GravityObject.cs

using UnityEngine;
using System.Collections.Generic;

/// <summary>Pull a PlayerControl (https://pastebin.com/9M9qyBmP) GameObject toward a Collider.
/// Will work with a MeshCollider, but a SphereCollider or BoxCollider is optimal
/// Latest version at: https://pastebin.com/71fHgXaA</summary>
/// <description>MIT License - TL;DR - This code is free, don't bother me about it!</description>
/// <author email="mvaganov@hotmail.com">Michael Vaganov</author>
public class GravityObject : GravitySource {
    #region public API
    [Tooltip("If false, gravity will be based on the transform.position of this object, not it's collider")]
    public bool useColliderGravity = true;

    public override Vector3 CalculateGravityDirectionFrom(Vector3 point) {
        if(!useColliderGravity) { return (transform.position - point).normalized; }
        Vector3 dir = Vector3.zero;
        switch(colliderType) {
        case ColliderType.box: {
                Vector3 p = NearestPointToBox(myCollider as BoxCollider, point);
                Vector3 delta = p - point;
                dir = delta.normalized;
            }
            break;
        case ColliderType.mesh: {
                Vector3 normal;
                Vector3 p = nearestPointOnMeshCalculationObject.NearestPointTo(point, out normal);
                dir = (p - point).normalized;
            }
            break;
        case ColliderType.sphere: {
                SphereCollider sc = myCollider as SphereCollider;
                Vector3 p = transform.position + sc.center;
                dir = (p - point).normalized;
            }
            break;
        default:
            dir = (transform.position - point).normalized;
            break;
        }
        return dir;
    }
    public static Vector3 NearestPointToBox(BoxCollider box, Vector3 point) {
        Transform t = box.transform;
        Quaternion rot = t.rotation;
        Vector3 delta = point - t.position;
        Vector3 rotatedPoint = (Quaternion.Inverse(rot) * delta) + t.position;
        t.rotation = Quaternion.identity;
        Vector3 nearestPoint = box.ClosestPointOnBounds(rotatedPoint);
        t.rotation = rot;
        delta = nearestPoint - t.position;
        delta = rot * delta;
        nearestPoint = t.position + delta;
        return nearestPoint;
    }
    #endregion
    #region Calculate near-points
    private enum ColliderType { none, mesh, box, sphere };
    private ColliderType colliderType = ColliderType.none;
    private Collider myCollider;
    NearestPointOnMeshCalculationObject nearestPointOnMeshCalculationObject = null;

    public class NearestPointOnMeshCalculationObject {
        Mesh mesh;
        Vector3[] verts;
        Vector3[] norms;
        VertTriList vt;
        KDTree kd;
        Transform transform;

