TileIndex GetTileIndexFromLocalCoordinate(int region_x, int region_y, int local_x, int local_y)

{

	assert(local_y >= 0 && local_y < WATER_REGION_EDGE_LENGTH);

	return TileXY(WATER_REGION_EDGE_LENGTH * region_x + local_x, WATER_REGION_EDGE_LENGTH * region_y + local_y);

}