Add road/tram type flag to disallow collisions with trains

src/vehicle.cpp

@@ -561,6 +561,22 @@ static Vehicle *EnsureNoVehicleProcZ(Vehicle *v, void *data)
 	return v;
 }
 
+/**
+ * Callback that returns 'real' train-collidable road vehicles lower or at height \c *(int*)data .
+ * @param v Vehicle to examine.
+ * @param data Pointer to height data.
+ * @return \a v if conditions are met, else \c nullptr.
+ */
+static Vehicle *EnsureNoTrainCollidableRoadVehicleProcZ(Vehicle *v, void *data)
+{
+	int z = static_cast<int>(reinterpret_cast<intptr_t>(data));
+
+	if (v->z_pos > z) return nullptr;
+	if (HasBit(_roadtypes_non_train_colliding, RoadVehicle::From(v)->roadtype)) return nullptr;
+
+	return v;
+}
+
 /**
  * Callback that returns 'real' vehicles lower or at height \c *(int*)data .
  * @param v Vehicle to examine.
@@ -623,6 +639,13 @@ CommandCost EnsureNoRoadVehicleOnGround(TileIndex tile)
 	return CommandCost();
 }
 
+bool IsTrainCollidableRoadVehicleOnGround(TileIndex tile)
+{
+	int z = GetTileMaxPixelZ(tile);
+
+	return VehicleFromPos(tile, VEH_ROAD, reinterpret_cast<void *>(static_cast<intptr_t>(z)), &EnsureNoTrainCollidableRoadVehicleProcZ, true) != nullptr;
+}
+
 struct GetVehicleTunnelBridgeProcData {
 	const Vehicle *v;
 	TileIndex t;