path: root/OpenSim/Region/PhysicsModules/Ode/ODEDynamics.c_comments

/*
 * Revised August 26 2009 by Kitto Flora. ODEDynamics.cs replaces
 * ODEVehicleSettings.cs. It and ODEPrim.cs are re-organised:
 * ODEPrim.cs contains methods dealing with Prim editing, Prim
 * characteristics and Kinetic motion.
 * ODEDynamics.cs contains methods dealing with Prim Physical motion
 * (dynamics) and the associated settings. Old Linear and angular
 * motors for dynamic motion have been replace with  MoveLinear()
 * and MoveAngular(); 'Physical' is used only to switch ODE dynamic 
 * simualtion on/off; VEHICAL_TYPE_NONE/VEHICAL_TYPE_<other> is to
 * switch between 'VEHICLE' parameter use and general dynamics
 * settings use.
 * 
 * Copyright (c) Contributors, http://opensimulator.org/
 * 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:
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name of the OpenSimulator Project nor the
 *       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
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

using System;
using System.Collections.Generic;
using System.Reflection;
using System.Runtime.InteropServices;
using log4net;
using OpenMetaverse;
using Ode.NET;
using OpenSim.Framework;
using OpenSim.Region.Physics.Manager;

namespace OpenSim.Region.Physics.OdePlugin
{
    public class ODEDynamics
    {
        public Vehicle Type
        {        
            get { return m_type; }
        }

        public IntPtr Body
        {
            get { return m_body; }
        }

        private int frcount = 0;										// Used to limit dynamics debug output to 
        																// every 100th frame

        // private OdeScene m_parentScene = null;
        private IntPtr m_body = IntPtr.Zero;
        private IntPtr m_jointGroup = IntPtr.Zero;
        private IntPtr m_aMotor = IntPtr.Zero;
 

        // Vehicle properties
        private Vehicle m_type = Vehicle.TYPE_NONE;						// If a 'VEHICLE', and what kind
        // private Quaternion m_referenceFrame = Quaternion.Identity;	// Axis modifier
        private VehicleFlag m_flags = (VehicleFlag) 0;					// Boolean settings:
																		// HOVER_TERRAIN_ONLY
																		// HOVER_GLOBAL_HEIGHT
																		// NO_DEFLECTION_UP
																		// HOVER_WATER_ONLY
																		// HOVER_UP_ONLY
																		// LIMIT_MOTOR_UP
																		// LIMIT_ROLL_ONLY
        
        // Linear properties
        private Vector3 m_linearMotorDirection = Vector3.Zero;			// velocity requested by LSL, decayed by time
        private Vector3 m_linearMotorDirectionLASTSET = Vector3.Zero;	// velocity requested by LSL
        private Vector3 m_dir = Vector3.Zero;							// velocity applied to body
        private Vector3 m_linearFrictionTimescale = Vector3.Zero;
        private float m_linearMotorDecayTimescale = 0;
        private float m_linearMotorTimescale = 0;
        private Vector3 m_lastLinearVelocityVector = Vector3.Zero;
		// private bool m_LinearMotorSetLastFrame = false;
        // private Vector3 m_linearMotorOffset = Vector3.Zero;
        
        //Angular properties
        private Vector3 m_angularMotorDirection = Vector3.Zero;
        private Vector3 m_angularMotorDirectionLASTSET = Vector3.Zero;
        private Vector3 m_angularFrictionTimescale = Vector3.Zero;
        private float m_angularMotorDecayTimescale = 0;
        private float m_angularMotorTimescale = 0;
        private Vector3 m_lastAngularVelocityVector = Vector3.Zero;

		//Deflection properties        
        // private float m_angularDeflectionEfficiency = 0;
        // private float m_angularDeflectionTimescale = 0;
        // private float m_linearDeflectionEfficiency = 0;
        // private float m_linearDeflectionTimescale = 0;
        
        //Banking properties
        // private float m_bankingEfficiency = 0;
        // private float m_bankingMix = 0;
        // private float m_bankingTimescale = 0;
        
