summaryrefslogtreecommitdiff
path: root/src/pathfind.cpp
blob: 9152e88a0fe1a32c9d1e492860ba3c0ab0865d99 (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
/* $Id$ */

/** @file pathfind.cpp Implementation of the oldest supported pathfinder. */

#include "stdafx.h"
#include "station_map.h"
#include "settings_type.h"
#include "pathfind.h"
#include "debug.h"
#include "tunnelbridge_map.h"
#include "core/random_func.hpp"
#include "core/alloc_type.hpp"
#include "tunnelbridge.h"

/* remember which tiles we have already visited so we don't visit them again. */
static bool TPFSetTileBit(TrackPathFinder *tpf, TileIndex tile, int dir)
{
	uint hash, val, offs;
	TrackPathFinderLink *link, *new_link;
	uint bits = 1 << dir;

	if (tpf->disable_tile_hash)
		return true;

	hash = PATHFIND_HASH_TILE(tile);

	val = tpf->hash_head[hash];

	if (val == 0) {
		/* unused hash entry, set the appropriate bit in it and return true
		 * to indicate that a bit was set. */
		tpf->hash_head[hash] = bits;
		tpf->hash_tile[hash] = tile;
		return true;
	} else if (!(val & 0x8000)) {
		/* single tile */

		if (tile == tpf->hash_tile[hash]) {
			/* found another bit for the same tile,
			 * check if this bit is already set, if so, return false */
			if (val & bits)
				return false;

			/* otherwise set the bit and return true to indicate that the bit
			 * was set */
			tpf->hash_head[hash] = val | bits;
			return true;
		} else {
			/* two tiles with the same hash, need to make a link */

			/* allocate a link. if out of links, handle this by returning
			 * that a tile was already visisted. */
			if (tpf->num_links_left == 0) {
				return false;
			}
			tpf->num_links_left--;
			link = tpf->new_link++;

			/* move the data that was previously in the hash_??? variables
			 * to the link struct, and let the hash variables point to the link */
			link->tile = tpf->hash_tile[hash];
			tpf->hash_tile[hash] = PATHFIND_GET_LINK_OFFS(tpf, link);

			link->flags = tpf->hash_head[hash];
			tpf->hash_head[hash] = 0xFFFF; // multi link

			link->next = 0xFFFF;
		}
	} else {
		/* a linked list of many tiles,
		 * find the one corresponding to the tile, if it exists.
		 * otherwise make a new link */

		offs = tpf->hash_tile[hash];
		do {
			link = PATHFIND_GET_LINK_PTR(tpf, offs);
			if (tile == link->tile) {
				/* found the tile in the link list,
				 * check if the bit was alrady set, if so return false to indicate that the
				 * bit was already set */
				if (link->flags & bits)
					return false;
				link->flags |= bits;
				return true;
			}
		} while ((offs=link->next) != 0xFFFF);
	}

	/* get here if we need to add a new link to link,
	 * first, allocate a new link, in the same way as before */
	if (tpf->num_links_left == 0) {
			return false;
	}
	tpf->num_links_left--;
	new_link = tpf->new_link++;

	/* then fill the link with the new info, and establish a ptr from the old
	 * link to the new one */
	new_link->tile = tile;
	new_link->flags = bits;
	new_link->next = 0xFFFF;

	link->next = PATHFIND_GET_LINK_OFFS(tpf, new_link);
	return true;
}

static void TPFModeShip(TrackPathFinder *tpf, TileIndex tile, DiagDirection direction)
{
	assert(tpf->tracktype == TRANSPORT_WATER);

	if (IsTileType(tile, MP_TUNNELBRIDGE)) {
		/* wrong track type */
		if (GetTunnelBridgeTransportType(tile) != tpf->tracktype) return;

		DiagDirection dir = GetTunnelBridgeDirection(tile);
		/* entering tunnel / bridge? */
		if (dir == direction) {
			TileIndex endtile = GetOtherTunnelBridgeEnd(tile);

			tpf->rd.cur_length += GetTunnelBridgeLength(tile, endtile) + 1;

			TPFSetTileBit(tpf, tile, 14);
			TPFSetTileBit(tpf, endtile, 14);

			tile = endtile;
		} else {
			/* leaving tunnel / bridge? */
			if (ReverseDiagDir(dir) != direction) return;
		}
	}

