Path3D Up Vector miscalculation

[crmsncreates]

Godot version

v4.2.dev4.mono.official [549fcce]

System information

Godot v4.2.dev4.mono - Windows 10.0.19045 - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 3080 (NVIDIA; 31.0.15.3619) - Intel(R) Core(TM) i9-10900KF CPU @ 3.70GHz (20 Threads)

Issue description

Since somewhere around 4.1, when a point on a Path3D is moved on the Y-axis, it flips itself and all points after it upside-down:

Moving one of the points that come before it on the X-axis seems to fix the problem?

Though even this seems to have a few errors here and there: (from the repro project)

Expected no flipping, as it worked in previous versions such as v4.0.3.stable.mono.official [5222a99] here:

Steps to reproduce

1. Create a Path3D
2. Add 2 points at the same Y position
3. Move one of them on the Y-axis

Minimal reproduction project

PathBug.zip

[rmmh]

The repro project let me bisect this to 42aa539, part of #72842.

The changes to curve.cpp look relevant.

@TokageItLab, can you have a look?

[kleonc]

The repro project let me bisect this to 42aa539, part of #72842.

The changes to curve.cpp look relevant.

Looking at these changes I think this line:

godot/scene/resources/curve.cpp

Line 1686 in e3e2528

rotate.rotate_to_align(frame_prev.get_column(2), forward);

should have also been changed to accomodate the changed direction, specifically to something like:

rotate.rotate_to_align(-frame_prev.get_column(2), forward);

as -Z basis vector should be now interpreted as forward.

(Haven't tested it at all, just looked at the changed code.)

[rmmh]

Looking at these changes I think this line:

godot/scene/resources/curve.cpp

Line 1686 in e3e2528

rotate.rotate_to_align(frame_prev.get_column(2), forward);

should have also been changed to accomodate the changed direction, specifically to something like:

rotate.rotate_to_align(-frame_prev.get_column(2), forward);

This fixes the repro case, I can try to figure out a regression test and make a PR?