrfSpecFeature GetGrfSpecFeatureForParentScope(GrfSpecFeature feature);
 
 inline GrfSpecFeature GetGrfSpecFeatureForScope(GrfSpecFeature feature, VarSpriteGroupScope scope)
@@ -474,6 +490,7 @@ struct DeterministicSpriteGroup : SpriteGroup {
 	DeterministicSpriteGroup() : SpriteGroup(SGT_DETERMINISTIC) {}
 
 	VarSpriteGroupScope var_scope;
+	VarSpriteGroupScopeOffset var_scope_count;
 	DeterministicSpriteGroupSize size;
 	bool calculated_result;
 	DeterministicSpriteGroupFlags dsg_flags = DSGF_NONE;
@@ -505,10 +522,10 @@ struct RandomizedSpriteGroup : SpriteGroup {
 	RandomizedSpriteGroup() : SpriteGroup(SGT_RANDOMIZED) {}
 
 	VarSpriteGroupScope var_scope;  ///< Take this object:
+	VarSpriteGroupScopeOffset var_scope_count;
 
 	RandomizedSpriteGroupCompareMode cmp_mode; ///< Check for these triggers:
 	byte triggers;
-	byte count;
 
 	byte lowest_randbit; ///< Look for this in the per-object randomized bitmask:
 
@@ -690,7 +707,7 @@ struct ResolverObject {
 
 	virtual const SpriteGroup *ResolveReal(const RealSpriteGroup *group) const;
 
-	virtual ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, byte relative = 0);
+	virtual ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, VarSpriteGroupScopeOffset relative = 0);
 
 	/**
 	 * Returns the waiting triggers that did not trigger any rerandomisation.
diff --git a/src/newgrf_station.h b/src/newgrf_station.h
index e4f6e79235..cff5d68db4 100644
--- a/src/newgrf_station.h
+++ b/src/newgrf_station.h
@@ -59,7 +59,7 @@ struct StationResolverObject : public ResolverObject {
 
 	TownScopeResolver *GetTown();
 
-	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, byte relative = 0) override
+	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, VarSpriteGroupScopeOffset relative = 0) override
 	{
 		switch (scope) {
 			case VSG_SCOPE_SELF:
diff --git a/src/newgrf_town.h b/src/newgrf_town.h
index b08232a766..d3313336df 100644
--- a/src/newgrf_town.h
+++ b/src/newgrf_town.h
@@ -62,7 +62,7 @@ struct TownResolverObject : public ResolverObject {
 
 	TownResolverObject(const struct GRFFile *grffile, Town *t, bool readonly);
 
-	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, byte relative = 0) override
+	ScopeResolver *GetScope(VarSpriteGroupScope scope = VSG_SCOPE_SELF, VarSpriteGroupScopeOffset relative = 0) override
 	{
 		switch (scope) {
 			case VSG_SCOPE_SELF: return &town_scope;