aboutsummaryrefslogtreecommitdiff
path: root/graph.c
blob: 1350bdde3be4346e8bc2038c57e4883d0ab12b25 (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
#include "cache.h"
#include "commit.h"
#include "color.h"
#include "graph.h"
#include "diff.h"
#include "revision.h"

/* Internal API */

/*
 * Output a padding line in the graph.
 * This is similar to graph_next_line().  However, it is guaranteed to
 * never print the current commit line.  Instead, if the commit line is
 * next, it will simply output a line of vertical padding, extending the
 * branch lines downwards, but leaving them otherwise unchanged.
 */
static void graph_padding_line(struct git_graph *graph, struct strbuf *sb);

/*
 * Print a strbuf to stdout.  If the graph is non-NULL, all lines but the
 * first will be prefixed with the graph output.
 *
 * If the strbuf ends with a newline, the output will end after this
 * newline.  A new graph line will not be printed after the final newline.
 * If the strbuf is empty, no output will be printed.
 *
 * Since the first line will not include the graph output, the caller is
 * responsible for printing this line's graph (perhaps via
 * graph_show_commit() or graph_show_oneline()) before calling
 * graph_show_strbuf().
 */
static void graph_show_strbuf(struct git_graph *graph, struct strbuf const *sb);

/*
 * TODO:
 * - Limit the number of columns, similar to the way gitk does.
 *   If we reach more than a specified number of columns, omit
 *   sections of some columns.
 */

struct column {
	/*
	 * The parent commit of this column.
	 */
	struct commit *commit;
	/*
	 * The color to (optionally) print this column in.  This is an
	 * index into column_colors.
	 */
	unsigned short color;
};

enum graph_state {
	GRAPH_PADDING,
	GRAPH_SKIP,
	GRAPH_PRE_COMMIT,
	GRAPH_COMMIT,
	GRAPH_POST_MERGE,
	GRAPH_COLLAPSING
};

static const char **column_colors;
static unsigned short column_colors_max;

void graph_set_column_colors(const char **colors, unsigned short colors_max)
{
	column_colors = colors;
	column_colors_max = colors_max;
}

static const char *column_get_color_code(unsigned short color)
{
	return column_colors[color];
}

static void strbuf_write_column(struct strbuf *sb, const struct column *c,
				char col_char)
{
	if (c->color < column_colors_max)
		strbuf_addstr(sb, column_get_color_code(c->color));
	strbuf_addch(sb, col_char);
	if (c->color < column_colors_max)
		strbuf_addstr(sb, column_get_color_code(column_colors_max));
}

struct git_graph {
	/*
	 * The commit currently being processed
	 */
	struct commit *commit;
	/* The rev-info used for the current traversal */
	struct rev_info *revs;
	/*
	 * The number of interesting parents that this commit has.
	 *
	 * Note that this is not the same as the actual number of parents.
	 * This count excludes parents that won't be printed in the graph
	 * output, as determined by graph_is_interesting().
	 */
	int num_parents;
	/*
	 * The width of the graph output for this commit.
	 * All rows for this commit are padded to this width, so that
	 * messages printed after the graph output are aligned.
	 */
	int width;
	/*
	 * The next expansion row to print
	 * when state is GRAPH_PRE_COMMIT
	 */
	int expansion_row;
	/*
	 * The current output state.
	 * This tells us what kind of line graph_next_line() should output.
	 */
	enum graph_state state;
	/*
	 * The output state for the previous line of output.
	 * This is primarily used to determine how the first merge line
	 * should appear, based on the last line of the previous commit.
	 */
	enum graph_state prev_state;
	/*
	 * The index of the column that refers to this commit.
	 *
	 * If none of the incoming columns refer to this commit,
	 * this will be equal to num_columns.
	 */
	int commit_index;
	/*
	 * The commit_index for the previously displayed commit.
	 *
	 * This is used to determine how the first line of a merge
	 * graph output should appear, based on the last line of the
	 * previous commit.
	 */
	int prev_commit_index;
	/*
	 * The maximum number of columns that can be stored in the columns
	 * and new_columns arrays.  This is also half the number of entries
	 * that can be stored in the mapping and new_mapping arrays.
	 */
	int column_capacity;
	/*
	 * The number of columns (also called "branch lines" in some places)
	 */
	int num_columns;
	/*
	 * The number of columns in the new_columns array
	 */
	int num_new_columns;
	/*
	 * The number of entries in the mapping array
	 */
	int mapping_size;
	/*
	 * The column state before we output the current commit.
	 */
	struct column *columns;
	/*
	 * The new column state after we output the current commit.
	 * Only valid when state is GRAPH_COLLAPSING.
	 */
	struct column *new_columns;
	/*
	 * An array that tracks the current state of each
	 * character in the output line during state GRAPH_COLLAPSING.
	 * Each entry is -1 if this character is empty, or a non-negative
	 * integer if the character contains a branch line.  The value of
	 * the integer indicates the target position for this branch line.
	 * (I.e., this array maps the current column positions to their
	 * desired positions.)
	 *
	 * The maximum capacity of this array is always
	 * sizeof(int) * 2 * column_capacity.
	 */
	int *mapping;
	/*
	 * A temporary array for computing the next mapping state
	 * while we are outputting a mapping line.  This is stored as part
	 * of the git_graph simply so we don't have to allocate a new
	 * temporary array each time we have to output a collapsing line.
	 */
	int *new_mapping;
	/*
	 * The current default column color being used.  This is
	 * stored as an index into the array column_colors.
	 */
	unsigned short default_column_color;
};

