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#### Advtrains - Lua Automation features

This mod offers components that run LUA code and interface with each other through a global environment. It makes complex automated railway systems possible.

### atlatc
The mod is sometimes abbreviated as 'atlatc'. This stands for AdvTrainsLuaATC. This short name has been chosen for user convenience, since the name of this mod ('advtrains_luaautomation') is very long.

### Privilege
To perform any operations using this mod (except executing operation panels), players need the "atlatc" privilege.
This privilege should never be granted to anyone except trusted administrators. Even though the LUA environment is sandboxed, it is still possible to DoS the server by coding infinite loops or requesting expotentially growing interrupts. 

### Active and passive
Active components are these who have LUA code running in them. They are triggered on specific events. Passive components are dumb, they only have a state and can be set to another state, they can't perform actions themselves.

### Environments

Each active component is assigned to an environment. This is where all data are held. Components in different environments can't inferface with each other.
This system allows multiple independent automation systems to run simultaneously without polluting each other's environment.

/env_create <env_name>
Create environment with the given name. To be able to do anything, you first need to create an environment. Choose the name wisely, you can't change it afterwards.

/env_setup <env_name>
Invoke the form to edit the environment's initialization code. For more information, see the section on active components. You can also delete an environment from here.

### Active components

The code of every active component is run on specific events which are explained soon. When run, every variable written that is not local and is no function or userdata is saved over code re-runs and over server restarts. Additionally, the following global variables are defined:

# event
The variable 'event' contains a table with information on the current event. How this table can look is explained below.

# S
The variable 'S' contains a table which is shared between all components of the environment. Its contents are persistent over server restarts. May not contain functions, every other value is allowed.
Example:
Component 1: S.stuff="foo"
Component 2: print(S.stuff)
-> foo

# F
The variable 'F' also contains a table which is shared between all components of the environment. Its contents are discarded on server shutdown or when the init code gets re-run. Every data type is allowed, even functions.
The purpose of this table is not to save data, but to provide static value and function definitions. The table should be populated by the init code.

# Standard Lua functions
The following standard Lua libraries are available:
string, math, table, os
The following standard Lua functions are available:
assert, error, ipairs, pairs, next, select, tonumber, tostring, type, unpack

Every attempt to overwrite any of the predefined values results in an error.

# LuaAutomation-specific global functions

POS(x,y,z)
Shorthand function to create a position vector {x=?, y=?, z=?} with less characters

getstate(pos)
Get the state of the passive component at position 'pos'. See section on passive components for more info.
pos can be either a position vector (created by POS()) or a string, the name of this passive component.

setstate(pos, newstate)
Set the state of the passive component at position 'pos'.
pos can be either a position vector (created by POS()) or a string, the name of this passive component.

interrupt(time, message)
Cause LuaAutomation to trigger an 'int' event on this component after the given time in seconds with the specified 'message' field. 'message' can be of any Lua data type.
Not available in init code!

interrupt_pos(pos, message)
Immediately trigger an 'ext_int' event on the active component at position pos. 'message' is like in interrupt().
USE WITH CARE, or better don't use! Incorrect use can result in expotential growth of interrupts.

## Components and events

The event table is a table of the following format:
{
	type = "<type>",
	<type> = true,
	... additional content ...
}
You can check for the event type by either using
if event.type == "wanted" then ...do stuff... end
or
if event.wanted then ...do stuff... end
(if 'wanted' is the event type to check for)

# Init code
The initialization code is not a component as such, but rather a part of the whole environment. It can (and should) be used to make definitions that other components can refer to.
Examples:
A function to define behavior for trains in subway stations:
function F.station()
	if event.train then atc_send("B0WOL") end
	if event.int and event.message="depart" then atc_send("OCD1SM") end
end

The init code is run whenever the F table needs to be refilled with data. This is the case on server startup and whenever the init code is changed and you choose to run it.
Functions are run in the environment of the currently active node, regardless of where they were defined. So, the 'event' table always reflects the state of the calling node.

The 'event' table of the init code is always {type="init", init=true}.

# ATC rails
The Lua-controlled ATC rails are the only components that can actually interface with trains. The following event types are generated:

{type="train", train=true, id="<train_id>"}
This event is fired when a train enters the rail. The field 'id' is the unique train ID, which is a long string (generated by concatenating os.time() and os.clock() at creation time). The Itrainmap mod displays the last 4 digits of this ID.

