FABRIKTest

using Unity.Mathmatics;
using UnityEngine;

public class FABRIKTest : MonoBehaviour
{
    void Awake() => camera = Camera.main;

    void Update()
    {
            float3 mousePosition = Input.mousePosition;
        mousePosition.z = -camera.transform.position.z;
        float3 worldMousePosition = new float3(camera.ScreenToWorldPoint(mousePosition));

        float3 screenCenter = camera.ViewportToWorldPoint(new float3(new float2(0.5f, 0.5f), -camera.transform.position.z));

        Debug.DrawLine(screenCenter + new float3(-0.1f, 0, 0), screenCenter + new float3(0.1f, 0, 0));
        Debug.DrawLine(screenCenter + new float3(0, -0.1f, 0), screenCenter + new float3(0, 0.1f, 0));

        if (Input.GetMouseButton(0))
            target = math.lerp(worldMousePosition.xy - screenCenter.xy, target, math.pow(2, -5 * Time.deltaTime));

        if (Input.GetMouseButton(1))
        {
            float3 newCameraPosition = camera.transform.position;
            newCameraPosition = math.lerp(worldMousePosition + new float3(0, 0, camera.transform.position.z), newCameraPosition, math.pow(2, -Time.deltaTime));
            camera.transform.position = newCameraPosition;
        }

        float2 root = segments[segments.Length - 1];

        for (int i = 0; segments.Length - 1 > i; i++)
        {
            float2 r = Reach(segments[i], segments[i + 1], target);
            segments[i] = target;
            target = r;
        }

        segments[segments.Length - 1] = target;

        target = root;

        for (int i = segments.Length - 1; i > 0; i--)
        {
            float2 r = Reach(segments[i], segments[i - 1], target);
            segments[i] = target;
            target = r;
        }

        segments[0] = target;

        for (int i = 0; segments.Length - 1 > i; i++)
        {
            solutions[i + 1] = screenCenter + new float3(segments[i], 0);
            solutions[i + 2] = screenCenter + new float3(segments[i + 1], 0);
        }

        solutions[0] = solutions[1];
        solutions[solutions.Length - 1] = solutions[solutions.Length - 2];

        for (int i = 0; solutions.Length - 1 > i; i++)
            Debug.DrawLine(solutions[i], solutions[i + 1]);
    }

    private float2 Reach(float2 head, float2 tail, float2 target)
    {
        float2 direction = tail - target;
        return target + (direction * math.length(tail - head) / math.length(direction));
    }

    float2[] segments = new float2[6] { new float2(5, 4), new float2(4, 3), new float2(3, 2), new float2(2, 1), new float2(1, 0), new float2(0, 0) };
    float3[] solutions = new float3[6 + 2];
    float2 target = float2.zero;
}