Function GetRoadTypeTranslation

src/newgrf_roadtype.cpp:171–193

* Translate an index to the GRF-local road/tramtype-translation table into a RoadType. * @param rtt Whether to index the road- or tramtype-table. * @param tracktype Index into GRF-local translation table. * @param grffile Originating GRF file. * @return RoadType or INVALID_ROADTYPE if the roadtype is unknown. */

 * @return RoadType or INVALID_ROADTYPE if the roadtype is unknown.
 */
RoadType GetRoadTypeTranslation(RoadTramType rtt, uint8_t tracktype, const GRFFile *grffile)
{
	/* Because OpenTTD mixes RoadTypes and TramTypes into the same type,
	 * the mapping of the original road- and tramtypes does not match the default GRF-local mapping.
	 * So, this function cannot provide any similar behavior to GetCargoTranslation() and GetRailTypeTranslation()
	 * when the GRF defines no translation table.
	 * But since there is only one default road/tram-type, this makes little sense anyway.
	 * So for GRF without translation table, we always return INVALID_ROADTYPE.
	 */

	if (grffile == nullptr) return INVALID_ROADTYPE;

	const auto &list = rtt == RTT_TRAM ? grffile->tramtype_list : grffile->roadtype_list;
	if (tracktype >= list.size()) return INVALID_ROADTYPE;

	/* Look up roadtype including alternate labels. */
	RoadType result = GetRoadTypeByLabel(list[tracktype]);

	/* Check whether the result is actually the wanted road/tram-type */
	if (result != INVALID_ROADTYPE && GetRoadTramType(result) != rtt) return INVALID_ROADTYPE;

	return result;
}

/**
 * Perform a reverse roadtype lookup to get the GRF internal ID.