DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

Header

Untracked file

Line Code
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 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560 1561 1562 1563 1564 1565 1566 1567 1568 1569 1570 1571 1572 1573 1574 1575 1576 1577 1578 1579 1580 1581 1582 1583 1584 1585 1586 1587 1588 1589 1590 1591 1592 1593 1594 1595 1596 1597 1598 1599 1600 1601 1602 1603 1604 1605 1606 1607 1608 1609 1610 1611 1612 1613 1614 1615 1616 1617 1618 1619 1620 1621 1622 1623 1624 1625 1626 1627 1628 1629 1630 1631 1632 1633 1634 1635 1636 1637 1638 1639 1640 1641 1642 1643 1644 1645 1646 1647 1648 1649 1650 1651 1652 1653 1654 1655 1656 1657 1658 1659 1660 1661 1662 1663 1664 1665 1666 1667 1668 1669 1670 1671 1672 1673 1674 1675 1676 1677 1678 1679 1680 1681 1682 1683 1684 1685 1686 1687 1688 1689 1690 1691 1692 1693 1694 1695 1696 1697 1698 1699 1700 1701 1702 1703 1704 1705 1706 1707 1708 1709 1710 1711 1712 1713 1714 1715 1716 1717 1718 1719 1720 1721 1722 1723 1724 1725 1726 1727 1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743 1744 1745 1746 1747 1748 1749 1750 1751 1752 1753 1754 1755 1756 1757 1758 1759 1760 1761 1762 1763 1764 1765 1766 1767 1768 1769 1770 1771 1772 1773 1774 1775 1776 1777 1778 1779 1780 1781 1782 1783 1784 1785 1786 1787 1788 1789 1790 1791 1792 1793 1794 1795 1796 1797 1798 1799 1800 1801 1802 1803
/* Libart_LGPL - library of basic graphic primitives
 * Copyright (C) 2001 Raph Levien
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

/* This file contains a testbed implementation of the new intersection
   code.
*/

#include "config.h"
#include "art_svp_intersect.h"

#include <math.h> /* for sqrt */

/* Sanitychecking verifies the main invariant on every priority queue
   point. Do not use in production, as it slows things down way too
   much. */
#define noSANITYCHECK

/* This can be used in production, to prevent hangs. Eventually, it
   should not be necessary. */
#define CHEAP_SANITYCHECK

#define noVERBOSE

#include "art_misc.h"

/* A priority queue - perhaps move to a separate file if it becomes
   needed somewhere else */

#define ART_PRIQ_USE_HEAP

typedef struct _ArtPriQ ArtPriQ;
typedef struct _ArtPriPoint ArtPriPoint;

struct _ArtPriQ {
  int n_items;
  int n_items_max;
  ArtPriPoint **items;
};

struct _ArtPriPoint {
  double x;
  double y;
  void *user_data;
};

static ArtPriQ *
art_pri_new (void)
{
  ArtPriQ *result = art_new (ArtPriQ, 1);

  result->n_items = 0;
  result->n_items_max = 16;
  result->items = art_new (ArtPriPoint *, result->n_items_max);
  return result;
}

static void
art_pri_free (ArtPriQ *pq)
{
  art_free (pq->items);
  art_free (pq);
}

static art_boolean
art_pri_empty (ArtPriQ *pq)
{
  return pq->n_items == 0;
}

#ifdef ART_PRIQ_USE_HEAP

/* This heap implementation is based on Vasek Chvatal's course notes:
   http://www.cs.rutgers.edu/~chvatal/notes/pq.html#heap */

static void
art_pri_bubble_up (ArtPriQ *pq, int vacant, ArtPriPoint *missing)
{
  ArtPriPoint **items = pq->items;
  int parent;

  parent = (vacant - 1) >> 1;
  while (vacant > 0 && (missing->y < items[parent]->y ||
			(missing->y == items[parent]->y &&
			 missing->x < items[parent]->x)))
    {
      items[vacant] = items[parent];
      vacant = parent;
      parent = (vacant - 1) >> 1;
    }

  items[vacant] = missing;
}

static void
art_pri_insert (ArtPriQ *pq, ArtPriPoint *point)
{
  if (pq->n_items == pq->n_items_max)
    art_expand (pq->items, ArtPriPoint *, pq->n_items_max);

  art_pri_bubble_up (pq, pq->n_items++, point);
}

static void
art_pri_sift_down_from_root (ArtPriQ *pq, ArtPriPoint *missing)
{
  ArtPriPoint **items = pq->items;
  int vacant = 0, child = 2;
  int n = pq->n_items;

  while (child < n)
    {
      if (items[child - 1]->y < items[child]->y ||
	  (items[child - 1]->y == items[child]->y &&
	   items[child - 1]->x < items[child]->x))
	child--;
      items[vacant] = items[child];
      vacant = child;
      child = (vacant + 1) << 1;
    }
  if (child == n)
    {
      items[vacant] = items[n - 1];
      vacant = n - 1;
    }

  art_pri_bubble_up (pq, vacant, missing);
}

static ArtPriPoint *
art_pri_choose (ArtPriQ *pq)
{
  ArtPriPoint *result = pq->items[0];

  art_pri_sift_down_from_root (pq, pq->items[--pq->n_items]);
  return result;
}

#else

/* Choose least point in queue */
static ArtPriPoint *
art_pri_choose (ArtPriQ *pq)
{
  int i;
  int best = 0;
  double best_x, best_y;
  double y;
  ArtPriPoint *result;

  if (pq->n_items == 0)
    return NULL;

  best_x = pq->items[best]->x;
  best_y = pq->items[best]->y;

  for (i = 1; i < pq->n_items; i++)
    {
      y = pq->items[i]->y;
      if (y < best_y || (y == best_y && pq->items[i]->x < best_x))
	{
	  best = i;
	  best_x = pq->items[best]->x;
	  best_y = y;
	}
    }
  result = pq->items[best];
  pq->items[best] = pq->items[--pq->n_items];
  return result;
}

static void
art_pri_insert (ArtPriQ *pq, ArtPriPoint *point)
{
  if (pq->n_items == pq->n_items_max)
    art_expand (pq->items, ArtPriPoint *, pq->n_items_max);

  pq->items[pq->n_items++] = point;
}

#endif

#ifdef TEST_PRIQ

#include <stdlib.h> /* for rand() */
#include <stdio.h>

static double
double_rand (double lo, double hi, int quant)
{
  int tmp = rand () / (RAND_MAX * (1.0 / quant)) + 0.5;
  return lo + tmp * ((hi - lo) / quant);
}

