Add: [NewGRF] vehicle variable 63 to test the tracktype of the current tile against a given tracktype.

src/newgrf_railtype.cpp

@@ -138,6 +138,28 @@ SpriteID GetCustomSignalSprite(const RailtypeInfo *rti, TileIndex tile, SignalTy
 	return group->GetResult();
 }
 
+/**
+ * Translate an index to the GRF-local railtype-translation table into a RailType.
+ * @param railtype  Index into GRF-local translation table.
+ * @param grffile   Originating GRF file.
+ * @return RailType or INVALID_RAILTYPE if the railtype is unknown.
+ */
+RailType GetRailTypeTranslation(uint8 railtype, const GRFFile *grffile)
+{
+	if (grffile == nullptr || grffile->railtype_list.size() == 0) {
+		/* No railtype table present. Return railtype as-is (if valid), so it works for original railtypes. */
+		if (railtype >= RAILTYPE_END || GetRailTypeInfo(static_cast<RailType>(railtype))->label == 0) return INVALID_RAILTYPE;
+
+		return static_cast<RailType>(railtype);
+	} else {
+		/* Railtype table present, but invalid index, return invalid type. */
+		if (railtype >= grffile->railtype_list.size()) return INVALID_RAILTYPE;
+
+		/* Look up railtype including alternate labels. */
+		return GetRailTypeByLabel(grffile->railtype_list[railtype]);
+	}
+}
+
 /**
  * Perform a reverse railtype lookup to get the GRF internal ID.
  * @param railtype The global (OpenTTD) railtype.