LuaATC Programming Interface

LuaATC (Lua Advanced Train Control, also called LuaAutomation) utilises the Lua programming language to provide an immensely powerful automation system for Advtrains. Prior knowledge of Lua is highly reccommended.

The standard Lua globals are available in the LuaATC environment:

• string
• math
• table
• from os:
  • os.clock()
  • os.difftime()
  • os.time()
  • os.date() ¹⁾

The standard Lua functions are available in the LuaATC environment:

• assert
• error
• ipairs
• pairs
• next
• select
• tonumber
• tostring
• type
• unpack

Certain aspects of LuaAutomation can only be done at certain times, and others require specific conditions to be useful. These are noted under the section headings.

In the following functions, all parameters named pos designate a position. You can use either:

• a default Minetest position vector (like {x=34, y=2, z=-18})
• the POS(34,2,-18) shorthand
• a string, the name of a passive component.

A shorthand function to designate a Minetest position vector like {x=?, y=?, z=?}.

Switches (turnouts), simple signals and mesecon switches are so-called “Passive Components”. These functions are used to interact with them.

Gets the state of a passive component at position pos. The returned states are component-specific, see Passive Components.

Sets the state of a passive component at position pos to the value new_state. The states are component-specific, see Passive Components.

Checks whether there is a passive component at position pos. If pos is a string, checks whether this passive component name exists.

Train control is arguably the most important aspect of automating a rail system. The following functions can only be used from ATC Tracks.

To control a train, this train must be positioned on the ATC rail.²⁾ It does not matter which portion of the train is on the ATC rail, and whether the train is moving or not.

These fields are populated every time a train is occupying a LuaATC track.

The 6 digit ID of the train passing the rail as a string. nil if no there is no train.

The current speed of the train passing the rail, in metres per second. nil if no there is no train.

Whether the train is driving in direction of the arrows on the ATC rail. nil if no there is no train.

Note: this code does not indicate whether there is a train on the rail, as both false and nil evaluate to false:

-- BAD
if not atc_arrow then
    -- ...do stuff
end
 
-- GOOD
if atc_arrow == false then
    -- ...do stuff
end

Sends the specified ATC command to the train and returns true. If there is no train, returns false and does nothing.

since version 2.3.0

Sends the specified ATC command to the train specified by its 6 digit train ID and returns true. If there is no train with such an ID, returns false and does nothing. Calling this function from an ATC rail is independent of any train that stands on the rail and does not affect it (except of course when train_id happens to be the ID of the train on the rail).

Note: train_id MUST be a string. Train IDs can begin with 0, which is ignored when the variable is of type number, resulting in an invalid 5 digit ID.

Resets the train's current ATC command and returns true. If there is no train, returns false and does nothing.

Sets the text shown on the outside of the train and returns true. If there is no train, returns false and does nothing.

Sets the text shown inside the train and returns true. If there is no train, returns false and does nothing.

Gets the outside/inside text currently set on the train.

Returns the line property of the train, as a string. This string can be used to distinguish trains of different lines and route them properly.

This property is also used by the interlocking system for Automatic Routesetting.

If there is no train, the Lua program stored in the rail will exit immediately:

2019-01-01 15:00:00: WARNING[Server]: [advtrains]LuaAutomation ATC interface rail at (0,0,0) : LUA Error: …/mods/advtrains/advtrains_luaautomation/atc_rail.lua:93: attempt to index upvalue 'train' (a nil value)

This is a bug.

Sets the line property of the train, as a string.

On subway trains, in the Basic Trains modpack, the line is automatically displayed on the outside of the trains, if the first character is a number between 0 and 9 (where 0 is displayed as “Line 10”).

If there is no train, same behavior as get_line() applies.

Returns the routing code of the train, as a string. This property is used by the interlocking system for Automatic Routesetting.

If there is no train, same behavior as get_line() applies.

Sets the routing code of the train, as a string. This property is used by the interlocking system for Automatic Routesetting.

If there is no train, same behavior as get_line() applies.

since version 2.3.0

Enables (value == false) or disables (value == true) interlocking for this train. The train will not trigger automatic route setting on signals based on ARS.

This function has essentially the same effect as the ATC command A<enable_ARS>.

since version 2.3.0

Adds a Temporary Speed Restriction at the current rail, so that the train is passing the rail at the specified speed, or at a lower speed.

Calling this function from an approach event has essentially the same effect as a Point Speed Restriction Rail. Note that due to internal implementation details, you must call this function again on any subsequent approach events received. (see Events)

• This function is available only when the approach callback mechanism is enabled.
• This function is only accessible during approach events

Aside from basic train control, LuaAutomation enables automatic and complex shunting operations to be performed.

There are several functions available especially for shunting operations. Some of these functions make use of Freight Codes (FC) set in the Wagon Properties of each wagon.³⁾

FCs are composed of strings separated by !, for instance foo!bar!baz. Lists ending in ? have a special function (see step_fc() below.) Each wagon has a current FC, indicating its next destination. By default this is an empty string.

Splits the train at the specified index, into a train with index-1 wagons and a second train starting with the index-th wagon. The atc_command specified is sent to the second train after decoupling. S0 or B0 is common to ensure any locomotives in the remaining train don't continue to move.

since version 2.4.3

Returns a table with the entire FC list for each wagon in the train.

since version 2.4.3

Overwrites the FC list of the entire train according to a table fc_list. A false or nil entry in the table will leave the wagon unaffecetd, however all others will be overwritten.

Useful for mass-programming freight trains that use FC shunting instead of walking to each wagon individually.

