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 * See CONTRIBUTORS.TXT for a full list of copyright holders.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
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 *       notice, this list of conditions and the following disclaimer.
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 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
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 *       names of its contributors may be used to endorse or promote products
 *       derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE CONTRIBUTORS BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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 */
using System;
using System.Collections.Generic;
using System.Text;

using OMV = OpenMetaverse;
using OpenSim.Framework;
using OpenSim.Region.PhysicsModules.SharedBase;

namespace OpenSim.Region.PhysicsModule.BulletS
{
/*
 * Class to wrap all objects.
 * The rest of BulletSim doesn't need to keep checking for avatars or prims
 *        unless the difference is significant.
 *
 *  Variables in the physicsl objects are in three forms:
 *      VariableName: used by the simulator and performs taint operations, etc
 *      RawVariableName: direct reference to the BulletSim storage for the variable value
 *      ForceVariableName: direct reference (store and fetch) to the value in the physics engine.
 *  The last one should only be referenced in taint-time.
 */

/*
 * As of 20121221, the following are the call sequences (going down) for different script physical functions:
 * llApplyImpulse       llApplyRotImpulse           llSetTorque             llSetForce
 * SOP.ApplyImpulse     SOP.ApplyAngularImpulse     SOP.SetAngularImpulse   SOP.SetForce
 * SOG.ApplyImpulse     SOG.ApplyAngularImpulse     SOG.SetAngularImpulse
 * PA.AddForce          PA.AddAngularForce          PA.Torque = v           PA.Force = v
 * BS.ApplyCentralForce BS.ApplyTorque
 */

// Flags used to denote which properties updates when making UpdateProperties calls to linksets, etc.
public enum UpdatedProperties : uint
{
    Position                = 1 << 0,
    Orientation             = 1 << 1,
    Velocity                = 1 << 2,
    Acceleration            = 1 << 3,
    RotationalVelocity      = 1 << 4,
    EntPropUpdates          = Position | Orientation | Velocity | Acceleration | RotationalVelocity,
}
public abstract class BSPhysObject : PhysicsActor
{
    protected BSPhysObject()
    {
    }
    protected BSPhysObject(BSScene parentScene, uint localID, string name, string typeName)
    {
        IsInitialized = false;

        PhysScene = parentScene;
        LocalID = localID;
        PhysObjectName = name;
        Name = name;    // PhysicsActor also has the name of the object. Someday consolidate.
        TypeName = typeName;

        // Oddity if object is destroyed and recreated very quickly it could still have the old body.
        if (!PhysBody.HasPhysicalBody)
            PhysBody = new BulletBody(localID);

        // Clean out anything that might be in the physical actor list.
        // Again, a workaround for destroying and recreating an object very quickly.
        PhysicalActors.Dispose();

        UserSetCenterOfMassDisplacement = null;

        PrimAssetState = PrimAssetCondition.Unknown;

        // Initialize variables kept in base.
        // Beware that these cause taints to be queued whch can cause race conditions on startup.
        GravModifier = 1.0f;
        Gravity = new OMV.Vector3(0f, 0f, BSParam.Gravity);
        HoverActive = false;

        // Default material type. Also sets Friction, Restitution and Density.
        SetMaterial((int)MaterialAttributes.Material.Wood);

        CollisionsLastTickStep = -1;

        SubscribedEventsMs = 0;
        // Crazy values that will never be true
        CollidingStep = BSScene.NotASimulationStep;
        CollidingGroundStep = BSScene.NotASimulationStep;
        CollisionAccumulation = BSScene.NotASimulationStep;
        ColliderIsMoving = false;
        CollisionScore = 0;

        // All axis free.
        LockedLinearAxis = LockedAxisFree;
        LockedAngularAxis = LockedAxisFree;
    }

    // Tell the object to clean up.
    public virtual void Destroy()
    {
        PhysicalActors.Enable(false);
        PhysScene.TaintedObject(LocalID, "BSPhysObject.Destroy", delegate()
        {
            PhysicalActors.Dispose();
        });
    }

    public BSScene PhysScene { get; protected set; }
    // public override uint LocalID { get; set; } // Use the LocalID definition in PhysicsActor
    public string PhysObjectName { get; protected set; }
    public string TypeName { get; protected set; }

    // Set to 'true' when the object is completely initialized.
    // This mostly prevents property updates and collisions until the object is completely here.
    public bool IsInitialized { get; protected set; }

