Calling the difference function did not yield the correct result

[YangQiBoy]

I would like to start with saying thank you for the great library. I encountered a problem while calling the difference function.

The code is as follows:

Clipper2Lib::PathD temp;
temp.emplace_back(-3, -1);
temp.emplace_back(11, -1);
temp.emplace_back(12, 1);
temp.emplace_back(12, 2);
temp.emplace_back(11, 5);
temp.emplace_back(10, 6);
temp.emplace_back(7, 6);
temp.emplace_back(3, 6);
temp.emplace_back(0, 6);
temp.emplace_back(-3, 5);
temp.emplace_back(-4, 3);
temp.emplace_back(-4, 2);
Clipper2Lib::PathD temp1;
temp1.emplace_back(-3, -1);
temp1.emplace_back(11, -1);
temp1.emplace_back(12, 1);
temp1.emplace_back(12, 2);
temp1.emplace_back(11, 3);
temp1.emplace_back(11, 5);
temp1.emplace_back(10, 6);
temp1.emplace_back(7, 6);
temp1.emplace_back(4, 5);
temp1.emplace_back(3, 6);
temp1.emplace_back(0, 6);
temp1.emplace_back(-3, 5);
temp1.emplace_back(-4, 3);
temp1.emplace_back(-4, 2);
Clipper2Lib::PathsD res;
res.emplace_back(temp);
Clipper2Lib::PathsD res1;
res1.emplace_back(temp1);
Clipper2Lib::PathsD res2=Clipper2Lib::Difference(res, res1, Clipper2Lib::FillRule::NonZero, 8);

The purpose of the code is to subtract the closed path temp1 from the closed path temp, resulting in res2 having only one closed path with a set of points {7, 6,4,5,3,6}. The actual difference result should also have a closed path {11,3,12,11,5}, but the program did not obtain this result. What is the reason for this?

[AngusJohnson]

Your problem is simply due to rounding. Just scale all your coordinates up by a factor of 10 (or whatever).

[YangQiBoy]

HI Angus：
I have scaled all my coordinates up by a factor of 10,the result is still only one closed path.I still can't get another closed path,I'm sorry,due to a typing error, I gave the wrong result in my first question，it should be {11,3,12,2,11,5}, not{11,3,12,11,5};

[AngusJohnson]

You're absolutely right, there is a problem here.
And I'm sorry I didn't look more closely at this the first time.
I'll post a fix shortly.

[AngusJohnson]

In clipper.engine.cpp @ 1525ff, amend (as shown) the last line of the following method:

inline void ClipperBase::UpdateEdgeIntoAEL(Active* e)
  {
    e->bot = e->top;
    e->vertex_top = NextVertex(*e);
    e->top = e->vertex_top->pt;
    e->curr_x = e->bot.x;
    SetDx(*e);
    if (IsJoined(*e)) Split(*e, e->bot);
    if (IsHorizontal(*e)) return;
    InsertScanline(e->top.y);
    CheckJoinLeft(*e, e->bot);
    CheckJoinRight(*e, e->bot, true); //nb: 3rd param = true!
  }

[YangQiBoy]

Thank you for your correction. Now that I have obtained the correct results, I sincerely hope that this library can become more and more perfect