static struct strbuf *diff_output_prefix_callback(struct diff_options *opt, void *data)
{
	struct git_graph *graph = data;
	static struct strbuf msgbuf = STRBUF_INIT;

	assert(opt);
	assert(graph);

	opt->output_prefix_length = graph->width;
	strbuf_reset(&msgbuf);
	graph_padding_line(graph, &msgbuf);
	return &msgbuf;
}

struct git_graph *graph_init(struct rev_info *opt)
{
	struct git_graph *graph = xmalloc(sizeof(struct git_graph));

	if (!column_colors)
		graph_set_column_colors(column_colors_ansi,
					column_colors_ansi_max);

	graph->commit = NULL;
	graph->revs = opt;
	graph->num_parents = 0;
	graph->expansion_row = 0;
	graph->state = GRAPH_PADDING;
	graph->prev_state = GRAPH_PADDING;
	graph->commit_index = 0;
	graph->prev_commit_index = 0;
	graph->num_columns = 0;
	graph->num_new_columns = 0;
	graph->mapping_size = 0;
	/*
	 * Start the column color at the maximum value, since we'll
	 * always increment it for the first commit we output.
	 * This way we start at 0 for the first commit.
	 */
	graph->default_column_color = column_colors_max - 1;

	/*
	 * Allocate a reasonably large default number of columns
	 * We'll automatically grow columns later if we need more room.
	 */
	graph->column_capacity = 30;
	ALLOC_ARRAY(graph->columns, graph->column_capacity);
	ALLOC_ARRAY(graph->new_columns, graph->column_capacity);
	ALLOC_ARRAY(graph->mapping, 2 * graph->column_capacity);
	ALLOC_ARRAY(graph->new_mapping, 2 * graph->column_capacity);

	/*
	 * The diff output prefix callback, with this we can make
	 * all the diff output to align with the graph lines.
	 */
	opt->diffopt.output_prefix = diff_output_prefix_callback;
	opt->diffopt.output_prefix_data = graph;
	opt->diffopt.output_prefix_length = 0;

	return graph;
}

static void graph_update_state(struct git_graph *graph, enum graph_state s)
{
	graph->prev_state = graph->state;
	graph->state = s;
}

static void graph_ensure_capacity(struct git_graph *graph, int num_columns)
{
	if (graph->column_capacity >= num_columns)
		return;

	do {
		graph->column_capacity *= 2;
	} while (graph->column_capacity < num_columns);

	REALLOC_ARRAY(graph->columns, graph->column_capacity);
	REALLOC_ARRAY(graph->new_columns, graph->column_capacity);
	REALLOC_ARRAY(graph->mapping, graph->column_capacity * 2);
	REALLOC_ARRAY(graph->new_mapping, graph->column_capacity * 2);
}

/*
 * Returns 1 if the commit will be printed in the graph output,
 * and 0 otherwise.
 */
static int graph_is_interesting(struct git_graph *graph, struct commit *commit)
{
	/*
	 * If revs->boundary is set, commits whose children have
	 * been shown are always interesting, even if they have the
	 * UNINTERESTING or TREESAME flags set.
	 */
	if (graph->revs && graph->revs->boundary) {
		if (commit->object.flags & CHILD_SHOWN)
			return 1;
	}

	/*
	 * Otherwise, use get_commit_action() to see if this commit is
	 * interesting
	 */
	return get_commit_action(graph->revs, commit) == commit_show;
}

static struct commit_list *next_interesting_parent(struct git_graph *graph,
						   struct commit_list *orig)
{
	struct commit_list *list;

	/*
	 * If revs->first_parent_only is set, only the first
	 * parent is interesting.  None of the others are.
	 */
	if (graph->revs->first_parent_only)
		return NULL;

	/*
	 * Return the next interesting commit after orig
	 */
	for (list = orig->next; list; list = list->next) {
		if (graph_is_interesting(graph, list->item))
			return list;
	}

	return NULL;
}

static struct commit_list *first_interesting_parent(struct git_graph *graph)
{
	struct commit_list *parents = graph->commit->parents;

	/*
	 * If this commit has no parents, ignore it
	 */
	if (!parents)
		return NULL;