    // Set to 'true' if an object (mesh/linkset/sculpty) is not completely constructed.
    // This test is used to prevent some updates to the object when it only partially exists.
    // There are several reasons and object might be incomplete:
    //     Its underlying mesh/sculpty is an asset which must be fetched from the asset store
    //     It is a linkset who is being added to or removed from
    //     It is changing state (static to physical, for instance) which requires rebuilding
    // This is a computed value based on the underlying physical object construction
    abstract public bool IsIncomplete { get; }

    // Return the object mass without calculating it or having side effects
    public abstract float RawMass { get; }
    // Set the raw mass but also update physical mass properties (inertia, ...)
    // 'inWorld' true if the object has already been added to the dynamic world.
    public abstract void UpdatePhysicalMassProperties(float mass, bool inWorld);

    // The gravity being applied to the object. A function of default grav, GravityModifier and Buoyancy.
    public virtual OMV.Vector3 Gravity { get; set; }
    // The last value calculated for the prim's inertia
    public OMV.Vector3 Inertia { get; set; }

    // Reference to the physical body (btCollisionObject) of this object
    public BulletBody PhysBody = new BulletBody(0);
    // Reference to the physical shape (btCollisionShape) of this object
    public BSShape PhysShape = new BSShapeNull();

    // The physical representation of the prim might require an asset fetch.
    // The asset state is first 'Unknown' then 'Waiting' then either 'Failed' or 'Fetched'.
    public enum PrimAssetCondition
    {
        Unknown, Waiting, FailedAssetFetch, FailedMeshing, Fetched
    }
    public PrimAssetCondition PrimAssetState { get; set; }
    public virtual bool AssetFailed()
    {
        return ( (this.PrimAssetState == PrimAssetCondition.FailedAssetFetch)
              || (this.PrimAssetState == PrimAssetCondition.FailedMeshing) );
    }

    // The objects base shape information. Null if not a prim type shape.
    public PrimitiveBaseShape BaseShape { get; protected set; }

    // When the physical properties are updated, an EntityProperty holds the update values.
    // Keep the current and last EntityProperties to enable computation of differences
    //      between the current update and the previous values.
    public EntityProperties CurrentEntityProperties { get; set; }
    public EntityProperties LastEntityProperties { get; set; }

    public virtual OMV.Vector3 Scale { get; set; }

    // It can be confusing for an actor to know if it should move or update an object
    //    depeneding on the setting of 'selected', 'physical, ...
    // This flag is the true test -- if true, the object is being acted on in the physical world
    public abstract bool IsPhysicallyActive { get; }

    // Detailed state of the object.
    public abstract bool IsSolid { get; }
    public abstract bool IsStatic { get; }
    public abstract bool IsSelected { get; }
    public abstract bool IsVolumeDetect { get; }

    // Materialness
    public MaterialAttributes.Material Material { get; private set; }
    public override void SetMaterial(int material)
    {
        Material = (MaterialAttributes.Material)material;

        // Setting the material sets the material attributes also.
        // TODO: decide if this is necessary -- the simulator does this.
        MaterialAttributes matAttrib = BSMaterials.GetAttributes(Material, false);
        Friction = matAttrib.friction;
        Restitution = matAttrib.restitution;
        Density = matAttrib.density;
        // DetailLog("{0},{1}.SetMaterial,Mat={2},frict={3},rest={4},den={5}", LocalID, TypeName, Material, Friction, Restitution, Density);
    }

    public override float Density
    {
        get
        {
            return base.Density;
        }
        set
        {
            DetailLog("{0},BSPhysObject.Density,set,den={1}", LocalID, value);
            base.Density = value;
        }
    }

    // Stop all physical motion.
    public abstract void ZeroMotion(bool inTaintTime);
    public abstract void ZeroAngularMotion(bool inTaintTime);

    // Update the physical location and motion of the object. Called with data from Bullet.
    public abstract void UpdateProperties(EntityProperties entprop);

    public virtual OMV.Vector3 RawPosition { get; set; }
    public abstract OMV.Vector3 ForcePosition { get; set; }

    public virtual OMV.Quaternion RawOrientation { get; set; }
    public abstract OMV.Quaternion ForceOrientation { get; set; }

    public virtual OMV.Vector3 RawVelocity { get; set; }
    public abstract OMV.Vector3 ForceVelocity { get; set; }

