AddTriangle draws lines with nonuniform thickness

[nem0]

Version/Branch of Dear ImGui:

Version: 1.74 WIP (3c238ec latest commit at this time, but the same issue is even in much older versions)
Branch: master

Back-ends: imgui_impl_dx11.cpp + imgui_impl_win32.cpp
Compiler: msvc 2019
Operating System: Win10

My Issue/Question:

Lines of a triangle have nonuniform thickness

Screenshots/Video

Standalone, minimal, complete and verifiable example:

        ImGui::Begin("test");
        auto dl = ImGui::GetWindowDrawList();
        const ImVec2 o = ImGui::GetCursorScreenPos();

        dl->AddTriangle(o, ImVec2(o.x + 100, o.y + 0), ImVec2(o.x + 0, o.y + 100), IM_COL32(0, 255, 0, 255), 3);
        ImGui::End();

If I do this, the triangle looks allright:

[ocornut]

Hi !

I believe this is the same as #2183 in particular there's a suggestion #2183 (comment)
(the change referred in that comment is #2518 by @rmitton)

I haven't looked at your suggestion is detail, it seems simpler to implement than mentioned in the comment above (tho the sqrt is costly), I just have no idea if it is right.

We probably need a little portable suite that shows a bunch of test cases so we can compare algorithms.

Pasting actual text for your patch would help :)

[nem0]

Oh yes, it is indeed the same issue. I'm sorry for that. I tried to search for something similar without success. My fix is probably not robust/complete, since I did not understand what IM_FIXNORMAL2F supposed to do and did not investigate further. I will try to improve the fix.
Closing this now and I will continue in #2183 if I think of anyhting.

[ocornut]

There was actually an issue which creeped in January 2019 and made this worst>
See #4053, fix pushed.