        public NearestPointOnMeshCalculationObject(GameObject go) {
            transform = go.transform;
            mesh = go.GetComponent<MeshFilter>().mesh;
            verts = mesh.vertices;
            norms = mesh.normals;
            vt = new VertTriList(mesh);
            kd = KDTree.MakeFromPoints(verts);
        }
        public Vector3 NearestVertexTo(Vector3 point) {
            // convert point to local space
            point = transform.InverseTransformPoint(point);
            float minDistanceSqr = Mathf.Infinity;
            Vector3 nearestVertex = Vector3.zero;
            // scan all vertices to find nearest
            foreach(Vector3 vertex in verts) {
                Vector3 diff = point-vertex;
                float distSqr = diff.sqrMagnitude;
                if(distSqr < minDistanceSqr) {
                    minDistanceSqr = distSqr;
                    nearestVertex = vertex;
                }
            }
            // convert nearest vertex back to world space
            return transform.TransformPoint(nearestVertex);
        }
        public Vector3 NearestPointTo(Vector3 point, out Vector3 ptNormal) {
            Vector3 objSpacePt = transform.InverseTransformPoint(point);
            Vector3 meshPt = NearestPointOnMesh(objSpacePt, verts, kd, mesh.triangles, vt, out ptNormal);
            Vector3 closest = transform.TransformPoint(meshPt);
            ptNormal = transform.TransformVector(ptNormal).normalized;
            return closest;
        }
        public Vector3 NearestPointTo(Vector3 point) {
            Vector3 objSpacePt = transform.InverseTransformPoint(point);
            Vector3 meshPt = NearestPointOnMesh(objSpacePt, verts, mesh.triangles, vt);
            Vector3 closest = transform.TransformPoint(meshPt);
            return closest;
        }
        public static float GetDistPointToLine(Vector3 origin, Vector3 direction, Vector3 point) {
            Vector3 point2origin = origin - point;
            Vector3 point2closestPointOnLine = point2origin - Vector3.Dot(point2origin, direction) * direction;
            return point2closestPointOnLine.magnitude;
        }
        Vector3 NearestPointOnMesh(Vector3 pt, Vector3[] verts, KDTree vertProx, int[] tri, VertTriList vt, out Vector3 pointNormal) {
            //  find nearest vertex (point must be on triangle useing this vertex if the mesh is convex)
            int nearest = vertProx.FindNearest(pt);
            pointNormal = Vector3.zero;
            //  Get the list of triangles in which the nearest vert "participates".
            int[] nearTris = vt[nearest];
            Vector3 nearestPt = Vector3.zero;
            float nearestSqDist = float.PositiveInfinity;
            TriangleSection ts;
            for(int i = 0; i < nearTris.Length; i++) {
                int triOff = nearTris[i] * 3;
                Vector3 a = verts[tri[triOff]], b = verts[tri[triOff + 1]], c = verts[tri[triOff + 2]];
                Vector3 possNearestPt = NearestPointOnTri(pt, a, b, c, out ts);
                float possNearestSqDist = (pt - possNearestPt).sqrMagnitude;
                if(possNearestSqDist < nearestSqDist) {
                    nearestPt = possNearestPt;
                    nearestSqDist = possNearestSqDist;
                    switch(ts) {
                    case TriangleSection.side_ab: {
                            Vector3 norm1 = norms[tri[triOff+0]], norm2 = norms[tri[triOff+1]];
                            pointNormal = (norm1+norm2)/2;
                        }
                        break;
                    case TriangleSection.side_bc: {
                            Vector3 norm1 = norms[tri[triOff+1]], norm2 = norms[tri[triOff+2]];
                            pointNormal = (norm1+norm2)/2;
                        }
                        break;
                    case TriangleSection.side_ca: {
                            Vector3 norm1 = norms[tri[triOff+2]], norm2 = norms[tri[triOff+0]];
                            pointNormal = (norm1+norm2)/2;
                        }
                        break;
                    case TriangleSection.surface: {
                            Vector3 AB = b - a, AC = c - a;
                            pointNormal = Vector3.Normalize(Vector3.Cross(AB, AC));
                        }
                        break;
                    }
                }
            }
            return nearestPt;
        }
        /// <summary>easier if we don't need to get the normal!</summary>
        Vector3 NearestPointOnMesh(Vector3 pt, Vector3[] verts, int[] tri, VertTriList vt) {
            //  find nearest vertex (point must be on triangle useing this vertex if the mesh is convex)
            int nearest = -1;
            float nearestSqDist = float.PositiveInfinity;
            for(int i = 0; i < verts.Length; i++) {
                float sqDist = (verts[i] - pt).sqrMagnitude;
                if(sqDist < nearestSqDist) {
                    nearest = i;
                    nearestSqDist = sqDist;
                }
            }
            //  Get the list of triangles in which the nearest vert "participates".
            int[] nearTris = vt[nearest];
            Vector3 nearestPt = Vector3.zero;
            nearestSqDist = float.PositiveInfinity;
            TriangleSection ts;
            for(int i = 0; i < nearTris.Length; i++) {
                int triOff = nearTris[i] * 3;
                Vector3 a = verts[tri[triOff]];
                Vector3 b = verts[tri[triOff + 1]];
                Vector3 c = verts[tri[triOff + 2]];
                Vector3 possNearestPt = NearestPointOnTri(pt, a, b, c, out ts);
                float possNearestSqDist = (pt - possNearestPt).sqrMagnitude;
                if(possNearestSqDist < nearestSqDist) {
                    nearestPt = possNearestPt;
                    nearestSqDist = possNearestSqDist;
                }
            }
            return nearestPt;
        }