	/* This addition will sometimes overflow by a single tile.
	 * The use of TILE_MASK here makes sure that we still point at a valid
	 * tile, and then this tile will be in the sentinel row/col, so GetTileTrackStatus will fail. */
	tile = TILE_MASK(tile + TileOffsByDiagDir(direction));

	if (++tpf->rd.cur_length > 50)
		return;

	TrackBits bits = TrackStatusToTrackBits(GetTileTrackStatus(tile, tpf->tracktype, tpf->sub_type)) & DiagdirReachesTracks(direction);
	if (bits == TRACK_BIT_NONE) return;

	assert(TileX(tile) != MapMaxX() && TileY(tile) != MapMaxY());

	bool only_one_track = true;
	do {
		Track track = RemoveFirstTrack(&bits);
		if (bits != TRACK_BIT_NONE) only_one_track = false;
		RememberData rd = tpf->rd;

		/* Change direction 4 times only */
		if (!only_one_track && track != tpf->rd.last_choosen_track) {
			if (++tpf->rd.depth > 4) {
				tpf->rd = rd;
				return;
			}
			tpf->rd.last_choosen_track = track;
		}

		tpf->the_dir = TrackEnterdirToTrackdir(track, direction);

		if (!tpf->enum_proc(tile, tpf->userdata, tpf->the_dir, tpf->rd.cur_length)) {
			TPFModeShip(tpf, tile, TrackdirToExitdir(tpf->the_dir));
		}

		tpf->rd = rd;
	} while (bits != TRACK_BIT_NONE);

}

/**
 * Checks if any vehicle can enter/leave tile in given diagdir
 * Checks only for rail/road depots and road non-drivethrough stations
 * @param tile tile to check
 * @param side side of tile we are trying to leave/enter
 * @param tracktype type of transport
 * @pre tile has trackbit at that diagdir
 * @return true iff vehicle can enter/leve the tile in given side
 */
static inline bool CanAccessTileInDir(TileIndex tile, DiagDirection side, TransportType tracktype)
{
	if (tracktype == TRANSPORT_RAIL) {
		/* depot from wrong side */
		if (IsRailDepotTile(tile) && GetRailDepotDirection(tile) != side) return false;
	} else if (tracktype == TRANSPORT_ROAD) {
		/* depot from wrong side */
		if (IsRoadDepotTile(tile) && GetRoadDepotDirection(tile) != side) return false;
		/* non-driverthrough road station from wrong side */
		if (IsStandardRoadStopTile(tile) && GetRoadStopDir(tile) != side) return false;
	}

	return true;
}

static void TPFModeNormal(TrackPathFinder *tpf, TileIndex tile, DiagDirection direction)
{
	const TileIndex tile_org = tile;

	if (IsTileType(tile, MP_TUNNELBRIDGE)) {
		/* wrong track type */
		if (GetTunnelBridgeTransportType(tile) != tpf->tracktype) return;

		DiagDirection dir = GetTunnelBridgeDirection(tile);
		/* entering tunnel / bridge? */
		if (dir == direction) {
			TileIndex endtile = GetOtherTunnelBridgeEnd(tile);

			tpf->rd.cur_length += GetTunnelBridgeLength(tile, endtile) + 1;

			TPFSetTileBit(tpf, tile, 14);
			TPFSetTileBit(tpf, endtile, 14);

			tile = endtile;
		} else {
			/* leaving tunnel / bridge? */
			if (ReverseDiagDir(dir) != direction) return;
		}
	} else {
		/* can we leave tile in this dir? */
		if (!CanAccessTileInDir(tile, direction, tpf->tracktype)) return;
	}

	tile += TileOffsByDiagDir(direction);

	/* can we enter tile in this dir? */
	if (!CanAccessTileInDir(tile, ReverseDiagDir(direction), tpf->tracktype)) return;

	/* Check if the new tile is a tunnel or bridge head and that the direction
	 * and transport type match */
	if (IsTileType(tile, MP_TUNNELBRIDGE)) {
		if (GetTunnelBridgeDirection(tile) != direction ||
				GetTunnelBridgeTransportType(tile) != tpf->tracktype) {
			return;
		}
	}

