aboutsummaryrefslogtreecommitdiff
path: root/advtrains/trainlogic.lua
blob: 70939295556c77cebd0d58428d1fd1304c5299f7 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
--trainlogic.lua
--controls train entities stuff about connecting/disconnecting/colliding trains and other things

local setting_overrun_mode = minetest.settings:get("advtrains_overrun_mode")

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

--acceleration for lever modes (trainhud.lua), per wagon
local t_accel_all={
	[0] = -10,
	[1] = -3,
	[11] = -2, -- calculation base for LZB
	[2] = -0.5,
	[4] = 0.5,
}
--acceleration per engine
local t_accel_eng={
	[0] = 0,
	[1] = 0,
	[11] = 0,
	[2] = 0,
	[4] = 1.5,
}

local VLEVER_EMERG = 0
local VLEVER_BRAKE = 1
local VLEVER_LZBCALC = 11
local VLEVER_ROLL = 2
local VLEVER_HOLD = 3
local VLEVER_ACCEL = 4

-- How far in front of a whole index with LZB 0 restriction the train should come to a halt
-- value must be between 0 and 0.5, exclusively
local LZB_ZERO_APPROACH_DIST = 0.1
-- Speed the train temporarily approaches the stop point with
local LZB_ZERO_APPROACH_SPEED = 0.2



tp_player_tmr = 0

advtrains.mainloop_trainlogic=function(dtime, stepno)
	--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:get_pos()))
			advtrains.playersbypts[ptspos]=player
		end
	end
	
	if tp_player_tmr<=0 then
		-- teleport players to their train every 2 seconds
		for _, player in pairs(minetest.get_connected_players()) do
			advtrains.tp_player_to_train(player)
		end
		tp_player_tmr = 2
	else
		tp_player_tmr = tp_player_tmr - dtime
	end
	--regular train step
	--[[ structure:
	1. make trains calculate their occupation windows when needed (a)
	2. when occupation tells us so, restore the occupation tables (a)
	4. make trains move and update their new occupation windows and write changes
	   to occupation tables (b)
	5. make trains do other stuff (c)
	]]--
	local t=os.clock()
	
	for k,v in pairs(advtrains.trains) do
		advtrains.atprint_context_tid=k
		--atprint("=== Step",stepno,"===")
		advtrains.train_ensure_init(k, v)
	end
	
	advtrains.lock_path_inval = true
	
	for k,v in pairs(advtrains.trains) do
		advtrains.atprint_context_tid=k
		advtrains.train_step_b(k, v, dtime)
	end
	
	for k,v in pairs(advtrains.trains) do
		advtrains.atprint_context_tid=k
		advtrains.train_step_c(k, v, dtime)
	end
	
	advtrains.lock_path_inval = false
	
	advtrains.atprint_context_tid=nil
	
	atprintbm("trainsteps", t)
	endstep()
end

function advtrains.tp_player_to_train(player)
	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:set_pos(train.last_pos)
	end
end
minetest.register_on_joinplayer(function(player)
		advtrains.hud[player:get_player_name()] = nil
		advtrains.hhud[player:get_player_name()] = nil
		--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()
		local id=advtrains.player_to_train_mapping[pname]
		if id then
			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)


minetest.register_on_dieplayer(function(player)
		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
			-- just in case no wagon felt responsible for this player: clear train mapping
			advtrains.player_to_train_mapping[pname] = nil
		end
end)

--[[

Zone diagram of a train (copy from occupation.lua!):
              |___| |___| --> Direction of travel
              oo oo+oo oo
=|=======|===|===========|===|=======|===================|========|===
 |SafetyB|CpB|   Train   |CpF|SafetyF|        Brake      |Aware   |
[1]     [2] [3]         [4] [5]     [6]                 [7]      [8]
This mapping from indices in occwindows to zone ids is contained in WINDOW_ZONE_IDS


The occupation system has been abandoned. The constants will still be used
to determine the couple distance
(because of the reverse lookup, the couple system simplifies a lot...)

]]--
-- unless otherwise stated, in meters.
local SAFETY_ZONE = 10
local COUPLE_ZONE = 2 --value in index positions!
local BRAKE_SPACE = 10
local AWARE_ZONE = 10
local WINDOW_ZONE_IDS = {
	2, -- 1 - SafetyB
	4, -- 2 - CpB
	1, -- 3 - Train
	5, -- 4 - CpF
	3, -- 5 - SafetyF
	6, -- 6 - Brake
	7, -- 7 - Aware
}


-- If a variable does not exist in the table, it is assigned the default value
local function assertdef(tbl, var, def)
	if not tbl[var] then
		tbl[var] = def
	end
end

function advtrains.get_acceleration(train, lever)
	local acc_all = t_accel_all[lever]
	if not acc_all then return 0 end
	
	local acc_eng = t_accel_eng[lever]
	local nwagons = #train.trainparts
	if nwagons == 0 then
		-- empty train! avoid division through zero
		return -1
	end
	local acc = acc_all + (acc_eng*train.locomotives_in_train)/nwagons
	return acc
end

-- Small local util function to recalculate train's end index
local function recalc_end_index(train)
	train.end_index = advtrains.path_get_index_by_offset(train, train.index, -train.trainlen)
end

-- Occupation Callback system
-- see occupation.lua
-- signature is advtrains.te_register_on_<?>(function(id, train) ... end)

local function mkcallback(name)
	local callt = {}
	advtrains["te_register_on_"..name] = function(func)
		assertt(func, "function")
		table.insert(callt, func)
	end
	return callt, function(id, train, param1, param2, param3)
		for _,f in ipairs(callt) do
			f(id, train, param1, param2, param3)
		end
	end
end

local callbacks_new_path, run_callbacks_new_path = mkcallback("new_path")
local callbacks_invahead
callbacks_invahead, advtrains.run_callbacks_invahead = mkcallback("invalidate_ahead") -- (id, train, start_idx)
local callbacks_update, run_callbacks_update = mkcallback("update")
local callbacks_create, run_callbacks_create = mkcallback("create")
local callbacks_remove, run_callbacks_remove = mkcallback("remove")


