Case where union operation of clipping work as difference

[MikhailFarbshteyn]

Describe the bug Have a nice day! I found a bug with using clipping. In some case when I made union operetion with 2 regions it make them difference. Could you check this case?

To Reproduce please try this code

import json
from ezdxf.math import Vec2, clipping
from SPD.helper import drawing
from pathlib import Path

with open("SPD/regions.json", "r") as file:
    data = json.load(file)

Doc = ezdxf.new()

data_vecs = [[Vec2(pt[0], pt[1]) for pt in region] for region in data]

for region in data:
    Doc.modelspace().add_lwpolyline(points=region, close=True) # show raw data

unions = clipping.greiner_hormann_union(data_vecs[0], data_vecs[1])

for region in unions:
    Doc.modelspace().add_lwpolyline(points=region, close=True, dxfattribs={"color": ezdxf.colors.YELLOW}) # show clipping result

Doc.saveas("SPD/regions_test.dxf")

print(Path("SPD/regions_test.dxf").absolute())

regions.json FILE

[
  [
    [
      -18.900001889999952,
      1450.7000002308125
    ],
    [
      -18.900001889999952,
      1470.7351470734998
    ],
    [
      1278.90012789,
      1470.7351470734998
    ],
    [
      1278.90012789,
      1450.70001562087
    ],
    [
      1503.6001841952093,
      1450.7000156208703
    ],
    [
      1503.6001841952093,
      1388.3850000081884
    ],
    [
      1503.6001841952093,
      1388.3850000081884
    ],
    [
      1647.3246376764234,
      1388.3850000081884
    ],
    [
      1647.3246376764234,
      1548.1475422037274
    ],
    [
      1831.0471719722357,
      1548.1475422037274
    ],
    [
      1831.0471719722357,
      1388.3850000081884
    ],
    [
      1831.0471719722357,
      1388.3850000081884
    ],
    [
      1980.6216566984945,
      1388.3850000081884
    ],
    [
      1980.6216566984945,
      1224.6149999918116
    ],
    [
      1831.0471719722357,
      1224.6149999918116
    ],
    [
      1831.0471719722357,
      1160.3525263520064
    ],
    [
      1647.3246376764234,
      1160.3525263520064
    ],
    [
      1647.3246376764234,
      1160.3525263520064
    ],
    [
      1647.3246376764234,
      1224.6149999918116
    ],
    [
      1647.3246376764234,
      1224.6149999918116
    ],
    [
      1503.6001841952093,
      1224.6149999918116
    ],
    [
      1503.6001841952093,
      1162.2999997691875
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    [
      1278.90012789,
      1162.2999997691877
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      1278.90012789,
      1162.2999997691877
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    [
      1278.90012789,
      286.7000156208702
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    [
      1503.6001841952093,
      286.70001562087026
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    [
      1503.6001841952093,
      224.3850000081885
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    [
      1503.6001841952093,
      224.3850000081885
    ],
    [
      1647.3246376764234,
      224.3850000081885
    ],
    [
      1647.3246376764234,
      384.1475422037275
    ],
    [
      1831.0471719722357,
      384.1475422037275
    ],
    [
      1831.0471719722357,
      224.3850000081885
    ],
    [
      1831.0471719722357,
      224.3850000081885
    ],
    [
      1980.6216566984945,
      224.3850000081885
    ],
    [
      1980.6216566984945,
      60.61499999181149
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      1831.0471719722357,
      60.614999991811544
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      1831.0471719722357,
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      1647.3246376764234,
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      1647.3246376764234,
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    [
      1647.3246376764234,
      60.61499999181149
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    [
      1647.3246376764234,
      60.61499999181149
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    [
      1503.6001841952093,
      60.61499999181149
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    [
      1503.6001841952093,
      -1.7000002308124635
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    [
      1278.90012789,
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    [
      1278.90012789,
      -1.7000002308124635
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    [
      1278.90012789,
      -21.735002173499993
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    [
      -18.900001890000045,
      -21.735002173499993
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    [
      -18.900001890000045,
      -21.735002173499993
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    [
      -18.900001890000045,
      -1.7000156208705448
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    [
      -243.6001841952094,
      -1.7000156208702606
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    [
      -243.6001841952094,
      -1.7000156208702606
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    [
      -243.6001841952094,
      60.61499999181149
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    [
      -243.6001841952094,
      60.61499999181149
    ],
    [
      -237.7502641782885,
      60.61499999181149
    ],
    [
      -237.7502641782885,
      224.3850000081885
    ],
    [
      -243.6001841952094,
      224.3850000081885
    ],
    [
      -243.6001841952094,
      286.70000023081246
    ],
    [
      -18.900001890000027,
      286.7000002308125
    ],
    [
      -18.900001890000027,
      286.7000002308125
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    [
      -18.90000188999997,
      1162.2999843791297
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    [
      -243.6001841952094,
      1162.2999843791297
    ],
    [
      -243.6001841952094,
      1162.2999843791297
    ],
    [
      -243.6001841952094,
      1450.7000002308125
    ],
    [
      -18.900001889999952,
      1450.7000002308125
    ]
  ],
  [
    [
      -392.2502641782885,
      1224.6149999918116
    ],
    [
      -237.7502641782885,
      1224.6149999918116
    ],
    [
      -237.7502641782885,
      1388.3850000081884
    ],
    [
      -392.2502641782885,
      1388.3850000081884
    ],
    [
      -392.2502641782885,
      1224.6149999918116
    ]
  ]
]

[mozman]

UPDATE: the is_inside_polygon() function is incorrect!

There is a bug in the intersection function for parallel or collinear lines. If I "jiggle" the points a little, the result is correct:

def jiggle(points: list[Vec2]) -> list[Vec2]:
    return [Vec2(random.random(), random.random()) + p for p in points]