	/*
	 * If the first parent is interesting, return it
	 */
	if (graph_is_interesting(graph, parents->item))
		return parents;

	/*
	 * Otherwise, call next_interesting_parent() to get
	 * the next interesting parent
	 */
	return next_interesting_parent(graph, parents);
}

static unsigned short graph_get_current_column_color(const struct git_graph *graph)
{
	if (!want_color(graph->revs->diffopt.use_color))
		return column_colors_max;
	return graph->default_column_color;
}

/*
 * Update the graph's default column color.
 */
static void graph_increment_column_color(struct git_graph *graph)
{
	graph->default_column_color = (graph->default_column_color + 1) %
		column_colors_max;
}

static unsigned short graph_find_commit_color(const struct git_graph *graph,
					      const struct commit *commit)
{
	int i;
	for (i = 0; i < graph->num_columns; i++) {
		if (graph->columns[i].commit == commit)
			return graph->columns[i].color;
	}
	return graph_get_current_column_color(graph);
}

static void graph_insert_into_new_columns(struct git_graph *graph,
					  struct commit *commit,
					  int *mapping_index)
{
	int i;

	/*
	 * If the commit is already in the new_columns list, we don't need to
	 * add it.  Just update the mapping correctly.
	 */
	for (i = 0; i < graph->num_new_columns; i++) {
		if (graph->new_columns[i].commit == commit) {
			graph->mapping[*mapping_index] = i;
			*mapping_index += 2;
			return;
		}
	}

	/*
	 * This commit isn't already in new_columns.  Add it.
	 */
	graph->new_columns[graph->num_new_columns].commit = commit;
	graph->new_columns[graph->num_new_columns].color = graph_find_commit_color(graph, commit);
	graph->mapping[*mapping_index] = graph->num_new_columns;
	*mapping_index += 2;
	graph->num_new_columns++;
}

static void graph_update_width(struct git_graph *graph,
			       int is_commit_in_existing_columns)
{
	/*
	 * Compute the width needed to display the graph for this commit.
	 * This is the maximum width needed for any row.  All other rows
	 * will be padded to this width.
	 *
	 * Compute the number of columns in the widest row:
	 * Count each existing column (graph->num_columns), and each new
	 * column added by this commit.
	 */
	int max_cols = graph->num_columns + graph->num_parents;

	/*
	 * Even if the current commit has no parents to be printed, it
	 * still takes up a column for itself.
	 */
	if (graph->num_parents < 1)
		max_cols++;

	/*
	 * We added a column for the current commit as part of
	 * graph->num_parents.  If the current commit was already in
	 * graph->columns, then we have double counted it.
	 */
	if (is_commit_in_existing_columns)
		max_cols--;

	/*
	 * Each column takes up 2 spaces
	 */
	graph->width = max_cols * 2;
}

static void graph_update_columns(struct git_graph *graph)
{
	struct commit_list *parent;
	struct column *tmp_columns;
	int max_new_columns;
	int mapping_idx;
	int i, seen_this, is_commit_in_columns;

	/*
	 * Swap graph->columns with graph->new_columns
	 * graph->columns contains the state for the previous commit,
	 * and new_columns now contains the state for our commit.
	 *
	 * We'll re-use the old columns array as storage to compute the new
	 * columns list for the commit after this one.
	 */
	tmp_columns = graph->columns;
	graph->columns = graph->new_columns;
	graph->num_columns = graph->num_new_columns;

	graph->new_columns = tmp_columns;
	graph->num_new_columns = 0;

	/*
	 * Now update new_columns and mapping with the information for the
	 * commit after this one.
	 *
	 * First, make sure we have enough room.  At most, there will
	 * be graph->num_columns + graph->num_parents columns for the next
	 * commit.
	 */
	max_new_columns = graph->num_columns + graph->num_parents;
	graph_ensure_capacity(graph, max_new_columns);

	/*
	 * Clear out graph->mapping
	 */
	graph->mapping_size = 2 * max_new_columns;
	for (i = 0; i < graph->mapping_size; i++)
		graph->mapping[i] = -1;

	/*
	 * Populate graph->new_columns and graph->mapping
	 *
	 * Some of the parents of this commit may already be in
	 * graph->columns.  If so, graph->new_columns should only contain a
	 * single entry for each such commit.  graph->mapping should
	 * contain information about where each current branch line is
	 * supposed to end up after the collapsing is performed.
	 */
	seen_this = 0;
	mapping_idx = 0;
	is_commit_in_columns = 1;
	for (i = 0; i <= graph->num_columns; i++) {
		struct commit *col_commit;
		if (i == graph->num_columns) {
			if (seen_this)
				break;
			is_commit_in_columns = 0;
			col_commit = graph->commit;
		} else {
			col_commit = graph->columns[i].commit;
		}

