Add signals_style_lookahead_single_signal_only signal style property

docs/newgrf-additions-nml.html

@@ -508,10 +508,21 @@ item (FEAT_GLOBALVARS) {
 			Set the look-ahead extra aspects for the most recently defined style (defined using the <span class="code">define_style</span> property).<br />
 			This property only makes a difference when the "limit train lookahead to signal aspect" game setting is enabled.<br />
 			This limits the signal aspect which the hypothetical train driver can "read" from the signal without affecting signal aspect propagation to other signals, or variable <span class="code">extra_callback_info2</span>.<br />
-			Example values could include: 1 for traditional banner repeater signals, or 0 for shunt signals.<br />
+			Example values could include: 1 for traditional banner repeater signals.<br />
+			Shunt signals should use <span class="code">style_lookahead_single_signal_only</span> instead.<br />
 			The value is clamped to be less than or equal to the value set in the <span class="code">extra_aspects</span> property.
 		</td>
 	</tr>
+	<tr><td>style_lookahead_single_signal_only</td><td>0 or 1</td>
+		<td>
+			Set the look-ahead to single signal only mode for the most recently defined style (defined using the <span class="code">define_style</span> property).<br />
+			This property only makes a difference when the "limit train lookahead to signal aspect" game setting is enabled.<br />
+			This is similar to <span class="code">style_lookahead_extra_aspects</span> with a value of 0, except the lookahead always ends at the
+			next signal, even if that signal type sets <span class="code">style_no_aspect_increase</span>.<br />
+			If enabled, this property overrides <span class="code">style_lookahead_extra_aspects</span>.<br />
+			This can be used for shunt signals.
+		</td>
+	</tr>
 	<tr><td>style_opposite_side</td><td>0 or 1</td>
 		<td>
 			Set whether signals should be drawn on the opposite side of the track for the most recently defined style (defined using the <span class="code">define_style</span> property).

docs/newgrf-additions.html

@@ -475,11 +475,23 @@
 	<p>This applies to the most recent custom signal style defined using the <a href="#signals_define_style">signals_define_style</a> property.<br />
 	This property only makes a difference when the "limit train lookahead to signal aspect" game setting is enabled.<br />
 	This limits the signal aspect which the hypothetical train driver can "read" from the signal without affecting signal aspect propagation to other signals, or variable 0x18.<br />
-	Example values could include: 1 for traditional banner repeater signals, or 0 for shunt signals.</p>
+	Example values could include: 1 for traditional banner repeater signals.<br />
+	Shunt signals should use <a href="#signals_style_lookahead_single_signal_only#">signals_style_lookahead_single_signal_only</a> instead.</p>
 	<p>The property length is 1 byte. The value is clamped to be less than or equal to the value set in the <a href="#signals_extra_aspects">signals_extra_aspects</a> property.<br />
 	The Action 0 Id field is not used, the value is ignored.
 	</p>
 	<p>This is indicated by the feature name: <font face="monospace">action0_signals_style</font>, version 1</p>
+	<h4 id="signals_style_lookahead_single_signal_only">Set custom signal style train look-ahead to single signal only mode (mappable property: signals_style_lookahead_single_signal_only)</h4>
+	<p>This applies to the most recent custom signal style defined using the <a href="#signals_define_style">signals_define_style</a> property.<br />
+	This property only makes a difference when the "limit train lookahead to signal aspect" game setting is enabled.<br />
+	This is similar to <a href="#signals_style_lookahead_extra_aspects">signals_style_lookahead_extra_aspects</a> with a value of 0, except the lookahead always ends at the
+	next signal, even if that signal type sets <a href="#signals_style_no_aspect_increase">signals_style_no_aspect_increase</a>.<br />
+	If enabled, this property overrides <a href="#signals_style_lookahead_extra_aspects">signals_style_lookahead_extra_aspects</a>.<br />
+	This can be used for shunt signals.</p>
+	<p>The property length is 1 byte. 0 is disabled (default). 1 is enabled.<br />
+	The Action 0 Id field is not used, the value is ignored.
+	</p>
+	<p>This is indicated by the feature name: <font face="monospace">action0_signals_style</font>, version 1</p>
 	<h4 id="signals_style_opposite_side">Set custom signal style signal drawn on opposite side (mappable property: signals_style_opposite_side)</h4>
 	<p>This applies to the most recent custom signal style defined using the <a href="#signals_define_style">signals_define_style</a> property.<br />
 	When enabled, signals using this style are drawn on the opposite side of the track.</p>

src/newgrf.cpp

@@ -4253,6 +4253,15 @@ static ChangeInfoResult SignalsChangeInfo(uint id, int numinfo, int prop, const
 				break;
 			}
 