/*
 * This custom allocator for priority queue points is here so I can
 * test speed. It doesn't look like it will be that significant, but
 * if I want a small improvement later, it's something.
 */

typedef ArtPriPoint *ArtPriPtPool;

static ArtPriPtPool *
art_pri_pt_pool_new (void)
{
  ArtPriPtPool *result = art_new (ArtPriPtPool, 1);
  *result = NULL;
  return result;
}

static ArtPriPoint *
art_pri_pt_alloc (ArtPriPtPool *pool)
{
  ArtPriPoint *result = *pool;
  if (result == NULL)
    return art_new (ArtPriPoint, 1);
  else
    {
      *pool = result->user_data;
      return result;
    }
}

static void
art_pri_pt_free (ArtPriPtPool *pool, ArtPriPoint *pt)
{
  pt->user_data = *pool;
  *pool = pt;
}

static void
art_pri_pt_pool_free (ArtPriPtPool *pool)
{
  ArtPriPoint *pt = *pool;
  while (pt != NULL)
    {
      ArtPriPoint *next = pt->user_data;
      art_free (pt);
      pt = next;
    }
  art_free (pool);
}

int
main (int argc, char **argv)
{
  ArtPriPtPool *pool = art_pri_pt_pool_new ();
  ArtPriQ *pq;
  int i, j;
  const int n_iter = 1;
  const int pq_size = 100;

  for (j = 0; j < n_iter; j++)
    {
      pq = art_pri_new ();

      for (i = 0; i < pq_size; i++)
	{
	  ArtPriPoint *pt = art_pri_pt_alloc (pool);
	  pt->x = double_rand (0, 1, 100);
	  pt->y = double_rand (0, 1, 100);
	  pt->user_data = (void *)i;
	  art_pri_insert (pq, pt);
	}

      while (!art_pri_empty (pq))
	{
	  ArtPriPoint *pt = art_pri_choose (pq);
	  if (n_iter == 1)
	    printf ("(%g, %g), %d\n", pt->x, pt->y, (int)pt->user_data);
	  art_pri_pt_free (pool, pt);
	}

      art_pri_free (pq);
    }
  art_pri_pt_pool_free (pool);
  return 0;
}

#else /* TEST_PRIQ */

/* A virtual class for an "svp writer". A client of this object creates an
   SVP by repeatedly calling "add segment" and "add point" methods on it.
*/

typedef struct _ArtSvpWriterRewind ArtSvpWriterRewind;

/* An implementation of the svp writer virtual class that applies the
   winding rule. */

struct _ArtSvpWriterRewind {
  ArtSvpWriter super;
  ArtWindRule rule;
  ArtSVP *svp;
  int n_segs_max;
  int *n_points_max;
};

static int
art_svp_writer_rewind_add_segment (ArtSvpWriter *self, int wind_left,
				   int delta_wind, double x, double y)
{
  ArtSvpWriterRewind *swr = (ArtSvpWriterRewind *)self;
  ArtSVP *svp;
  ArtSVPSeg *seg;
  art_boolean left_filled, right_filled;
  int wind_right = wind_left + delta_wind;
  int seg_num;
  const int init_n_points_max = 4;

  switch (swr->rule)
    {
    case ART_WIND_RULE_NONZERO:
      left_filled = (wind_left != 0);
      right_filled = (wind_right != 0);
      break;
    case ART_WIND_RULE_INTERSECT:
      left_filled = (wind_left > 1);
      right_filled = (wind_right > 1);
      break;
    case ART_WIND_RULE_ODDEVEN:
      left_filled = (wind_left & 1);
      right_filled = (wind_right & 1);
      break;
    case ART_WIND_RULE_POSITIVE:
      left_filled = (wind_left > 0);
      right_filled = (wind_right > 0);
      break;
    default:
      art_die ("Unknown wind rule %d\n", swr->rule);
    }
  if (left_filled == right_filled)
    {
      /* discard segment now */
#ifdef VERBOSE
      art_dprint ("swr add_segment: %d += %d (%g, %g) --> -1\n",
	      wind_left, delta_wind, x, y);
#endif
      return -1;
   }

  svp = swr->svp;
  seg_num = svp->n_segs++;
  if (swr->n_segs_max == seg_num)
    {
      swr->n_segs_max <<= 1;
      svp = (ArtSVP *)art_realloc (svp, sizeof(ArtSVP) +
				   (swr->n_segs_max - 1) *
				   sizeof(ArtSVPSeg));
      swr->svp = svp;
      swr->n_points_max = art_renew (swr->n_points_max, int,
				     swr->n_segs_max);
    }
  seg = &svp->segs[seg_num];
  seg->n_points = 1;
  seg->dir = right_filled;
  swr->n_points_max[seg_num] = init_n_points_max;
  seg->bbox.x0 = x;
  seg->bbox.y0 = y;
  seg->bbox.x1 = x;
  seg->bbox.y1 = y;
  seg->points = art_new (ArtPoint, init_n_points_max);
  seg->points[0].x = x;
  seg->points[0].y = y;
#ifdef VERBOSE
    art_dprint ("swr add_segment: %d += %d (%g, %g) --> %d(%s)\n",
	    wind_left, delta_wind, x, y, seg_num,
	    seg->dir ? "v" : "^");
#endif
  return seg_num;
}

static void
art_svp_writer_rewind_add_point (ArtSvpWriter *self, int seg_id,
				 double x, double y)
{
  ArtSvpWriterRewind *swr = (ArtSvpWriterRewind *)self;
  ArtSVPSeg *seg;
  int n_points;

#ifdef VERBOSE
  art_dprint ("swr add_point: %d (%g, %g)\n", seg_id, x, y);
#endif
  if (seg_id < 0)
    /* omitted segment */
    return;

  seg = &swr->svp->segs[seg_id];
  n_points = seg->n_points++;
  if (swr->n_points_max[seg_id] == n_points)
    art_expand (seg->points, ArtPoint, swr->n_points_max[seg_id]);
  seg->points[n_points].x = x;
  seg->points[n_points].y = y;
  if (x < seg->bbox.x0)
    seg->bbox.x0 = x;
  if (x > seg->bbox.x1)
    seg->bbox.x1 = x;
  seg->bbox.y1 = y;
}

static void
art_svp_writer_rewind_close_segment (ArtSvpWriter *self, int seg_id)
{
  /* Not needed for this simple implementation. A potential future
     optimization is to merge segments that can be merged safely. */
#ifdef SANITYCHECK
  ArtSvpWriterRewind *swr = (ArtSvpWriterRewind *)self;
  ArtSVPSeg *seg;

  if (seg_id >= 0)
    {
      seg = &swr->svp->segs[seg_id];
      if (seg->n_points < 2)
	art_warn ("*** closing segment %d with only %d point%s\n",
		  seg_id, seg->n_points, seg->n_points == 1 ? "" : "s");
    }
#endif

#ifdef VERBOSE
  art_dprint ("swr close_segment: %d\n", seg_id);
#endif
}

ArtSVP *
art_svp_writer_rewind_reap (ArtSvpWriter *self)
{
  ArtSvpWriterRewind *swr = (ArtSvpWriterRewind *)self;
  ArtSVP *result = swr->svp;

  art_free (swr->n_points_max);
  art_free (swr);
  return result;
}

ArtSvpWriter *
art_svp_writer_rewind_new (ArtWindRule rule)
{
  ArtSvpWriterRewind *result = art_new (ArtSvpWriterRewind, 1);

  result->super.add_segment = art_svp_writer_rewind_add_segment;
  result->super.add_point = art_svp_writer_rewind_add_point;
  result->super.close_segment = art_svp_writer_rewind_close_segment;

  result->rule = rule;
  result->n_segs_max = 16;
  result->svp = art_alloc (sizeof(ArtSVP) + 
			   (result->n_segs_max - 1) * sizeof(ArtSVPSeg));
  result->svp->n_segs = 0;
  result->n_points_max = art_new (int, result->n_segs_max);

  return &result->super;
}

/* Now, data structures for the active list */

typedef struct _ArtActiveSeg ArtActiveSeg;

/* Note: BNEG is 1 for \ lines, and 0 for /. Thus,
   x[(flags & BNEG) ^ 1] <= x[flags & BNEG] */
#define ART_ACTIVE_FLAGS_BNEG 1