-- train_ensure_init: responsible for creating a state that we can work on, after one of the following events has happened:
-- - the train's path got cleared
-- - save files were loaded
-- Additionally, this gets called outside the step cycle to initialize and/or remove a train, then occ_write_mode is set.
function advtrains.train_ensure_init(id, train)
	if not train then
		atwarn("train_ensure_init: Called with id =",id,"but a nil train!")
		atwarn(debug.traceback())
		return nil
	end
	
	train.dirty = true
	if train.no_step then
		--atprint("in ensure_init: no_step set, train step ignored!")
		return nil
	end

	assertdef(train, "velocity", 0)
	--assertdef(train, "tarvelocity", 0)
	assertdef(train, "acceleration", 0)
	assertdef(train, "id", id)
	
	
	if not train.drives_on or not train.max_speed then
		--atprint("in ensure_init: missing properties, updating!")
		advtrains.update_trainpart_properties(id)
	end
	
	--restore path
	if not train.path then
		--atprint("in ensure_init: Needs restoring path...")
		if not train.last_pos then
			atlog("Train",id,": Restoring path failed, no last_pos set! Train will be disabled. You can try to fix the issue in the save file.")
			train.no_step = true
			return nil
		end
		if not train.last_connid then
			atwarn("Train",id,": Restoring path: no last_connid set! Will assume 1")
			train.last_connid = 1
			--[[
			Why this fix was necessary:
			Issue: Migration problems on Grand Theft Auto Minetest
			1. Run of this code, warning printed.
			2. path_create failed with result==nil (there was an unloaded node, wait_for_path set)
			3. in consequence, the supposed call to path_setrestore does not happen
			4. train.last_connid is still unset
			5. next step, warning is printed again
			Result: log flood.
			]]
		end
		
		local result = advtrains.path_create(train, train.last_pos, train.last_connid or 1, train.last_frac or 0)
		
		--atprint("in ensure_init: path_create result ",result)
		
		if result==false then
			atlog("Train",id,": Restoring path failed, node at",train.last_pos,"is gone! Train will be disabled. You can try to place a rail at this position and restart the server.")
			train.no_step = true
			return nil
		elseif result==nil then
			if not train.wait_for_path then
				atlog("Train",id,": Can't initialize: Waiting for the (yet unloaded) node at",train.last_pos," to be loaded.")
			end
			train.wait_for_path = true
			return false
		end
		-- by now, we should have a working initial path
		train.wait_for_path = false
		
		advtrains.update_trainpart_properties(id)
		recalc_end_index(train)
		
		--atdebug("Train",id,": Successfully restored path at",train.last_pos," connid",train.last_connid," frac",train.last_frac)
		
		-- run on_new_path callbacks
		run_callbacks_new_path(id, train)
	end
	
	train.dirty = false -- TODO einbauen!
	return true
end

local function v_target_apply(v_targets, lever, vel)
	v_targets[lever] = v_targets[lever] and math.min(v_targets[lever], vel) or vel
end

function advtrains.train_step_b(id, train, dtime)
	if train.no_step or train.wait_for_path or not train.path then return end
	
	-- in this code, we check variables such as path_trk_? and path_dist. We need to ensure that the path is known for the whole 'Train' zone
	advtrains.path_get(train, atfloor(train.index + 2))
	advtrains.path_get(train, atfloor(train.end_index - 1))
	
	-- run pre-move hooks
	-- TODO: if more pre-move hooks are added, make a separate callback hook
	advtrains.lzb_look_ahead(id, train)
	
	--[[ again, new velocity control:
	There are two heterogenous means of control:
	-> set a fixed acceleration and ignore speed (user)
	-> steer towards a target speed, distance doesn't matter
		-> needs to specify the maximum acceleration/deceleration values they are willing to accelerate/brake with
	-> Reach a target speed after a certain distance (LZB, handled specially)
	
	]]--
	
	--- 3. handle velocity influences ---
	
	local v0 = train.velocity
	local sit_v_cap = train.max_speed -- Maximum speed in current situation (multiple limit factors)
	-- The desired speed change issued by the active control (user or atc)
	local ctrl_v_tar -- desired speed which should not be crossed by braking or accelerating
	local ctrl_accelerating = false -- whether the train should accelerate
	local ctrl_braking = false -- whether the train should brake
	local ctrl_lever -- the lever value to use to calculate the acceleration
	-- the final speed change after applying LZB
	local v_cap -- absolute maximum speed
	local v_tar -- desired speed which should not be crossed by braking or accelerating
	local accelerating = false-- whether the train should accelerate
	local braking = false -- whether the train should brake
	local lever -- the lever value to use to calculate the acceleration
	local train_moves = (v0 > 0)
	
	if train.recently_collided_with_env then
		if not train_moves then
			train.recently_collided_with_env=nil--reset status when stopped
		end
		--atprint("in train_step_b: applying collided_with_env")
		sit_v_cap = 0
	elseif train.locomotives_in_train==0 then
		--atprint("in train_step_b: applying no_locomotives")
		sit_v_cap = 0
	-- interlocking speed restriction
	elseif train.speed_restriction then
		--atprint("in train_step_b: applying interlocking speed restriction",train.speed_restriction)
		sit_v_cap = train.speed_restriction
	end
	
	--apply off-track handling:
	local front_off_track = train.index>train.path_trk_f
	local back_off_track=train.end_index<train.path_trk_b
	train.off_track = front_off_track or back_off_track
	
	if back_off_track and (not v_cap or v_cap > 1) then
		--atprint("in train_step_b: applying back_off_track")
		sit_v_cap = 1
	elseif front_off_track then
		--atprint("in train_step_b: applying front_off_track")
		sit_v_cap = 0
	end
	