        //Hover and Buoyancy properties
        private float m_VhoverHeight = 0f;
        private float m_VhoverEfficiency = 0f;
        private float m_VhoverTimescale = 0f;
        private float m_VhoverTargetHeight = -1.0f;     // if <0 then no hover, else its the current target height 
        private float m_VehicleBuoyancy = 0f;			//KF: m_VehicleBuoyancy is set by VEHICLE_BUOYANCY for a vehicle.
        			// Modifies gravity. Slider between -1 (double-gravity) and 1 (full anti-gravity) 
        			// KF: So far I have found no good method to combine a script-requested .Z velocity and gravity.
        			// Therefore only m_VehicleBuoyancy=1 (0g) will use the script-requested .Z velocity. 
        												
		//Attractor properties        												
        private float m_verticalAttractionEfficiency = 0;
        private float m_verticalAttractionTimescale = 0;
        
        



        internal void ProcessFloatVehicleParam(Vehicle pParam, float pValue)
        {
            switch (pParam)
            {
                case Vehicle.ANGULAR_DEFLECTION_EFFICIENCY:
                    if (pValue < 0.01f) pValue = 0.01f;
                    // m_angularDeflectionEfficiency = pValue;
                    break;
                case Vehicle.ANGULAR_DEFLECTION_TIMESCALE:
                    if (pValue < 0.01f) pValue = 0.01f;
                    // m_angularDeflectionTimescale = pValue;
                    break;
                case Vehicle.ANGULAR_MOTOR_DECAY_TIMESCALE:
                    if (pValue < 0.01f) pValue = 0.01f;
                    m_angularMotorDecayTimescale = pValue;
                    break;
                case Vehicle.ANGULAR_MOTOR_TIMESCALE:
                    if (pValue < 0.01f) pValue = 0.01f;
                    m_angularMotorTimescale = pValue;
                    break;
                case Vehicle.BANKING_EFFICIENCY:
                    if (pValue < 0.01f) pValue = 0.01f;
                    // m_bankingEfficiency = pValue;
                    break;
                case Vehicle.BANKING_MIX:
                    if (pValue < 0.01f) pValue = 0.01f;
                    // m_bankingMix = pValue;
                    break;
                case Vehicle.BANKING_TIMESCALE:
                    if (pValue < 0.01f) pValue = 0.01f;
                    // m_bankingTimescale = pValue;
                    break;
                case Vehicle.BUOYANCY:
                	if (pValue < -1f) pValue = -1f;
                	if (pValue > 1f) pValue = 1f;
                    m_VehicleBuoyancy = pValue;
                    break;
                case Vehicle.HOVER_EFFICIENCY:
                	if (pValue < 0f) pValue = 0f;
                	if (pValue > 1f) pValue = 1f;
                    m_VhoverEfficiency = pValue;
                    break;
                case Vehicle.HOVER_HEIGHT:
                    m_VhoverHeight = pValue;
                    break;
                case Vehicle.HOVER_TIMESCALE:
                    if (pValue < 0.01f) pValue = 0.01f;
                    m_VhoverTimescale = pValue;
                    break;
                case Vehicle.LINEAR_DEFLECTION_EFFICIENCY:
                    if (pValue < 0.01f) pValue = 0.01f;
                    // m_linearDeflectionEfficiency = pValue;
                    break;
                case Vehicle.LINEAR_DEFLECTION_TIMESCALE:
                    if (pValue < 0.01f) pValue = 0.01f;
                    // m_linearDeflectionTimescale = pValue;
                    break;
                case Vehicle.LINEAR_MOTOR_DECAY_TIMESCALE:
                    if (pValue < 0.01f) pValue = 0.01f;
                    m_linearMotorDecayTimescale = pValue;
                    break;
                case Vehicle.LINEAR_MOTOR_TIMESCALE:
                    if (pValue < 0.01f) pValue = 0.01f;
                    m_linearMotorTimescale = pValue;
                    break;
                case Vehicle.VERTICAL_ATTRACTION_EFFICIENCY:
                    if (pValue < 0.0f) pValue = 0.0f;
                    if (pValue > 1.0f) pValue = 1.0f;
                    m_verticalAttractionEfficiency = pValue;
                    break;
                case Vehicle.VERTICAL_ATTRACTION_TIMESCALE:
                    if (pValue < 0.01f) pValue = 0.01f;
                    m_verticalAttractionTimescale = pValue;
                    break;
                    