{type="int", int=true, message=<message>}
Fired when an interrupt set by the 'interrupt' function runs out. 'message' is the message passed to the interrupt function.
{type="ext_int", ext_int=true, message=<message>}
Fired when another node called 'interrupt_pos' on this position. 'message' is the message passed to the interrupt_pos function.

In addition to the default environment functions, the following functions are available:

atc_send(<atc_command>)
	Sends the specified ATC command to the train and returns true. If there is no train, returns false and does nothing.
atc_reset()
	Resets the train's current ATC command. If there is no train, returns false and does nothing.
atc_arrow
	Boolean, true when the train is driving in the direction of the arrows of the ATC rail. Nil if there is no train.
atc_id
	Train ID of the train currently passing the controller. Nil if there's no train.
atc_speed
	Speed of the train, or nil if there is no train.
atc_set_text_outside(text)
	Set text shown on the outside of the train. Pass nil to show no text.
atc_set_text_inside(text)
	Set text shown to train passengers. Pass nil to show no text.
set_line(number)
	Only for subway wagons: Display a line number (1-9) on the train.

# Operator panel
This simple node executes its actions when punched. It can be used to change a switch and update the corresponding signals or similar applications.

The event fired is {type="punch", punch=true} by default. In case of an interrupt, the events are similar to the ones of the ATC rail.

### Passive components

All passive components can be interfaced with the setstate and getstate functions(see above).
Below, each apperance is mapped to the "state" of that node.

## Signals
The light signals are interfaceable, the analog signals are not.
"green" - Signal shows green light
"red" - Signal shows red light

## Switches
All default rail switches are interfaceable, independent of orientation.
"cr" - The switch is set in the direction that is not straight.
"st" - The switch is set in the direction that is straight.

## Mesecon Switch
The Mesecon switch can be switched using LuaAutomation. Note that this is not possible on levers, only the full-node 'Switch' block.
"on" - the switch is switched on
"off" - the switch is switched off

##Andrew's Cross
"on" - it blinks
"off" - it does not blink

### Passive component naming
You can assign names to passive components using the Passive Component Naming tool.
Once you set a name for any component, you can reference it by that name in the getstate() and setstate() functions, like this:
(Imagine a signal that you have named "Stn_P1_out" at position (1,2,3) )
setstate("Stn_P1_out", "green") instead of setstate(POS(1,2,3), "green")
This way, you don't need to memorize positions.

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--trainlogic.lua
--controls train entities stuff about connecting/disconnecting/colliding trains and other things


local benchmark=false
local bm={}
local bmlt=0
local bmsteps=0
local bmstepint=200
atprintbm=function(action, ta)
	if not benchmark then return end
	local t=(os.clock()-ta)*1000
	if not bm[action] then
		bm[action]=t
	else
		bm[action]=bm[action]+t
	end
	bmlt=bmlt+t
end
function endstep()
	if not benchmark then return end
	bmsteps=bmsteps-1
	if bmsteps<=0 then
		bmsteps=bmstepint
		for key, value in pairs(bm) do
			minetest.chat_send_all(key.." "..(value/bmstepint).." ms avg.")
		end
		minetest.chat_send_all("Total time consumed by all advtrains actions per step: "..(bmlt/bmstepint).." ms avg.")
		bm={}
		bmlt=0
	end
end

advtrains.train_accel_force=2--per second and divided by number of wagons
advtrains.train_brake_force=3--per second, not divided by number of wagons
advtrains.train_roll_force=0.5--per second, not divided by number of wagons, acceleration when rolling without brake
advtrains.train_emerg_force=10--for emergency brakes(when going off track)


advtrains.mainloop_trainlogic=function(dtime)
	--build a table of all players indexed by pts. used by damage and door system.
	advtrains.playersbypts={}
	for _, player in pairs(minetest.get_connected_players()) do
		if not advtrains.player_to_train_mapping[player:get_player_name()] then
			--players in train are not subject to damage
			local ptspos=minetest.pos_to_string(vector.round(player:getpos()))
			advtrains.playersbypts[ptspos]=player
		end
	end
	--regular train step
	-- do in two steps: 
	--  a: predict path and add all nodes to the advtrains.detector.on_node table
	--  b: check for collisions based on these data
	--  (and more)
	local t=os.clock()
	advtrains.detector.on_node={}
	for k,v in pairs(advtrains.trains) do
		advtrains.atprint_context_tid=sid(k)
		advtrains.atprint_context_tid_full=k
		advtrains.train_step_a(k, v, dtime)
	end
	for k,v in pairs(advtrains.trains) do
		advtrains.atprint_context_tid=sid(k)
		advtrains.atprint_context_tid_full=k
		advtrains.train_step_b(k, v, dtime)
	end
	