/* This flag is set if the segment has been inserted into the active
   list. */
#define ART_ACTIVE_FLAGS_IN_ACTIVE 2

/* This flag is set when the segment is to be deleted in the
   horiz commit process. */
#define ART_ACTIVE_FLAGS_DEL 4

/* This flag is set if the seg_id is a valid output segment. */
#define ART_ACTIVE_FLAGS_OUT 8

/* This flag is set if the segment is in the horiz list. */
#define ART_ACTIVE_FLAGS_IN_HORIZ 16

struct _ArtActiveSeg {
  int flags;
  int wind_left, delta_wind;
  ArtActiveSeg *left, *right; /* doubly linked list structure */

  const ArtSVPSeg *in_seg;
  int in_curs;

  double x[2];
  double y0, y1;
  double a, b, c; /* line equation; ax+by+c = 0 for the line, a^2 + b^2 = 1,
		     and a>0 */

  /* bottom point and intersection point stack */
  int n_stack;
  int n_stack_max;
  ArtPoint *stack;

  /* horiz commit list */
  ArtActiveSeg *horiz_left, *horiz_right;
  double horiz_x;
  int horiz_delta_wind;
  int seg_id;
};

typedef struct _ArtIntersectCtx ArtIntersectCtx;

struct _ArtIntersectCtx {
  const ArtSVP *in;
  ArtSvpWriter *out;

  ArtPriQ *pq;

  ArtActiveSeg *active_head;

  double y;
  ArtActiveSeg *horiz_first;
  ArtActiveSeg *horiz_last;

  /* segment index of next input segment to be added to pri q */
  int in_curs;
};

#define EPSILON_A 1e-5 /* Threshold for breaking lines at point insertions */

/**
 * art_svp_intersect_setup_seg: Set up an active segment from input segment.
 * @seg: Active segment.
 * @pri_pt: Priority queue point to initialize.
 *
 * Sets the x[], a, b, c, flags, and stack fields according to the
 * line from the current cursor value. Sets the priority queue point
 * to the bottom point of this line. Also advances the input segment
 * cursor.
 **/
static void
art_svp_intersect_setup_seg (ArtActiveSeg *seg, ArtPriPoint *pri_pt)
{
  const ArtSVPSeg *in_seg = seg->in_seg;
  int in_curs = seg->in_curs++;
  double x0, y0, x1, y1;
  double dx, dy, s;
  double a, b, r2;

  x0 = in_seg->points[in_curs].x;
  y0 = in_seg->points[in_curs].y;
  x1 = in_seg->points[in_curs + 1].x;
  y1 = in_seg->points[in_curs + 1].y;
  pri_pt->x = x1;
  pri_pt->y = y1;
  dx = x1 - x0;
  dy = y1 - y0;
  r2 = dx * dx + dy * dy;
  s = r2 == 0 ? 1 : 1 / sqrt (r2);
  seg->a = a = dy * s;
  seg->b = b = -dx * s;
  seg->c = -(a * x0 + b * y0);
  seg->flags = (seg->flags & ~ART_ACTIVE_FLAGS_BNEG) | (dx > 0);
  seg->x[0] = x0;
  seg->x[1] = x1;
  seg->y0 = y0;
  seg->y1 = y1;
  seg->n_stack = 1;
  seg->stack[0].x = x1;
  seg->stack[0].y = y1;
}

/**
 * art_svp_intersect_add_horiz: Add point to horizontal list.
 * @ctx: Intersector context.
 * @seg: Segment with point to insert into horizontal list.
 *
 * Inserts @seg into horizontal list, keeping it in ascending horiz_x
 * order.
 *
 * Note: the horiz_commit routine processes "clusters" of segs in the
 * horiz list, all sharing the same horiz_x value. The cluster is
 * processed in active list order, rather than horiz list order. Thus,
 * the order of segs in the horiz list sharing the same horiz_x
 * _should_ be irrelevant. Even so, we use b as a secondary sorting key,
 * as a "belt and suspenders" defensive coding tactic.
 **/
static void
art_svp_intersect_add_horiz (ArtIntersectCtx *ctx, ArtActiveSeg *seg)
{
  ArtActiveSeg **pp = &ctx->horiz_last;
  ArtActiveSeg *place;
  ArtActiveSeg *place_right = NULL;


#ifdef CHEAP_SANITYCHECK
  if (seg->flags & ART_ACTIVE_FLAGS_IN_HORIZ)
    {
      art_warn ("*** attempt to put segment in horiz list twice\n");
      return;
    }
  seg->flags |= ART_ACTIVE_FLAGS_IN_HORIZ;
#endif

#ifdef VERBOSE
  art_dprint ("add_horiz %lx, x = %g\n", (unsigned long) seg, seg->horiz_x);
#endif
  for (place = *pp; place != NULL && (place->horiz_x > seg->horiz_x ||
				      (place->horiz_x == seg->horiz_x &&
				       place->b < seg->b));
       place = *pp)
    {
      place_right = place;
      pp = &place->horiz_left;
    }
  *pp = seg;
  seg->horiz_left = place;
  seg->horiz_right = place_right;
  if (place == NULL)
    ctx->horiz_first = seg;
  else
    place->horiz_right = seg;
}

static void
art_svp_intersect_push_pt (ArtIntersectCtx *ctx, ArtActiveSeg *seg,
			   double x, double y)
{
  ArtPriPoint *pri_pt;
  int n_stack = seg->n_stack;

  if (n_stack == seg->n_stack_max)
    art_expand (seg->stack, ArtPoint, seg->n_stack_max);
  seg->stack[n_stack].x = x;
  seg->stack[n_stack].y = y;
  seg->n_stack++;

  seg->x[1] = x;
  seg->y1 = y;

  pri_pt = art_new (ArtPriPoint, 1);
  pri_pt->x = x;
  pri_pt->y = y;
  pri_pt->user_data = seg;
  art_pri_insert (ctx->pq, pri_pt);
}

typedef enum {
  ART_BREAK_LEFT = 1,
  ART_BREAK_RIGHT = 2
} ArtBreakFlags;

/**
 * art_svp_intersect_break: Break an active segment.
 *
 * Note: y must be greater than the top point's y, and less than
 * the bottom's.
 *
 * Return value: x coordinate of break point.
 */
static double
art_svp_intersect_break (ArtIntersectCtx *ctx, ArtActiveSeg *seg,
			 double x_ref, double y, ArtBreakFlags break_flags)
{
  double x0, y0, x1, y1;
  const ArtSVPSeg *in_seg = seg->in_seg;
  int in_curs = seg->in_curs;
  double x;

  x0 = in_seg->points[in_curs - 1].x;
  y0 = in_seg->points[in_curs - 1].y;
  x1 = in_seg->points[in_curs].x;
  y1 = in_seg->points[in_curs].y;
  x = x0 + (x1 - x0) * ((y - y0) / (y1 - y0));
  if ((break_flags == ART_BREAK_LEFT && x > x_ref) ||
      (break_flags == ART_BREAK_RIGHT && x < x_ref))
    {
#ifdef VERBOSE
      art_dprint ("art_svp_intersect_break: limiting x to %f, was %f, %s\n",
		  x_ref, x, break_flags == ART_BREAK_LEFT ? "left" : "right");
      x = x_ref;
#endif
    }