    // RawForce is a constant force applied to object (see Force { set; } )
    public OMV.Vector3 RawForce { get; set; }
    public OMV.Vector3 RawTorque { get; set; }

    public override void AddAngularForce(OMV.Vector3 force, bool pushforce)
    {
        AddAngularForce(false, force);
    }
    public abstract void AddAngularForce(bool inTaintTime, OMV.Vector3 force);
    public abstract void AddForce(bool inTaintTime, OMV.Vector3 force);

    public abstract OMV.Vector3 ForceRotationalVelocity { get; set; }

    public abstract float ForceBuoyancy { get; set; }

    public virtual bool ForceBodyShapeRebuild(bool inTaintTime) { return false; }

    public override bool PIDActive 
    {
        get { return MoveToTargetActive; }
        set { MoveToTargetActive = value; } 
    }

    public override OMV.Vector3 PIDTarget { set { MoveToTargetTarget = value; } }
    public override float PIDTau { set { MoveToTargetTau = value; } }

    public bool MoveToTargetActive { get; set; }
    public OMV.Vector3 MoveToTargetTarget { get; set; }
    public float MoveToTargetTau { get; set; }

    // Used for llSetHoverHeight and maybe vehicle height. Hover Height will override MoveTo target's Z
    public override bool PIDHoverActive {get {return HoverActive;}  set { HoverActive = value; } }
    public override float PIDHoverHeight { set { HoverHeight = value; } }
    public override PIDHoverType PIDHoverType { set { HoverType = value; } }
    public override float PIDHoverTau { set { HoverTau = value; } }

    public bool HoverActive { get; set; }
    public float HoverHeight { get;  set; }
    public PIDHoverType HoverType { get;  set; }
    public float HoverTau { get; set; }

    // For RotLookAt
    public override OMV.Quaternion APIDTarget { set { return; } }
    public override bool APIDActive { set { return; } }
    public override float APIDStrength { set { return; } }
    public override float APIDDamping { set { return; } }

    // The current velocity forward
    public virtual float ForwardSpeed
    {
        get
        {
            OMV.Vector3 characterOrientedVelocity = RawVelocity * OMV.Quaternion.Inverse(OMV.Quaternion.Normalize(RawOrientation));
            return characterOrientedVelocity.X;
        }
    }
    // The forward speed we are trying to achieve (TargetVelocity)
    public virtual float TargetVelocitySpeed
    {
        get
        {
            OMV.Vector3 characterOrientedVelocity = TargetVelocity * OMV.Quaternion.Inverse(OMV.Quaternion.Normalize(RawOrientation));
            return characterOrientedVelocity.X;
        }
    }

    // The user can optionally set the center of mass. The user's setting will override any
    //    computed center-of-mass (like in linksets).
    // Note this is a displacement from the root's coordinates. Zero means use the root prim as center-of-mass.
    public OMV.Vector3? UserSetCenterOfMassDisplacement { get; set; }

    public OMV.Vector3 LockedLinearAxis;   // zero means locked. one means free.
    public OMV.Vector3 LockedAngularAxis;  // zero means locked. one means free.
    public const float FreeAxis = 1f;
    public const float LockedAxis = 0f;
    public readonly OMV.Vector3 LockedAxisFree = new OMV.Vector3(FreeAxis, FreeAxis, FreeAxis);  // All axis are free

    // If an axis is locked (flagged above) then the limits of that axis are specified here.
    // Linear axis limits are relative to the object's starting coordinates.
    // Angular limits are limited to -PI to +PI
    public OMV.Vector3 LockedLinearAxisLow;
    public OMV.Vector3 LockedLinearAxisHigh;
    public OMV.Vector3 LockedAngularAxisLow;
    public OMV.Vector3 LockedAngularAxisHigh;

    // Enable physical actions. Bullet will keep sleeping non-moving physical objects so
    //     they need waking up when parameters are changed.
    // Called in taint-time!!
    public void ActivateIfPhysical(bool forceIt)
    {
        if (PhysBody.HasPhysicalBody)
        {
            if (IsPhysical)
            {
                // Physical objects might need activating
                PhysScene.PE.Activate(PhysBody, forceIt);
            }
            else
            {
                // Clear the collision cache since we've changed some properties.
                PhysScene.PE.ClearCollisionProxyCache(PhysScene.World, PhysBody);
            }
        }
    }