	
	--interpret ATC command and apply auto-lever control when not actively controlled
	local userc = train.ctrl_user
	if userc then
		--atprint("in train_step_b: ctrl_user active",userc)
		advtrains.atc.train_reset_command(train)
		
		if userc >= VLEVER_ACCEL then
			ctrl_accelerating = true
		else
			ctrl_braking = true
		end
		ctrl_lever = userc
	else
		if train.atc_command then
			if (not train.atc_delay or 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
		elseif train.atc_delay then
			train.atc_delay = nil
		end
	
		local braketar = train.atc_brake_target
		local emerg = false -- atc_brake_target==-1 means emergency brake (BB command)
		if braketar == -1 then
			braketar = 0
			emerg = true
		end
		--atprint("in train_step_b: ATC: brake state braketar=",braketar,"emerg=",emerg)
		if braketar and braketar>=v0 then
			--atprint("in train_step_b: ATC: brake target cleared")
			train.atc_brake_target=nil
			braketar = nil
		end
		--if train.tarvelocity and train.velocity==train.tarvelocity then
		--	train.tarvelocity = nil
		--end
		if train.atc_wait_finish then
			if not train.atc_brake_target and (not train.tarvelocity or train.velocity==train.tarvelocity) then
				train.atc_wait_finish=nil
			end
		end
		
		if train.tarvelocity and train.tarvelocity>v0 then
			--atprint("in train_step_b: applying ATC ACCEL", train.tarvelocity)
			ctrl_accelerating = true
			ctrl_lever = VLEVER_ACCEL
		elseif train.tarvelocity and train.tarvelocity<v0 then
			ctrl_braking = true
			
			if (braketar and braketar<v0) then
				if emerg then
					--atprint("in train_step_b: applying ATC EMERG", train.tarvelocity)
					ctrl_lever = VLEVER_EMERG
				else
					--atprint("in train_step_b: applying ATC BRAKE", train.tarvelocity)
					ctrl_v_tar = braketar
					ctrl_lever = VLEVER_BRAKE
				end
			else
				--atprint("in train_step_b: applying ATC ROLL", train.tarvelocity)
				ctrl_v_tar = train.tarvelocity
				ctrl_lever = VLEVER_ROLL
			end
		end
	end
	
	--- 2b. look at v_target, determine the effective v_target and desired acceleration ---
	--atprint("in train_step_b: Resulting control before LZB: accelerating",ctrl_accelerating,"braking",ctrl_braking,"lever", ctrl_lever, "target", ctrl_v_tar)
	--train.debug = dump({tv_target,tv_lever})
	
	--atprint("in train_step_b: Current index",train.index,"end",train.end_index,"vel",v0)
	--- 3a. calculate the acceleration required to reach the speed restriction in path_speed (LZB) ---
	-- Iterates over the path nodes we WOULD pass if we were continuing with the current speed
	-- and determines the MINIMUM of path_speed in this range.
	-- Then, determines acceleration so that we can reach this 'overridden' target speed in this step (but short-circuited)
	local lzb_next_zero_barrier -- if defined, train should not pass this point as it's a 0-LZB
	local new_index_curr_tv -- pre-calculated new train index in lzb check
	local lzb_v_cap -- the maximum speed that LZB dictates
	
	local dst_curr_v = v0 * dtime
	new_index_curr_tv = advtrains.path_get_index_by_offset(train, train.index, dst_curr_v)
	local i = atfloor(train.index)
	local psp
	while true do
		psp = train.path_speed[i]
		if psp then
			lzb_v_cap = lzb_v_cap and math.min(lzb_v_cap, psp) or psp
			if psp == 0 and not lzb_next_zero_barrier then
				--atprint("in train_step_b: Found zero barrier: ",i)
				lzb_next_zero_barrier = i - LZB_ZERO_APPROACH_DIST
			end
		end
		if i > new_index_curr_tv then
			break
		end
		i = i + 1
	end
	
	if lzb_next_zero_barrier and train.index < lzb_next_zero_barrier then
		lzb_v_cap = LZB_ZERO_APPROACH_SPEED
	end
	
	--atprint("in train_step_b: LZB calculation yields newindex=",new_index_curr_tv,"lzbtarget=",lzb_v_cap,"zero_barr=",lzb_next_zero_barrier,"")
	
	-- LZB HUD: decrement timer and delete when 0
	if train.hud_lzb_effect_tmr then
		if train.hud_lzb_effect_tmr <=0 then
			train.hud_lzb_effect_tmr = nil
		else
			train.hud_lzb_effect_tmr = train.hud_lzb_effect_tmr - 1
		end
	end
	
	-- We now need to bring ctrl_*, sit_v_cap and lzb_v_cap together to determine the final controls.
	local v_cap = sit_v_cap -- always defined, by default train.max_speed
	if lzb_v_cap and lzb_v_cap < v_cap then
		v_cap = lzb_v_cap
		lever = VLEVER_BRAKE -- actually irrelevant, acceleration is not considered anyway unless v_tar is also set.
		-- display LZB control override in the HUD
		if lzb_v_cap <= v0 then
			train.hud_lzb_effect_tmr = 1
			-- This is to signal the HUD that LZB is active. This works as a timer to avoid HUD blinking
		end
	end
	
	v_tar = ctrl_v_tar
	-- if v_cap is smaller than the current speed, we need to brake in all cases.
	if v_cap < v0 then
		braking = true
		lever = VLEVER_BRAKE
		-- set v_tar to v_cap to not slow down any further than required.
		-- unless control wants us to brake too, then we use control's v_tar.
		if not ctrl_v_tar or ctrl_v_tar > v_cap then
			v_tar = v_cap
		end
	else -- else, use what the ctrl says
		braking = ctrl_braking
		accelerating = ctrl_accelerating and not braking
		lever = ctrl_lever
	end
	train.lever = lever
	
