a question about difference

[YangQiBoy]

Hello,AngusJohnson.
The two figures are sub and clip, and sub is the convex hull of clip. I perform a difference operation on sub and clip, and the result in res is two sets of points. All points in these two sets are the same as all points in sub and clip respectively. Why did I get such a result? The code is shown below.

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PathsD sub, clip;
PathsD res;

sub.push_back(MakePathD({ 27.500, 39.500, 85.125, 39.500, 142.750, 39.500,
204.250, 41.750, 219.000, 87.500, 228.500, 122.125, 238.000, 156.750,
205.250, 195.000, 153.250, 197.750, 88.875, 185.750, 24.500, 173.750, -2.000,
132.000, -4.750, 109.375, -7.500, 86.750 }));

clip.push_back(MakePathD({ 142.750, 39.500, 145.390, 42.674, 146.625, 41.750,
159.500, 54.000, 204.250, 41.750, 190.333, 69.187, 213.750, 76.375, 209.745,
84.271, 219.000, 87.500, 207.844, 95.867, 223.250, 111.000, 219.245, 118.896,
228.500, 122.125, 216.121, 125.054, 212.666, 131.865, 238.000, 156.750, 205.250,
164.500, 205.250, 195.000, 175.901, 179.596, 153.250, 197.750, 108.000, 174.000,
88.875, 185.750, 72.000, 172.750, 24.500, 173.750, 32.000, 157.480, 21.750, 151.125,
27.297, 139.092, 27.136, 138.887, -2.000, 132.000, 14.000, 121.000, -4.750, 109.375,
4.250, 101.750, -7.500, 86.750, 33.530, 79.509, 30.250, 62.125, 31.560, 61.016, 27.500, 39.500, 68.750, 52.000, 85.125, 39.500, 88.155, 42.383, 89.000, 41.750, 110.609, 48.298 }));

res = Difference(sub, clip, FillRule::EvenOdd, 8);

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The sub and clip are shown in the following figure, where the blue outline is sub and the red outline is clip

The final result should be all the shapes pointed by the black arrows in the figure below. Can we use a separate set of points to represent the shapes pointed by each arrow?