	TrackdirBits trackdirbits = TrackStatusToTrackdirBits(GetTileTrackStatus(tile, tpf->tracktype, tpf->sub_type));

	/* Check in case of rail if the owner is the same */
	if (tpf->tracktype == TRANSPORT_RAIL) {
		if (trackdirbits != TRACKDIR_BIT_NONE && TrackStatusToTrackdirBits(GetTileTrackStatus(tile_org, TRANSPORT_RAIL, 0)) != TRACKDIR_BIT_NONE) {
			if (GetTileOwner(tile_org) != GetTileOwner(tile)) return;
		}
	}

	tpf->rd.cur_length++;

	trackdirbits &= DiagdirReachesTrackdirs(direction);
	TrackBits bits = TrackdirBitsToTrackBits(trackdirbits);

	if (bits != TRACK_BIT_NONE) {
		if (!tpf->disable_tile_hash || (tpf->rd.cur_length <= 64 && (KillFirstBit(bits) == 0 || ++tpf->rd.depth <= 7))) {
			do {
				Track track = RemoveFirstTrack(&bits);

				tpf->the_dir = TrackEnterdirToTrackdir(track, direction);
				RememberData rd = tpf->rd;

				/* make sure we are not leaving from invalid side */
				if (TPFSetTileBit(tpf, tile, tpf->the_dir) && CanAccessTileInDir(tile, TrackdirToExitdir(tpf->the_dir), tpf->tracktype) &&
						!tpf->enum_proc(tile, tpf->userdata, tpf->the_dir, tpf->rd.cur_length) ) {
					TPFModeNormal(tpf, tile, TrackdirToExitdir(tpf->the_dir));
				}
				tpf->rd = rd;
			} while (bits != TRACK_BIT_NONE);
		}
	}
}

void FollowTrack(TileIndex tile, PathfindFlags flags, TransportType tt, uint sub_type, DiagDirection direction, TPFEnumProc *enum_proc, TPFAfterProc *after_proc, void *data)
{
	assert(IsValidDiagDirection(direction));

	SmallStackSafeStackAlloc<TrackPathFinder, 1> tpf;

	/* initialize path finder variables */
	tpf->userdata = data;
	tpf->enum_proc = enum_proc;
	tpf->new_link = tpf->links;
	tpf->num_links_left = lengthof(tpf->links);

	tpf->rd.cur_length = 0;
	tpf->rd.depth = 0;
	tpf->rd.last_choosen_track = INVALID_TRACK;

	tpf->disable_tile_hash = (flags & PATHFIND_FLAGS_DISABLE_TILE_HASH) != 0;

	tpf->tracktype = tt;
	tpf->sub_type = sub_type;

	if ((flags & PATHFIND_FLAGS_SHIP_MODE) != 0) {
		tpf->enum_proc(tile, data, INVALID_TRACKDIR, 0);
		TPFModeShip(tpf, tile, direction);
	} else {
		/* clear the hash_heads */
		memset(tpf->hash_head, 0, sizeof(tpf->hash_head));
		TPFModeNormal(tpf, tile, direction);
	}

	if (after_proc != NULL) after_proc(tpf);
}

struct StackedItem {
	TileIndex tile;
	uint16 cur_length; ///< This is the current length to this tile.
	uint16 priority;   ///< This is the current length + estimated length to the goal.
	TrackdirByte track;
	byte depth;
	byte state;
	byte first_track;
};

struct HashLink {
	TileIndex tile;
	uint16 typelength;
	uint16 next;
};

struct NewTrackPathFinder {
	NTPEnumProc *enum_proc;
	void *userdata;
	TileIndex dest;

	TransportType tracktype;
	RailTypes railtypes;
	uint maxlength;

	HashLink *new_link;
	uint num_links_left;

	uint nstack;
	StackedItem stack[256];     ///< priority queue of stacked items

	uint16 hash_head[0x400];    ///< hash heads. 0 means unused. 0xFFFC = length, 0x3 = dir
	TileIndex hash_tile[0x400]; ///< tiles. or links.