	advtrains.atprint_context_tid=nil
	advtrains.atprint_context_tid_full=nil
	
	atprintbm("trainsteps", t)
	endstep()
end

minetest.register_on_joinplayer(function(player)
	return advtrains.pcall(function()
		local pname=player:get_player_name()
		local id=advtrains.player_to_train_mapping[pname]
		if id then
			local train=advtrains.trains[id]
			if not train then advtrains.player_to_train_mapping[pname]=nil return end
			--set the player to the train position.
			--minetest will emerge the area and load the objects, which then will call reattach_all().
			--because player is in mapping, it will not be subject to dying.
			player:setpos(train.last_pos_prev)
			--independent of this, cause all wagons of the train which are loaded to reattach their players
			--needed because already loaded wagons won't call reattach_all()
			for _,wagon in pairs(minetest.luaentities) do
				if wagon.is_wagon and wagon.initialized and wagon.train_id==id then
					wagon:reattach_all()
				end
			end
		end
	end)
end)

minetest.register_on_dieplayer(function(player)
	return advtrains.pcall(function()
		local pname=player:get_player_name()
		local id=advtrains.player_to_train_mapping[pname]
		if id then
			local train=advtrains.trains[id]
			if not train then advtrains.player_to_train_mapping[pname]=nil return end
			for _,wagon in pairs(minetest.luaentities) do
				if wagon.is_wagon and wagon.initialized and wagon.train_id==id then
					--when player dies, detach him from the train
					--call get_off_plr on every wagon since we don't know which one he's on.
					wagon:get_off_plr(pname)
				end
			end
		end
	end)
end)
--[[
train step structure:


- legacy stuff
- preparing the initial path and creating index
- setting node coverage old indices
- handle velocity influences:
	- off-track
	- atc
	- player controls
	- environment collision
- update index = move
- create path
- call stay_node on all old positions to register train there, for collision system
- do less important stuff such as checking trainpartload or removing

-- break --
- Call enter_node and leave_node callbacks (required here because stay_node needs to be called on all trains first)
- handle train collisions

]]

function advtrains.train_step_a(id, train, dtime)
	--atprint("--- runcnt ",advtrains.mainloop_runcnt,": index",train.index,"end_index", train.end_index,"| max_iot", train.max_index_on_track, "min_iot", train.min_index_on_track, "<> pe_min", train.path_extent_min,"pe_max", train.path_extent_max)
	if train.min_index_on_track then
		assert(math.floor(train.min_index_on_track)==train.min_index_on_track)
	end
	--- 1. LEGACY STUFF ---
	if not train.drives_on or not train.max_speed then
		advtrains.update_trainpart_properties(id)
	end
	--TODO check for all vars to be present
	if not train.velocity then
		train.velocity=0
	end
	if not train.movedir or (train.movedir~=1 and train.movedir~=-1) then
		train.movedir=1
	end
	--- 2. prepare initial path and index if needed ---
	if not train.index then train.index=0 end
	if not train.path then
		if not train.last_pos then
			--no chance to recover
			atwarn("Unable to restore train ",id,": missing last_pos")
			advtrains.trains[id]=nil
			return false
		end
		
		local node_ok=advtrains.get_rail_info_at(advtrains.round_vector_floor_y(train.last_pos), train.drives_on)
		
		if node_ok==nil then
			--block not loaded, do nothing
			atprint("last_pos", advtrains.round_vector_floor_y(train.last_pos), "not loaded and not in ndb, waiting")
			return nil
		elseif node_ok==false then
			atprint("Unable to restore train ",id,": No rail at train's position")
			return false
		end
		
		if not train.last_pos_prev then
			--no chance to recover
			atwarn("Unable to restore train ",id,": missing last_pos_prev")
			advtrains.trains[id]=nil
			return false
		end
		
		local prevnode_ok=advtrains.get_rail_info_at(advtrains.round_vector_floor_y(train.last_pos_prev), train.drives_on)
		
		if prevnode_ok==nil then
			--block not loaded, do nothing
			atprint("last_pos_prev", advtrains.round_vector_floor_y(train.last_pos_prev), "not loaded and not in ndb, waiting")
			return nil
		elseif prevnode_ok==false then
			atprint("Unable to restore train ",id,": No rail at train's position")
			return false
		end
		
		train.index=(train.restore_add_index or 0)+(train.savedpos_off_track_index_offset or 0)
		--restore_add_index is set by save() to prevent trains hopping to next round index. should be between -0.5 and 0.5
		--savedpos_off_track_index_offset is set if train went off track. see below.
		train.path={}
		train.path_dist={}
		train.path[0]=train.last_pos
		train.path[-1]=train.last_pos_prev
		train.path_dist[-1]=vector.distance(train.last_pos, train.last_pos_prev)
		train.path_extent_min=-1
		train.path_extent_max=0
		train.min_index_on_track=-1
		train.max_index_on_track=0
		