+			case A0RPI_SIGNALS_STYLE_LOOKAHEAD_SINGLE_SIGNAL_ONLY: {
+				if (MappedPropertyLengthMismatch(buf, 1, mapping_entry)) break;
+				uint8 value = buf->ReadByte();
+				if (_cur.grffile->current_new_signal_style != nullptr) {
+					SB(_cur.grffile->current_new_signal_style->style_flags, NSSF_LOOKAHEAD_SINGLE_SIGNAL, 1, (value != 0 ? 1 : 0));
+				}
+				break;
+			}
+
 			case A0RPI_SIGNALS_STYLE_SEMAPHORE_ENABLED: {
 				if (MappedPropertyLengthMismatch(buf, 4, mapping_entry)) break;
 				uint32 mask = buf->ReadDWord();

src/newgrf_extension.cpp

@@ -97,6 +97,7 @@ extern const GRFPropertyMapDefinition _grf_action0_remappable_properties[] = {
 	GRFPropertyMapDefinition(GSF_SIGNALS, A0RPI_SIGNALS_STYLE_NO_ASPECT_INCREASE, "signals_style_no_aspect_increase"),
 	GRFPropertyMapDefinition(GSF_SIGNALS, A0RPI_SIGNALS_STYLE_ALWAYS_RESERVE_THROUGH, "signals_style_always_reserve_through"),
 	GRFPropertyMapDefinition(GSF_SIGNALS, A0RPI_SIGNALS_STYLE_LOOKAHEAD_EXTRA_ASPECTS, "signals_style_lookahead_extra_aspects"),
+	GRFPropertyMapDefinition(GSF_SIGNALS, A0RPI_SIGNALS_STYLE_LOOKAHEAD_SINGLE_SIGNAL_ONLY, "signals_style_lookahead_single_signal_only"),
 	GRFPropertyMapDefinition(GSF_SIGNALS, A0RPI_SIGNALS_STYLE_SEMAPHORE_ENABLED, "signals_style_semaphore_enabled"),
 	GRFPropertyMapDefinition(GSF_SIGNALS, A0RPI_SIGNALS_STYLE_ELECTRIC_ENABLED, "signals_style_electric_enabled"),
 	GRFPropertyMapDefinition(GSF_SIGNALS, A0RPI_SIGNALS_STYLE_OPPOSITE_SIDE, "signals_style_opposite_side"),

src/newgrf_extension.h

@@ -41,6 +41,7 @@ enum Action0RemapPropertyIds {
 	A0RPI_SIGNALS_STYLE_NO_ASPECT_INCREASE,
 	A0RPI_SIGNALS_STYLE_ALWAYS_RESERVE_THROUGH,
 	A0RPI_SIGNALS_STYLE_LOOKAHEAD_EXTRA_ASPECTS,
+	A0RPI_SIGNALS_STYLE_LOOKAHEAD_SINGLE_SIGNAL_ONLY,
 	A0RPI_SIGNALS_STYLE_SEMAPHORE_ENABLED,
 	A0RPI_SIGNALS_STYLE_ELECTRIC_ENABLED,
 	A0RPI_SIGNALS_STYLE_OPPOSITE_SIDE,

src/newgrf_newsignals.h

@@ -29,6 +29,7 @@ enum NewSignalStyleFlags {
 	NSSF_ALWAYS_RESERVE_THROUGH         = 1,
 	NSSF_LOOKAHEAD_ASPECTS_SET          = 2,
 	NSSF_OPPOSITE_SIDE                  = 3,
+	NSSF_LOOKAHEAD_SINGLE_SIGNAL        = 4,
 };
 
 struct NewSignalStyle {

src/pbs.cpp

@@ -664,6 +664,9 @@ static PBSTileInfo FollowReservation(Owner o, RailTypes rts, TileIndex tile, Tra
 					if (HasBit(_non_aspect_inc_style_mask, signal_style)) {
 						SetBit(signal_flags, TRSLAI_NO_ASPECT_INC);
 					}
+					if (HasBit(_next_only_style_mask, signal_style)) {
+						SetBit(signal_flags, TRSLAI_NEXT_ONLY);
+					}
 					lookahead->AddSignal(signal_speed, 0, z, signal_flags);
 					lookahead->SetNextExtendPositionIfUnset();
 				}
@@ -1000,8 +1003,10 @@ void SetTrainReservationLookaheadEnd(Train *v)
 