		if (col_commit == graph->commit) {
			int old_mapping_idx = mapping_idx;
			seen_this = 1;
			graph->commit_index = i;
			for (parent = first_interesting_parent(graph);
			     parent;
			     parent = next_interesting_parent(graph, parent)) {
				/*
				 * If this is a merge, or the start of a new
				 * childless column, increment the current
				 * color.
				 */
				if (graph->num_parents > 1 ||
				    !is_commit_in_columns) {
					graph_increment_column_color(graph);
				}
				graph_insert_into_new_columns(graph,
							      parent->item,
							      &mapping_idx);
			}
			/*
			 * We always need to increment mapping_idx by at
			 * least 2, even if it has no interesting parents.
			 * The current commit always takes up at least 2
			 * spaces.
			 */
			if (mapping_idx == old_mapping_idx)
				mapping_idx += 2;
		} else {
			graph_insert_into_new_columns(graph, col_commit,
						      &mapping_idx);
		}
	}

	/*
	 * Shrink mapping_size to be the minimum necessary
	 */
	while (graph->mapping_size > 1 &&
	       graph->mapping[graph->mapping_size - 1] < 0)
		graph->mapping_size--;

	/*
	 * Compute graph->width for this commit
	 */
	graph_update_width(graph, is_commit_in_columns);
}

void graph_update(struct git_graph *graph, struct commit *commit)
{
	struct commit_list *parent;

	/*
	 * Set the new commit
	 */
	graph->commit = commit;

	/*
	 * Count how many interesting parents this commit has
	 */
	graph->num_parents = 0;
	for (parent = first_interesting_parent(graph);
	     parent;
	     parent = next_interesting_parent(graph, parent))
	{
		graph->num_parents++;
	}

	/*
	 * Store the old commit_index in prev_commit_index.
	 * graph_update_columns() will update graph->commit_index for this
	 * commit.
	 */
	graph->prev_commit_index = graph->commit_index;

	/*
	 * Call graph_update_columns() to update
	 * columns, new_columns, and mapping.
	 */
	graph_update_columns(graph);

	graph->expansion_row = 0;

	/*
	 * Update graph->state.
	 * Note that we don't call graph_update_state() here, since
	 * we don't want to update graph->prev_state.  No line for
	 * graph->state was ever printed.
	 *
	 * If the previous commit didn't get to the GRAPH_PADDING state,
	 * it never finished its output.  Goto GRAPH_SKIP, to print out
	 * a line to indicate that portion of the graph is missing.
	 *
	 * If there are 3 or more parents, we may need to print extra rows
	 * before the commit, to expand the branch lines around it and make
	 * room for it.  We need to do this only if there is a branch row
	 * (or more) to the right of this commit.
	 *
	 * If there are less than 3 parents, we can immediately print the
	 * commit line.
	 */
	if (graph->state != GRAPH_PADDING)
		graph->state = GRAPH_SKIP;
	else if (graph->num_parents >= 3 &&
		 graph->commit_index < (graph->num_columns - 1))
		graph->state = GRAPH_PRE_COMMIT;
	else
		graph->state = GRAPH_COMMIT;
}

static int graph_is_mapping_correct(struct git_graph *graph)
{
	int i;

	/*
	 * The mapping is up to date if each entry is at its target,
	 * or is 1 greater than its target.
	 * (If it is 1 greater than the target, '/' will be printed, so it
	 * will look correct on the next row.)
	 */
	for (i = 0; i < graph->mapping_size; i++) {
		int target = graph->mapping[i];
		if (target < 0)
			continue;
		if (target == (i / 2))
			continue;
		return 0;
	}

	return 1;
}

static void graph_pad_horizontally(struct git_graph *graph, struct strbuf *sb,
				   int chars_written)
{
	/*
	 * Add additional spaces to the end of the strbuf, so that all
	 * lines for a particular commit have the same width.
	 *
	 * This way, fields printed to the right of the graph will remain
	 * aligned for the entire commit.
	 */
	int extra;
	if (chars_written >= graph->width)
		return;

	extra = graph->width - chars_written;
	strbuf_addf(sb, "%*s", (int) extra, "");
}

static void graph_output_padding_line(struct git_graph *graph,
				      struct strbuf *sb)
{
	int i;

	/*
	 * We could conceivable be called with a NULL commit
	 * if our caller has a bug, and invokes graph_next_line()
	 * immediately after graph_init(), without first calling
	 * graph_update().  Return without outputting anything in this
	 * case.
	 */
	if (!graph->commit)
		return;