  /* I think we can count on min(x0, x1) <= x <= max(x0, x1) with sane
     arithmetic, but it might be worthwhile to check just in case. */

  if (y > ctx->y)
    art_svp_intersect_push_pt (ctx, seg, x, y);
  else
    {
      seg->x[0] = x;
      seg->y0 = y;
      seg->horiz_x = x;
      art_svp_intersect_add_horiz (ctx, seg);
    }

  return x;
}

/**
 * art_svp_intersect_add_point: Add a point, breaking nearby neighbors.
 * @ctx: Intersector context.
 * @x: X coordinate of point to add.
 * @y: Y coordinate of point to add.
 * @seg: "nearby" segment, or NULL if leftmost.
 *
 * Return value: Segment immediately to the left of the new point, or
 * NULL if the new point is leftmost.
 **/
static ArtActiveSeg *
art_svp_intersect_add_point (ArtIntersectCtx *ctx, double x, double y,
			     ArtActiveSeg *seg, ArtBreakFlags break_flags)
{
  ArtActiveSeg *left, *right;
  double x_min = x, x_max = x;
  art_boolean left_live, right_live;
  double d;
  double new_x;
  ArtActiveSeg *test, *result = NULL;
  double x_test;

  left = seg;
  if (left == NULL)
    right = ctx->active_head;
  else
    right = left->right; 
  left_live = (break_flags & ART_BREAK_LEFT) && (left != NULL);
  right_live = (break_flags & ART_BREAK_RIGHT) && (right != NULL);
  while (left_live || right_live)
    {
      if (left_live)
	{
	  if (x <= left->x[left->flags & ART_ACTIVE_FLAGS_BNEG] &&
	      /* It may be that one of these conjuncts turns out to be always
		 true. We test both anyway, to be defensive. */
	      y != left->y0 && y < left->y1)
	    {
	      d = x_min * left->a + y * left->b + left->c;
	      if (d < EPSILON_A)
		{
		  new_x = art_svp_intersect_break (ctx, left, x_min, y,
						   ART_BREAK_LEFT);
		  if (new_x > x_max)
		    {
		      x_max = new_x;
		      right_live = (right != NULL);
		    }
		  else if (new_x < x_min)
		    x_min = new_x;
		  left = left->left;
		  left_live = (left != NULL);
		}
	      else
		left_live = ART_FALSE;
	    }
	  else
	    left_live = ART_FALSE;
	}
      else if (right_live)
	{
	  if (x >= right->x[(right->flags & ART_ACTIVE_FLAGS_BNEG) ^ 1] &&
	      /* It may be that one of these conjuncts turns out to be always
		 true. We test both anyway, to be defensive. */
	      y != right->y0 && y < right->y1)
	    {
	      d = x_max * right->a + y * right->b + right->c;
	      if (d > -EPSILON_A)
		{
		  new_x = art_svp_intersect_break (ctx, right, x_max, y,
						   ART_BREAK_RIGHT);
		  if (new_x < x_min)
		    {
		      x_min = new_x;
		      left_live = (left != NULL);
		    }
		  else if (new_x >= x_max)
		    x_max = new_x;
		  right = right->right;
		  right_live = (right != NULL);
		}
	      else
		right_live = ART_FALSE;
	    }
	  else
	    right_live = ART_FALSE;
	}
    }

  /* Ascending order is guaranteed by break_flags. Thus, we don't need
     to actually fix up non-ascending pairs. */

  /* Now, (left, right) defines an interval of segments broken. Sort
     into ascending x order. */
  test = left == NULL ? ctx->active_head : left->right;
  result = left;
  if (test != NULL && test != right)
    {
      if (y == test->y0)
	x_test = test->x[0];
      else /* assert y == test->y1, I think */
      x_test = test->x[1];
      for (;;)
	{
	  if (x_test <= x)
	    result = test;
	  test = test->right;
	  if (test == right)
	    break;
	  new_x = x_test;
	  if (new_x < x_test)
	    {
	      art_warn ("art_svp_intersect_add_point: non-ascending x\n");
	    }
	  x_test = new_x;
	}
    }
  return result;
}

static void
art_svp_intersect_swap_active (ArtIntersectCtx *ctx,
			       ArtActiveSeg *left_seg, ArtActiveSeg *right_seg)
{
  right_seg->left = left_seg->left;
  if (right_seg->left != NULL)
    right_seg->left->right = right_seg;
  else
    ctx->active_head = right_seg;
  left_seg->right = right_seg->right;
  if (left_seg->right != NULL)
    left_seg->right->left = left_seg;
  left_seg->left = right_seg;
  right_seg->right = left_seg;
}

/**
 * art_svp_intersect_test_cross: Test crossing of a pair of active segments.
 * @ctx: Intersector context.
 * @left_seg: Left segment of the pair.
 * @right_seg: Right segment of the pair.
 * @break_flags: Flags indicating whether to break neighbors.
 *
 * Tests crossing of @left_seg and @right_seg. If there is a crossing,
 * inserts the intersection point into both segments.
 *
 * Return value: True if the intersection took place at the current
 * scan line, indicating further iteration is needed.
 **/
static art_boolean
art_svp_intersect_test_cross (ArtIntersectCtx *ctx,
			      ArtActiveSeg *left_seg, ArtActiveSeg *right_seg,
			      ArtBreakFlags break_flags)
{
  double left_x0, left_y0, left_x1;
  double left_y1 = left_seg->y1;
  double right_y1 = right_seg->y1;
  double d;

  const ArtSVPSeg *in_seg;
  int in_curs;
  double d0, d1, t;
  double x, y; /* intersection point */

#ifdef VERBOSE 
  static int count = 0;

  art_dprint ("art_svp_intersect_test_cross %lx <-> %lx: count=%d\n",
	  (unsigned long)left_seg, (unsigned long)right_seg, count++);
#endif

  if (left_seg->y0 == right_seg->y0 && left_seg->x[0] == right_seg->x[0])
    {
      /* Top points of left and right segments coincide. This case
	 feels like a bit of duplication - we may want to merge it
	 with the cases below. However, this way, we're sure that this
	 logic makes only localized changes. */

      if (left_y1 < right_y1)
	{
	  /* Test left (x1, y1) against right segment */
	  double left_x1 = left_seg->x[1];

	  if (left_x1 <
	      right_seg->x[(right_seg->flags & ART_ACTIVE_FLAGS_BNEG) ^ 1] ||
	      left_y1 == right_seg->y0)
	    return ART_FALSE;
	  d = left_x1 * right_seg->a + left_y1 * right_seg->b + right_seg->c;
	  if (d < -EPSILON_A)
	    return ART_FALSE;
	  else if (d < EPSILON_A)
	    {
	      /* I'm unsure about the break flags here. */
	      double right_x1 = art_svp_intersect_break (ctx, right_seg,
							 left_x1, left_y1,
							 ART_BREAK_RIGHT);
	      if (left_x1 <= right_x1)
		return ART_FALSE;
	}
	}
      else if (left_y1 > right_y1)
	{
	  /* Test right (x1, y1) against left segment */
	  double right_x1 = right_seg->x[1];