        public enum TriangleSection { unknown, surface, side_ab, side_bc, side_ca };
        /// <param name="ptNormal">Point normal. If on the triangle surface, returns the surface normal</param>
        public Vector3 NearestPointOnTri(Vector3 pt, Vector3 a, Vector3 b, Vector3 c, out TriangleSection pointDetail) {
            pointDetail = TriangleSection.unknown;
            Vector3 edge1 = b - a;
            Vector3 edge2 = c - a;
            Vector3 edge3 = c - b;
            float edge1Len = edge1.magnitude;
            float edge2Len = edge2.magnitude;
            float edge3Len = edge3.magnitude;
            Vector3 ptLineA = pt - a;
            Vector3 ptLineB = pt - b;
            Vector3 ptLineC = pt - c;
            Vector3 xAxis = edge1 / edge1Len;
            Vector3 zAxis = Vector3.Cross(edge1, edge2).normalized;
            Vector3 yAxis = Vector3.Cross(zAxis, xAxis);
            Vector3 edge1Cross = Vector3.Cross(edge1, ptLineA);
            Vector3 edge2Cross = Vector3.Cross(edge2, -ptLineC);
            Vector3 edge3Cross = Vector3.Cross(edge3, ptLineB);
            bool edge1On = Vector3.Dot(edge1Cross, zAxis) > 0f;
            bool edge2On = Vector3.Dot(edge2Cross, zAxis) > 0f;
            bool edge3On = Vector3.Dot(edge3Cross, zAxis) > 0f;
            //  If the point is inside the triangle then return its coordinate.
            if(edge1On && edge2On && edge3On) {
                pointDetail = TriangleSection.surface;
                float xExtent = Vector3.Dot(ptLineA, xAxis);
                float yExtent = Vector3.Dot(ptLineA, yAxis);
                return a + xAxis * xExtent + yAxis * yExtent;
            }
            //  Otherwise, the nearest point is somewhere along one of the edges.
            Vector3 edge1Norm = xAxis;
            Vector3 edge2Norm = edge2.normalized;
            Vector3 edge3Norm = edge3.normalized;
            float edge1Ext = Mathf.Clamp(Vector3.Dot(edge1Norm, ptLineA), 0f, edge1Len);
            float edge2Ext = Mathf.Clamp(Vector3.Dot(edge2Norm, ptLineA), 0f, edge2Len);
            float edge3Ext = Mathf.Clamp(Vector3.Dot(edge3Norm, ptLineB), 0f, edge3Len);
            Vector3 edge1Pt = a + edge1Ext * edge1Norm;
            Vector3 edge2Pt = a + edge2Ext * edge2Norm;
            Vector3 edge3Pt = b + edge3Ext * edge3Norm;
            float sqDist1 = (pt - edge1Pt).sqrMagnitude;
            float sqDist2 = (pt - edge2Pt).sqrMagnitude;
            float sqDist3 = (pt - edge3Pt).sqrMagnitude;
            if(sqDist1 < sqDist2) {
                if(sqDist1 < sqDist3) {
                    pointDetail = TriangleSection.side_ab;
                    return edge1Pt;
                } else {
                    pointDetail = TriangleSection.side_bc;
                    return edge3Pt;
                }
            } else if(sqDist2 < sqDist3) {
                pointDetail = TriangleSection.side_ca;
                return edge2Pt;
            } else {
                pointDetail = TriangleSection.side_bc;
                return edge3Pt;
            }
        }
    }
    #endregion // Calculate near-points
    #region VertTriList
    //  lookup table for a mesh identifying which vertexes reference which triangles
    public class VertTriList {
        public int[][] list;
        public int[] aliases;