                // These are vector properties but the engine lets you use a single float value to 
                // set all of the components to the same value
                case Vehicle.ANGULAR_FRICTION_TIMESCALE:
                    m_angularFrictionTimescale = new Vector3(pValue, pValue, pValue);
                    break;
                case Vehicle.ANGULAR_MOTOR_DIRECTION:
                    m_angularMotorDirection = new Vector3(pValue, pValue, pValue);
                    m_angularMotorDirectionLASTSET = new Vector3(pValue, pValue, pValue);
                    break;
                case Vehicle.LINEAR_FRICTION_TIMESCALE:
                    m_linearFrictionTimescale = new Vector3(pValue, pValue, pValue);
                    break;
                case Vehicle.LINEAR_MOTOR_DIRECTION:
                    m_linearMotorDirection = new Vector3(pValue, pValue, pValue);
                    m_linearMotorDirectionLASTSET = new Vector3(pValue, pValue, pValue);
                    break;
                case Vehicle.LINEAR_MOTOR_OFFSET:
                    // m_linearMotorOffset = new Vector3(pValue, pValue, pValue);
                    break;

            }
            
        }//end ProcessFloatVehicleParam

        internal void ProcessVectorVehicleParam(Vehicle pParam, PhysicsVector pValue)
        {
            switch (pParam)
            {
                case Vehicle.ANGULAR_FRICTION_TIMESCALE:
                    m_angularFrictionTimescale = new Vector3(pValue.X, pValue.Y, pValue.Z);
                    break;
                case Vehicle.ANGULAR_MOTOR_DIRECTION:
                    m_angularMotorDirection = new Vector3(pValue.X, pValue.Y, pValue.Z);
                    m_angularMotorDirectionLASTSET = new Vector3(pValue.X, pValue.Y, pValue.Z);
                    break;
                case Vehicle.LINEAR_FRICTION_TIMESCALE:
                    m_linearFrictionTimescale = new Vector3(pValue.X, pValue.Y, pValue.Z);
                    break;
                case Vehicle.LINEAR_MOTOR_DIRECTION:
                    m_linearMotorDirection = new Vector3(pValue.X, pValue.Y, pValue.Z);
                    m_linearMotorDirectionLASTSET = new Vector3(pValue.X, pValue.Y, pValue.Z);
                    break;
                case Vehicle.LINEAR_MOTOR_OFFSET:
                    // m_linearMotorOffset = new Vector3(pValue.X, pValue.Y, pValue.Z);
                    break;
            }
            
        }//end ProcessVectorVehicleParam

        internal void ProcessRotationVehicleParam(Vehicle pParam, Quaternion pValue)
        {
            switch (pParam)
            {
                case Vehicle.REFERENCE_FRAME:
                    // m_referenceFrame = pValue;
                    break;
            }
            
        }//end ProcessRotationVehicleParam

        internal void ProcessTypeChange(Vehicle pType)
        {
Console.WriteLine("ProcessTypeChange to " + pType);
         