	  if (right_x1 > left_seg->x[left_seg->flags & ART_ACTIVE_FLAGS_BNEG] ||
	      right_y1 == left_seg->y0)
	    return ART_FALSE;
	  d = right_x1 * left_seg->a + right_y1 * left_seg->b + left_seg->c;
	  if (d > EPSILON_A)
	    return ART_FALSE;
	  else if (d > -EPSILON_A)
	    {
	      /* See above regarding break flags. */
	      double left_x1 = art_svp_intersect_break (ctx, left_seg,
							right_x1, right_y1,
							ART_BREAK_LEFT);
	      if (left_x1 <= right_x1)
		return ART_FALSE;
	    }
	}
      else /* left_y1 == right_y1 */
	{
	  double left_x1 = left_seg->x[1];
	  double right_x1 = right_seg->x[1];

	  if (left_x1 <= right_x1)
	return ART_FALSE;
    }
      art_svp_intersect_swap_active (ctx, left_seg, right_seg);
      return ART_TRUE;
    }

  if (left_y1 < right_y1)
    {
      /* Test left (x1, y1) against right segment */
      double left_x1 = left_seg->x[1];

      if (left_x1 <
	  right_seg->x[(right_seg->flags & ART_ACTIVE_FLAGS_BNEG) ^ 1] ||
	  left_y1 == right_seg->y0)
	return ART_FALSE;
      d = left_x1 * right_seg->a + left_y1 * right_seg->b + right_seg->c;
      if (d < -EPSILON_A)
	return ART_FALSE;
      else if (d < EPSILON_A)
	{
	  double right_x1 = art_svp_intersect_break (ctx, right_seg,
						     left_x1, left_y1,
						     ART_BREAK_RIGHT);
	  if (left_x1 <= right_x1)
	    return ART_FALSE;
	}
    }
  else if (left_y1 > right_y1)
    {
      /* Test right (x1, y1) against left segment */
      double right_x1 = right_seg->x[1];

      if (right_x1 > left_seg->x[left_seg->flags & ART_ACTIVE_FLAGS_BNEG] ||
	  right_y1 == left_seg->y0)
	return ART_FALSE;
      d = right_x1 * left_seg->a + right_y1 * left_seg->b + left_seg->c;
      if (d > EPSILON_A)
	return ART_FALSE;
      else if (d > -EPSILON_A)
	{
	  double left_x1 = art_svp_intersect_break (ctx, left_seg,
						    right_x1, right_y1,
						    ART_BREAK_LEFT);
	  if (left_x1 <= right_x1)
	    return ART_FALSE;
	}
    }
  else /* left_y1 == right_y1 */
    { 
      double left_x1 = left_seg->x[1];
      double right_x1 = right_seg->x[1];

      if (left_x1 <= right_x1)
	return ART_FALSE;
    }

  /* The segments cross. Find the intersection point. */

  in_seg = left_seg->in_seg;
  in_curs = left_seg->in_curs;
  left_x0 = in_seg->points[in_curs - 1].x;
  left_y0 = in_seg->points[in_curs - 1].y;
  left_x1 = in_seg->points[in_curs].x;
  left_y1 = in_seg->points[in_curs].y;
  d0 = left_x0 * right_seg->a + left_y0 * right_seg->b + right_seg->c;
  d1 = left_x1 * right_seg->a + left_y1 * right_seg->b + right_seg->c;
  if (d0 == d1)
    {
      x = left_x0;
      y = left_y0;
    }
  else
    {
      /* Is this division always safe? It could possibly overflow. */
      t = d0 / (d0 - d1);
      if (t <= 0)
	{
	  x = left_x0;
	  y = left_y0;
	}
      else if (t >= 1)
	{
	  x = left_x1;
	  y = left_y1;
	}
      else
	{
	  x = left_x0 + t * (left_x1 - left_x0);
	  y = left_y0 + t * (left_y1 - left_y0);
	}
    }

  /* Make sure intersection point is within bounds of right seg. */
  if (y < right_seg->y0)
    {
      x = right_seg->x[0];
      y = right_seg->y0;
    }
  else if (y > right_seg->y1)
    {
      x = right_seg->x[1];
      y = right_seg->y1;
    }
  else if (x < right_seg->x[(right_seg->flags & ART_ACTIVE_FLAGS_BNEG) ^ 1])
    x = right_seg->x[(right_seg->flags & ART_ACTIVE_FLAGS_BNEG) ^ 1];
  else if (x > right_seg->x[right_seg->flags & ART_ACTIVE_FLAGS_BNEG])
    x = right_seg->x[right_seg->flags & ART_ACTIVE_FLAGS_BNEG];

  if (y == left_seg->y0)
    {
      if (y != right_seg->y0)
	{
#ifdef VERBOSE
	  art_dprint ("art_svp_intersect_test_cross: intersection (%g, %g) matches former y0 of %lx, %lx\n",
		    x, y, (unsigned long)left_seg, (unsigned long)right_seg);
#endif
	  art_svp_intersect_push_pt (ctx, right_seg, x, y);
	  if ((break_flags & ART_BREAK_RIGHT) && right_seg->right != NULL)
	    art_svp_intersect_add_point (ctx, x, y, right_seg->right,
					 break_flags);
	}
      else
	{
	  /* Intersection takes place at current scan line; process
	     immediately rather than queueing intersection point into
	     priq. */
	  ArtActiveSeg *winner, *loser;

	  /* Choose "most vertical" segement */
	  if (left_seg->a > right_seg->a)
	    {
	      winner = left_seg;
	      loser = right_seg;
	    }
	  else
	    {
	      winner = right_seg;
	      loser = left_seg;
	    }

	  loser->x[0] = winner->x[0];
	  loser->horiz_x = loser->x[0];
	  loser->horiz_delta_wind += loser->delta_wind;
	  winner->horiz_delta_wind -= loser->delta_wind;

	  art_svp_intersect_swap_active (ctx, left_seg, right_seg);
	  return ART_TRUE;
	}
    }
  else if (y == right_seg->y0)
    {
#ifdef VERBOSE
      art_dprint ("*** art_svp_intersect_test_cross: intersection (%g, %g) matches latter y0 of %lx, %lx\n",
	      x, y, (unsigned long)left_seg, (unsigned long)right_seg);
#endif
      art_svp_intersect_push_pt (ctx, left_seg, x, y);
      if ((break_flags & ART_BREAK_LEFT) && left_seg->left != NULL)
	art_svp_intersect_add_point (ctx, x, y, left_seg->left,
				     break_flags);
    }
  else
    {
#ifdef VERBOSE
      art_dprint ("Inserting (%g, %g) into %lx, %lx\n",
	      x, y, (unsigned long)left_seg, (unsigned long)right_seg);
#endif
      /* Insert the intersection point into both segments. */
      art_svp_intersect_push_pt (ctx, left_seg, x, y);
      art_svp_intersect_push_pt (ctx, right_seg, x, y);
      if ((break_flags & ART_BREAK_LEFT) && left_seg->left != NULL)
	art_svp_intersect_add_point (ctx, x, y, left_seg->left, break_flags);
      if ((break_flags & ART_BREAK_RIGHT) && right_seg->right != NULL)
	art_svp_intersect_add_point (ctx, x, y, right_seg->right, break_flags);
    }
  return ART_FALSE;
}

/**
 * art_svp_intersect_active_delete: Delete segment from active list.
 * @ctx: Intersection context.
 * @seg: Segment to delete.
 *
 * Deletes @seg from the active list.
 **/
static /* todo inline */ void
art_svp_intersect_active_delete (ArtIntersectCtx *ctx, ArtActiveSeg *seg)
{
  ArtActiveSeg *left = seg->left, *right = seg->right;

  if (left != NULL)
    left->right = right;
  else
    ctx->active_head = right;
  if (right != NULL)
    right->left = left;
}