    // 'actors' act on the physical object to change or constrain its motion. These can range from
    //       hovering to complex vehicle motion.
    // May be called at non-taint time as this just adds the actor to the action list and the real
    //    work is done during the simulation step.
    // Note that, if the actor is already in the list and we are disabling same, the actor is just left
    //    in the list disabled.
    public delegate BSActor CreateActor();
    public void EnableActor(bool enableActor, string actorName, CreateActor creator)
    {
        lock (PhysicalActors)
        {
            BSActor theActor;
            if (PhysicalActors.TryGetActor(actorName, out theActor))
            {
                // The actor already exists so just turn it on or off
                DetailLog("{0},BSPhysObject.EnableActor,enablingExistingActor,name={1},enable={2}", LocalID, actorName, enableActor);
                theActor.Enabled = enableActor;
            }
            else
            {
                // The actor does not exist. If it should, create it.
                if (enableActor)
                {
                    DetailLog("{0},BSPhysObject.EnableActor,creatingActor,name={1}", LocalID, actorName);
                    theActor = creator();
                    PhysicalActors.Add(actorName, theActor);
                    theActor.Enabled = true;
                }
                else
                {
                    DetailLog("{0},BSPhysObject.EnableActor,notCreatingActorSinceNotEnabled,name={1}", LocalID, actorName);
                }
            }
        }
    }

    #region Collisions

    // Requested number of milliseconds between collision events. Zero means disabled.
    protected int SubscribedEventsMs { get; set; }
    // Given subscription, the time that a collision may be passed up
    protected int NextCollisionOkTime { get; set; }
    // The simulation step that last had a collision
    protected long CollidingStep { get; set; }
    // The simulation step that last had a collision with the ground
    protected long CollidingGroundStep { get; set; }
    // The simulation step that last collided with an object
    protected long CollidingObjectStep { get; set; }
    // The collision flags we think are set in Bullet
    protected CollisionFlags CurrentCollisionFlags { get; set; }
    // On a collision, check the collider and remember if the last collider was moving
    //    Used to modify the standing of avatars (avatars on stationary things stand still)
    public bool ColliderIsMoving;
    // 'true' if the last collider was a volume detect object
    public bool ColliderIsVolumeDetect;
    // Used by BSCharacter to manage standing (and not slipping)
    public bool IsStationary;

    // Count of collisions for this object
    protected long CollisionAccumulation { get; set; }

    public override bool IsColliding {
        get { return (CollidingStep == PhysScene.SimulationStep); }
        set {
            if (value)
                CollidingStep = PhysScene.SimulationStep;
            else
                CollidingStep = BSScene.NotASimulationStep;
            }
    }
    // Complex objects (like linksets) need to know if there is a collision on any part of
    //    their shape. 'IsColliding' has an existing definition of reporting a collision on
    //    only this specific prim or component of linksets.
    // 'HasSomeCollision' is defined as reporting if there is a collision on any part of
    //    the complex body that this prim is the root of.
    public virtual bool HasSomeCollision
    {
        get { return IsColliding; }
        set { IsColliding = value; }
    }
    public override bool CollidingGround {
        get { return (CollidingGroundStep == PhysScene.SimulationStep); }
        set
        {
            if (value)
                CollidingGroundStep = PhysScene.SimulationStep;
            else
                CollidingGroundStep = BSScene.NotASimulationStep;
        }
    }
    public override bool CollidingObj {
        get { return (CollidingObjectStep == PhysScene.SimulationStep); }
        set {
            if (value)
                CollidingObjectStep = PhysScene.SimulationStep;
            else
                CollidingObjectStep = BSScene.NotASimulationStep;
        }
    }

    // The collisions that have been collected for the next collision reporting (throttled by subscription)
    protected CollisionEventUpdate CollisionCollection = new CollisionEventUpdate();
    // This is the collision collection last reported to the Simulator.
    public CollisionEventUpdate CollisionsLastReported = new CollisionEventUpdate();
    // Remember the collisions recorded in the last tick for fancy collision checking
    //     (like a BSCharacter walking up stairs).
    public CollisionEventUpdate CollisionsLastTick = new CollisionEventUpdate();
    private long CollisionsLastTickStep = -1;