	/*
	 * Output a padding row, that leaves all branch lines unchanged
	 */
	for (i = 0; i < graph->num_new_columns; i++) {
		strbuf_write_column(sb, &graph->new_columns[i], '|');
		strbuf_addch(sb, ' ');
	}

	graph_pad_horizontally(graph, sb, graph->num_new_columns * 2);
}

static void graph_output_skip_line(struct git_graph *graph, struct strbuf *sb)
{
	/*
	 * Output an ellipsis to indicate that a portion
	 * of the graph is missing.
	 */
	strbuf_addstr(sb, "...");
	graph_pad_horizontally(graph, sb, 3);

	if (graph->num_parents >= 3 &&
	    graph->commit_index < (graph->num_columns - 1))
		graph_update_state(graph, GRAPH_PRE_COMMIT);
	else
		graph_update_state(graph, GRAPH_COMMIT);
}

static void graph_output_pre_commit_line(struct git_graph *graph,
					 struct strbuf *sb)
{
	int num_expansion_rows;
	int i, seen_this;
	int chars_written;

	/*
	 * This function formats a row that increases the space around a commit
	 * with multiple parents, to make room for it.  It should only be
	 * called when there are 3 or more parents.
	 *
	 * We need 2 extra rows for every parent over 2.
	 */
	assert(graph->num_parents >= 3);
	num_expansion_rows = (graph->num_parents - 2) * 2;

	/*
	 * graph->expansion_row tracks the current expansion row we are on.
	 * It should be in the range [0, num_expansion_rows - 1]
	 */
	assert(0 <= graph->expansion_row &&
	       graph->expansion_row < num_expansion_rows);

	/*
	 * Output the row
	 */
	seen_this = 0;
	chars_written = 0;
	for (i = 0; i < graph->num_columns; i++) {
		struct column *col = &graph->columns[i];
		if (col->commit == graph->commit) {
			seen_this = 1;
			strbuf_write_column(sb, col, '|');
			strbuf_addf(sb, "%*s", graph->expansion_row, "");
			chars_written += 1 + graph->expansion_row;
		} else if (seen_this && (graph->expansion_row == 0)) {
			/*
			 * This is the first line of the pre-commit output.
			 * If the previous commit was a merge commit and
			 * ended in the GRAPH_POST_MERGE state, all branch
			 * lines after graph->prev_commit_index were
			 * printed as "\" on the previous line.  Continue
			 * to print them as "\" on this line.  Otherwise,
			 * print the branch lines as "|".
			 */
			if (graph->prev_state == GRAPH_POST_MERGE &&
			    graph->prev_commit_index < i)
				strbuf_write_column(sb, col, '\\');
			else
				strbuf_write_column(sb, col, '|');
			chars_written++;
		} else if (seen_this && (graph->expansion_row > 0)) {
			strbuf_write_column(sb, col, '\\');
			chars_written++;
		} else {
			strbuf_write_column(sb, col, '|');
			chars_written++;
		}
		strbuf_addch(sb, ' ');
		chars_written++;
	}

	graph_pad_horizontally(graph, sb, chars_written);

	/*
	 * Increment graph->expansion_row,
	 * and move to state GRAPH_COMMIT if necessary
	 */
	graph->expansion_row++;
	if (graph->expansion_row >= num_expansion_rows)
		graph_update_state(graph, GRAPH_COMMIT);
}

static void graph_output_commit_char(struct git_graph *graph, struct strbuf *sb)
{
	/*
	 * For boundary commits, print 'o'
	 * (We should only see boundary commits when revs->boundary is set.)
	 */
	if (graph->commit->object.flags & BOUNDARY) {
		assert(graph->revs->boundary);
		strbuf_addch(sb, 'o');
		return;
	}

	/*
	 * get_revision_mark() handles all other cases without assert()
	 */
	strbuf_addstr(sb, get_revision_mark(graph->revs, graph->commit));
}

/*
 * Draw an octopus merge and return the number of characters written.
 */
static int graph_draw_octopus_merge(struct git_graph *graph,
				    struct strbuf *sb)
{
	/*
	 * Here dashless_commits represents the number of parents
	 * which don't need to have dashes (because their edges fit
	 * neatly under the commit).
	 */
	const int dashless_commits = 2;
	int col_num, i;
	int num_dashes =
		((graph->num_parents - dashless_commits) * 2) - 1;
	for (i = 0; i < num_dashes; i++) {
		col_num = (i / 2) + dashless_commits + graph->commit_index;
		strbuf_write_column(sb, &graph->new_columns[col_num], '-');
	}
	col_num = (i / 2) + dashless_commits + graph->commit_index;
	strbuf_write_column(sb, &graph->new_columns[col_num], '.');
	return num_dashes + 1;
}

static void graph_output_commit_line(struct git_graph *graph, struct strbuf *sb)
{
	int seen_this = 0;
	int i, chars_written;