/**
 * art_svp_intersect_active_free: Free an active segment.
 * @seg: Segment to delete.
 *
 * Frees @seg.
 **/
static /* todo inline */ void
art_svp_intersect_active_free (ArtActiveSeg *seg)
{
  art_free (seg->stack);
#ifdef VERBOSE
  art_dprint ("Freeing %lx\n", (unsigned long) seg);
#endif
  art_free (seg);
}

/**
 * art_svp_intersect_insert_cross: Test crossings of newly inserted line.
 *
 * Tests @seg against its left and right neighbors for intersections.
 * Precondition: the line in @seg is not purely horizontal.
 **/
static void
art_svp_intersect_insert_cross (ArtIntersectCtx *ctx,
				ArtActiveSeg *seg)
{
  ArtActiveSeg *left = seg, *right = seg;

  for (;;)
    {
      if (left != NULL)
	{
	  ArtActiveSeg *leftc;

	  for (leftc = left->left; leftc != NULL; leftc = leftc->left)
	    if (!(leftc->flags & ART_ACTIVE_FLAGS_DEL))
	      break;
	  if (leftc != NULL &&
	      art_svp_intersect_test_cross (ctx, leftc, left,
					    ART_BREAK_LEFT))
	    {
	      if (left == right || right == NULL)
		right = left->right;
	    }
	  else
	    {
	      left = NULL;
	    }
	}
      else if (right != NULL && right->right != NULL)
	{
	  ArtActiveSeg *rightc;

	  for (rightc = right->right; rightc != NULL; rightc = rightc->right)
	    if (!(rightc->flags & ART_ACTIVE_FLAGS_DEL))
	      break;
	  if (rightc != NULL &&
	      art_svp_intersect_test_cross (ctx, right, rightc,
					    ART_BREAK_RIGHT))
	    {
	      if (left == right || left == NULL)
		left = right->left;
	    }
	  else
	    {
	      right = NULL;
	    }
	}
      else
	break;
    }
}

/**
 * art_svp_intersect_horiz: Add horizontal line segment.
 * @ctx: Intersector context.
 * @seg: Segment on which to add horizontal line.
 * @x0: Old x position.
 * @x1: New x position.
 *
 * Adds a horizontal line from @x0 to @x1, and updates the current
 * location of @seg to @x1.
 **/
static void
art_svp_intersect_horiz (ArtIntersectCtx *ctx, ArtActiveSeg *seg,
			 double x0, double x1)
{
  ArtActiveSeg *hs;

  if (x0 == x1)
    return;

  hs = art_new (ArtActiveSeg, 1);

  hs->flags = ART_ACTIVE_FLAGS_DEL | (seg->flags & ART_ACTIVE_FLAGS_OUT);
  if (seg->flags & ART_ACTIVE_FLAGS_OUT)
    {
      ArtSvpWriter *swr = ctx->out;

      swr->add_point (swr, seg->seg_id, x0, ctx->y);
    }
  hs->seg_id = seg->seg_id;
  hs->horiz_x = x0;
  hs->horiz_delta_wind = seg->delta_wind;
  hs->stack = NULL;

  /* Ideally, the (a, b, c) values will never be read. However, there
     are probably some tests remaining that don't check for _DEL
     before evaluating the line equation. For those, these
     initializations will at least prevent a UMR of the values, which
     can crash on some platforms. */
  hs->a = 0.0;
  hs->b = 0.0;
  hs->c = 0.0;

  seg->horiz_delta_wind -= seg->delta_wind;

  art_svp_intersect_add_horiz (ctx, hs);

  if (x0 > x1)
    {
      ArtActiveSeg *left;
      art_boolean first = ART_TRUE;

      for (left = seg->left; left != NULL; left = seg->left)
	{
	  int left_bneg = left->flags & ART_ACTIVE_FLAGS_BNEG;

	  if (left->x[left_bneg] <= x1)
	    break;
	  if (left->x[left_bneg ^ 1] <= x1 &&
	      x1 * left->a + ctx->y * left->b + left->c >= 0)
	    break;
	  if (left->y0 != ctx->y && left->y1 != ctx->y)
	    {
	      art_svp_intersect_break (ctx, left, x1, ctx->y, ART_BREAK_LEFT);
	    }
#ifdef VERBOSE
	  art_dprint ("x0=%g > x1=%g, swapping %lx, %lx\n",
		  x0, x1, (unsigned long)left, (unsigned long)seg);
#endif
	  art_svp_intersect_swap_active (ctx, left, seg);
	  if (first && left->right != NULL)
	    {
	      art_svp_intersect_test_cross (ctx, left, left->right,
					    ART_BREAK_RIGHT);
	      first = ART_FALSE;
	    }
	}
    }
  else
    {
      ArtActiveSeg *right;
      art_boolean first = ART_TRUE;

      for (right = seg->right; right != NULL; right = seg->right)
	{
	  int right_bneg = right->flags & ART_ACTIVE_FLAGS_BNEG;

	  if (right->x[right_bneg ^ 1] >= x1)
	    break;
	  if (right->x[right_bneg] >= x1 &&
	      x1 * right->a + ctx->y * right->b + right->c <= 0)
	    break;
	  if (right->y0 != ctx->y && right->y1 != ctx->y)
	    {
	      art_svp_intersect_break (ctx, right, x1, ctx->y,
				       ART_BREAK_LEFT);
	    }
#ifdef VERBOSE
	  art_dprint ("[right]x0=%g < x1=%g, swapping %lx, %lx\n",
		  x0, x1, (unsigned long)seg, (unsigned long)right);
#endif
	  art_svp_intersect_swap_active (ctx, seg, right);
	  if (first && right->left != NULL)
	    {
	      art_svp_intersect_test_cross (ctx, right->left, right,
					    ART_BREAK_RIGHT);
	      first = ART_FALSE;
	    }
	}
    }

  seg->x[0] = x1;
  seg->x[1] = x1;
  seg->horiz_x = x1;
  seg->flags &= ~ART_ACTIVE_FLAGS_OUT;
}

/**
 * art_svp_intersect_insert_line: Insert a line into the active list.
 * @ctx: Intersector context.
 * @seg: Segment containing line to insert.
 *
 * Inserts the line into the intersector context, taking care of any
 * intersections, and adding the appropriate horizontal points to the
 * active list.
 **/
static void
art_svp_intersect_insert_line (ArtIntersectCtx *ctx, ArtActiveSeg *seg)
{
  if (seg->y1 == seg->y0)
    {
#ifdef VERBOSE
      art_dprint ("art_svp_intersect_insert_line: %lx is horizontal\n",
	      (unsigned long)seg);
#endif
      art_svp_intersect_horiz (ctx, seg, seg->x[0], seg->x[1]);
    }
  else
    {
      art_svp_intersect_insert_cross (ctx, seg);
      art_svp_intersect_add_horiz (ctx, seg);
    }
}

static void
art_svp_intersect_process_intersection (ArtIntersectCtx *ctx,
					ArtActiveSeg *seg)
{
  int n_stack = --seg->n_stack;
  seg->x[1] = seg->stack[n_stack - 1].x;
  seg->y1 = seg->stack[n_stack - 1].y;
  seg->x[0] = seg->stack[n_stack].x;
  seg->y0 = seg->stack[n_stack].y;
  seg->horiz_x = seg->x[0];
  art_svp_intersect_insert_line (ctx, seg);
}

static void
art_svp_intersect_advance_cursor (ArtIntersectCtx *ctx, ArtActiveSeg *seg,
				  ArtPriPoint *pri_pt)
{
  const ArtSVPSeg *in_seg = seg->in_seg;
  int in_curs = seg->in_curs;
  ArtSvpWriter *swr = seg->flags & ART_ACTIVE_FLAGS_OUT ? ctx->out : NULL;

  if (swr != NULL)
    swr->add_point (swr, seg->seg_id, seg->x[1], seg->y1);
  if (in_curs + 1 == in_seg->n_points)
    {
      ArtActiveSeg *left = seg->left, *right = seg->right;