			// Set Defaults For Type
            m_type = pType;
            switch (pType)
            {
                case Vehicle.TYPE_SLED:
                    m_linearFrictionTimescale = new Vector3(30, 1, 1000);
                    m_angularFrictionTimescale = new Vector3(1000, 1000, 1000);
                    m_linearMotorDirection = Vector3.Zero;
                    m_linearMotorTimescale = 1000;
                    m_linearMotorDecayTimescale = 120;
                    m_angularMotorDirection = Vector3.Zero;
                    m_angularMotorTimescale = 1000;
                    m_angularMotorDecayTimescale = 120;
                    m_VhoverHeight = 0;
                    m_VhoverEfficiency = 1;
                    m_VhoverTimescale = 10;
                    m_VehicleBuoyancy = 0;
                    // m_linearDeflectionEfficiency = 1;
                    // m_linearDeflectionTimescale = 1;
                    // m_angularDeflectionEfficiency = 1;
                    // m_angularDeflectionTimescale = 1000;
                    // m_bankingEfficiency = 0;
                    // m_bankingMix = 1;
                    // m_bankingTimescale = 10;
                    // m_referenceFrame = Quaternion.Identity;
                    m_flags &=
                        ~(VehicleFlag.HOVER_WATER_ONLY | VehicleFlag.HOVER_TERRAIN_ONLY |
                          VehicleFlag.HOVER_GLOBAL_HEIGHT | VehicleFlag.HOVER_UP_ONLY);
                    m_flags |= (VehicleFlag.NO_DEFLECTION_UP | VehicleFlag.LIMIT_ROLL_ONLY | VehicleFlag.LIMIT_MOTOR_UP);
                    break;
                case Vehicle.TYPE_CAR:
                    m_linearFrictionTimescale = new Vector3(100, 2, 1000);
                    m_angularFrictionTimescale = new Vector3(1000, 1000, 1000);
                    m_linearMotorDirection = Vector3.Zero;
                    m_linearMotorTimescale = 1;
                    m_linearMotorDecayTimescale = 60;
                    m_angularMotorDirection = Vector3.Zero;
                    m_angularMotorTimescale = 1;
                    m_angularMotorDecayTimescale = 0.8f;
                    m_VhoverHeight = 0;
                    m_VhoverEfficiency = 0;
                    m_VhoverTimescale = 1000;
                    m_VehicleBuoyancy = 0;
                    // // m_linearDeflectionEfficiency = 1;
                    // // m_linearDeflectionTimescale = 2;
                    // // m_angularDeflectionEfficiency = 0;
                    // m_angularDeflectionTimescale = 10;
                    m_verticalAttractionEfficiency = 1;
                    m_verticalAttractionTimescale = 10;
                    // m_bankingEfficiency = -0.2f;
                    // m_bankingMix = 1;
                    // m_bankingTimescale = 1;
                    // m_referenceFrame = Quaternion.Identity;
                    m_flags &= ~(VehicleFlag.HOVER_WATER_ONLY | VehicleFlag.HOVER_TERRAIN_ONLY | VehicleFlag.HOVER_GLOBAL_HEIGHT);
                    m_flags |= (VehicleFlag.NO_DEFLECTION_UP | VehicleFlag.LIMIT_ROLL_ONLY | VehicleFlag.HOVER_UP_ONLY |
                                VehicleFlag.LIMIT_MOTOR_UP);
                    break;
                case Vehicle.TYPE_BOAT:
                    m_linearFrictionTimescale = new Vector3(10, 3, 2);
                    m_angularFrictionTimescale = new Vector3(10,10,10);
                    m_linearMotorDirection = Vector3.Zero;
                    m_linearMotorTimescale = 5;
                    m_linearMotorDecayTimescale = 60;
                    m_angularMotorDirection = Vector3.Zero;
                    m_angularMotorTimescale = 4;
                    m_angularMotorDecayTimescale = 4;
                    m_VhoverHeight = 0;
                    m_VhoverEfficiency = 0.5f;
                    m_VhoverTimescale = 2;
                    m_VehicleBuoyancy = 1;
                    // m_linearDeflectionEfficiency = 0.5f;
                    // m_linearDeflectionTimescale = 3;