	/*
	 * Output the row containing this commit
	 * Iterate up to and including graph->num_columns,
	 * since the current commit may not be in any of the existing
	 * columns.  (This happens when the current commit doesn't have any
	 * children that we have already processed.)
	 */
	seen_this = 0;
	chars_written = 0;
	for (i = 0; i <= graph->num_columns; i++) {
		struct column *col = &graph->columns[i];
		struct commit *col_commit;
		if (i == graph->num_columns) {
			if (seen_this)
				break;
			col_commit = graph->commit;
		} else {
			col_commit = graph->columns[i].commit;
		}

		if (col_commit == graph->commit) {
			seen_this = 1;
			graph_output_commit_char(graph, sb);
			chars_written++;

			if (graph->num_parents > 2)
				chars_written += graph_draw_octopus_merge(graph,
									  sb);
		} else if (seen_this && (graph->num_parents > 2)) {
			strbuf_write_column(sb, col, '\\');
			chars_written++;
		} else if (seen_this && (graph->num_parents == 2)) {
			/*
			 * This is a 2-way merge commit.
			 * There is no GRAPH_PRE_COMMIT stage for 2-way
			 * merges, so this is the first line of output
			 * for this commit.  Check to see what the previous
			 * line of output was.
			 *
			 * If it was GRAPH_POST_MERGE, the branch line
			 * coming into this commit may have been '\',
			 * and not '|' or '/'.  If so, output the branch
			 * line as '\' on this line, instead of '|'.  This
			 * makes the output look nicer.
			 */
			if (graph->prev_state == GRAPH_POST_MERGE &&
			    graph->prev_commit_index < i)
				strbuf_write_column(sb, col, '\\');
			else
				strbuf_write_column(sb, col, '|');
			chars_written++;
		} else {
			strbuf_write_column(sb, col, '|');
			chars_written++;
		}
		strbuf_addch(sb, ' ');
		chars_written++;
	}

	graph_pad_horizontally(graph, sb, chars_written);

	/*
	 * Update graph->state
	 */
	if (graph->num_parents > 1)
		graph_update_state(graph, GRAPH_POST_MERGE);
	else if (graph_is_mapping_correct(graph))
		graph_update_state(graph, GRAPH_PADDING);
	else
		graph_update_state(graph, GRAPH_COLLAPSING);
}

static struct column *find_new_column_by_commit(struct git_graph *graph,
						struct commit *commit)
{
	int i;
	for (i = 0; i < graph->num_new_columns; i++) {
		if (graph->new_columns[i].commit == commit)
			return &graph->new_columns[i];
	}
	return NULL;
}

static void graph_output_post_merge_line(struct git_graph *graph, struct strbuf *sb)
{
	int seen_this = 0;
	int i, j, chars_written;

	/*
	 * Output the post-merge row
	 */
	chars_written = 0;
	for (i = 0; i <= graph->num_columns; i++) {
		struct column *col = &graph->columns[i];
		struct commit *col_commit;
		if (i == graph->num_columns) {
			if (seen_this)
				break;
			col_commit = graph->commit;
		} else {
			col_commit = col->commit;
		}

		if (col_commit == graph->commit) {
			/*
			 * Since the current commit is a merge find
			 * the columns for the parent commits in
			 * new_columns and use those to format the
			 * edges.
			 */
			struct commit_list *parents = NULL;
			struct column *par_column;
			seen_this = 1;
			parents = first_interesting_parent(graph);
			assert(parents);
			par_column = find_new_column_by_commit(graph, parents->item);
			assert(par_column);

			strbuf_write_column(sb, par_column, '|');
			chars_written++;
			for (j = 0; j < graph->num_parents - 1; j++) {
				parents = next_interesting_parent(graph, parents);
				assert(parents);
				par_column = find_new_column_by_commit(graph, parents->item);
				assert(par_column);
				strbuf_write_column(sb, par_column, '\\');
				strbuf_addch(sb, ' ');
			}
			chars_written += j * 2;
		} else if (seen_this) {
			strbuf_write_column(sb, col, '\\');
			strbuf_addch(sb, ' ');
			chars_written += 2;
		} else {
			strbuf_write_column(sb, col, '|');
			strbuf_addch(sb, ' ');
			chars_written += 2;
		}
	}

	graph_pad_horizontally(graph, sb, chars_written);

	/*
	 * Update graph->state
	 */
	if (graph_is_mapping_correct(graph))
		graph_update_state(graph, GRAPH_PADDING);
	else
		graph_update_state(graph, GRAPH_COLLAPSING);
}

static void graph_output_collapsing_line(struct git_graph *graph, struct strbuf *sb)
{
	int i;
	int *tmp_mapping;
	short used_horizontal = 0;
	int horizontal_edge = -1;
	int horizontal_edge_target = -1;

	/*
	 * Clear out the new_mapping array
	 */
	for (i = 0; i < graph->mapping_size; i++)
		graph->new_mapping[i] = -1;

	for (i = 0; i < graph->mapping_size; i++) {
		int target = graph->mapping[i];
		if (target < 0)
			continue;