        //  Indexable - use "vertTri[i]" to get the list of triangles for vertex i.
        public int[] this[int index] {
            get { return list[aliases[index]]; }
        }
        public VertTriList(int[] tri, Vector3[] verts) { Init(tri, verts); }
        public VertTriList(Mesh mesh) { Init(mesh.triangles, mesh.vertices); }
        public void Init(int[] tri, Vector3[] verts) {
            int numVerts = verts.Length;
            // find duplicate verts, since many meshes are created with dups for rendering purposes
            List<int>[] duplicates = new List<int>[verts.Length];
            // create an alias table, so duplicate vertexes can point to the same triangles
            aliases = new int[verts.Length];
            for(int i = 0; i < duplicates.Length; ++i) { duplicates[i] = new List<int>(); }
            for(int i = 0; i < verts.Length; ++i) {
                for(int j = i + 1; j < verts.Length; ++j) {
                    if(verts[i] == verts[j]) {
                        if(!duplicates[i].Contains(j)) duplicates[i].Add(j);
                        if(!duplicates[j].Contains(i)) duplicates[j].Add(i);
                    }
                }
            }
            // sort duplicates, so the earliest verts are first, and add that as an aliases
            for(int i = 0; i < duplicates.Length; ++i) {
                duplicates[i].Sort();
                aliases[i] = (duplicates[i].Count>0) ? Mathf.Min(i, duplicates[i][0]) : i;
            }
            // go through the triangles, keeping a count of how many times each vert is used
            int[] counts = new int[numVerts];
            for(int i = 0; i < tri.Length; i++) { counts[tri[i]]++; }
            // merge aliases into earliest counts
            for(int i = 0; i < aliases.Length; ++i) {
                if(aliases[i] < i) {
                    int earliestIndex = aliases[i];
                    counts[earliestIndex] += counts[i];
                    counts[i] = 0;
                }
            }
            // initialise empty jagged array with appropriate number of elements for each vert.
            list = new int[numVerts][];
            for(int i = 0; i < counts.Length; i++) {
                if(counts[i] > 0) { list[i] = new int[counts[i]]; }
            }
            // assign appropriate triangle number each time given vert is encountered in triangles list
            for(int i = 0; i < tri.Length; i++) {
                int vert = tri[i];
                vert = aliases[vert]; // take aliases into account
                list[vert][--counts[vert]] = i / 3;
            }
        }
    }
    #endregion
    #region KDTree
    // KDTree.cs - A Stark, September 2009.
    //  This class implements a data structure that stores a list of points in space.
    //  A common task in game programming is to take a supplied point and discover which
    //  of a stored set of points is nearest to it. For example, in path-plotting, it is often
    //  useful to know which waypoint is nearest to the player's current
    //  position. The kd-tree allows this "nearest neighbour" search to be carried out quickly,
    //  or at least much more quickly than a simple linear search through the list.
    //  At present, the class only allows for construction (using the MakeFromPoints static method)
    //  and nearest-neighbour searching (using FindNearest). More exotic kd-trees are possible, and
    //  this class may be extended in the future if there seems to be a need.
    //  nearest-neighbour search returns integer index
    public class KDTree {
        public KDTree[] lr;
        public Vector3 pivot;
        public int pivotIndex, axis;
        //  faster if 2, for X,Y search
        const int numDims = 3;