	--atprint("in train_step_b: final control: accelerating",accelerating,"braking",braking,"lever", lever, "target", v_tar)
	
	-- reset train acceleration when holding speed
	if not braking and not accelerating then
		train.acceleration = 0
	end
	
	--- 3b. if braking, modify the velocity BEFORE the movement
	if braking then
		local dv = advtrains.get_acceleration(train, lever) * dtime
		local v1 = v0 + dv
		if v_tar and v1 < v_tar then
			--atprint("in train_step_b: Braking: Hit v_tar!")
			v1 = v_tar
		end
		if v1 > v_cap then
			--atprint("in train_step_b: Braking: Hit v_cap!")
			v1 = v_cap
		end
		if v1 < 0 then
			--atprint("in train_step_b: Braking: Hit 0!")
			v1 = 0
		end
		
		train.acceleration = (v1 - v0) / dtime
		train.velocity = v1
		--atprint("in train_step_b: Braking: New velocity",v1," (yields acceleration",train.acceleration,")")
		-- make saved new_index_curr_tv invalid because speed has changed
		new_index_curr_tv = nil
	end
	
	--- 4. move train ---
	-- if we have calculated the new end index before, don't do that again
	if not new_index_curr_tv then
		local dst_curr_v = train.velocity * dtime
		new_index_curr_tv = advtrains.path_get_index_by_offset(train, train.index, dst_curr_v)
		--atprint("in train_step_b: movement calculation (re)done, yields newindex=",new_index_curr_tv)
	else
		--atprint("in train_step_b: movement calculation reusing from LZB newindex=",new_index_curr_tv)
	end
	
	-- if the zeroappr mechanism has hit, go no further than zeroappr index
	if lzb_next_zero_barrier and new_index_curr_tv > lzb_next_zero_barrier then
		--atprint("in train_step_b: Zero barrier hit, clipping to newidx_tv=",new_index_curr_tv, "zb_idx=",lzb_next_zero_barrier)
		new_index_curr_tv = lzb_next_zero_barrier
	end
	train.index = new_index_curr_tv
	
	recalc_end_index(train)
	--atprint("in train_step_b: New index",train.index,"end",train.end_index,"vel",train.velocity)
	
	--- 4a. if accelerating, modify the velocity AFTER the movement
	if accelerating then
		local dv = advtrains.get_acceleration(train, lever) * dtime
		local v1 = v0 + dv
		if v_tar and v1 > v_tar then
			--atprint("in train_step_b: Accelerating: Hit v_tar!")
			v1 = v_tar
		end
		if v1 > v_cap then
			--atprint("in train_step_b: Accelerating: Hit v_cap!")
			v1 = v_cap
		end
		
		train.acceleration = (v1 - v0) / dtime
		train.velocity = v1
		--atprint("in train_step_b: Accelerating: New velocity",v1," (yields acceleration",train.acceleration,")")
	end
end

function advtrains.train_step_c(id, train, dtime)
	if train.no_step or train.wait_for_path or not train.path then return end
	
	-- all location/extent-critical actions have been done.
	-- calculate the new occupation window
	run_callbacks_update(id, train)
	
	-- Return if something(TM) damaged the path
	if train.no_step or train.wait_for_path or not train.path then return end
	
	advtrains.path_clear_unused(train)
	
	advtrains.path_setrestore(train)
	
	-- less important stuff
	
	train.check_trainpartload=(train.check_trainpartload or 0)-dtime
	if train.check_trainpartload<=0 then
		advtrains.spawn_wagons(id)
		train.check_trainpartload=2
	end
	
	--- 8. check for collisions with other trains and damage players ---
	
	local train_moves=(train.velocity~=0)
	
	--- Check whether this train can be coupled to another, and set couple entities accordingly
	if not train.was_standing and not train_moves then
		advtrains.train_check_couples(train)
	end
	train.was_standing = not train_moves
	
	if train_moves then
		
		local collided = false
		local coll_grace=1
		local collindex = advtrains.path_get_index_by_offset(train, train.index, -coll_grace)
		local collpos = advtrains.path_get(train, atround(collindex))
		if collpos then
			local rcollpos=advtrains.round_vector_floor_y(collpos)
			local is_loaded_area = advtrains.is_node_loaded(rcollpos)
			for x=-train.extent_h,train.extent_h do
				for z=-train.extent_h,train.extent_h do
					local testpos=vector.add(rcollpos, {x=x, y=0, z=z})
					--- 8a Check collision ---
					if not collided then

						local col_tr = advtrains.occ.check_collision(testpos, id)
						if col_tr then
							advtrains.train_check_couples(train)
							train.velocity = 0
							advtrains.atc.train_reset_command(train)
							collided = true
						end

						--- 8b damage players ---
						if is_loaded_area and train.velocity > 3 and (setting_overrun_mode=="drop" or setting_overrun_mode=="normal") then
							local testpts = minetest.pos_to_string(testpos)
							local player=advtrains.playersbypts[testpts]
							if player and player:get_hp()>0 and advtrains.is_damage_enabled(player:get_player_name()) then
								--atdebug("damage found",player:get_player_name())
								if setting_overrun_mode=="drop" then
									--instantly kill player
									--drop inventory contents first, to not to spawn bones
									local player_inv=player:get_inventory()
									for i=1,player_inv:get_size("main") do
										minetest.add_item(testpos, player_inv:get_stack("main", i))
									end
									for i=1,player_inv:get_size("craft") do
										minetest.add_item(testpos, player_inv:get_stack("craft", i))
									end
									-- empty lists main and craft
									player_inv:set_list("main", {})
									player_inv:set_list("craft", {})
								end
								player:set_hp(0)
							end
						end
					end
				end
			end
			--- 8c damage other objects ---
			if is_loaded_area then
				local objs = minetest.get_objects_inside_radius(rcollpos, 2)
				for _,obj in ipairs(objs) do
					if not obj:is_player() and obj:get_armor_groups().fleshy and obj:get_armor_groups().fleshy > 0 
							and obj:get_luaentity() and obj:get_luaentity().name~="signs_lib:text" then
						obj:punch(obj, 1, { full_punch_interval = 1.0, damage_groups = {fleshy = 1000}, }, nil)
					end
				end
			end
		end
	end
end

