InflatePaths output and input polygons intersect

[ccoustet]

I offset (negative offset) complex polygons (building footprints from real data) to produce interior walls footprints from exterior wall footprints. Most building wall footprints are correct, but some are broken: interior and exterior polygons intersect.

In this example, the interior polygon ends with 116 vertices while the exterior one has 117.
Code and output follow.

Paths64 polyline, solution;
Point64 coords[117] = {
{1436297462, 1349601198},
{1436108718, 1347587932},
{1431841014, 1348133192},
{1432029757, 1349936742},
{1432218501, 1352904212},
{1434294682, 1382725714},
{1439862620, 1382128026},
{1441529856, 1398192210},
{1435521516, 1398852813},
{1436653978, 1414350766},
{1437031465, 1419551703},
{1437408952, 1424857498},
{1437786440, 1429733376},
{1443805266, 1429093745},
{1444371497, 1433120276},
{1442054144, 1433445335},
{1442893005, 1440774881},
{1443459236, 1445126472},
{1440953139, 1445441044},
{1441236255, 1447884227},
{1443773809, 1447674511},
{1443836723, 1448209285},
{1445965332, 1447884227},
{1446437192, 1452026102},
{1439296389, 1452560876},
{1440009421, 1461882716},
{1440428851, 1467314340},
{1440995082, 1475807805},
{1451470356, 1474308342},
{1455884861, 1473637253},
{1462868378, 1472588677},
{1462774006, 1470889984},
{1468824289, 1469988209},
{1475010888, 1469075948},
{1474916516, 1467912028},
{1478156616, 1467366769},
{1478261473, 1468541174},
{1481742746, 1468027372},
{1487709143, 1467146568},
{1487719629, 1467366769},
{1495028204, 1466286735},
{1495028204, 1466821509},
{1502724751, 1465835848},
{1507453829, 1465217188},
{1506143109, 1454280540},
{1494000599, 1456094577},
{1494566830, 1460131594},
{1487237284, 1461316485},
{1487048540, 1458349015},
{1474350285, 1459848479},
{1474350285, 1459408077},
{1471288443, 1459848479},
{1471382815, 1460802683},
{1462207775, 1461882716},
{1462113403, 1461033370},
{1449499034, 1462627205},
{1448660173, 1451910758},
{1452550390, 1451585700},
{1451239670, 1440019907},
{1454018396, 1439694848},
{1453357793, 1432910561},
{1450484695, 1433120276},
{1450023322, 1428454113},
{1453263421, 1428013711},
{1453074678, 1426220646},
{1455203287, 1425895588},
{1453347308, 1417832038},
{1465122816, 1416447918},
{1464472699, 1411351839},
{1462501376, 1395853885},
{1455475917, 1396629832},
{1453724795, 1380660019},
{1450621010, 1380974592},
{1448639201, 1358084178},
{1488694804, 1354529505},
{1489166664, 1359950643},
{1493706998, 1359510241},
{1495300833, 1376392315},
{1483787469, 1377619149},
{1484836045, 1386899046},
{1486020936, 1386752246},
{1486587167, 1393316332},
{1492574536, 1392634757},
{1493277082, 1398685041},
{1494493430, 1398580183},
{1495521034, 1407912509},
{1487646228, 1408772342},
{1488673833, 1424270295},
{1492113162, 1423892808},
{1492480164, 1427237765},
{1491934904, 1427332137},
{1492679393, 1434126909},
{1496758354, 1433812337},
{1497230213, 1437629153},
{1498257818, 1448240742},
{1506604483, 1447391396},
{1505943880, 1439956992},
{1503720899, 1440166707},
{1503437783, 1436874179},
{1503154668, 1433696993},
{1505293763, 1433487278},
{1504633160, 1426052874},
{1502955438, 1426168218},
{1502598922, 1422781317},
{1504811418, 1422550630},
{1504433930, 1416825405},
{1503962071, 1410450063},
{1503773327, 1406947820},
{1503112724, 1397930066},
{1502640865, 1391565210},
{1501183345, 1375805112},
{1506059223, 1375312282},
{1503689441, 1344117146},
{1502116577, 1344242975},
{1470638326, 1346853929},
{1465479332, 1347294331},
{1445105500, 1348972052} };
  polyline.push_back(Path64(std::begin(coords), std::end(coords)));
  // offset polyline
  solution = InflatePaths(polyline, -209715, JoinType::Miter, EndType::Polygon);