        public KDTree() { lr = new KDTree[2]; }
        //  Make a new tree from a list of points.
        public static KDTree MakeFromPoints(params Vector3[] points) {
            int[] indices = Iota(points.Length);
            return MakeFromPointsInner(0, 0, points.Length - 1, points, indices);
        }
        //  Recursively build a tree by separating points at plane boundaries.
        static KDTree MakeFromPointsInner(int depth, int stIndex, int enIndex, Vector3[] points, int[] inds) {
            KDTree root = new KDTree();
            root.axis = depth % numDims;
            int splitPoint = FindPivotIndex(points, inds, stIndex, enIndex, root.axis);
            root.pivotIndex = inds[splitPoint];
            root.pivot = points[root.pivotIndex];
            int leftEndIndex = splitPoint - 1;
            if(leftEndIndex >= stIndex) {
                root.lr[0] = MakeFromPointsInner(depth + 1, stIndex, leftEndIndex, points, inds);
            }
            int rightStartIndex = splitPoint + 1;
            if(rightStartIndex <= enIndex) {
                root.lr[1] = MakeFromPointsInner(depth + 1, rightStartIndex, enIndex, points, inds);
            }
            return root;
        }
        static void SwapElements(int[] arr, int a, int b) {
            int temp = arr[a];
            arr[a] = arr[b];
            arr[b] = temp;
        }
        //  Simple "median of three" heuristic to find a reasonable splitting plane.
        static int FindSplitPoint(Vector3[] points, int[] inds, int stIndex, int enIndex, int axis) {
            float a = points[inds[stIndex]][axis];
            float b = points[inds[enIndex]][axis];
            int midIndex = (stIndex + enIndex) / 2;
            float m = points[inds[midIndex]][axis];
            if(a > b) {
                if(m > a) { return stIndex; }
                if(b > m) { return enIndex; }
                return midIndex;
            } else {
                if(a > m) { return stIndex; }
                if(m > b) { return enIndex; }
                return midIndex;
            }
        }
        //  a new pivot index from range by splitting points falling at either side of its plane.
        public static int FindPivotIndex(Vector3[] points, int[] inds, int stIndex, int enIndex, int axis) {
            int splitPoint = FindSplitPoint(points, inds, stIndex, enIndex, axis);
            // int splitPoint = Random.Range(stIndex, enIndex);
            Vector3 pivot = points[inds[splitPoint]];
            SwapElements(inds, stIndex, splitPoint);
            int currPt = stIndex + 1;
            int endPt = enIndex;
            while(currPt <= endPt) {
                Vector3 curr = points[inds[currPt]];
                if((curr[axis] > pivot[axis])) {
                    SwapElements(inds, currPt, endPt);
                    endPt--;
                } else {
                    SwapElements(inds, currPt - 1, currPt);
                    currPt++;
                }
            }
            return currPt - 1;
        }
        public static int[] Iota(int num) {
            int[] result = new int[num];
            for(int i = 0; i < num; i++) { result[i] = i; }
            return result;
        }
        //  Find the nearest point in the set to the supplied point.
        public int FindNearest(Vector3 pt) {
            float bestSqDist = float.PositiveInfinity;
            int bestIndex = -1;
            Search(pt, ref bestSqDist, ref bestIndex);
            return bestIndex;
        }
        //  Recursively search the tree.
        void Search(Vector3 pt, ref float bestSqSoFar, ref int bestIndex) {
            float mySqDist = (pivot - pt).sqrMagnitude;
            if(mySqDist < bestSqSoFar) {
                bestSqSoFar = mySqDist;
                bestIndex = pivotIndex;
            }
            float planeDist = pt[axis] - pivot[axis]; //DistFromSplitPlane(pt, pivot, axis);
            int selector = planeDist <= 0 ? 0 : 1;
            if(lr[selector] != null) {
                lr[selector].Search(pt, ref bestSqSoFar, ref bestIndex);
            }
            selector = (selector + 1) % 2;
            float sqPlaneDist = planeDist * planeDist;
            if((lr[selector] != null) && (bestSqSoFar > sqPlaneDist)) {
                lr[selector].Search(pt, ref bestSqSoFar, ref bestIndex);
            }
        }
        //  Get a point's distance from an axis-aligned plane.
        float DistFromSplitPlane(Vector3 pt, Vector3 planePt, int axis) {
            return pt[axis] - planePt[axis];
        }
        //  Simple output of tree structure - mainly useful for getting a rough
        //  idea of how deep the tree is (and therefore how well the splitting
        //  heuristic is performing).
        public string Dump(int level) {
            string result = pivotIndex.ToString().PadLeft(level) + "\n";
            if(lr[0] != null) { result += lr[0].Dump(level + 2); }
            if(lr[1] != null) { result += lr[1].Dump(level + 2); }
            return result;
        }
    }
    #endregion
    #region MonoBehaviour
    void Start() {
        myCollider = GetComponent<Collider>();
        if(myCollider is BoxCollider) { colliderType = ColliderType.box; } else if(myCollider is SphereCollider) { colliderType = ColliderType.sphere; } else if(myCollider is MeshCollider) {
            nearestPointOnMeshCalculationObject = new NearestPointOnMeshCalculationObject(gameObject);
            colliderType = ColliderType.mesh;
        }
    }
    #endregion // MonoBehaviour
}

