Add railtype variable for adjacent crossing information

src/newgrf_railtype.cpp

@@ -17,6 +17,7 @@
 #include "depot_base.h"
 #include "town.h"
 #include "signal_func.h"
+#include "road.h"
 
 #include "safeguards.h"
 
@@ -39,6 +40,7 @@
 			case A2VRI_RAILTYPE_SIGNAL_CONTEXT: return this->signal_context;
 			case A2VRI_RAILTYPE_SIGNAL_SIDE: return GetNewSignalsSideVariable();
 			case A2VRI_RAILTYPE_SIGNAL_VERTICAL_CLEARANCE: return 0xFF;
+			case A2VRI_RAILTYPE_ADJACENT_CROSSING: return 0;
 		}
 	}
 
@@ -66,6 +68,31 @@
 			return GetNewSignalsSideVariable();
 		case A2VRI_RAILTYPE_SIGNAL_VERTICAL_CLEARANCE:
 			return GetNewSignalsVerticalClearanceInfo(this->tile, this->z);
+		case A2VRI_RAILTYPE_ADJACENT_CROSSING: {
+			if (!IsLevelCrossingTile(this->tile) || !_settings_game.vehicle.adjacent_crossings) return 0;
+
+			auto is_usable_crossing = [&](TileIndex t) -> bool {
+				if (HasRoadTypeRoad(t) && !HasBit(_roadtypes_non_train_colliding, GetRoadTypeRoad(t))) return true;
+				if (HasRoadTypeTram(t) && !HasBit(_roadtypes_non_train_colliding, GetRoadTypeTram(t))) return true;
+				return false;
+			};
+			if (!is_usable_crossing(this->tile)) return 0;
+
+			const Axis axis = GetCrossingRoadAxis(this->tile);
+			const DiagDirection dir_s = AxisToDiagDir(axis);
+			const DiagDirection dir_n = ReverseDiagDir(dir_s);
+
+			uint32 result = 0;
+			auto test_dir = [&](DiagDirection dir, uint bit) {
+				const TileIndex t = TileAddByDiagDir(this->tile, dir);
+				if (t < MapSize() && IsLevelCrossingTile(t) && GetCrossingRoadAxis(t) == axis && is_usable_crossing(t)) {
+					SetBit(result, bit);
+				}
+			};
+			test_dir(dir_s, 0);
+			test_dir(dir_n, 1);
+			return result;
+		}
 	}
 
 	DEBUG(grf, 1, "Unhandled rail type tile variable 0x%X", variable);