horizontal edges

[cwangbh]

Hello, Angus,

It is well understood that the horizontal coedge can never be removed perfectly, and the test below can be fixed by a double union.
I am trying to understand the logic of processing the horizontal coedges and try to improve the runtime mentioned in the previous discussion. I am just curious that why the upper coedge in this pattern is cleaned but the bottom one remains there? Interestingly, if we remove one of the left vertical bars, the coedge can be removed.

this may be linked to this issue

TEST(Clipper2Tests, testUnionCoedge) {
    using namespace Clipper2Lib;
    Paths64 subject;
    subject.push_back(MakePath({50,60,60,60, 60,100, 50,100}));
    subject.push_back(MakePath({60,50,60,60, -80,60, -80,50}));
    subject.push_back(MakePath({60,30,60,40, -80,40, -80,30}));
    subject.push_back(MakePath({50,-10,60,-10, 60,30, 50,30}));
    subject.push_back(MakePath({-70,-10,-60,-10, -60,100, -70,100}));
    subject.push_back(MakePath({-50,-10,-40,-10, -40,100, -50,100}));
    Clipper64 cp;
    cp.PreserveCollinear = false;
    cp.AddSubject(subject);
    Paths64 clip_solution;

    const bool ret = cp.Execute(ClipType::Union, FillRule::Positive, clip_solution);

    SvgWriter svg;

    //SvgAddSolution(svg, subject, FillRule::Positive, true);
    SvgAddSolution(svg, clip_solution, FillRule::Positive, true);
    SvgSaveToFile(svg, "./produce_union.svg", 550, 550, 10);
}

[AngusJohnson]

Replace this line with

    if (IsHotEdge(horz)) 
    {
      OutPt* op = AddOutPt(horz, horz.top);
      AddTrialHorzJoin(op);
    }

[cwangbh]

amazing, this works.

I tried hard but havenot fixed it.

[cwangbh]

Hello, Angus,

I found another case that looks strange, the two rectangels are linked inside one outrect. It might be more reasonable to split the two rectangles. ProcessHorzJoins has captured this line, but it seems that there is no split logic in this function

TEST(Clipper2Tests, TestCoedge_1) {
    using namespace Clipper2Lib;
    Paths64 subject;
    subject.push_back(MakePath({ 15, 0, 15, 15, 0, 15, 0, 0, 45, 0, 45, 15, 30, 15,30,0}));
    std::reverse(subject.begin(), subject.end());
    Clipper64 cp;
    cp.PreserveCollinear = false;
    cp.AddSubject(subject);
    Paths64 clip_solution;

    const bool ret = cp.Execute(ClipType::Union, FillRule::Positive, clip_solution);

    SvgWriter svg;

    SvgAddSolution(svg, subject, FillRule::Positive, true);
    SvgAddSolution(svg, clip_solution, FillRule::Positive, true);
    SvgSaveToFile(svg, "./coedge_1_union.svg", 550, 550, 10);
}

[AngusJohnson]

Hi again Wang Chao.
I can't duplicate this behavior.
Have you tested this with the latest version in the repository?

[cwangbh]

thanks a lot, the edge is removed when i check out to the latest code.

By the way, i have tried to repace the active linked list with red black tree, while many unit tests in TestMultiplePolygons fails. When the test_number is larger than 130, there are many active edges and it is difficult to pass those tests. Meanwhile, the runtime has not improved much in my case, only the InsertLocalMinimaIntoAEL has some runtime improvement. I will probabily stop the replacement of active edge list and really appreciate your effort in this library.