		--[[
		Bugfix for trains randomly ignoring ATC rails:
		- Paths have been invalidated. 1 gets executed and ensures an initial path
		- 2a sets train end index. The problem is that path_dist is not known for the whole path, so train end index will be nearly trainlen
		- Since the detector indices are also unknown, they get set to the new (wrong) train_end_index. Enter_node calls are not executed for the nodes that lie in between real end_index and trainlen.
		- The next step, mistake is recognized, train leaves some positions. From there, everything works again.
		To overcome this, we will generate the full required path here so that path_dist is available for get_train_end_index(). 
		]]
		advtrains.pathpredict(id, train)
	end
	
	--- 2a. set train.end_index which is required in different places, IF IT IS NOT SET YET by STMT afterwards. ---
	---   table entry to avoid triple recalculation ---
	if not train.end_index then
		train.end_index=advtrains.get_train_end_index(train)
	end
	
	--- 2b. set node coverage old indices ---
	
	train.detector_old_index = atround(train.index)
	train.detector_old_end_index = atround(train.end_index)
	
	--- 3. handle velocity influences ---
	local train_moves=(train.velocity~=0)
	
	if train.recently_collided_with_env then
		train.tarvelocity=0
		if not train_moves then
			train.recently_collided_with_env=false--reset status when stopped
		end
	end
	if train.locomotives_in_train==0 then
		train.tarvelocity=0
	end
	
	--- 3a. this can be useful for debugs/warnings and is used for check_trainpartload ---
	local t_info, train_pos=sid(id), train.path[atround(train.index)]
	if train_pos then
		t_info=t_info.." @"..minetest.pos_to_string(train_pos)
		--atprint("train_pos:",train_pos)
	end
	
	--apply off-track handling:
	local front_off_track=train.max_index_on_track and train.index>train.max_index_on_track
	local back_off_track=train.min_index_on_track and train.end_index<train.min_index_on_track
	local pprint
	
	if front_off_track and back_off_track then--allow movement in both directions
		if train.tarvelocity>1 then
			train.tarvelocity=1
			atwarn("Train",t_info,"is off track at both ends. Clipping velocity to 1")
			pprint=true
		end
	elseif front_off_track then--allow movement only backward
		if train.movedir==1 and train.tarvelocity>0 then
			train.tarvelocity=0
			atwarn("Train",t_info,"is off track. Trying to drive further out. Velocity clipped to 0")
			pprint=true
		end
		if train.movedir==-1 and train.tarvelocity>1 then
			train.tarvelocity=1
			atwarn("Train",t_info,"is off track. Velocity clipped to 1")
			pprint=true
		end
	elseif back_off_track then--allow movement only forward
		if train.movedir==-1 and train.tarvelocity>0 then
			train.tarvelocity=0
			atwarn("Train",t_info,"is off track. Trying to drive further out. Velocity clipped to 0")
			pprint=true
		end
		if train.movedir==1 and train.tarvelocity>1 then
			train.tarvelocity=1
			atwarn("Train",t_info,"is off track. Velocity clipped to 1")
			pprint=true
		end
	end
	if pprint then
		atprint("max_iot", train.max_index_on_track, "min_iot", train.min_index_on_track, "<> index", train.index, "end_index", train.end_index)
	end
	
	--interpret ATC command
	if train.atc_brake_target and train.atc_brake_target>=train.velocity then
		train.atc_brake_target=nil
	end
	if train.atc_wait_finish then
		if not train.atc_brake_target and train.velocity==train.tarvelocity then
			train.atc_wait_finish=nil
		end
	end
	if train.atc_command then
		if train.atc_delay<=0 and not train.atc_wait_finish then
			advtrains.atc.execute_atc_command(id, train)
		else
			train.atc_delay=train.atc_delay-dtime
		end
	end
	
	--make brake adjust the tarvelocity if necessary
	if train.brake and (math.ceil(train.velocity)-1)<train.tarvelocity then
		train.tarvelocity=math.max((math.ceil(train.velocity)-1), 0)
	end
	