                    // m_angularDeflectionEfficiency = 0.5f;
                    // m_angularDeflectionTimescale = 5;
                    m_verticalAttractionEfficiency = 0.5f;
                    m_verticalAttractionTimescale = 5;
                    // m_bankingEfficiency = -0.3f;
                    // m_bankingMix = 0.8f;
                    // m_bankingTimescale = 1;
                    // m_referenceFrame = Quaternion.Identity;
                    m_flags &= ~(VehicleFlag.HOVER_TERRAIN_ONLY | VehicleFlag.LIMIT_ROLL_ONLY | 
                    		VehicleFlag.HOVER_GLOBAL_HEIGHT | VehicleFlag.HOVER_UP_ONLY);
                    m_flags |= (VehicleFlag.NO_DEFLECTION_UP | VehicleFlag.HOVER_WATER_ONLY |
                                VehicleFlag.LIMIT_MOTOR_UP);
                    break;
                case Vehicle.TYPE_AIRPLANE:
                    m_linearFrictionTimescale = new Vector3(200, 10, 5);
                    m_angularFrictionTimescale = new Vector3(20, 20, 20);
                    m_linearMotorDirection = Vector3.Zero;
                    m_linearMotorTimescale = 2;
                    m_linearMotorDecayTimescale = 60;
                    m_angularMotorDirection = Vector3.Zero;
                    m_angularMotorTimescale = 4;
                    m_angularMotorDecayTimescale = 4;
                    m_VhoverHeight = 0;
                    m_VhoverEfficiency = 0.5f;
                    m_VhoverTimescale = 1000;
                    m_VehicleBuoyancy = 0;
                    // m_linearDeflectionEfficiency = 0.5f;
                    // m_linearDeflectionTimescale = 3;
                    // m_angularDeflectionEfficiency = 1;
                    // m_angularDeflectionTimescale = 2;
                    m_verticalAttractionEfficiency = 0.9f;
                    m_verticalAttractionTimescale = 2;
                    // m_bankingEfficiency = 1;
                    // m_bankingMix = 0.7f;
                    // m_bankingTimescale = 2;
                    // m_referenceFrame = Quaternion.Identity;
                    m_flags &= ~(VehicleFlag.NO_DEFLECTION_UP | VehicleFlag.HOVER_WATER_ONLY | VehicleFlag.HOVER_TERRAIN_ONLY |
                        VehicleFlag.HOVER_GLOBAL_HEIGHT | VehicleFlag.HOVER_UP_ONLY | VehicleFlag.LIMIT_MOTOR_UP);
                    m_flags |= (VehicleFlag.LIMIT_ROLL_ONLY);
                    break;
                case Vehicle.TYPE_BALLOON:
                    m_linearFrictionTimescale = new Vector3(5, 5, 5);
                    m_angularFrictionTimescale = new Vector3(10, 10, 10);
                    m_linearMotorDirection = Vector3.Zero;
                    m_linearMotorTimescale = 5;
                    m_linearMotorDecayTimescale = 60;
                    m_angularMotorDirection = Vector3.Zero;
                    m_angularMotorTimescale = 6;
                    m_angularMotorDecayTimescale = 10;
                    m_VhoverHeight = 5;
                    m_VhoverEfficiency = 0.8f;
                    m_VhoverTimescale = 10;
                    m_VehicleBuoyancy = 1;
                    // m_linearDeflectionEfficiency = 0;
                    // m_linearDeflectionTimescale = 5;
                    // m_angularDeflectionEfficiency = 0;
                    // m_angularDeflectionTimescale = 5;
                    m_verticalAttractionEfficiency = 1;
                    m_verticalAttractionTimescale = 1000;
                    // m_bankingEfficiency = 0;
                    // m_bankingMix = 0.7f;
                    // m_bankingTimescale = 5;
                    // m_referenceFrame = Quaternion.Identity;
                    m_flags &= ~(VehicleFlag.NO_DEFLECTION_UP | VehicleFlag.HOVER_WATER_ONLY | VehicleFlag.HOVER_TERRAIN_ONLY |
                        VehicleFlag.HOVER_UP_ONLY | VehicleFlag.LIMIT_MOTOR_UP);
                    m_flags |= (VehicleFlag.LIMIT_ROLL_ONLY | VehicleFlag.HOVER_GLOBAL_HEIGHT);
                    break;

