How to detect On Trigger Enter like

[manurocker95]

Hi! I'd like to know how I can detect whenever a softbody is inside an area. Something like on Trigger enter and exit but for obi solver. Should I use obi colliders with the collider as On trigger and manually check if it's trigger or not with particle onCollision?

[josemendez]

Hi! I'd like to know how I can detect whenever a softbody is inside an area. Something like on Trigger enter and exit but for obi solver. Should I use obi colliders with the collider as On trigger and manually check if it's trigger or not with particle onCollision?

Triggers work fine with Obi, contacts with them will be reported in onCollision, but will not actually affect particle physics in any way.

This is enough if you want the equivalent to Unity's OnTriggerStay (determining if a particle is inside a trigger). If you also need trigger enter/exit events, there's many ways to do that. The simplest approach involves keeping both the current and the previous frame contacts, then looking for contacts that are new, or contacts that are gone. Here's a simple (not terribly well optimized) sample script that does just that:

Code:

using UnityEngine;
using UnityEngine.Events;
using System;
using System.Collections.Generic;

namespace Obi
{
    [RequireComponent(typeof(ObiSolver))]
    public class ObiContactEventDispatcher : MonoBehaviour
    {
        private ObiSolver solver;
        private Oni.Contact[] prevData;
        private int prevCount;
        private ContactComparer comparer;

        private class ContactComparer : IComparer<Oni.Contact>
        {
            ObiSolver solver;

            public ContactComparer(ObiSolver solver)
            {
                this.solver = solver;
            }

            public int Compare(Oni.Contact x, Oni.Contact y)
            {
                return CompareByRef(ref x, ref y, solver);
            }
        }

        private static int CompareByRef(ref Oni.Contact a, ref Oni.Contact b, ObiSolver solver)
        {
            if (a.other == b.other)
            {
                int hashA = solver.particleToActor[a.particle].actor.GetInstanceID();
                int hashB = solver.particleToActor[b.particle].actor.GetInstanceID();
                return hashA.CompareTo(hashB);
            }
            return a.other.CompareTo(b.other);
        }

        [System.Serializable]
        public class ContactCallback : UnityEvent<ObiSolver, Oni.Contact> { }

        public float distanceThreshold = 0.01f;
        public ContactCallback onContactEnter = new ContactCallback();
        public ContactCallback onContactStay = new ContactCallback();
        public ContactCallback onContactExit = new ContactCallback();

        void Awake()
        {
            solver = GetComponent<ObiSolver>();
            comparer = new ContactComparer(solver);
            prevData = new Oni.Contact[0];
        }

        void OnEnable()
        {
            solver.OnCollision += Solver_OnCollision;
        }

        void OnDisable()
        {
            solver.OnCollision -= Solver_OnCollision;
        }

        private int FilterOutDistantContacts(Oni.Contact[] data, int count)
        {
            int filteredCount = count;

            // simply iterate trough all contacts,
            // moving the ones above the threshold to the end of the array:
            for (int i = count -1 ; i >= 0; --i)
                if (data[i].distance > distanceThreshold)
                    ObiUtils.Swap(ref data[i], ref data[--filteredCount]);

            return filteredCount;
        }

        private int RemoveDuplicates(Oni.Contact[] data, int count)
        {
            if (count == 0)
                return 0;

            // assuming the array is sorted, iterate trough the array
            // replacing duplicates by the first contact that's different:
            int i = 0, r = 0;
            while (++i != count)
                if (CompareByRef(ref data[i], ref data[r], solver) != 0 && ++r != i)
                    data[r] = data[i];

            return ++r;
        }

        private void InvokeCallbacks(Oni.Contact[] data, int count)
        {
            int a = 0, b = 0;
            int lengthA = count, lengthB = prevCount;

            // while we haven't reached the end of either array:
            while (a < lengthA && b < lengthB)
            {
                // compare both contacts:
                int compare = CompareByRef(ref data[a], ref prevData[b], solver);

                // call the appropiate event depending on the comparison result:
                if (compare < 0)
                    onContactEnter.Invoke(solver, data[a++]);
                else if (compare > 0)
                    onContactExit.Invoke(solver, prevData[b++]);
                else
                {
                    onContactStay.Invoke(solver, data[a++]); b++;
                }
            }

            // finish iterating trough both lists:
            while (a < lengthA)
                onContactEnter.Invoke(solver, data[a++]);

            while (b < lengthB)
                onContactExit.Invoke(solver, prevData[b++]);
        }

        void Solver_OnCollision(object sender, ObiSolver.ObiCollisionEventArgs args)
        {
            // here we access the internal backing array (Data) directly,
            // instead of using the accessor property. This slightly improves performance.
            // note: the backing array length is the lists' capacity, so we
            // need to use args.contacts.Count to get the actual number of contacts.

            // skip all contacts above the distance threshold by moving them to the end of the array:
            int filteredCount = FilterOutDistantContacts(args.contacts.Data, args.contacts.Count);

            // sort the remaining contacts by collider, then by actor:
            Array.Sort(args.contacts.Data, 0, filteredCount, comparer);

            // remove duplicates:
            filteredCount = RemoveDuplicates(args.contacts.Data, filteredCount);

            // zip trough the current and previous contact lists once, invoking events when appropiate.
            InvokeCallbacks(args.contacts.Data, filteredCount);

            // store current contact list/count for next frame.
            // could get better performance by double buffering instead of copying:
            if (filteredCount > prevData.Length)
                Array.Resize(ref prevData, filteredCount);
            Array.Copy(args.contacts.Data, prevData, filteredCount);

            prevCount = filteredCount;
        }

    }
}