#if 0
      if (swr != NULL)
	swr->close_segment (swr, seg->seg_id);
      seg->flags &= ~ART_ACTIVE_FLAGS_OUT;
#endif
      seg->flags |= ART_ACTIVE_FLAGS_DEL;
      art_svp_intersect_add_horiz (ctx, seg);
      art_svp_intersect_active_delete (ctx, seg);
      if (left != NULL && right != NULL)
	art_svp_intersect_test_cross (ctx, left, right,
				      ART_BREAK_LEFT | ART_BREAK_RIGHT);
      art_free (pri_pt);
    }
  else
    {
      seg->horiz_x = seg->x[1];

      art_svp_intersect_setup_seg (seg, pri_pt);
      art_pri_insert (ctx->pq, pri_pt);
      art_svp_intersect_insert_line (ctx, seg);
    }
}

static void
art_svp_intersect_add_seg (ArtIntersectCtx *ctx, const ArtSVPSeg *in_seg)
{
  ArtActiveSeg *seg = art_new (ArtActiveSeg, 1);
  ArtActiveSeg *test;
  double x0, y0;
  ArtActiveSeg *beg_range;
  ArtActiveSeg *last = NULL;
  ArtActiveSeg *left, *right;
  ArtPriPoint *pri_pt = art_new (ArtPriPoint, 1);

  seg->flags = 0;
  seg->in_seg = in_seg;
  seg->in_curs = 0;

  seg->n_stack_max = 4;
  seg->stack = art_new (ArtPoint, seg->n_stack_max);

  seg->horiz_delta_wind = 0;

  seg->wind_left = 0;

  pri_pt->user_data = seg;
  art_svp_intersect_setup_seg (seg, pri_pt);
  art_pri_insert (ctx->pq, pri_pt);

  /* Find insertion place for new segment */
  /* This is currently a left-to-right scan, but should be replaced
     with a binary search as soon as it's validated. */

  x0 = in_seg->points[0].x;
  y0 = in_seg->points[0].y;
  beg_range = NULL;
  for (test = ctx->active_head; test != NULL; test = test->right)
    {
      double d;
      int test_bneg = test->flags & ART_ACTIVE_FLAGS_BNEG;

      if (x0 < test->x[test_bneg])
	{
	  if (x0 < test->x[test_bneg ^ 1])
	    break;
	  d = x0 * test->a + y0 * test->b + test->c;
	  if (d < 0)
	    break;
	}
      last = test;
    }

  left = art_svp_intersect_add_point (ctx, x0, y0, last, ART_BREAK_LEFT | ART_BREAK_RIGHT);
  seg->left = left;
  if (left == NULL)
    {
      right = ctx->active_head;
      ctx->active_head = seg;
    }
  else
    {
      right = left->right;
      left->right = seg;
    }
  seg->right = right;
  if (right != NULL)
    right->left = seg;

  seg->delta_wind = in_seg->dir ? 1 : -1;
  seg->horiz_x = x0;

  art_svp_intersect_insert_line (ctx, seg);
}

#ifdef SANITYCHECK
static void
art_svp_intersect_sanitycheck_winding (ArtIntersectCtx *ctx)
{
#if 0
  /* At this point, we seem to be getting false positives, so it's
     turned off for now. */

  ArtActiveSeg *seg;
  int winding_number = 0;

  for (seg = ctx->active_head; seg != NULL; seg = seg->right)
    {
      /* Check winding number consistency. */
      if (seg->flags & ART_ACTIVE_FLAGS_OUT)
	{
	  if (winding_number != seg->wind_left)
	    art_warn ("*** art_svp_intersect_sanitycheck_winding: seg %lx has wind_left of %d, expected %d\n",
		  (unsigned long) seg, seg->wind_left, winding_number);
	  winding_number = seg->wind_left + seg->delta_wind;
	}
    }
  if (winding_number != 0)
    art_warn ("*** art_svp_intersect_sanitycheck_winding: non-balanced winding number %d\n",
	      winding_number);
#endif
}
#endif

/**
 * art_svp_intersect_horiz_commit: Commit points in horiz list to output.
 * @ctx: Intersection context.
 *
 * The main function of the horizontal commit is to output new
 * points to the output writer.
 *
 * This "commit" pass is also where winding numbers are assigned,
 * because doing it here provides much greater tolerance for inputs
 * which are not in strict SVP order.
 *
 * Each cluster in the horiz_list contains both segments that are in
 * the active list (ART_ACTIVE_FLAGS_DEL is false) and that are not,
 * and are scheduled to be deleted (ART_ACTIVE_FLAGS_DEL is true). We
 * need to deal with both.
 **/
static void
art_svp_intersect_horiz_commit (ArtIntersectCtx *ctx)
{
  ArtActiveSeg *seg;
  int winding_number = 0; /* initialization just to avoid warning */
  int horiz_wind = 0;
  double last_x = 0; /* initialization just to avoid warning */

#ifdef VERBOSE
  art_dprint ("art_svp_intersect_horiz_commit: y=%g\n", ctx->y);
  for (seg = ctx->horiz_first; seg != NULL; seg = seg->horiz_right)
    art_dprint (" %lx: %g %+d\n",
	    (unsigned long)seg, seg->horiz_x, seg->horiz_delta_wind);
#endif

  /* Output points to svp writer. */
  for (seg = ctx->horiz_first; seg != NULL;)
    {
      /* Find a cluster with common horiz_x, */
      ArtActiveSeg *curs;
      double x = seg->horiz_x;

      /* Generate any horizontal segments. */
      if (horiz_wind != 0)
	{
	  ArtSvpWriter *swr = ctx->out;
	  int seg_id;

	  seg_id = swr->add_segment (swr, winding_number, horiz_wind,
				     last_x, ctx->y);
	  swr->add_point (swr, seg_id, x, ctx->y);
	  swr->close_segment (swr, seg_id);
	}

      /* Find first active segment in cluster. */

      for (curs = seg; curs != NULL && curs->horiz_x == x;
	   curs = curs->horiz_right)
	if (!(curs->flags & ART_ACTIVE_FLAGS_DEL))
	  break;

      if (curs != NULL && curs->horiz_x == x)
	{
	  /* There exists at least one active segment in this cluster. */