	HashLink links[0x400];      ///< hash links

};
#define NTP_GET_LINK_OFFS(tpf, link) ((byte*)(link) - (byte*)tpf->links)
#define NTP_GET_LINK_PTR(tpf, link_offs) (HashLink*)((byte*)tpf->links + (link_offs))

#define ARR(i) tpf->stack[(i)-1]

/** called after a new element was added in the queue at the last index.
 * move it down to the proper position */
static inline void HeapifyUp(NewTrackPathFinder *tpf)
{
	StackedItem si;
	int i = ++tpf->nstack;

	while (i != 1 && ARR(i).priority < ARR(i>>1).priority) {
		/* the child element is larger than the parent item.
		 * swap the child item and the parent item. */
		si = ARR(i); ARR(i) = ARR(i >> 1); ARR(i >> 1) = si;
		i >>= 1;
	}
}

/** called after the element 0 was eaten. fill it with a new element */
static inline void HeapifyDown(NewTrackPathFinder *tpf)
{
	StackedItem si;
	int i = 1, j;
	int n;

	assert(tpf->nstack > 0);
	n = --tpf->nstack;

	if (n == 0) return; // heap is empty so nothing to do?

	/* copy the last item to index 0. we use it as base for heapify. */
	ARR(1) = ARR(n + 1);

	while ((j = i * 2) <= n) {
		/* figure out which is smaller of the children. */
		if (j != n && ARR(j).priority > ARR(j + 1).priority)
			j++; // right item is smaller

		assert(i <= n && j <= n);
		if (ARR(i).priority <= ARR(j).priority)
			break; // base elem smaller than smallest, done!

		/* swap parent with the child */
		si = ARR(i); ARR(i) = ARR(j); ARR(j) = si;
		i = j;
	}
}

/** mark a tile as visited and store the length of the path.
 * if we already had a better path to this tile, return false.
 * otherwise return true. */
static bool NtpVisit(NewTrackPathFinder *tpf, TileIndex tile, DiagDirection dir, uint length)
{
	uint hash,head;
	HashLink *link, *new_link;

	assert(length < 16384-1);

	hash = PATHFIND_HASH_TILE(tile);

	/* never visited before? */
	if ((head=tpf->hash_head[hash]) == 0) {
		tpf->hash_tile[hash] = tile;
		tpf->hash_head[hash] = dir | (length << 2);
		return true;
	}

	if (head != 0xffff) {
		if (tile == tpf->hash_tile[hash] && (head & 0x3) == (uint)dir) {

			/* longer length */
			if (length >= (head >> 2)) return false;

			tpf->hash_head[hash] = dir | (length << 2);
			return true;
		}
		/* two tiles with the same hash, need to make a link
		 * allocate a link. if out of links, handle this by returning
		 * that a tile was already visisted. */
		if (tpf->num_links_left == 0) {
			DEBUG(ntp, 1, "No links left");
			return false;
		}

		tpf->num_links_left--;
		link = tpf->new_link++;

		/* move the data that was previously in the hash_??? variables
		 * to the link struct, and let the hash variables point to the link */
		link->tile = tpf->hash_tile[hash];
		tpf->hash_tile[hash] = NTP_GET_LINK_OFFS(tpf, link);

		link->typelength = tpf->hash_head[hash];
		tpf->hash_head[hash] = 0xFFFF; // multi link
		link->next = 0xFFFF;
	} else {
		/* a linked list of many tiles,
		 * find the one corresponding to the tile, if it exists.
		 * otherwise make a new link */

		uint offs = tpf->hash_tile[hash];
		do {
			link = NTP_GET_LINK_PTR(tpf, offs);
			if (tile == link->tile && (link->typelength & 0x3U) == (uint)dir) {
				if (length >= (uint)(link->typelength >> 2)) return false;
				link->typelength = dir | (length << 2);
				return true;
			}
		} while ((offs = link->next) != 0xFFFF);
	}

	/* get here if we need to add a new link to link,
	 * first, allocate a new link, in the same way as before */
	if (tpf->num_links_left == 0) {
		DEBUG(ntp, 1, "No links left");
		return false;
	}
	tpf->num_links_left--;
	new_link = tpf->new_link++;