-- Default occupation callbacks for node callbacks
-- (remember, train.end_index is set separately because callbacks are
--  asserted to rely on this)

local function mknodecallback(name)
	local callt = {}
	advtrains["tnc_register_on_"..name] = function(func, prio)
		assertt(func, "function")
		if prio then
			table.insert(callt, 1, func)
		else
			table.insert(callt, func)
		end
	end
	return callt, function(pos, id, train, index, paramx1, paramx2, paramx3)
		for _,f in ipairs(callt) do
			f(pos, id, train, index, paramx1, paramx2, paramx3)
		end
	end
end

-- enter/leave-node callbacks
-- signature is advtrains.tnc_register_on_enter/leave(function(pos, id, train, index) ... end)
local callbacks_enter_node, run_callbacks_enter_node = mknodecallback("enter")
local callbacks_leave_node, run_callbacks_leave_node = mknodecallback("leave")

-- Node callback for approaching
-- Might be called multiple times, whenever path is recalculated. Also called for the first node the train is standing on, then has_entered is true.
-- signature is function(pos, id, train, index, has_entered, lzbdata)
-- has_entered: true if the "enter" callback has already been executed for this train in this location
-- lzbdata: arbitrary data (shared between all callbacks), deleted when LZB is restarted.
-- These callbacks are called in order of distance as train progresses along tracks, so lzbdata can be used to
-- keep track of a train's state once it passes this point
local callbacks_approach_node, run_callbacks_approach_node = mknodecallback("approach")


local function tnc_call_enter_callback(pos, train_id, train, index)
	--atdebug("tnc enter",pos,train_id)
	local node = advtrains.ndb.get_node(pos) --this spares the check if node is nil, it has a name in any case
	local mregnode=minetest.registered_nodes[node.name]
	if mregnode and mregnode.advtrains and mregnode.advtrains.on_train_enter then
		mregnode.advtrains.on_train_enter(pos, train_id, train, index)
	end

	-- call other registered callbacks
	run_callbacks_enter_node(pos, train_id, train, index)
	
	-- check for split points
	if mregnode and mregnode.at_conns and #mregnode.at_conns == 3 and train.path_cp[index] == 3 then
		-- train came from connection 3 of a switch, so it split points.
		if not train.points_split then
			train.points_split = {}
		end
		train.points_split[advtrains.encode_pos(pos)] = true
		--atdebug(train_id,"split points at",pos)
	end
end
local function tnc_call_leave_callback(pos, train_id, train, index)
	--atdebug("tnc leave",pos,train_id)
	local node = advtrains.ndb.get_node(pos) --this spares the check if node is nil, it has a name in any case
	local mregnode=minetest.registered_nodes[node.name]
	if mregnode and mregnode.advtrains and mregnode.advtrains.on_train_leave then
		mregnode.advtrains.on_train_leave(pos, train_id, train, index)
	end
	
	-- call other registered callbacks
	run_callbacks_leave_node(pos, train_id, train, index)
	
	-- split points do not matter anymore. clear them
	if train.points_split then
		if train.points_split[advtrains.encode_pos(pos)] then
			train.points_split[advtrains.encode_pos(pos)] = nil
			--atdebug(train_id,"has passed split points at",pos)
		end
		-- any entries left?
		for _,_ in pairs(train.points_split) do
			return
		end
		train.points_split = nil
	end
	-- WARNING possibly unreachable place!
end

function advtrains.tnc_call_approach_callback(pos, train_id, train, index, lzbdata)
	--atdebug("tnc approach",pos,train_id, lzbdata)
	local has_entered = atround(train.index) == index
	
	local node = advtrains.ndb.get_node(pos) --this spares the check if node is nil, it has a name in any case
	local mregnode=minetest.registered_nodes[node.name]
	if mregnode and mregnode.advtrains and mregnode.advtrains.on_train_approach then
		mregnode.advtrains.on_train_approach(pos, train_id, train, index, has_entered, lzbdata)
	end
	
	-- call other registered callbacks
	run_callbacks_approach_node(pos, train_id, train, index, has_entered, lzbdata)
end

-- === te callback definition for tnc node callbacks ===

advtrains.te_register_on_new_path(function(id, train)
	train.tnc = {
		old_index = atround(train.index),
		old_end_index = atround(train.end_index),
	}
	--atdebug(id,"tnc init",train.index,train.end_index)
end)

advtrains.te_register_on_update(function(id, train)
	local new_index = atround(train.index)
	local new_end_index = atround(train.end_index)
	local old_index = train.tnc.old_index
	local old_end_index = train.tnc.old_end_index
	while old_index < new_index do
		old_index = old_index + 1
		local pos = advtrains.round_vector_floor_y(advtrains.path_get(train,old_index))
		tnc_call_enter_callback(pos, id, train, old_index)
	end
	while old_end_index < new_end_index do
		local pos = advtrains.round_vector_floor_y(advtrains.path_get(train,old_end_index))
		tnc_call_leave_callback(pos, id, train, old_end_index)
		old_end_index = old_end_index + 1
	end
	train.tnc.old_index = new_index
	train.tnc.old_end_index = new_end_index
end)

advtrains.te_register_on_create(function(id, train)
	local index = atround(train.index)
	local end_index = atround(train.end_index)
	while end_index <= index do
		local pos = advtrains.round_vector_floor_y(advtrains.path_get(train,end_index))
		tnc_call_enter_callback(pos, id, train, end_index)
		end_index = end_index + 1
	end
	--atdebug(id,"tnc create",train.index,train.end_index)
end)

advtrains.te_register_on_remove(function(id, train)
	local index = atround(train.index)
	local end_index = atround(train.end_index)
	while end_index <= index do
		local pos = advtrains.round_vector_floor_y(advtrains.path_get(train,end_index))
		tnc_call_leave_callback(pos, id, train, end_index)
		end_index = end_index + 1
	end
	--atdebug(id,"tnc remove",train.index,train.end_index)
end)

