Help Controlling specific particle force / custom constraints.

Code:

using UnityEngine;

using Obi;



public class SnakeController : MonoBehaviour

{

    public Transform headReferenceFrame;

    public float headSpeed = 20;

    public float upSpeed = 40;

    public float slitherSpeed = 10;



    private ObiRope rope;

    private ObiSolver solver;

    private float[] traction;

    private Vector3[] surfaceNormal;



    private void Start()

    {

        rope = GetComponent<ObiRope>();

        solver = rope.solver;



        // initialize traction array:

        traction = new float[rope.activeParticleCount];

        surfaceNormal = new Vector3[rope.activeParticleCount];



        // subscribe to solver events (to update surface information)

        solver.OnBeginStep += ResetSurfaceInfo;

        solver.OnCollision += AnalyzeContacts;

        solver.OnParticleCollision += AnalyzeContacts;

    }





    private void OnDestroy()

    {

        solver.OnBeginStep -= ResetSurfaceInfo;

        solver.OnCollision -= AnalyzeContacts;

        solver.OnParticleCollision -= AnalyzeContacts;

    }



    private void ResetSurfaceInfo(ObiSolver s, float stepTime)

    {

        // reset surface info:

        for (int i = 0; i < traction.Length; ++i)

        {

            traction[i] = 0;

            surfaceNormal[i] = Vector3.zero;

        }

    }



    private void AnalyzeContacts(object sender, ObiSolver.ObiCollisionEventArgs e)

    {

        // iterate trough all contacts:

        for (int i = 0; i < e.contacts.Count; ++i)

        {

            var contact = e.contacts.Data[i];

            if (contact.distance < 0.005f)

            {

                int simplexIndex = solver.simplices[contact.bodyA];

                var particleInActor = solver.particleToActor[simplexIndex];



                // using 1 here, could calculate a traction value based on the type of terrain, friction, etc.

                traction[particleInActor.indexInActor] = 1;



                // accumulate surface normal:

                surfaceNormal[particleInActor.indexInActor] += (Vector3)contact.normal;

            }

        }

    }



    public void Update()

    {

        if (Input.GetKey(KeyCode.J))

        {

            for (int i = 1; i < rope.activeParticleCount; ++i)

            {

                int solverIndex = rope.solverIndices[i];

                int prevSolverIndex = rope.solverIndices[i - 1];



                // direction from current particle to previous one, projected on the contact surface:

                Vector4 dir = Vector3.ProjectOnPlane(solver.positions[prevSolverIndex] - solver.positions[solverIndex], surfaceNormal[i]).normalized;



                // move in that direction:

                solver.velocities[solverIndex] += dir * traction[i] * slitherSpeed * Time.deltaTime;

            }

        }



        int headIndex = rope.solverIndices[0];



        if (headReferenceFrame != null)

        {

            Vector3 direction = Vector3.zero;



            // Determine movement direction:

            if (Input.GetKey(KeyCode.W))

            {

                direction += headReferenceFrame.forward * headSpeed;

            }

            if (Input.GetKey(KeyCode.A))

            {

                direction += -headReferenceFrame.right * headSpeed;

            }

            if (Input.GetKey(KeyCode.S))

            {

                direction += -headReferenceFrame.forward * headSpeed;

            }

            if (Input.GetKey(KeyCode.D))

            {

                direction += headReferenceFrame.right * headSpeed;

            }



            // flatten out the direction so that it's parallel to the ground:

            direction.y = 0;



            solver.velocities[headIndex] += (Vector4)direction * Time.deltaTime;

        }



        if (Input.GetKey(KeyCode.Space))

            solver.velocities[headIndex] += (Vector4)Vector3.up * Time.deltaTime * upSpeed;

    }

}

Code:

if (Input.GetKey(KeyCode.J))

{

        for (int i = 1; i < rope.activeParticleCount; ++i)

        {

                int solverIndex = rope.solverIndices[i];

                int prevSolverIndex = rope.solverIndices[i - 1];



                // direction from current particle to previous one, projected on the contact surface:

                Vector4 dir = Vector3.ProjectOnPlane(solver.positions[prevSolverIndex] - solver.positions[solverIndex], surfaceNormal[i]).normalized;



                // move in that direction:

                solver.velocities[solverIndex] += dir * traction[i] * slitherSpeed * Time.deltaTime;

        }

}