Skeleton 2D docs do not match Godot 4

[jivvy]

Your Godot version:

v4.0.beta.custom_build [4935493f7]

Issue description:

I think Godot 4 removed 2D IK chains, and replaced it with the Bone2D system.

There isn't really any documentation for how to use the Bone2D system, or how to use it to do IK.
If anyone knows how to use the new system, could you update the docs or explain here how it works?
Thanks!

URL to the documentation page:

This page is no longer relevant:
https://docs.godotengine.org/en/latest/tutorials/animation/cutout_animation.html

The information on this page is no longer correct:
https://docs.godotengine.org/en/latest/tutorials/animation/2d_skeletons.html

[jivvy]

I found that @TwistedTwigleg contributed this PR: New and improved IK in Skeleton2D

Also looks like a lot of the examples in https://github.com/TwistedTwigleg/Godot_GSOC_2020_2D_Project are broken in the latest GD4 build

[jivvy]

There is some documentation in the engine, but it does not really explain how to use the new Bones system.

Since GD4 is in beta now, I think proper long-form explanations / tutorials would go a long way toward usability

[Calinou]

PS: In the future, please use the Edit button (located behind the … icon in the top-right corner of your comments) instead of multi-posting.

Hey, now that Godot 4's going to come out soon, does anyone know how to use IK with Skeleton2D yet? I tried using FABRIK but it's just resulted in it spinning in circles.

Godot_v4.0-rc6_win64_BXmuFhHaEt.mp4

Edit: Better video

2023-02-28.13-48-10.mp4

Okay, I figured it out. The issue was that I was setting the target node to be a bone, when it should be outside the skeleton altogether, or at least not a node in the chain lol

Anyway, I think that we should remove https://docs.godotengine.org/en/latest/tutorials/animation/cutout_animation.html

Is there a way to use sprites with the skeleton2d?

[fguillen]

Where can I find updated documentation/tutorials on how to use Skeleton2D in Godot 4?

[hsandt]

Also, when you update the doc, mind how the Skeleton actions changed order and names:

"Make Rest Pose (From Bones)" => "Overwrite Rest Pose"
"Set Bones to Rest Pose" => "Reset to Rest Pose"

See godotengine/godot#54793

[hsandt]

Where can I find updated documentation/tutorials on how to use Skeleton2D in Godot 4?

Personally I started following 3rd party videos like: https://youtu.be/AMRjtW-3T0o
but this particular one is a mix of the Cutout Animation tutorial which uses sprites, but adding an actual Skeleton on top with bones in the middle... I'm adapting it to my needs as I use Polygons.

It may be nice to explain how the tutorials differ and be clear on how each develop can combine all the features:

• Sprite vs Polygon + Texture
• Skeleton at the top with Bones and Sprite/Polygon under each Bone vs Skeleton besides the Sprites/Polygons, which are in a flat hierarchy (using child index for Z ordering)
• If using Skeleton at the top: Use Remote Transforms vs Change Z ordering by setting Z index for each Sprite/Polygon (it's only mentioned in a note)

Right now, Cutout animation tutorial uses:

• Sprite
• No skeleton, hierarchy of sprites with "invisible bones" created via the Bone menu. Apparently this disappeared in Godot 4, you can only Make Bone2D from Node (which is clearer I think as user will see a proper Bone2D icon in the scene) -> so this will need to be completely replaced
• Use Remote Transforms (since the old bone creation method is equivalent to having a skeleton at the top)

The Skeleton tutorial uses:

• Polygon + Texture
• Skeleton besides polygons. Polygons are in flat hierarchy, using child index for Z order
• Since polygon order is used for Z ordering, no need to use Z index nor Remote Transforms

The video I linked uses:

• Sprite
• Skeleton at the top, with bones under it and sprites attached to bones
• Remote transforms to fix remaining bad Z ordering

It's not bad to have a tutorial that combines 3 methods to start with, esp. if Godot 4 has a canonical method; but summing up each option for each part of the problem would help developers make the final decision that fits their project.

EDIT: I continued with the tutorials and now I get the big difference between cutout and actual rigged skeleton: mesh deformation.

So we could make things clearer by explaining the differences in the intro of each page. Because both use the Skeleton, we should insist on rigging and mesh deformation:

• Cutout animation: puppet-style animation by purely rotating and translating body parts. We'll use the skeleton purely to manipulate body limbs, added as sprites under each bone (or rather, for convenience, build a tree of sprites, then use Make Bone from Node command to auto-create a Node and place the Sprite under it). The current intro is quite good at explaining this, but the given examples seems to sometimes deform meshes so I'm not sure if there are proper examples to give there.
• Skeleton page -> renamed to something like Skeleton rigging and Mesh deformation: we'll go further and animate body parts with texture deformation by using textured polygons instead of sprites, and defining a skeleton besides the polygons but binding it to them. We can of course define vertices so there is no deformation at all, but the method is more flexible as we can add deformation later if we want (at the cost of more painting work).