		/*
		 * Since update_columns() always inserts the leftmost
		 * column first, each branch's target location should
		 * always be either its current location or to the left of
		 * its current location.
		 *
		 * We never have to move branches to the right.  This makes
		 * the graph much more legible, since whenever branches
		 * cross, only one is moving directions.
		 */
		assert(target * 2 <= i);

		if (target * 2 == i) {
			/*
			 * This column is already in the
			 * correct place
			 */
			assert(graph->new_mapping[i] == -1);
			graph->new_mapping[i] = target;
		} else if (graph->new_mapping[i - 1] < 0) {
			/*
			 * Nothing is to the left.
			 * Move to the left by one
			 */
			graph->new_mapping[i - 1] = target;
			/*
			 * If there isn't already an edge moving horizontally
			 * select this one.
			 */
			if (horizontal_edge == -1) {
				int j;
				horizontal_edge = i;
				horizontal_edge_target = target;
				/*
				 * The variable target is the index of the graph
				 * column, and therefore target*2+3 is the
				 * actual screen column of the first horizontal
				 * line.
				 */
				for (j = (target * 2)+3; j < (i - 2); j += 2)
					graph->new_mapping[j] = target;
			}
		} else if (graph->new_mapping[i - 1] == target) {
			/*
			 * There is a branch line to our left
			 * already, and it is our target.  We
			 * combine with this line, since we share
			 * the same parent commit.
			 *
			 * We don't have to add anything to the
			 * output or new_mapping, since the
			 * existing branch line has already taken
			 * care of it.
			 */
		} else {
			/*
			 * There is a branch line to our left,
			 * but it isn't our target.  We need to
			 * cross over it.
			 *
			 * The space just to the left of this
			 * branch should always be empty.
			 *
			 * The branch to the left of that space
			 * should be our eventual target.
			 */
			assert(graph->new_mapping[i - 1] > target);
			assert(graph->new_mapping[i - 2] < 0);
			assert(graph->new_mapping[i - 3] == target);
			graph->new_mapping[i - 2] = target;
			/*
			 * Mark this branch as the horizontal edge to
			 * prevent any other edges from moving
			 * horizontally.
			 */
			if (horizontal_edge == -1)
				horizontal_edge = i;
		}
	}

	/*
	 * The new mapping may be 1 smaller than the old mapping
	 */
	if (graph->new_mapping[graph->mapping_size - 1] < 0)
		graph->mapping_size--;

	/*
	 * Output out a line based on the new mapping info
	 */
	for (i = 0; i < graph->mapping_size; i++) {
		int target = graph->new_mapping[i];
		if (target < 0)
			strbuf_addch(sb, ' ');
		else if (target * 2 == i)
			strbuf_write_column(sb, &graph->new_columns[target], '|');
		else if (target == horizontal_edge_target &&
			 i != horizontal_edge - 1) {
				/*
				 * Set the mappings for all but the
				 * first segment to -1 so that they
				 * won't continue into the next line.
				 */
				if (i != (target * 2)+3)
					graph->new_mapping[i] = -1;
				used_horizontal = 1;
			strbuf_write_column(sb, &graph->new_columns[target], '_');
		} else {
			if (used_horizontal && i < horizontal_edge)
				graph->new_mapping[i] = -1;
			strbuf_write_column(sb, &graph->new_columns[target], '/');

		}
	}

	graph_pad_horizontally(graph, sb, graph->mapping_size);

	/*
	 * Swap mapping and new_mapping
	 */
	tmp_mapping = graph->mapping;
	graph->mapping = graph->new_mapping;
	graph->new_mapping = tmp_mapping;

	/*
	 * If graph->mapping indicates that all of the branch lines
	 * are already in the correct positions, we are done.
	 * Otherwise, we need to collapse some branch lines together.
	 */
	if (graph_is_mapping_correct(graph))
		graph_update_state(graph, GRAPH_PADDING);
}

int graph_next_line(struct git_graph *graph, struct strbuf *sb)
{
	switch (graph->state) {
	case GRAPH_PADDING:
		graph_output_padding_line(graph, sb);
		return 0;
	case GRAPH_SKIP:
		graph_output_skip_line(graph, sb);
		return 0;
	case GRAPH_PRE_COMMIT:
		graph_output_pre_commit_line(graph, sb);
		return 0;
	case GRAPH_COMMIT:
		graph_output_commit_line(graph, sb);
		return 1;
	case GRAPH_POST_MERGE:
		graph_output_post_merge_line(graph, sb);
		return 0;
	case GRAPH_COLLAPSING:
		graph_output_collapsing_line(graph, sb);
		return 0;
	}

	assert(0);
	return 0;
}

static void graph_padding_line(struct git_graph *graph, struct strbuf *sb)
{
	int i;

	if (graph->state != GRAPH_COMMIT) {
		graph_next_line(graph, sb);
		return;
	}

	/*
	 * Output the row containing this commit
	 * Iterate up to and including graph->num_columns,
	 * since the current commit may not be in any of the existing
	 * columns.  (This happens when the current commit doesn't have any
	 * children that we have already processed.)
	 */
	for (i = 0; i < graph->num_columns; i++) {
		struct column *col = &graph->columns[i];
		strbuf_write_column(sb, col, '|');
		if (col->commit == graph->commit && graph->num_parents > 2)
			strbuf_addchars(sb, ' ', (graph->num_parents - 2) * 2);
		else
			strbuf_addch(sb, ' ');
	}

	graph_pad_horizontally(graph, sb, graph->num_columns);