--returns new id
function advtrains.create_new_train_at(pos, connid, ioff, trainparts)
	local new_id=advtrains.random_id()
	while advtrains.trains[new_id] do new_id=advtrains.random_id() end--ensure uniqueness
	
	local t={}
	t.id = new_id
	
	t.last_pos=pos
	t.last_connid=connid
	t.last_frac=ioff
	
	--t.tarvelocity=0
	t.velocity=0
	t.trainparts=trainparts
	
	advtrains.trains[new_id] = t
	--atdebug("Created new train:",t)
	
	if not advtrains.train_ensure_init(new_id, advtrains.trains[new_id]) then
		atwarn("create_new_train_at",pos,connid,"failed! This might lead to temporary bugs.")
		return
	end
	
	run_callbacks_create(new_id, advtrains.trains[new_id])
	
	return new_id
end

function advtrains.remove_train(id)
	local train = advtrains.trains[id]
	
	if not advtrains.train_ensure_init(id, train) then
		atwarn("remove_train",id,"failed! This might lead to temporary bugs.")
		return
	end
	
	run_callbacks_remove(id, train)
	
	advtrains.path_invalidate(train)
	advtrains.couple_invalidate(train)
	
	local tp = train.trainparts
	--atdebug("Removing train",id,"leftover trainparts:",tp)
	
	advtrains.trains[id] = nil
	
	return tp
	
end


function advtrains.add_wagon_to_train(wagon_id, train_id, index)
	local train=advtrains.trains[train_id]
	
	if not advtrains.train_ensure_init(train_id, train) then
		atwarn("Train",train_id,"is not initialized! Operation aborted!")
		return
	end
	
	if index then
		table.insert(train.trainparts, index, wagon_id)
	else
		table.insert(train.trainparts, wagon_id)
	end
	
	advtrains.update_trainpart_properties(train_id)
	recalc_end_index(train)
	run_callbacks_update(train_id, train)
end

-- Note: safe_decouple_wagon() has been moved to wagons.lua

-- this function sets wagon's pos_in_train(parts) properties and train's max_speed and drives_on (and more)
function advtrains.update_trainpart_properties(train_id, invert_flipstate)
	local train=advtrains.trains[train_id]
	train.drives_on=advtrains.merge_tables(advtrains.all_tracktypes)
	--FIX: deep-copy the table!!!
	train.max_speed=20
	train.extent_h = 0;
	
	local rel_pos=0
	local count_l=0
	local shift_dcpl_lock=false
	for i, w_id in ipairs(train.trainparts) do
		
		local data = advtrains.wagons[w_id]
		
		-- 1st: update wagon data (pos_in_train a.s.o)
		if data then
			local wagon = advtrains.wagon_prototypes[data.type or data.entity_name]
			if not wagon then
				atwarn("Wagon '",data.type,"' couldn't be found. Please check that all required modules are loaded!")
				wagon = advtrains.wagon_prototypes["advtrains:wagon_placeholder"]

			end
			rel_pos=rel_pos+wagon.wagon_span
			data.train_id=train_id
			data.pos_in_train=rel_pos
			data.pos_in_trainparts=i
			if wagon.is_locomotive then
				count_l=count_l+1
			end
			if invert_flipstate then
				data.wagon_flipped = not data.wagon_flipped
				shift_dcpl_lock, data.dcpl_lock = data.dcpl_lock, shift_dcpl_lock
			end
			rel_pos=rel_pos+wagon.wagon_span
			
			if wagon.drives_on then
				for k,_ in pairs(train.drives_on) do
					if not wagon.drives_on[k] then
						train.drives_on[k]=nil
					end
				end
			end
			train.max_speed=math.min(train.max_speed, wagon.max_speed)
			train.extent_h = math.max(train.extent_h, wagon.extent_h or 1);
		end
	end
	train.trainlen = rel_pos
	train.locomotives_in_train = count_l
end


local ablkrng = advtrains.wagon_load_range
-- This function checks whether entities need to be spawned for certain wagons, and spawns them.
-- Called from train_step_*(), not required to check init.
function advtrains.spawn_wagons(train_id)
	local train = advtrains.trains[train_id]
	
	for i = 1, #train.trainparts do
		local w_id = train.trainparts[i]
		local data = advtrains.wagons[w_id]
		if data then
			if data.train_id ~= train_id then
				atwarn("Train",train_id,"Wagon #",i,": Saved train ID",data.train_id,"did not match!")
				data.train_id = train_id
			end
			if not advtrains.wagon_objects[w_id] or not advtrains.wagon_objects[w_id]:get_yaw() then
				-- eventually need to spawn new object. check if position is loaded.
				local index = advtrains.path_get_index_by_offset(train, train.index, -data.pos_in_train)
				local pos   = advtrains.path_get(train, atfloor(index))
				
				if advtrains.position_in_range(pos, ablkrng) then
					--atdebug("wagon",w_id,"spawning")
					local wt = advtrains.get_wagon_prototype(data)
					local wagon = minetest.add_entity(pos, wt):get_luaentity()
					wagon:set_id(w_id)
				end
			end
		else
			atwarn("Train",train_id,"Wagon #",1,": A wagon with id",w_id,"does not exist! Wagon will be removed from train.")
			table.remove(train.trainparts, i)
			i = i - 1
		end
	end
end

