Wrong behaviour SkeletonIk3d. Godot 4.0.alpha15

[yakud]

Godot version

4.0.alpha15

System information

Windows 11, Vulkan

Issue description

It seems that SkeletonIk3d does not work correctly in Godot 4.0.alpha15. For some reason, the leg bones are not in the correct position.

In godot 3.5 everything looks correct and works without any problems.
It's hard for me to understand if this is a bug on my side or a problem only with Godot 4 alpha

Godot 4.0.alpha15:

Godot 3.5:

Steps to reproduce

Download test project ik_wb_4_alpha15.zip below. Select the scene with main_character then select SkeletonIk3d node and press "Play IK".

Minimal reproduction project

Example with wrong behaviour for Godot 4.0.alpha15:
ik_wb_4_alpha15.zip

Same for Gotod 3.5:
ik_ok_3_5.zip

[TokageItLab]

See #63588. SkeletonIK will be eliminated and replaced ModificationStackNode.

[yakud]

@TokageItLab so both method isn't working properly on my case unfortunately. Tried to solve it by SkeletonModification3DTwoBoneIK but it also looks strange.
btw for my skeleton arms TwoBoneIK works fine.

There is test scene in order to confirm if i'm doing everything correctly
ik_wb2_4_alpha15.zip

[yakud]

I found that UpperLeg bone was rotated on it base for some reason. And there is no way to turn it back.
Does anyone have any advice on how to fix this?

ik-bug.mp4

[addmix]

To me it looks like it is rotated the negative amount it should be. I have the same exact issue with the thigh/hip bone on a rig that I myself created. I wonder if it has to do with the roll of the Godot-generated "hip" bones, or if it has to do with one of the bone's basis vectors being negative. Maybe the thigh bones being attached in the opposite direction of the spine bones causes this?

[yakud]

@addmix I found that my leg bones was rotated to opposite direction regarding the hips bone. I have rolled it to the same direction and export again from blender to godot:

Screenshot

But the result didn't change at all.

Screenshot

I also tried to add two pelvis bones. The result is better but not ideal. You can see that character knee look bad.

Screenshot

I beleive that the issue like the same. The UpLeg bone are little distorted for some reason:

Screenshot

[Naurk]

I have the same problem (in beta 2) with a mixamo rigged model. Found any solution?