    // The simulation step is telling this object about a collision.
    // I'm the 'collider', the thing I'm colliding with is the 'collidee'.
    // Return 'true' if a collision was processed and should be sent up.
    // Return 'false' if this object is not enabled/subscribed/appropriate for or has already seen this collision.
    // Called at taint time from within the Step() function
    public virtual bool Collide(BSPhysObject collidee, OMV.Vector3 contactPoint, OMV.Vector3 contactNormal, float pentrationDepth)
    {
        bool ret = false;

        // if 'collidee' is null, that means it is terrain
        uint collideeLocalID = (collidee == null) ? BSScene.TERRAIN_ID : collidee.LocalID;
        // All terrain goes by the TERRAIN_ID id when passed up as a collision
        if (collideeLocalID <= PhysScene.TerrainManager.HighestTerrainID) {
            collideeLocalID = BSScene.TERRAIN_ID;
        }

        // The following lines make IsColliding(), CollidingGround() and CollidingObj work
        CollidingStep = PhysScene.SimulationStep;
        if (collideeLocalID == BSScene.TERRAIN_ID)
        {
            CollidingGroundStep = PhysScene.SimulationStep;
        }
        else
        {
            CollidingObjectStep = PhysScene.SimulationStep;
        }

        CollisionAccumulation++;

        // For movement tests, if the collider is me, remember if we are colliding with an object that is moving.
        // Here the 'collider'/'collidee' thing gets messed up. In the larger context, when something is checking
        //     if the thing it is colliding with is moving, for instance, it asks if the its collider is moving.
        ColliderIsMoving = collidee != null ? (collidee.RawVelocity != OMV.Vector3.Zero || collidee.RotationalVelocity != OMV.Vector3.Zero) : false;
        ColliderIsVolumeDetect = collidee != null ? (collidee.IsVolumeDetect) : false;


        // Make a collection of the collisions that happened the last simulation tick.
        // This is different than the collection created for sending up to the simulator as it is cleared every tick.
        if (CollisionsLastTickStep != PhysScene.SimulationStep)
        {
            CollisionsLastTick = new CollisionEventUpdate();
            CollisionsLastTickStep = PhysScene.SimulationStep;
        }
        CollisionsLastTick.AddCollider(collideeLocalID, new ContactPoint(contactPoint, contactNormal, pentrationDepth));

        // If someone has subscribed for collision events log the collision so it will be reported up
        if (SubscribedEvents()) {
            ContactPoint newContact = new ContactPoint(contactPoint, contactNormal, pentrationDepth);

            // Collision sound requires a velocity to know it should happen. This is a lot of computation for a little used feature.
            OMV.Vector3 relvel = OMV.Vector3.Zero;
            if (IsPhysical)
                relvel = RawVelocity;
            if (collidee != null && collidee.IsPhysical)
                relvel -= collidee.RawVelocity;
            newContact.RelativeSpeed = OMV.Vector3.Dot(relvel, contactNormal);
            // DetailLog("{0},{1}.Collision.AddCollider,vel={2},contee.vel={3},relvel={4},relspeed={5}",
            //         LocalID, TypeName, RawVelocity, (collidee == null ? OMV.Vector3.Zero : collidee.RawVelocity), relvel, newContact.RelativeSpeed);
                    
            lock (PhysScene.CollisionLock)
            {
                CollisionCollection.AddCollider(collideeLocalID, newContact);
            }
            DetailLog("{0},{1}.Collision.AddCollider,call,with={2},point={3},normal={4},depth={5},speed={6},colliderMoving={7}",
                            LocalID, TypeName, collideeLocalID, contactPoint, contactNormal, pentrationDepth,
                            newContact.RelativeSpeed, ColliderIsMoving);

            ret = true;
        }
        return ret;
    }

    // Send the collected collisions into the simulator.
    // Called at taint time from within the Step() function thus no locking problems
    //      with CollisionCollection and ObjectsWithNoMoreCollisions.
    // Called with BSScene.CollisionLock locked to protect the collision lists.
    // Return 'true' if there were some actual collisions passed up
    public virtual bool SendCollisions()
    {
        bool ret = true;

        // If no collisions this call but there were collisions last call, force the collision
        //     event to be happen right now so quick collision_end.
        bool force = (CollisionCollection.Count == 0 && CollisionsLastReported.Count != 0);

        // throttle the collisions to the number of milliseconds specified in the subscription
        if (force || (PhysScene.SimulationNowTime >= NextCollisionOkTime))
        {
            NextCollisionOkTime = PhysScene.SimulationNowTime + SubscribedEventsMs;