	/* then fill the link with the new info, and establish a ptr from the old
	 * link to the new one */
	new_link->tile = tile;
	new_link->typelength = dir | (length << 2);
	new_link->next = 0xFFFF;

	link->next = NTP_GET_LINK_OFFS(tpf, new_link);
	return true;
}

/**
 * Checks if the shortest path to the given tile/dir so far is still the given
 * length.
 * @return true if the length is still the same
 * @pre    The given tile/dir combination should be present in the hash, by a
 *         previous call to NtpVisit().
 */
static bool NtpCheck(NewTrackPathFinder *tpf, TileIndex tile, uint dir, uint length)
{
	uint hash,head,offs;
	HashLink *link;

	hash = PATHFIND_HASH_TILE(tile);
	head=tpf->hash_head[hash];
	assert(head);

	if (head != 0xffff) {
		assert( tpf->hash_tile[hash] == tile && (head & 3) == dir);
		assert( (head >> 2) <= length);
		return length == (head >> 2);
	}

	/* else it's a linked list of many tiles */
	offs = tpf->hash_tile[hash];
	for (;;) {
		link = NTP_GET_LINK_PTR(tpf, offs);
		if (tile == link->tile && (link->typelength & 0x3U) == dir) {
			assert((uint)(link->typelength >> 2) <= length);
			return length == (uint)(link->typelength >> 2);
		}
		offs = link->next;
		assert(offs != 0xffff);
	}
}


static uint DistanceMoo(TileIndex t0, TileIndex t1)
{
	const uint dx = Delta(TileX(t0), TileX(t1));
	const uint dy = Delta(TileY(t0), TileY(t1));

	const uint straightTracks = 2 * min(dx, dy); // The number of straight (not full length) tracks
	/* OPTIMISATION:
	 * Original: diagTracks = max(dx, dy) - min(dx,dy);
	 * Proof:
	 * (dx-dy) - straightTracks  == (min + max) - straightTracks = min + // max - 2 * min = max - min */
	const uint diagTracks = dx + dy - straightTracks; // The number of diagonal (full tile length) tracks.

	return diagTracks*DIAG_FACTOR + straightTracks*STR_FACTOR;
}

/* These has to be small cause the max length of a track
 * is currently limited to 16384 */

static const byte _length_of_track[16] = {
	DIAG_FACTOR, DIAG_FACTOR, STR_FACTOR, STR_FACTOR, STR_FACTOR, STR_FACTOR, 0, 0,
	DIAG_FACTOR, DIAG_FACTOR, STR_FACTOR, STR_FACTOR, STR_FACTOR, STR_FACTOR, 0, 0
};

/* new more optimized pathfinder for trains...
 * Tile is the tile the train is at.
 * direction is the tile the train is moving towards. */

static void NTPEnum(NewTrackPathFinder *tpf, TileIndex tile, DiagDirection direction)
{
	TrackBits bits, allbits;
	Trackdir track;
	TileIndex tile_org;
	StackedItem si;
	int estimation;



	/* Need to have a special case for the start.
	 * We shouldn't call the callback for the current tile. */
	si.cur_length = 1; // Need to start at 1 cause 0 is a reserved value.
	si.depth = 0;
	si.state = 0;
	si.first_track = 0xFF;
	goto start_at;

	for (;;) {
		/* Get the next item to search from from the priority queue */
		do {
			if (tpf->nstack == 0)
				return; // nothing left? then we're done!
			si = tpf->stack[0];
			tile = si.tile;

			HeapifyDown(tpf);
			/* Make sure we havn't already visited this tile. */
		} while (!NtpCheck(tpf, tile, ReverseDiagDir(TrackdirToExitdir(ReverseTrackdir(si.track))), si.cur_length));

		/* Add the length of this track. */
		si.cur_length += _length_of_track[si.track];

callback_and_continue:
		if (tpf->enum_proc(tile, tpf->userdata, si.first_track, si.cur_length))
			return;

		assert(si.track <= 13);
		direction = TrackdirToExitdir(si.track);

start_at:
		/* If the tile is the entry tile of a tunnel, and we're not going out of the tunnel,
		 *   need to find the exit of the tunnel. */
		if (IsTileType(tile, MP_TUNNELBRIDGE)) {
			if (GetTunnelBridgeDirection(tile) != ReverseDiagDir(direction)) {
				/* We are not just driving out of the tunnel/bridge */
				if (GetTunnelBridgeDirection(tile) != direction ||
						GetTunnelBridgeTransportType(tile) != tpf->tracktype) {
					/* We are not driving into the tunnel/bridge, or it is an invalid tunnel/bridge */
					continue;
				}
				if (!HasBit(tpf->railtypes, GetRailType(tile))) {
					bits = TRACK_BIT_NONE;
					break;
				}