#region Base GravitySource
public class GravitySource : MonoBehaviour {
    [Tooltip("apply gravity if player hits this collider")]
    public bool entangleOnCollision = true;
    [Tooltip("apply gravity if player enters this collider trigger")]
    public bool entangleOnTrigger = true;
    [Tooltip("apply gravity power on player")]
    public bool forceGravitypower = false;
    [Tooltip("How much acceleration to apply to the PlayerControl, if gravity power is forced")]
    public float power = 9.81f;

    public virtual Vector3 CalculateGravityDirectionFrom(Vector3 point) {
        Vector3 delta = transform.position - point;
        return delta.normalized;
    }
    public void OnCollisionEnter(Collision col) {
        if(!enabled) return;
        if(entangleOnCollision) { EntanglePlayer(col.gameObject.GetComponent<PlayerControl>()); }
    }
    public void OnTriggerEnter(Collider col) {
        if(entangleOnTrigger) { EntanglePlayer(col.GetComponent<PlayerControl>()); }
    }
    public void EntanglePlayer(PlayerControl p) {
        if(p && p.gravityApplication != PlayerControl.GravityState.none) {
            GravityPuller gp = p.gameObject.GetComponent<GravityPuller>();
            if(!gp) { gp = p.gameObject.AddComponent<GravityPuller>(); }
            if(gp.gravitySource != this) { gp.Init(this); } else { gp.Refresh(); }
        }
    }
}
#endregion // Base GravitySource

#region Gravity Puller (additional script for PlayerControl)
public class GravityPuller : MonoBehaviour {
    public GravitySource gravitySource;
    private GravitySource lastGravitySource;
    private float timeOfLastSource;
    private PlayerControl p;
    [Tooltip("If true, will re-orient velocity to match any changes to gravity. useful for making tight video-gamey motion on small gravity wells.")]
    public bool velocityFollowsGravity = true;

    public void Init(GravitySource gs) {
        if(gs != this && (gs != lastGravitySource || Time.time > timeOfLastSource+1)) {
            timeOfLastSource = Time.time;
            lastGravitySource = gravitySource;
            gravitySource = gs;
            p = GetComponent<PlayerControl>();
            Refresh();
        }
    }
    public void Refresh() {
        Vector3 nextDir = gravitySource.CalculateGravityDirectionFrom(transform.position);
        Rigidbody rb = p.rb;
        if(velocityFollowsGravity && nextDir != p.gravity.dir && rb != null) {
            Vector3 localVelocity = p.transform.InverseTransformDirection(rb.velocity);
            float angle = Vector3.Angle(nextDir, p.gravity.dir);
            Vector3 axis = Vector3.Cross(p.gravity.dir, nextDir).normalized;
            Quaternion q = Quaternion.AngleAxis(angle, axis);
            p.transform.rotation = Quaternion.LookRotation(q*transform.forward, q*transform.up);
            rb.velocity = p.transform.TransformDirection (localVelocity);
        }
        p.gravity.dir = nextDir;
        if (gravitySource.forceGravitypower) {
            p.gravity.power = gravitySource.power;
        }
    }
    void FixedUpdate() { Refresh(); }
    public Vector3 PullAsIfFrom(Vector3 alternateLocation) {
        return gravitySource.CalculateGravityDirectionFrom(alternateLocation);
    }
}
#endregion // Gravity Puller (additional script for PlayerControl)