 	int32 threshold = v->lookahead->current_position + 24;
 	uint8 known_signals_ahead = 1;
+	bool allow_skip_no_aspect_inc = false;
 	if (v->IsInDepot()) {
 		known_signals_ahead = _extra_aspects + 1;
+		allow_skip_no_aspect_inc = true;
 	}
 	for (const TrainReservationLookAheadItem &item : v->lookahead->items) {
 		if (item.end >= v->lookahead->reservation_end_position) break;
@@ -1010,10 +1015,11 @@ void SetTrainReservationLookaheadEnd(Train *v)
 				/* Signal is within visual range */
 				uint8 style = item.data_aux >> 8;
 				uint8 max_aspect = (style == 0) ? _extra_aspects : _new_signal_styles[style - 1].lookahead_extra_aspects;
-				max_aspect += (HasBit(item.data_aux, TRSLAI_NO_ASPECT_INC) ? 1 : 2);
+				if (!HasBit(item.data_aux, TRSLAI_NEXT_ONLY)) allow_skip_no_aspect_inc = true;
+				max_aspect += ((HasBit(item.data_aux, TRSLAI_NO_ASPECT_INC) && allow_skip_no_aspect_inc) ? 1 : 2);
 				if (max_aspect > known_signals_ahead) known_signals_ahead = max_aspect;
 			}
-			if (!HasBit(item.data_aux, TRSLAI_NO_ASPECT_INC)) {
+			if (!HasBit(item.data_aux, TRSLAI_NO_ASPECT_INC) || !allow_skip_no_aspect_inc) {
 				known_signals_ahead--;
 				if (known_signals_ahead == 0) {
 					if (item.start > v->lookahead->lookahead_end_position) v->lookahead->lookahead_end_position = item.start;

src/pbs.h

@@ -60,6 +60,7 @@ enum TrainReservationLookAheadItemType : byte {
 
 enum TrainReservationSignalLookAheadItemFlags {
 	TRSLAI_NO_ASPECT_INC   = 0,           ///< This signal does not increase the signal aspect (e.g. banner repeater)
+	TRSLAI_NEXT_ONLY       = 1,           ///< This signal only permits lookahead up to the next physical signal, even if that has TRSLAI_NO_ASPECT_INC (e.g. shunt)
 };
 
 struct TrainReservationLookAheadItem {

src/signal.cpp

@@ -31,6 +31,7 @@
 uint8 _extra_aspects = 0;
 uint64 _aspect_cfg_hash = 0;
 uint16 _non_aspect_inc_style_mask = 0;
+uint16 _next_only_style_mask = 0;
 uint16 _always_reserve_through_style_mask = 0;
 uint16 _no_tunnel_bridge_style_mask = 0;
 uint16 _signal_opposite_side_style_mask = 0;
@@ -1512,6 +1513,7 @@ static bool DetermineExtraAspectsVariable()
 	uint8 new_extra_aspects = 0;
 
 	_non_aspect_inc_style_mask = 0;
+	_next_only_style_mask = 0;
 	_no_tunnel_bridge_style_mask = 0;
 	_always_reserve_through_style_mask = 0;
 	_signal_opposite_side_style_mask = 0;
@@ -1533,7 +1535,10 @@ static bool DetermineExtraAspectsVariable()
 				SetBit(_always_reserve_through_style_mask, i + 1);
 				SetBit(_no_tunnel_bridge_style_mask, i + 1);
 			}
-			if (HasBit(_new_signal_styles[i].style_flags, NSSF_LOOKAHEAD_ASPECTS_SET)) {
+			if (HasBit(_new_signal_styles[i].style_flags, NSSF_LOOKAHEAD_SINGLE_SIGNAL)) {
+				_new_signal_styles[i].lookahead_extra_aspects = 0;
+				SetBit(_next_only_style_mask, i + 1);
+			} else if (HasBit(_new_signal_styles[i].style_flags, NSSF_LOOKAHEAD_ASPECTS_SET)) {
 				_new_signal_styles[i].lookahead_extra_aspects = std::min<uint8>(_new_signal_styles[i].lookahead_extra_aspects, _new_signal_styles[i].grffile->new_signal_extra_aspects);
 			} else {
 				_new_signal_styles[i].lookahead_extra_aspects = _new_signal_styles[i].grffile->new_signal_extra_aspects;

src/signal_func.h

@@ -22,6 +22,7 @@
 extern uint8 _extra_aspects;
 extern uint64 _aspect_cfg_hash;
 extern uint16 _non_aspect_inc_style_mask;
+extern uint16 _next_only_style_mask;
 extern uint16 _always_reserve_through_style_mask;
 extern uint16 _no_tunnel_bridge_style_mask;
 extern uint16 _signal_opposite_side_style_mask;

src/table/newgrf_debug_data.h

@@ -278,6 +278,7 @@ class NIHVehicle : public NIHelper {
 						case TRLIT_SIGNAL:
 							b += seprintf(b, lastof(buffer), "signal: target speed: %u, style: %u, flags:", item.data_id, item.data_aux >> 8);
 							if (HasBit(item.data_aux, TRSLAI_NO_ASPECT_INC)) b += seprintf(b, lastof(buffer), "n");
+							if (HasBit(item.data_aux, TRSLAI_NEXT_ONLY)) b += seprintf(b, lastof(buffer), "s");
 							if (_settings_game.vehicle.realistic_braking_aspect_limited == TRBALM_ON && l.lookahead_end_position == item.start) {
 								b += seprintf(b, lastof(buffer), ", lookahead end");
 								print_braking_speed(item.start, 0, item.z_pos);