            }
        }//end SetDefaultsForType

        internal void Enable(IntPtr pBody, OdeScene pParentScene)
        {
//Console.WriteLine("Enable  m_type=" + m_type + "   m_VehicleBuoyancy=" + m_VehicleBuoyancy);
            if (m_type == Vehicle.TYPE_NONE)
                return;

            m_body = pBody;
            //KF: This  used to set up the linear and angular joints
        }

        internal void Step(float pTimestep,  OdeScene pParentScene)
        {
            if (m_body == IntPtr.Zero || m_type == Vehicle.TYPE_NONE)
                return;
            frcount++;					// used to limit debug comment output
            if (frcount > 100)
                frcount = 0;

  			MoveLinear(pTimestep, pParentScene);
            MoveAngular(pTimestep);
        }// end Step

        private void MoveLinear(float pTimestep, OdeScene _pParentScene)
        {
            if (!m_linearMotorDirection.ApproxEquals(Vector3.Zero, 0.01f))		// requested m_linearMotorDirection is significant
            {
            	 if(!d.BodyIsEnabled (Body))  d.BodyEnable (Body);

                // add drive to body
                Vector3 addAmount = m_linearMotorDirection/(m_linearMotorTimescale/pTimestep);
                m_lastLinearVelocityVector += (addAmount*10);					// lastLinearVelocityVector is the current body velocity vector?
        
                // This will work temporarily, but we really need to compare speed on an axis
                // KF: Limit body velocity to applied velocity?
                if (Math.Abs(m_lastLinearVelocityVector.X) > Math.Abs(m_linearMotorDirectionLASTSET.X))
                    m_lastLinearVelocityVector.X = m_linearMotorDirectionLASTSET.X;
                if (Math.Abs(m_lastLinearVelocityVector.Y) > Math.Abs(m_linearMotorDirectionLASTSET.Y))
                    m_lastLinearVelocityVector.Y = m_linearMotorDirectionLASTSET.Y;
                if (Math.Abs(m_lastLinearVelocityVector.Z) > Math.Abs(m_linearMotorDirectionLASTSET.Z))
                    m_lastLinearVelocityVector.Z = m_linearMotorDirectionLASTSET.Z;
                
                // decay applied velocity
                Vector3 decayfraction = ((Vector3.One/(m_linearMotorDecayTimescale/pTimestep)));
                //Console.WriteLine("decay: " + decayfraction);
                m_linearMotorDirection -= m_linearMotorDirection * decayfraction;
                //Console.WriteLine("actual: " + m_linearMotorDirection);
            }
            else
            {		// requested is not significant
					// if what remains of applied is small, zero it.
				if (m_lastLinearVelocityVector.ApproxEquals(Vector3.Zero, 0.01f))
					m_lastLinearVelocityVector = Vector3.Zero;
			}
			            
			
			// convert requested object velocity to world-referenced vector
            m_dir = m_lastLinearVelocityVector;
            d.Quaternion rot = d.BodyGetQuaternion(Body);
	        Quaternion rotq = new Quaternion(rot.X, rot.Y, rot.Z, rot.W);	// rotq = rotation of object
	        m_dir *= rotq;							// apply obj rotation to velocity vector

			// add Gravity andBuoyancy
			// KF: So far I have found no good method to combine a script-requested
			// .Z velocity and gravity. Therefore only 0g will used script-requested
			// .Z velocity. >0g (m_VehicleBuoyancy < 1) will used modified gravity only.
            Vector3 grav = Vector3.Zero;
			if(m_VehicleBuoyancy < 1.0f)
			{
				// There is some gravity, make a gravity force vector
				// that is applied after object velocity.     
	            d.Mass objMass;
	            d.BodyGetMass(Body, out objMass);
	            // m_VehicleBuoyancy: -1=2g; 0=1g; 1=0g; 
	            grav.Z = _pParentScene.gravityz * objMass.mass * (1f - m_VehicleBuoyancy);
	            // Preserve the current Z velocity
				d.Vector3 vel_now = d.BodyGetLinearVel(Body);
	            m_dir.Z = vel_now.Z;		// Preserve the accumulated falling velocity
	        } // else its 1.0, no gravity.
	        