function advtrains.split_train_at_fc(train, count_empty, length_limit)
	-- splits train at first different current FC by convention,
	-- locomotives have empty FC so are ignored
	-- count_empty is used to split off locomotives
	-- length_limit limits the length of the first train to length_limit wagons
	local train_id = train.id
	local fc = false
	local ind = 0
	for i = 1, #train.trainparts do
		local w_id = train.trainparts[i]
		local data = advtrains.wagons[w_id]
		if length_limit and i > length_limit then
			ind = i
			break
		end
		if data then
			local wfc = advtrains.get_cur_fc(data)
			if  wfc ~= "" or count_empty then
				if  fc then
					if fc ~= wfc then
						ind = i
						break
					end
				else
					fc = wfc
				end
			end
		end
	end
	if ind > 0 then
		return advtrains.split_train_at_index(train, ind), fc
	end
	if fc then
		return nil, fc
	end
end

function advtrains.train_step_fc(train)
	for i=1,#train.trainparts do
		local w_id = train.trainparts[i]
		local data = advtrains.wagons[w_id]
		if data then
			advtrains.step_fc(data)
		end
	end
end

function advtrains.split_train_at_index(train, index)
	-- this function splits a train at index, creating a new train from the back part of the train.

	local train_id=train.id
	if index > #train.trainparts then
		-- index specified too long
		return
	end
	local w_id = train.trainparts[index]
	local data = advtrains.wagons[w_id]
	local _, wagon = advtrains.get_wagon_prototype(data)
	if not advtrains.train_ensure_init(train_id, train) then
		atwarn("Train",train_id,"is not initialized! Operation aborted!")
		return
	end
	
	-- make sure that the train is fully on track before splitting. May cause problems otherwise
	if train.index > train.path_trk_f or train.end_index < train.path_trk_b then
		atwarn("Train",train_id,": cannot split train because it is off track!")
		return
	end

	local p_index=advtrains.path_get_index_by_offset(train, train.index, - data.pos_in_train + wagon.wagon_span)
	local pos, connid, frac = advtrains.path_getrestore(train, p_index)
	local tp = {}
	for k,v in ipairs(train.trainparts) do
		if k >= index then
			table.insert(tp, v)
			train.trainparts[k] = nil
		end
	end
	advtrains.update_trainpart_properties(train_id)
	recalc_end_index(train)
	run_callbacks_update(train_id, train)
	
	--create subtrain
	local newtrain_id=advtrains.create_new_train_at(pos, connid, frac, tp)
	local newtrain=advtrains.trains[newtrain_id]
	
	newtrain.velocity=train.velocity
	-- copy various properties from the old to the new train
	newtrain.door_open = train.door_open
	newtrain.text_outside = train.text_outside
	newtrain.text_inside = train.text_inside
	newtrain.line = train.line
	newtrain.routingcode = train.routingcode
	newtrain.speed_restriction = train.speed_restriction
	newtrain.is_shunt = train.is_shunt
	newtrain.points_split = advtrains.merge_tables(train.points_split)
	newtrain.autocouple = train.autocouple

	return newtrain_id -- return new train ID, so new train can be manipulated

end

function advtrains.split_train_at_wagon(wagon_id)
	--get train
	local data = advtrains.wagons[wagon_id]
	advtrains.split_train_at_index(advtrains.trains[data.train_id], data.pos_in_trainparts)
end

-- coupling
local CPL_CHK_DST = -1
local CPL_ZONE = 2

-- train.couple_* contain references to ObjectRefs of couple objects, which contain all relevant information
-- These objectRefs will delete themselves once the couples no longer match
local function createcouple(pos, train1, t1_is_front, train2, t2_is_front)
	local id1 = train1.id
	local id2 = train2.id
	if train1.autocouple or train2.autocouple then
		-- couple trains
		train1.autocouple = nil
		train2.autocouple = nil		
		minetest.after(0, advtrains.safe_couple_trains, id1, id2, t1_is_front, t2_is_front, false, false, train1.velocity, train2.velocity)
		return
	end
	
	local obj=minetest.add_entity(pos, "advtrains:couple")
	if not obj then error("Failed creating couple object!") return end
	local le=obj:get_luaentity()
	le.train_id_1=id1
	le.train_id_2=id2
	le.t1_is_front=t1_is_front
	le.t2_is_front=t2_is_front
	--atdebug("created couple between",train1.id,t1_is_front,train2.id,t2_is_front)
	if t1_is_front then
		train1.cpl_front = obj
	else
		train1.cpl_back = obj
	end
	if t2_is_front then
		train2.cpl_front = obj
	else
		train2.cpl_back = obj
	end
	