	/*
	 * Update graph->prev_state since we have output a padding line
	 */
	graph->prev_state = GRAPH_PADDING;
}

int graph_is_commit_finished(struct git_graph const *graph)
{
	return (graph->state == GRAPH_PADDING);
}

void graph_show_commit(struct git_graph *graph)
{
	struct strbuf msgbuf = STRBUF_INIT;
	int shown_commit_line = 0;

	if (!graph)
		return;

	/*
	 * When showing a diff of a merge against each of its parents, we
	 * are called once for each parent without graph_update having been
	 * called.  In this case, simply output a single padding line.
	 */
	if (graph_is_commit_finished(graph)) {
		graph_show_padding(graph);
		shown_commit_line = 1;
	}

	while (!shown_commit_line && !graph_is_commit_finished(graph)) {
		shown_commit_line = graph_next_line(graph, &msgbuf);
		fwrite(msgbuf.buf, sizeof(char), msgbuf.len, stdout);
		if (!shown_commit_line)
			putchar('\n');
		strbuf_setlen(&msgbuf, 0);
	}

	strbuf_release(&msgbuf);
}

void graph_show_oneline(struct git_graph *graph)
{
	struct strbuf msgbuf = STRBUF_INIT;

	if (!graph)
		return;

	graph_next_line(graph, &msgbuf);
	fwrite(msgbuf.buf, sizeof(char), msgbuf.len, stdout);
	strbuf_release(&msgbuf);
}

void graph_show_padding(struct git_graph *graph)
{
	struct strbuf msgbuf = STRBUF_INIT;

	if (!graph)
		return;

	graph_padding_line(graph, &msgbuf);
	fwrite(msgbuf.buf, sizeof(char), msgbuf.len, stdout);
	strbuf_release(&msgbuf);
}

int graph_show_remainder(struct git_graph *graph)
{
	struct strbuf msgbuf = STRBUF_INIT;
	int shown = 0;

	if (!graph)
		return 0;

	if (graph_is_commit_finished(graph))
		return 0;

	for (;;) {
		graph_next_line(graph, &msgbuf);
		fwrite(msgbuf.buf, sizeof(char), msgbuf.len, stdout);
		strbuf_setlen(&msgbuf, 0);
		shown = 1;

		if (!graph_is_commit_finished(graph))
			putchar('\n');
		else
			break;
	}
	strbuf_release(&msgbuf);

	return shown;
}


static void graph_show_strbuf(struct git_graph *graph, struct strbuf const *sb)
{
	char *p;

	if (!graph) {
		fwrite(sb->buf, sizeof(char), sb->len, stdout);
		return;
	}

	/*
	 * Print the strbuf line by line,
	 * and display the graph info before each line but the first.
	 */
	p = sb->buf;
	while (p) {
		size_t len;
		char *next_p = strchr(p, '\n');
		if (next_p) {
			next_p++;
			len = next_p - p;
		} else {
			len = (sb->buf + sb->len) - p;
		}
		fwrite(p, sizeof(char), len, stdout);
		if (next_p && *next_p != '\0')
			graph_show_oneline(graph);
		p = next_p;
	}
}

void graph_show_commit_msg(struct git_graph *graph,
			   struct strbuf const *sb)
{
	int newline_terminated;

	if (!graph) {
		/*
		 * If there's no graph, just print the message buffer.
		 *
		 * The message buffer for CMIT_FMT_ONELINE and
		 * CMIT_FMT_USERFORMAT are already missing a terminating
		 * newline.  All of the other formats should have it.
		 */
		fwrite(sb->buf, sizeof(char), sb->len, stdout);
		return;
	}

	newline_terminated = (sb->len && sb->buf[sb->len - 1] == '\n');

	/*
	 * Show the commit message
	 */
	graph_show_strbuf(graph, sb);

	/*
	 * If there is more output needed for this commit, show it now
	 */
	if (!graph_is_commit_finished(graph)) {
		/*
		 * If sb doesn't have a terminating newline, print one now,
		 * so we can start the remainder of the graph output on a
		 * new line.
		 */
		if (!newline_terminated)
			putchar('\n');

		graph_show_remainder(graph);

		/*
		 * If sb ends with a newline, our output should too.
		 */
		if (newline_terminated)
			putchar('\n');
	}
}