				TileIndex endtile = GetOtherTunnelBridgeEnd(tile);
				si.cur_length += DIAG_FACTOR * (GetTunnelBridgeLength(tile, endtile) + 1);
				tile = endtile;
				/* tile now points to the exit tile of the tunnel/bridge */
			}
		}

		/* This is a special loop used to go through
		 * a rail net and find the first intersection */
		tile_org = tile;
		for (;;) {
			assert(direction <= 3);
			tile += TileOffsByDiagDir(direction);

			/* too long search length? bail out. */
			if (si.cur_length >= tpf->maxlength) {
				DEBUG(ntp, 1, "Cur_length too big");
				bits = TRACK_BIT_NONE;
				break;
			}

			/* Not a regular rail tile?
			 * Then we can't use the code below, but revert to more general code. */
			if (!IsTileType(tile, MP_RAILWAY) || !IsPlainRailTile(tile)) {
				/* We found a tile which is not a normal railway tile.
				 * Determine which tracks that exist on this tile. */
				bits = TrackdirBitsToTrackBits(TrackStatusToTrackdirBits(GetTileTrackStatus(tile, TRANSPORT_RAIL, 0)) & DiagdirReachesTrackdirs(direction));

				/* Check that the tile contains exactly one track */
				if (bits == 0 || KillFirstBit(bits) != 0) break;

				if (!HasBit(tpf->railtypes, GetRailType(tile))) {
					bits = TRACK_BIT_NONE;
					break;
				}

				/*******************
				 * If we reach here, the tile has exactly one track.
				 *   tile - index to a tile that is not rail tile, but still straight (with optional signals)
				 *   bits - bitmask of which track that exist on the tile (exactly one bit is set)
				 *   direction - which direction are we moving in?
				 *******************/
				si.track = TrackEnterdirToTrackdir(FindFirstTrack(bits), direction);
				si.cur_length += _length_of_track[si.track];
				goto callback_and_continue;
			}

			/* Regular rail tile, determine which tracks exist. */
			allbits = GetTrackBits(tile);
			/* Which tracks are reachable? */
			bits = allbits & DiagdirReachesTracks(direction);

			/* The tile has no reachable tracks => End of rail segment
			 * or Intersection => End of rail segment. We check this agains all the
			 * bits, not just reachable ones, to prevent infinite loops. */
			if (bits == TRACK_BIT_NONE || TracksOverlap(allbits)) break;

			if (!HasBit(tpf->railtypes, GetRailType(tile))) {
				bits = TRACK_BIT_NONE;
				break;
			}

			/* If we reach here, the tile has exactly one track, and this
			 track is reachable = > Rail segment continues */

			track = TrackEnterdirToTrackdir(FindFirstTrack(bits), direction);
			assert(track != INVALID_TRACKDIR);

			si.cur_length += _length_of_track[track];

			/* Check if this rail is an upwards slope. If it is, then add a penalty. */
			if (IsDiagonalTrackdir(track) && IsUphillTrackdir(GetTileSlope(tile, NULL), track)) {
				// upwards slope. add some penalty.
				si.cur_length += 4 * DIAG_FACTOR;
			}

			/* railway tile with signals..? */
			if (HasSignals(tile)) {
				if (!HasSignalOnTrackdir(tile, track)) {
					/* if one way signal not pointing towards us, stop going in this direction => End of rail segment. */
					if (HasSignalOnTrackdir(tile, ReverseTrackdir(track)) && IsOnewaySignal(tile, TrackdirToTrack(track))) {
						bits = TRACK_BIT_NONE;
						break;
					}
				} else if (GetSignalStateByTrackdir(tile, track) == SIGNAL_STATE_GREEN) {
					/* green signal in our direction. either one way or two way. */
					si.state |= 3;
				} else {
					/* reached a red signal. */
					if (HasSignalOnTrackdir(tile, ReverseTrackdir(track))) {
						/* two way red signal. unless we passed another green signal on the way,
						 * stop going in this direction => End of rail segment.
						 * this is to prevent us from going into a full platform. */
						if (!(si.state & 1)) {
							bits = TRACK_BIT_NONE;
							break;
						}
					}
					if (!(si.state & 2)) {
						/* Is this the first signal we see? And it's red... add penalty */
						si.cur_length += 10 * DIAG_FACTOR;
						si.state += 2; // remember that we added penalty.
						/* Because we added a penalty, we can't just continue as usual.
						 * Need to get out and let A* do it's job with
						 * possibly finding an even shorter path. */
						break;
					}
				}