	        // Check if hovering
	        if( (m_flags & (VehicleFlag.HOVER_WATER_ONLY | VehicleFlag.HOVER_TERRAIN_ONLY | VehicleFlag.HOVER_GLOBAL_HEIGHT)) != 0)
	        {	
	        	// We should hover, get the target height
        		d.Vector3 pos = d.BodyGetPosition(Body);
	        	if((m_flags & VehicleFlag.HOVER_WATER_ONLY) == VehicleFlag.HOVER_WATER_ONLY)
	        	{
	        		m_VhoverTargetHeight = _pParentScene.GetWaterLevel() + m_VhoverHeight;
	        	}
	        	else if((m_flags & VehicleFlag.HOVER_TERRAIN_ONLY) == VehicleFlag.HOVER_TERRAIN_ONLY)
	        	{
	        		m_VhoverTargetHeight = _pParentScene.GetTerrainHeightAtXY(pos.X, pos.Y) + m_VhoverHeight;
	        	}
	        	else if((m_flags & VehicleFlag.HOVER_GLOBAL_HEIGHT) == VehicleFlag.HOVER_GLOBAL_HEIGHT)
	        	{
	        		m_VhoverTargetHeight = m_VhoverHeight;
	        	}
	        	
				if((m_flags & VehicleFlag.HOVER_UP_ONLY) == VehicleFlag.HOVER_UP_ONLY)
				{
					// If body is aready heigher, use its height as target height
					if(pos.Z > m_VhoverTargetHeight) m_VhoverTargetHeight = pos.Z;
				}
				
//	            m_VhoverEfficiency = 0f;	// 0=boucy, 1=Crit.damped
//				m_VhoverTimescale = 0f;		// time to acheive height
//				pTimestep  is time since last frame,in secs 
				float herr0 = pos.Z - m_VhoverTargetHeight;
//if(frcount == 0) Console.WriteLine("herr0=" + herr0);			
				// Replace Vertical speed with correction figure if significant
				if(Math.Abs(herr0) > 0.01f )
				{
		            d.Mass objMass;
		            d.BodyGetMass(Body, out objMass);
					m_dir.Z = - ( (herr0 * pTimestep * 50.0f) / m_VhoverTimescale);
					// m_VhoverEfficiency is not yet implemented
				}
				else
				{
					m_dir.Z = 0f;
				}
			}
	        	
	        // Apply velocity
	        d.BodySetLinearVel(Body, m_dir.X, m_dir.Y, m_dir.Z);        
//if(frcount == 0) Console.WriteLine("Move  " + Body + ":"+ m_dir.X + " " + m_dir.Y + " " + m_dir.Z);
            // apply gravity force
			d.BodyAddForce(Body, grav.X, grav.Y, grav.Z);		
//if(frcount == 0) Console.WriteLine("Force " + Body + ":" + grav.X + " " + grav.Y + " " + grav.Z);     


			// apply friction
            Vector3 decayamount = Vector3.One / (m_linearFrictionTimescale / pTimestep);
            m_lastLinearVelocityVector -= m_lastLinearVelocityVector * decayamount;
        } // end MoveLinear()
        
        private void MoveAngular(float pTimestep)
        {
        
        	// m_angularMotorDirection  			is the latest value from the script, and is decayed here
        	// m_angularMotorDirectionLASTSET 		is the latest value from the script
        	// m_lastAngularVelocityVector			is what is being applied to the Body, varied up and down here
        	
            if (!m_angularMotorDirection.ApproxEquals(Vector3.Zero, 0.01f))
            {
				if(!d.BodyIsEnabled (Body))  d.BodyEnable (Body);
				// ramp up to new value
                Vector3 addAmount = m_angularMotorDirection / (m_angularMotorTimescale / pTimestep);
                m_lastAngularVelocityVector += (addAmount * 10f);
//if(frcount == 0) Console.WriteLine("add: " + addAmount);