end

function advtrains.train_check_couples(train)
	--atdebug("rechecking couples")
	if train.cpl_front then
		if not train.cpl_front:get_yaw() then
			-- objectref is no longer valid. reset.
			train.cpl_front = nil
		end
	end
	if not train.cpl_front then
		-- recheck front couple
		local front_trains, pos = advtrains.occ.get_occupations(train, atround(train.index) + CPL_CHK_DST)
		if advtrains.is_node_loaded(pos) then -- if the position is loaded...
			for tid, idx in pairs(front_trains) do
				local other_train = advtrains.trains[tid]
				if not advtrains.train_ensure_init(tid, other_train) then
					atwarn("Train",tid,"is not initialized! Couldn't check couples!")
					return
				end
				--atdebug(train.id,"front: ",idx,"on",tid,atround(other_train.index),atround(other_train.end_index))
				if other_train.velocity == 0 then
					if idx>=other_train.index and idx<=other_train.index + CPL_ZONE then
						createcouple(pos, train, true, other_train, true)
						break
					end
					if idx<=other_train.end_index and idx>=other_train.end_index - CPL_ZONE then
						createcouple(pos, train, true, other_train, false)
						break
					end
				end
			end
		end
	end
	if train.cpl_back then
		if not train.cpl_back:get_yaw() then
			-- objectref is no longer valid. reset.
			train.cpl_back = nil
		end
	end
	if not train.cpl_back then
		-- recheck back couple
		local back_trains, pos = advtrains.occ.get_occupations(train, atround(train.end_index) - CPL_CHK_DST)
		if advtrains.is_node_loaded(pos) then -- if the position is loaded...
			for tid, idx in pairs(back_trains) do
				local other_train = advtrains.trains[tid]
				if not advtrains.train_ensure_init(tid, other_train) then
					atwarn("Train",tid,"is not initialized! Couldn't check couples!")
					return
				end
				if other_train.velocity == 0 then
					if idx>=other_train.index and idx<=other_train.index + CPL_ZONE then
						createcouple(pos, train, false, other_train, true)
						break
					end
					if idx<=other_train.end_index and idx>=other_train.end_index - CPL_ZONE then
						createcouple(pos, train, false, other_train, false)
						break
					end
				end
			end
		end
	end
end

function advtrains.couple_invalidate(train)
	if train.cpl_back then
		train.cpl_back:remove()
		train.cpl_back = nil
	end
	if train.cpl_front then
		train.cpl_front:remove()
		train.cpl_front = nil
	end
	train.was_standing = nil
end

-- relevant code for this comment is in couple.lua

--there are 4 cases:
--1/2. F<->R F<->R regular, put second train behind first
--->frontpos of first train will match backpos of second
--3.   F<->R R<->F flip one of these trains, take the other as new train
--->backpos's will match
--4.   R<->F F<->R flip one of these trains and take it as new parent
--->frontpos's will match


function advtrains.do_connect_trains(first_id, second_id, vel)
	local first, second=advtrains.trains[first_id], advtrains.trains[second_id]
	
	if not advtrains.train_ensure_init(first_id, first) then
		atwarn("Train",first_id,"is not initialized! Operation aborted!")
		return
	end
	if not advtrains.train_ensure_init(second_id, second) then
		atwarn("Train",second_id,"is not initialized! Operation aborted!")
		return
	end
	
	local first_wagoncnt=#first.trainparts
	local second_wagoncnt=#second.trainparts
	
	for _,v in ipairs(second.trainparts) do
		table.insert(first.trainparts, v)
	end
	
	advtrains.remove_train(second_id)
	if vel < 0 then
		advtrains.invert_train(first_id)
		vel = -vel
	end
	first.velocity= vel or 0
	
	advtrains.update_trainpart_properties(first_id)
	advtrains.couple_invalidate(first)
	return true
end

function advtrains.invert_train(train_id)
	local train=advtrains.trains[train_id]
	
	if not advtrains.train_ensure_init(train_id, train) then
		atwarn("Train",train_id,"is not initialized! Operation aborted!")
		return
	end
	
	advtrains.path_setrestore(train, true)
	
	-- rotate some other stuff
	if train.door_open then
		train.door_open = - train.door_open
	end
	if train.atc_command then
		train.atc_arrow = not train.atc_arrow
	end
	
	advtrains.path_invalidate(train, true)
	advtrains.couple_invalidate(train)
	
	local old_trainparts=train.trainparts
	train.trainparts={}
	for k,v in ipairs(old_trainparts) do
		table.insert(train.trainparts, 1, v)--notice insertion at first place
	end
	advtrains.update_trainpart_properties(train_id, true)
	
	-- recalculate path
	advtrains.train_ensure_init(train_id, train)
	
	-- If interlocking present, check whether this train is in a section and then set as shunt move after reversion
	if advtrains.interlocking and train.il_sections and #train.il_sections > 0 then
		train.is_shunt = true
		train.speed_restriction = advtrains.SHUNT_SPEED_MAX
	else
		train.is_shunt = false
		train.speed_restriction = nil
	end
end

-- returns: train id, index of one of the trains that stand at this position.
function advtrains.get_train_at_pos(pos)
	local t = advtrains.occ.get_trains_at(pos)
	for tid,idx in pairs(t) do
		return tid, idx
	end
end


-- ehm... I never adapted this function to the new path system ?!
function advtrains.invalidate_all_paths(pos)
	local tab
	if pos then
		-- if position given, check occupation system
		tab = advtrains.occ.get_trains_over(pos)
	else
		tab = advtrains.trains
	end
	
	for id, _ in pairs(tab) do
		advtrains.invalidate_path(id)
	end
end

-- Calls invalidate_path_ahead on all trains occupying (having paths over) this node
-- Can be called during train step.
function advtrains.invalidate_all_paths_ahead(pos)
	local tab = advtrains.occ.get_trains_over(pos)
	
	for id,index in pairs(tab) do
		local train = advtrains.trains[id]
		advtrains.path_invalidate_ahead(train, index, true)
	end
end

function advtrains.invalidate_path(id)
	--atdebug("Path invalidate:",id)
	local v=advtrains.trains[id]
	if not v then return end
	advtrains.path_invalidate(v)
	advtrains.couple_invalidate(v)
	v.dirty = true
end

--not blocking trains group
function advtrains.train_collides(node)
	if node and minetest.registered_nodes[node.name] then
		local ndef = minetest.registered_nodes[node.name]
		-- if the node is drawtype normal (that is a full cube) then it does collide
		if ndef.drawtype == "normal" then
			-- except if it is not_blocking_trains
			if ndef.groups.not_blocking_trains and ndef.groups.not_blocking_trains ~= 0 then
				return false
			end
			return true
		end
	end
	return false
end