Скелет 2D: кости, веса и IK

using Reckfell;

public partial class SkinArmDemo : Entity2D
{
    public Skeleton2D Skeleton { get; private set; } = null!;
    public Bone2D Upper { get; private set; } = null!;
    public Bone2D Lower { get; private set; } = null!;
    public Polygon2D Skin { get; private set; } = null!;
    public AnimationPlayer Player { get; private set; } = null!;

    public override void _Ready()
    {
        Skeleton = new Skeleton2D { Name="Skeleton" };
        Upper = new Bone2D { Name="Upper" };
        Lower = new Bone2D { Name="Lower", Position=new Vector2(80,0) };
        Upper.SetAutocalculateLengthAndAngle(false); Upper.SetLength(80);
        Lower.SetAutocalculateLengthAndAngle(false); Lower.SetLength(80);
        Upper.Rest=Upper.Transform; Lower.Rest=Lower.Transform;
        Upper.AddChild(Lower); Skeleton.AddChild(Upper); AddChild(Skeleton);
        Skin = new Polygon2D
        {
            Name="Skin", Skeleton=new EntityPath("../Skeleton"),
            Polygon=[new(0,-20),new(80,-20),new(160,-20),new(160,20),new(80,20),new(0,20),new(80,0)],
            InternalVertexCount=1,
            UV=[new(0,0),new(32,0),new(64,0),new(64,16),new(32,16),new(0,16),new(32,8)],
            Polygons=new Reckfell.Collections.Array
            {
                new int[]{0,1,6},new int[]{1,2,6},new int[]{2,3,6},
                new int[]{3,4,6},new int[]{4,5,6},new int[]{5,0,6}
            }
        };
        using var image=Image.CreateEmpty(64,16,false,Image.Format.Rgba8);
        for(int x=0;x<64;x++)
            for(int y=0;y<16;y++)
                image.SetPixel(x,y,(x/8)%2==0 ? new Color(.15f,.35f,1) : Colors.White);
        Skin.Texture=ImageTexture.CreateFromImage(image);
        Skin.AddBone(new EntityPath("Upper"),new float[]{1,.5f,0,0,.5f,1,.5f});
        Skin.AddBone(new EntityPath("Upper/Lower"),new float[]{0,.5f,1,1,.5f,0,.5f});
        AddChild(Skin);
        Player = new AnimationPlayer { Name="AnimationPlayer",RootEntity=new EntityPath("..") };
        AddChild(Player);
        var bend=new Animation { Length=2,LoopMode=Animation.LoopModeEnum.Linear };
        int track=bend.AddTrack(Animation.TrackType.Value);
        bend.TrackSetPath(track,new EntityPath("Skeleton/Upper/Lower:rotation"));
        bend.TrackInsertKey(track,0,0f); bend.TrackInsertKey(track,1,.8f); bend.TrackInsertKey(track,2,0f);
        var library=new AnimationLibrary(); library.AddAnimation("bend",bend);
        Player.AddAnimationLibrary("",library); Player.Play("bend");
    }

    public void ApplyRestPose()
    {
        Player.Stop(keepState:true);
        Upper.ApplyRest(); Lower.ApplyRest();
    }

    public override void _UnhandledInput(InputEvent @event)
    {
        if (!@event.IsActionPressed("animation_pause")) return;
        if (Player.IsPlaying()) Player.Pause(); else Player.Play("bend");
        GetViewport().SetInputAsHandled();
    }
}

using Reckfell;

public partial class TwoBoneIkDemo : SkinArmDemo
{
    public Entity2D Target { get; private set; } = null!;
    public SkeletonModificationStack2D Stack { get; private set; } = null!;

    public override void _Ready()
    {
        base._Ready();
        ApplyRestPose();
        Target = new Entity2D { Name="Target",Position=new Vector2(100,60) };
        Target.AddChild(new Polygon2D
        {
            Polygon=[new(-5,0),new(0,-5),new(5,0),new(0,5)],
            Color=Colors.White
        });
        AddChild(Target);
        _ = Skeleton.GetBoneCount();
        var ik=new SkeletonModification2DTwoBoneIK { Enabled=true };
        ik.SetJointOneBone2DEntity(new EntityPath("Upper"));
        ik.SetJointTwoBone2DEntity(new EntityPath("Upper/Lower"));
        ik.SetTargetEntity(Skeleton.GetPathTo(Target));
        Stack=new SkeletonModificationStack2D { Enabled=true,Strength=1 };
        Stack.AddModification(ik);
        Skeleton.SetModificationStack(Stack);
    }

    public void SetIkEnabled(bool enabled)
    {
        Stack.Enabled=enabled;
        if (!enabled) ApplyRestPose();
    }

    public override void _UnhandledInput(InputEvent @event)
    {
        // The IK stack owns this pose; do not restart the base clip here.
    }
}