  //print polyline and inflated solution
  std::cout << polyline << "=====>\n" << solution;


1436297462,1349601198 , 1436108718,1347587932 , 1431841014,1348133192 , 1432029757,1349936742 , 1432218501,1352904212 , 1434294682,1382725714 , 1439862620,1382128026 , 1441529856,1398192210 , 1435521516,1398852813 , 1436653978,1414350766 , 1437031465,1419551703 , 1437408952,1424857498 , 1437786440,1429733376 , 1443805266,1429093745 , 1444371497,1433120276 , 1442054144,1433445335 , 1442893005,1440774881 , 1443459236,1445126472 , 1440953139,1445441044 , 1441236255,1447884227 , 1443773809,1447674511 , 1443836723,1448209285 , 1445965332,1447884227 , 1446437192,1452026102 , 1439296389,1452560876 , 1440009421,1461882716 , 1440428851,1467314340 , 1440995082,1475807805 , 1451470356,1474308342 , 1455884861,1473637253 , 1462868378,1472588677 , 1462774006,1470889984 , 1468824289,1469988209 , 1475010888,1469075948 , 1474916516,1467912028 , 1478156616,1467366769 , 1478261473,1468541174 , 1481742746,1468027372 , 1487709143,1467146568 , 1487719629,1467366769 , 1495028204,1466286735 , 1495028204,1466821509 , 1502724751,1465835848 , 1507453829,1465217188 , 1506143109,1454280540 , 1494000599,1456094577 , 1494566830,1460131594 , 1487237284,1461316485 , 1487048540,1458349015 , 1474350285,1459848479 , 1474350285,1459408077 , 1471288443,1459848479 , 1471382815,1460802683 , 1462207775,1461882716 , 1462113403,1461033370 , 1449499034,1462627205 , 1448660173,1451910758 , 1452550390,1451585700 , 1451239670,1440019907 , 1454018396,1439694848 , 1453357793,1432910561 , 1450484695,1433120276 , 1450023322,1428454113 , 1453263421,1428013711 , 1453074678,1426220646 , 1455203287,1425895588 , 1453347308,1417832038 , 1465122816,1416447918 , 1464472699,1411351839 , 1462501376,1395853885 , 1455475917,1396629832 , 1453724795,1380660019 , 1450621010,1380974592 , 1448639201,1358084178 , 1488694804,1354529505 , 1489166664,1359950643 , 1493706998,1359510241 , 1495300833,1376392315 , 1483787469,1377619149 , 1484836045,1386899046 , 1486020936,1386752246 , 1486587167,1393316332 , 1492574536,1392634757 , 1493277082,1398685041 , 1494493430,1398580183 , 1495521034,1407912509 , 1487646228,1408772342 , 1488673833,1424270295 , 1492113162,1423892808 , 1492480164,1427237765 , 1491934904,1427332137 , 1492679393,1434126909 , 1496758354,1433812337 , 1497230213,1437629153 , 1498257818,1448240742 , 1506604483,1447391396 , 1505943880,1439956992, 1503720899,1440166707 , 1503437783,1436874179 , 1503154668,1433696993 , 1505293763,1433487278 , 1504633160,1426052874 , 1502955438,1426168218 , 1502598922,1422781317 , 1504811418,1422550630 , 1504433930,1416825405 , 1503962071,1410450063 , 1503773327,1406947820 , 1503112724,1397930066 , 1502640865,1391565210 , 1501183345,1375805112 , 1506059223,1375312282 , 1503689441,1344117146 , 1502116577,1344242975 , 1470638326,1346853929 , 1465479332,1347294331 , 1445105500,1348972052 
=====>