NOTE: get_fc() and set_fc() currently only work when the wagon is in a loaded area. They will fail silently when not in a loaded area. This is a bug.

Splits the train in such a way thay all wagons with non-empty current FC of the first part of the train have the same FC. atc_command is sent to the remainder of the train, as with split_at_index. It returns the FC of the wagons of the first part.

The optional arguement len specifies a maximum train length to be split off.

Similar to split_at_fc, this function will separate the first group of wagons with an empty FC, generally locomotives. atc_command and len area as above with split_at_fc.

Steps the FCs of all wagons forward, selecting the next code after the !. If the end of the string is reached, then the code loops back and the first code is selected. If the string ends in a ? however, the order of codes is reversed instead.

Returns the number of wagons in a train.

Enables Autocouple mode. When the train hits another standing train, it couples to it and continues with its current ATC target speed in the same direction.

In contrast to the Cpl ATC command, the autocouple property does not reset after coupling. It needs to be explicitly disabled using unset_autocouple(). Note that the ATC Cpl command and the LuaATC autocouple flag are independent and can be used at the same time.

since version 2.4.0

The train that is initiating the coupling (that is, the train that is driving and whose mode is set to autocouple) is guaranteed to retain its Train ID.

Disables the Autocouple mode.

Deprecated

Enables shunting mode for the currently passing train and returns true. This mode permanently restricts the train speed to 6 m/s (or 21.6 km/h). When in shunt mode, the train will couple to trains it collides with, and will obey shunt signals.

Further details on the “Shunt Mode” are explained in the Interlocking section. (Missing Reference)

If there is no train, returns false and does nothing.

Deprecated

Disables shunting mode as set above

These functions allow to schedule interrupts, a.k.a events to be executed at a later time. They are not available in init code.

The time counter and queue handling these interrupts is synchronized to minetest's internal step time. It is written in a very simple fashion, and is NOT secured against “interrupt bombs”. Be careful!

-- an example for an "interrupt bomb"
-- NEVER DO THIS!
if event.int then
  interrupt(1,"A")
  interrupt(1,"B")
-- run 1: {A,B}
-- run 2: {A,B,A,B}
-- run 3: {A,B,A,B,A,B,A,B}...

Causes the LuaAutomation mod to trigger an int event (the Advtrains equivalent of Mesecons' interrupt) on this component after the given time, in seconds, with the specified message. message can be of any Lua data type.

Use of this function is discouraged, as “fork bombs” can easily be built. Please use interrupt_safe() or make sure to clear_interrupts() in appropriate places.

since version 2.3.0

Like interrupt(), but returns false when an interrupt (of any type) is already present for this component and does not add an interrupt. Returns true when interrupt was successfully added.

Triggers immediately an ext_int event on the active component at pos. message can be of any Lua data type.

since version 2.3.0

Removes any pending interrupts (both of type 'int' and 'ext_int') set on this node.

When advtrains_line_automation is enabled, all Railway time functions are exposed as rwt.* and can safely be used in LuaATC code.

For the available functions, see Railway Time API.

--Example: print the time of the next full minute
local now = rwt.now()
local next_minute = rwt.next_rpt(now, "01;00", 0)

This is a separate schedule queue. In contrast to the interrupt system, which is the original and established way to schedule interrupts, it relies on the Railway Time system and therefore is only accessible when advtrains_line_automation is enabled.

There are two important considerations to this:

1. While the interrupt system is always synchronized to minetest step time, the RWT scheduler follows the RWT time flow. In particular, this means that you must be able to handle “time jumps” that occur when RWT is set up to adapt to real time.
2. The RWT scheduler has a built-in protection against “interrupt bombs”. There is a limit on how many interrupts can be enqueued from a single LuaATC component. At the time of this writing, this limit is set to 1.

Clicking “Save” on the code edit form clears all events currently scheduled in the RWT scheduler. It does NOT clear the interrupt scheduler events.

Triggers a schedule event AT the specified Railway Time. The time value here is an absolute value. msg can be any data type and is accessible in event.msg.

  -- Example: schedule a "depart" event on the next full 5 minutes
  local now = rwt.now()
  local next_5minutes = rwt.next_rpt(now, "05;00", 0)
  schedule(next_5minutes, "depart")

Like schedule(), but the passed time is relative.

  -- Example: schedule a "depart" event in 1 minute
  schedule_in("01;00", "depart")

Sends a digiline message on the specified channel. See the digilines ContentDB page for more information.

This function is not available in init code.

Interlocking functions are available when the advtrains_interlocking mod is enabled.

Checks whether it is possible to set the route designated by route_name from the signal at position pos.

It emits a warning and halts execution of Lua code in the following cases:

• the node at specified position is not a signal:

LUA Error: …: There's no signal at (0,0,0)

• pos is a string, and the named passive component does not exist:

LUA Error: …: Invalid position supplied to ???: “…”

• the specified route does not exist:

LUA Error: …: No route called B at (0,0,0)

Requests the route designated by route_name from the signal at position pos. Has the same effect as clicking the “Set Route” in the formspec from the designated signal.

Same warnings apply as for can_set_route.

If the route can't be set, the signal remains red and waits for conflicting problems to be solved. Execution continues immediately.

There is currently no way to emit an event when the signal becomes green.

Cancels the route that is set from the signal at position pos. Has the same effect as clicking the “Cancel Route” in the formspec from the designated signal.

Same warnings apply as for can_set_route.

If the route has already been canceled, nothing happens.

Gets the aspect of the signal at pos. The aspect format is described in the Signal page.

Same warnings apply as for can_set_route.