				// limit applied value to what was set by script
                // This will work temporarily, but we really need to compare speed on an axis
                if (Math.Abs(m_lastAngularVelocityVector.X) > Math.Abs(m_angularMotorDirectionLASTSET.X))
                    m_lastAngularVelocityVector.X = m_angularMotorDirectionLASTSET.X;
                if (Math.Abs(m_lastAngularVelocityVector.Y) > Math.Abs(m_angularMotorDirectionLASTSET.Y))
                    m_lastAngularVelocityVector.Y = m_angularMotorDirectionLASTSET.Y;
                if (Math.Abs(m_lastAngularVelocityVector.Z) > Math.Abs(m_angularMotorDirectionLASTSET.Z))
                    m_lastAngularVelocityVector.Z = m_angularMotorDirectionLASTSET.Z;

				// decay the requested value
                Vector3 decayfraction = ((Vector3.One / (m_angularMotorDecayTimescale / pTimestep)));
                //Console.WriteLine("decay: " + decayfraction);
                m_angularMotorDirection -= m_angularMotorDirection * decayfraction;
                //Console.WriteLine("actual: " + m_linearMotorDirection);
            }
            // KF: m_lastAngularVelocityVector is rotational speed in rad/sec ?
            
            // Vertical attractor section
            
//            d.Mass objMass;
//            d.BodyGetMass(Body, out objMass);
//            float servo = 100f * objMass.mass * m_verticalAttractionEfficiency / (m_verticalAttractionTimescale * pTimestep);
            float servo = 0.1f * m_verticalAttractionEfficiency / (m_verticalAttractionTimescale * pTimestep);
            // get present body rotation
            d.Quaternion rot = d.BodyGetQuaternion(Body);
            Quaternion rotq = new Quaternion(rot.X, rot.Y, rot.Z, rot.W);
            // make a vector pointing up
			Vector3 verterr = Vector3.Zero;
			verterr.Z = 1.0f;
			// rotate it to Body Angle
			verterr = verterr * rotq;
			// verterr.X and .Y are the World error ammounts. They are 0 when there is no error (Vehicle Body is 'vertical'), and .Z will be 1.
			// As the body leans to its side |.X| will increase to 1 and .Z fall to 0. As body inverts |.X| will fall and .Z will go
			// negative. Similar for tilt and |.Y|. .X and .Y must be modulated to prevent a stable inverted body.
			if (verterr.Z < 0.0f)
			{
				verterr.X = 2.0f - verterr.X;
				verterr.Y = 2.0f - verterr.Y;
			}
			// Error is 0 (no error) to +/- 2 (max error)
			// scale it by servo
			verterr = verterr * servo;
			
			// rotate to object frame
	//		verterr = verterr * rotq;
			
			// As the body rotates around the X axis, then verterr.Y increases; Rotated around Y then .X increases, so 
			// Change  Body angular velocity  X based on Y, and Y based on X. Z is not changed.
			m_lastAngularVelocityVector.X += verterr.Y;
			m_lastAngularVelocityVector.Y -= verterr.X;
/*
if(frcount == 0) 
	{
//			Console.WriteLine("AngleMotor " + m_lastAngularVelocityVector);
			Console.WriteLine(String.Format("VA Body:{0} servo:{1} err:<{2},{3},{4}>  VAE:{5}", 
					Body, servo, verterr.X, verterr.Y, verterr.Z, m_verticalAttractionEfficiency)); 
	}
	*/
			d.BodySetAngularVel (Body, m_lastAngularVelocityVector.X, m_lastAngularVelocityVector.Y, m_lastAngularVelocityVector.Z);
			// apply friction
            Vector3 decayamount = Vector3.One / (m_angularFrictionTimescale / pTimestep);
            m_lastAngularVelocityVector -= m_lastAngularVelocityVector * decayamount;

        } //end MoveAngular
    }
}