SkeletonIK acting oddly

[dsobiera]

Godot version: 3.2.3, 3.3

OS/device including version:

Ubuntu Linux 64 bit 20.04, OpenGL ES 3.0 Renderer: GeForce GTX 960/PCIe/SSE2, NVidia 460.73.01

Issue description:

Attached video shows that when I do a simple export from Blender and bring into godot, and set up a SkeletonIK, a weird stair stepping bend happens to the object when I "Play IK" and move the target object. I tried asking in some user group areas but nobody seemed to have any idea why this was happening. So, I am filing this issue for more "official" help :) .

ikbend.mp4

Steps to reproduce:
See video

Minimal reproduction project:

[Calinou]

Possible duplicate of #48078 ? Also look at other SkeletonIK issues: https://github.com/godotengine/godot/issues?q=is%3Aissue+is%3Aopen+sort%3Aupdated-desc+skeletonik

[dsobiera]

Here is the godot project in the video:

ikbend4github.zip

[akien-mga]

I tested the project in 3.3-stable, and in 3.x with #48251 applied, to see if it makes a difference.

In both versions:

• Opening the project triggers this error:

ERROR: get_global_transform: Condition "!is_inside_tree()" is true. Returned: Transform()
   At: scene/3d/spatial.cpp:252.

• The "stair stepping" behavior can be reproduced when moving the target mesh. I don't have experience with IK so I can't say if it's expected or a bug.

In 3.3-stable only, fixed by #48251:

• Clicking "Play IK" triggered a massive spam of this error:

ERROR: set_look_at: Condition "v_x.length() == 0" is true.
   At: core/math/transform.cpp:97.

That also goes together with a weird inflection of the bones. So that part might be a duplicate of some other issue fixed by #48251, but the initial report was for 3.2.3-stable and this is still reproducible.

CC @TwistedTwigleg @AndreaCatania FYI.

[dsobiera]

For what it is worth knowing, I tried this in 3.3.2-stable with the same odd results.