	  /* Find beginning of cluster. */
	  for (; curs->left != NULL; curs = curs->left)
	    if (curs->left->horiz_x != x)
	      break;

	  if (curs->left != NULL)
	    winding_number = curs->left->wind_left + curs->left->delta_wind;
	  else
	    winding_number = 0;

	  do
	    {
#ifdef VERBOSE
	      art_dprint (" curs %lx: winding_number = %d += %d\n",
		      (unsigned long)curs, winding_number, curs->delta_wind);
#endif
	      if (!(curs->flags & ART_ACTIVE_FLAGS_OUT) ||
		  curs->wind_left != winding_number)
		{
		  ArtSvpWriter *swr = ctx->out;

		  if (curs->flags & ART_ACTIVE_FLAGS_OUT)
		    {
		      swr->add_point (swr, curs->seg_id,
				      curs->horiz_x, ctx->y);
		      swr->close_segment (swr, curs->seg_id);
		    }

		  curs->seg_id = swr->add_segment (swr, winding_number,
						   curs->delta_wind,
						   x, ctx->y);
		  curs->flags |= ART_ACTIVE_FLAGS_OUT;
		}
	      curs->wind_left = winding_number;
	      winding_number += curs->delta_wind;
	      curs = curs->right;
	    }
	  while (curs != NULL && curs->horiz_x == x);
	}

      /* Skip past cluster. */
      do
	{
	  ArtActiveSeg *next = seg->horiz_right;

	  seg->flags &= ~ART_ACTIVE_FLAGS_IN_HORIZ;
	  horiz_wind += seg->horiz_delta_wind;
	  seg->horiz_delta_wind = 0;
	  if (seg->flags & ART_ACTIVE_FLAGS_DEL)
	    {
	      if (seg->flags & ART_ACTIVE_FLAGS_OUT)
		{
		  ArtSvpWriter *swr = ctx->out;
		  swr->close_segment (swr, seg->seg_id);
		}
	      art_svp_intersect_active_free (seg);
	    }
	  seg = next;
	}
      while (seg != NULL && seg->horiz_x == x);

      last_x = x;
    }
  ctx->horiz_first = NULL;
  ctx->horiz_last = NULL;
#ifdef SANITYCHECK
  art_svp_intersect_sanitycheck_winding (ctx);
#endif
}

#ifdef VERBOSE
static void
art_svp_intersect_print_active (ArtIntersectCtx *ctx)
{
  ArtActiveSeg *seg;

  art_dprint ("Active list (y = %g):\n", ctx->y);
  for (seg = ctx->active_head; seg != NULL; seg = seg->right)
    {
      art_dprint (" %lx: (%g, %g)-(%g, %g), (a, b, c) = (%g, %g, %g)\n",
	      (unsigned long)seg,
	      seg->x[0], seg->y0, seg->x[1], seg->y1,
	      seg->a, seg->b, seg->c);
    }
}
#endif

#ifdef SANITYCHECK
static void
art_svp_intersect_sanitycheck (ArtIntersectCtx *ctx)
{
  ArtActiveSeg *seg;
  ArtActiveSeg *last = NULL;
  double d;

  for (seg = ctx->active_head; seg != NULL; seg = seg->right)
    {
      if (seg->left != last)
	{
	  art_warn ("*** art_svp_intersect_sanitycheck: last=%lx, seg->left=%lx\n",
		    (unsigned long)last, (unsigned long)seg->left);
	}
      if (last != NULL)
	{
	  /* pairwise compare with previous seg */

	  /* First the top. */
	  if (last->y0 < seg->y0)
	    {
	    }
	  else
	    {
	    }

	  /* Then the bottom. */
	  if (last->y1 < seg->y1)
	    {
	      if (!((last->x[1] <
		     seg->x[(seg->flags & ART_ACTIVE_FLAGS_BNEG) ^ 1]) ||
		    last->y1 == seg->y0))
		{
		  d = last->x[1] * seg->a + last->y1 * seg->b + seg->c;
		  if (d >= -EPSILON_A)
		    art_warn ("*** bottom (%g, %g) of %lx is not clear of %lx to right (d = %g)\n",
			      last->x[1], last->y1, (unsigned long) last,
			      (unsigned long) seg, d);
		}
	    }
	  else if (last->y1 > seg->y1)

	    {
	      if (!((seg->x[1] >
		     last->x[last->flags & ART_ACTIVE_FLAGS_BNEG]) ||
		    seg->y1 == last->y0))
	      {
		d = seg->x[1] * last->a + seg->y1 * last->b + last->c;
		if (d <= EPSILON_A)
		  art_warn ("*** bottom (%g, %g) of %lx is not clear of %lx to left (d = %g)\n",
			      seg->x[1], seg->y1, (unsigned long) seg,
			      (unsigned long) last, d);
	      }
	    }
	  else
	    {
	      if (last->x[1] > seg->x[1])
		art_warn ("*** bottoms (%g, %g) of %lx and (%g, %g) of %lx out of order\n",
			  last->x[1], last->y1, (unsigned long)last,
			  seg->x[1], seg->y1, (unsigned long)seg);
	    }
	}
      last = seg;
    }
}
#endif

void
art_svp_intersector (const ArtSVP *in, ArtSvpWriter *out)
{
  ArtIntersectCtx *ctx;
  ArtPriQ *pq;
  ArtPriPoint *first_point;
#ifdef VERBOSE
  int count = 0;
#endif

  if (in->n_segs == 0)
    return;

  ctx = art_new (ArtIntersectCtx, 1);
  ctx->in = in;
  ctx->out = out;
  pq = art_pri_new ();
  ctx->pq = pq;

  ctx->active_head = NULL;

  ctx->horiz_first = NULL;
  ctx->horiz_last = NULL;

  ctx->in_curs = 0;
  first_point = art_new (ArtPriPoint, 1);
  first_point->x = in->segs[0].points[0].x;
  first_point->y = in->segs[0].points[0].y;
  first_point->user_data = NULL;
  ctx->y = first_point->y;
  art_pri_insert (pq, first_point);

  while (!art_pri_empty (pq))
    {
      ArtPriPoint *pri_point = art_pri_choose (pq);
      ArtActiveSeg *seg = (ArtActiveSeg *)pri_point->user_data;

#ifdef VERBOSE
      art_dprint ("\nIntersector step %d\n", count++);
      art_svp_intersect_print_active (ctx);
      art_dprint ("priq choose (%g, %g) %lx\n", pri_point->x, pri_point->y,
	      (unsigned long)pri_point->user_data);
#endif
#ifdef SANITYCHECK
      art_svp_intersect_sanitycheck(ctx);
#endif

      if (ctx->y != pri_point->y)
	{
	  art_svp_intersect_horiz_commit (ctx);
	  ctx->y = pri_point->y;
	}

      if (seg == NULL)
	{
	  /* Insert new segment from input */
	  const ArtSVPSeg *in_seg = &in->segs[ctx->in_curs++];
	  art_svp_intersect_add_seg (ctx, in_seg);
	  if (ctx->in_curs < in->n_segs)
	    {
	      const ArtSVPSeg *next_seg = &in->segs[ctx->in_curs];
	      pri_point->x = next_seg->points[0].x;
	      pri_point->y = next_seg->points[0].y;
	      /* user_data is already NULL */
	      art_pri_insert (pq, pri_point);
	    }
	  else
	    art_free (pri_point);
	}
      else
	{
	  int n_stack = seg->n_stack;

	  if (n_stack > 1)
	    {
	      art_svp_intersect_process_intersection (ctx, seg);
	      art_free (pri_point);
	    }
	  else
	    {
	      art_svp_intersect_advance_cursor (ctx, seg, pri_point);
	    }
	}
    }

  art_svp_intersect_horiz_commit (ctx);

  art_pri_free (pq);
  art_free (ctx);
}

#endif /* not TEST_PRIQ */