	--- 3a. actually calculate new velocity ---
	if train.velocity~=train.tarvelocity then
		local applydiff=0
		local mass=#train.trainparts
		local diff=train.tarvelocity-train.velocity
		if diff>0 then--accelerating, force will be brought on only by locomotives.
			--atprint("accelerating with default force")
			applydiff=(math.min((advtrains.train_accel_force*train.locomotives_in_train*dtime)/mass, math.abs(diff)))
		else--decelerating
			if front_off_track or back_off_track or train.recently_collided_with_env then --every wagon has a brake, so not divided by mass.
				--atprint("braking with emergency force")
				applydiff= -(math.min((advtrains.train_emerg_force*dtime), math.abs(diff)))
			elseif train.brake or (train.atc_brake_target and train.atc_brake_target<train.velocity) then
				--atprint("braking with default force")
				--no math.min, because it can grow beyond tarvelocity, see up there
				--dont worry, it will never fall below zero.
				applydiff= -((advtrains.train_brake_force*dtime))
			else
				--atprint("roll")
				applydiff= -(math.min((advtrains.train_roll_force*dtime), math.abs(diff)))
			end
		end
		train.last_accel=(applydiff*train.movedir)
		train.velocity=math.min(math.max( train.velocity+applydiff , 0), train.max_speed or 10)
	else
		train.last_accel=0
	end
	
	--- 4. move train ---
	
	train.index=train.index and train.index+(((train.velocity*train.movedir)/(train.path_dist[math.floor(train.index)] or 1))*dtime) or 0
	
	--- 4a. update train.end_index to the new position ---
	train.end_index=advtrains.get_train_end_index(train)
	
	--- 5. extend path as necessary ---
	--why this is an extra function, see under 3.
	advtrains.pathpredict(id, train, true)
	
	--- 5a. make pos/yaw available for possible recover calls ---
	if train.max_index_on_track<train.index then --whoops, train went too far. the saved position will be the last one that lies on a track, and savedpos_off_track_index_offset will hold how far to go from here
		train.savedpos_off_track_index_offset=atround(train.index)-train.max_index_on_track
		train.last_pos=train.path[train.max_index_on_track]
		train.last_pos_prev=train.path[train.max_index_on_track-1]
		atprint("train is off-track (front), last positions kept at", train.last_pos, "/", train.last_pos_prev)
	elseif train.min_index_on_track+1>train.index then --whoops, train went even more far. same behavior
		train.savedpos_off_track_index_offset=atround(train.index)-train.min_index_on_track
		train.last_pos=train.path[train.min_index_on_track+1]
		train.last_pos_prev=train.path[train.min_index_on_track]
		atprint("train is off-track (back), last positions kept at", train.last_pos, "/", train.last_pos_prev)
	else --regular case
		train.savedpos_off_track_index_offset=nil
		train.last_pos=train.path[math.floor(train.index+1)]
		train.last_pos_prev=train.path[math.floor(train.index)]
	end
	
	--- 5b. Remove path items that are no longer used ---
	-- Necessary since path items are no longer invalidated in save steps
	local path_pregen_keep=20
	local offtrack_keep=4
	local gen_front_keep= path_pregen_keep
	local gen_back_keep= atround(- train.trainlen - path_pregen_keep)
	
	local delete_min=math.min(train.max_index_on_track - offtrack_keep, atround(train.index)+gen_back_keep)
	local delete_max=math.max(train.min_index_on_track + offtrack_keep, atround(train.index)+gen_front_keep)
	
	if train.path_extent_min<delete_min then
		--atprint(sid(id),"clearing path min ",train.path_extent_min," to ",delete_min)
		for i=train.path_extent_min,delete_min-1 do
			train.path[i]=nil
			train.path_dist[i]=nil
		end
		train.path_extent_min=delete_min
		train.min_index_on_track=math.max(train.min_index_on_track, delete_min)
	end
	if train.path_extent_max>delete_max then
		--atprint(sid(id),"clearing path max ",train.path_extent_max," to ",delete_max)
		train.path_dist[delete_max]=nil
		for i=delete_max+1,train.path_extent_max do
			train.path[i]=nil
			train.path_dist[i]=nil
		end
		train.path_extent_max=delete_max
		train.max_index_on_track=math.min(train.max_index_on_track, delete_max)
	end
	
	--- 6b. call stay_node to register trains in the location table - actual enter_node stuff is done in step b ---