				if (tpf->enum_proc(tile, tpf->userdata, si.first_track, si.cur_length))
					return; // Don't process this tile any further
			}

			/* continue with the next track */
			direction = TrackdirToExitdir(track);

			/* safety check if we're running around chasing our tail... (infinite loop) */
			if (tile == tile_org) {
				bits = TRACK_BIT_NONE;
				break;
			}
		}

		/* There are no tracks to choose between.
		 * Stop searching in this direction */
		if (bits == TRACK_BIT_NONE)
			continue;

		/****************
		 * We got multiple tracks to choose between (intersection).
		 * Branch the search space into several branches.
		 ****************/

		/* Check if we've already visited this intersection.
		 * If we've already visited it with a better length, then
		 * there's no point in visiting it again. */
		if (!NtpVisit(tpf, tile, direction, si.cur_length))
			continue;

		/* Push all possible alternatives that we can reach from here
		 * onto the priority heap.
		 * 'bits' contains the tracks that we can choose between. */

		/* First compute the estimated distance to the target.
		 * This is used to implement A* */
		estimation = 0;
		if (tpf->dest != 0)
			estimation = DistanceMoo(tile, tpf->dest);

		si.depth++;
		if (si.depth == 0)
			continue; // We overflowed our depth. No more searching in this direction.
		si.tile = tile;
		while (bits != TRACK_BIT_NONE) {
			Track track = RemoveFirstTrack(&bits);
			si.track = TrackEnterdirToTrackdir(track, direction);
			assert(si.track != 0xFF);
			si.priority = si.cur_length + estimation;

			/* out of stack items, bail out? */
			if (tpf->nstack >= lengthof(tpf->stack)) {
				DEBUG(ntp, 1, "Out of stack");
				break;
			}

			tpf->stack[tpf->nstack] = si;
			HeapifyUp(tpf);
		};

		/* If this is the first intersection, we need to fill the first_track member.
		 * so the code outside knows which path is better.
		 * also randomize the order in which we search through them. */
		if (si.depth == 1) {
			assert(tpf->nstack == 1 || tpf->nstack == 2 || tpf->nstack == 3);
			if (tpf->nstack != 1) {
				uint32 r = Random();
				if (r & 1) Swap(tpf->stack[0].track, tpf->stack[1].track);
				if (tpf->nstack != 2) {
					TrackdirByte t = tpf->stack[2].track;
					if (r & 2) Swap(tpf->stack[0].track, t);
					if (r & 4) Swap(tpf->stack[1].track, t);
					tpf->stack[2].first_track = tpf->stack[2].track = t;
				}
				tpf->stack[0].first_track = tpf->stack[0].track;
				tpf->stack[1].first_track = tpf->stack[1].track;
			}
		}

		/* Continue with the next from the queue... */
	}
}


/** new pathfinder for trains. better and faster. */
void NewTrainPathfind(TileIndex tile, TileIndex dest, RailTypes railtypes, DiagDirection direction, NTPEnumProc *enum_proc, void *data)
{
	SmallStackSafeStackAlloc<NewTrackPathFinder, 1> tpf;

	tpf->dest = dest;
	tpf->userdata = data;
	tpf->enum_proc = enum_proc;
	tpf->tracktype = TRANSPORT_RAIL;
	tpf->railtypes = railtypes;
	tpf->maxlength = min(_settings_game.pf.opf.pf_maxlength * 3, 10000);
	tpf->nstack = 0;
	tpf->new_link = tpf->links;
	tpf->num_links_left = lengthof(tpf->links);
	memset(tpf->hash_head, 0, sizeof(tpf->hash_head));

	NTPEnum(tpf, tile, direction);
}