            // We are called if we previously had collisions. If there are no collisions
            //   this time, send up one last empty event so OpenSim can sense collision end.
            if (CollisionCollection.Count == 0)
            {
                // If I have no collisions this time, remove me from the list of objects with collisions.
                ret = false;
            }

            DetailLog("{0},{1}.SendCollisionUpdate,call,numCollisions={2}", LocalID, TypeName, CollisionCollection.Count);
            base.SendCollisionUpdate(CollisionCollection);

            // Remember the collisions from this tick for some collision specific processing.
            CollisionsLastReported = CollisionCollection;

            // The CollisionCollection instance is passed around in the simulator.
            // Make sure we don't have a handle to that one and that a new one is used for next time.
            //    This fixes an interesting 'gotcha'. If we call CollisionCollection.Clear() here,
            //    a race condition is created for the other users of this instance.
            CollisionCollection = new CollisionEventUpdate();
        }
        return ret;
    }

    // Subscribe for collision events.
    // Parameter is the millisecond rate the caller wishes collision events to occur.
    public override void SubscribeEvents(int ms) {
        // DetailLog("{0},{1}.SubscribeEvents,subscribing,ms={2}", LocalID, TypeName, ms);
        SubscribedEventsMs = ms;
        if (ms > 0)
        {
            // make sure first collision happens
            NextCollisionOkTime = Util.EnvironmentTickCountSubtract(SubscribedEventsMs);

            PhysScene.TaintedObject(LocalID, TypeName+".SubscribeEvents", delegate()
            {
                if (PhysBody.HasPhysicalBody)
                {
                    CurrentCollisionFlags = PhysScene.PE.AddToCollisionFlags(PhysBody, CollisionFlags.BS_SUBSCRIBE_COLLISION_EVENTS);
                    DetailLog("{0},{1}.SubscribeEvents,setting collision. ms={2}, collisionFlags={3:x}",
                            LocalID, TypeName, ms, CurrentCollisionFlags);
                }
            });
        }
        else
        {
            // Subscribing for zero or less is the same as unsubscribing
            UnSubscribeEvents();
        }
    }
    public override void UnSubscribeEvents() {
        // DetailLog("{0},{1}.UnSubscribeEvents,unsubscribing", LocalID, TypeName);
        SubscribedEventsMs = 0;
        PhysScene.TaintedObject(LocalID, TypeName+".UnSubscribeEvents", delegate()
        {
            // Make sure there is a body there because sometimes destruction happens in an un-ideal order.
            if (PhysBody.HasPhysicalBody)
                CurrentCollisionFlags = PhysScene.PE.RemoveFromCollisionFlags(PhysBody, CollisionFlags.BS_SUBSCRIBE_COLLISION_EVENTS);
        });
    }
    // Return 'true' if the simulator wants collision events
    public override bool SubscribedEvents() {
        return (SubscribedEventsMs > 0);
    }
    // Because 'CollisionScore' is called many times while sorting, it should not be recomputed
    //    each time called. So this is built to be light weight for each collision and to do
    //    all the processing when the user asks for the info.
    public void ComputeCollisionScore()
    {
        // Scale the collision count by the time since the last collision.
        // The "+1" prevents dividing by zero.
        long timeAgo = PhysScene.SimulationStep - CollidingStep + 1;
        CollisionScore = CollisionAccumulation / timeAgo;
    }
    public override float CollisionScore { get; set; }

    #endregion // Collisions

    #region Per Simulation Step actions

    public BSActorCollection PhysicalActors = new BSActorCollection();

    // When an update to the physical properties happens, this event is fired to let
    //    different actors to modify the update before it is passed around
    public delegate void PreUpdatePropertyAction(ref EntityProperties entprop);
    public event PreUpdatePropertyAction OnPreUpdateProperty;
    protected void TriggerPreUpdatePropertyAction(ref EntityProperties entprop)
    {
        PreUpdatePropertyAction actions = OnPreUpdateProperty;
        if (actions != null)
            actions(ref entprop);
    }

    #endregion // Per Simulation Step actions

    // High performance detailed logging routine used by the physical objects.
    protected void DetailLog(string msg, params Object[] args)
    {
        if (PhysScene.PhysicsLogging.Enabled)
            PhysScene.DetailLog(msg, args);
    }

}
}