1503496278,1344342983 , 1502133301,1344452022 , 1470655661,1347062926 , 1465497170,1347503286 , 1445122711,1349181060 , 1436107808,1349824994 , 1435920162,1347823442 , 1432070925,1348315237 , 1432238333,1349914914 , 1432427793,1352890900 , 1434488770,1382493959 , 1440049489,1381897047 , 1441759968,1398377888 , 1435745407,1399039175 , 1436863135,1414335483 , 1437240630,1419536522 , 1437618138,1424842615 , 1437978871,1429502029 , 1443984706,1428863780 , 1444608383,1433298816 , 1442285746,1433624616 , 1443101360,1440751035 , 1443694381,1445308317 , 1441185371,1445623254 , 1441421217,1447658511 , 1443958419,1447448824 , 1444019640,1447969205 , 1446149039,1447644027 , 1446670234,1452218952 , 1439521512,1452754318 , 1440218525,1461866722 , 1440637944,1467298194 , 1441189285,1475568153 , 1451440640,1474100743 , 1455853342,1473429920 , 1462648393,1472409642 , 1462554010,1470710742 , 1468793373,1469780785 , 1474785985,1468897128 , 1474691934,1467737158 , 1478345342,1467122346 , 1478450602,1468301273 , 1481712126,1467819904 , 1487907606,1466905282 , 1487918090,1467125448 , 1495237919,1466583224 , 1502698111,1465627832 , 1507220917,1465036155 , 1505960573,1454519852 , 1494237150,1456271279 , 1494803038,1460305846 , 1487042658,1461560386 , 1486853299,1458583241 , 1474140570,1460084415 , 1474140570,1459650114 , 1471516886,1460027494 , 1471611772,1460986894 , 1462022653,1462115670 , 1461928480,1461268117 , 1449307122,1462862836 , 1448434817,1451719142 , 1452317687,1451394698 , 1451007759,1439835891 , 1453789733,1439510451 , 1453168903,1433134621 , 1450296109,1433344314 , 1449794730,1428273540 , 1453033557,1427833311 , 1452845163,1426043549 , 1454948224,1425722391 , 1453090456,1417651070 , 1464887984,1416264361 , 1464264670,1411378378 , 1462319365,1396084977 , 1455290328,1396861320 , 1453539001,1380889638 , 1450430433,1381204697 , 1448412217,1357893782 , 1488885513,1354302042 , 1489357223,1359721460 , 1493896022,1359281207 , 1495529095,1376578894 , 1484019554,1377805320 , 1485020632,1386664858 , 1486211168,1386517359 , 1486777583,1393083586 , 1492758717,1392402721 , 1493461913,1398458614 , 1494679469,1398353652 , 1495752464,1408098201 , 1487868780,1408959003 , 1488868602,1424037943 , 1492298753,1423661464 , 1492710122,1427410797 , 1492164832,1427505174 , 1492865741,1433902200 , 1496941912,1433587843 , 1497438344,1437603423 , 1498446242,1448010769 , 1506377265,1447203718 , 1505753650,1440185584 , 1503530071,1440395356 , 1503228839,1436892146 , 1502927331,1433508560 , 1505066477,1433298840 , 1504442462,1426276194 , 1502768048,1426391311 , 1502368384,1422594502 , 1504588874,1422362981 , 1504224669,1416839202 , 1503752928,1410465542 , 1503563916,1406959106 , 1502903569,1397945388 , 1502431724,1391580715 , 1500955372,1375617371 , 1505834616,1375124200 

[AngusJohnson]

It looks OK in Delphi and C# so it seems this is a bug specific to C++. I'll investigate.

[AngusJohnson]

The problem is here in clipper.engine.cpp at the bottom of ProcessIntersectList().

CheckJoinLeft(*node.edge2, node.pt, true); // make sure the third parameter = true

As I said this looks OK in the C# and Delphi code.