correct the default avatar_terminal_velocity value that I accidentally left in whilst testing

If velocity reaches 256 in any vector then bad things happen with ODE, so we now clamp this value.
In addition, a falling avatar is clamped by default at 54 m/s, which is the same as a falling skydiver.
This also appears to be the value used on the linden lab grid.
This should resolve http://opensimulator.org/mantis/view.php?id=5882

OpenSim/Region/Framework/Scenes/ScenePresence.cs

@@ -291,13 +291,10 @@ namespace OpenSim.Region.Framework.Scenes
         /// </summary>
         public PhysicsActor PhysicsActor { get; private set; }
 
-        private byte m_movementflag;
-
-        public byte MovementFlag
-        {
-            set { m_movementflag = value; }
-            get { return m_movementflag; }
-        }
+        /// <summary>
+        /// Record user movement inputs.
+        /// </summary>
+        public byte MovementFlag { get; private set; }
 
         private bool m_updateflag;
 

OpenSim/Region/Physics/OdePlugin/ODECharacter.cs

@@ -156,6 +156,22 @@ namespace OpenSim.Region.Physics.OdePlugin
         internal UUID m_uuid { get; private set; }
         internal bool bad = false;
 
+        /// <summary>
+        /// ODE Avatar.
+        /// </summary>
+        /// <param name="avName"></param>
+        /// <param name="parent_scene"></param>
+        /// <param name="pos"></param>
+        /// <param name="size"></param>
+        /// <param name="pid_d"></param>
+        /// <param name="pid_p"></param>
+        /// <param name="capsule_radius"></param>
+        /// <param name="tensor"></param>
+        /// <param name="density">
+        /// Only used right now to return information to LSL.  Not actually used to set mass in ODE!
+        /// </param>
+        /// <param name="walk_divisor"></param>
+        /// <param name="rundivisor"></param>
         public OdeCharacter(
             String avName, OdeScene parent_scene, Vector3 pos, Vector3 size, float pid_d, float pid_p,
             float capsule_radius, float tensor, float density,
@@ -786,6 +802,10 @@ namespace OpenSim.Region.Physics.OdePlugin
             Vector3 vec = Vector3.Zero;
             d.Vector3 vel = d.BodyGetLinearVel(Body);
 
+//            m_log.DebugFormat(
+//                "[ODE CHARACTER]: Current velocity in Move() is <{0},{1},{2}>, target {3} for {4}",
+//                vel.X, vel.Y, vel.Z, _target_velocity, Name);
+
             float movementdivisor = 1f;
 
             if (!m_alwaysRun)
@@ -884,18 +904,20 @@ namespace OpenSim.Region.Physics.OdePlugin
 
                 if (flying)
                 {
+                    // This also acts as anti-gravity so that we hover when flying rather than fall.
                     vec.Z = (_target_velocity.Z - vel.Z) * (PID_D);
                 }
             }
 
             if (flying)
             {
+                // Anti-gravity so that we hover when flying rather than fall.
                 vec.Z += ((-1 * _parent_scene.gravityz) * m_mass);
 
                 //Added for auto fly height. Kitto Flora
                 //d.Vector3 pos = d.BodyGetPosition(Body);
                 float target_altitude = _parent_scene.GetTerrainHeightAtXY(_position.X, _position.Y) + MinimumGroundFlightOffset;
-                
+
                 if (_position.Z < target_altitude)
                 {
                     vec.Z += (target_altitude - _position.Z) * PID_P * 5.0f;
@@ -921,6 +943,25 @@ namespace OpenSim.Region.Physics.OdePlugin
 
                 return;
             }
+
+            d.Vector3 newVel = d.BodyGetLinearVel(Body);
+            if (newVel.X >= 256 || newVel.X <= 256 || newVel.Y >= 256 || newVel.Y <= 256 || newVel.Z >= 256 || newVel.Z <= 256)
+            {
+//                m_log.DebugFormat(
+//                    "[ODE CHARACTER]: Limiting falling velocity from {0} to {1} for {2}", newVel.Z, -9.8, Name);
+
+                newVel.X = Util.Clamp<float>(newVel.X, -255f, 255f);
+                newVel.Y = Util.Clamp<float>(newVel.Y, -255f, 255f);
+
+                if (!flying)
+                    newVel.Z
+                        = Util.Clamp<float>(
+                            newVel.Z, -_parent_scene.AvatarTerminalVelocity, _parent_scene.AvatarTerminalVelocity);
+                else
+                    newVel.Z = Util.Clamp<float>(newVel.Z, -255f, 255f);
+
+                d.BodySetLinearVel(Body, newVel.X, newVel.Y, newVel.Z);
+            }
         }
 
         /// <summary>

OpenSim/Region/Physics/OdePlugin/OdeScene.cs

@@ -144,6 +144,8 @@ namespace OpenSim.Region.Physics.OdePlugin
         public float gravityy = 0f;
         public float gravityz = -9.8f;
 
+        public float AvatarTerminalVelocity { get; set; }
+
         private float contactsurfacelayer = 0.001f;
 
         private int worldHashspaceLow = -4;
@@ -459,6 +461,15 @@ namespace OpenSim.Region.Physics.OdePlugin
                     gravityy = physicsconfig.GetFloat("world_gravityy", 0f);
                     gravityz = physicsconfig.GetFloat("world_gravityz", -9.8f);
 
+                    float avatarTerminalVelocity = physicsconfig.GetFloat("avatar_terminal_velocity", 54f);
+                    AvatarTerminalVelocity = Util.Clamp<float>(avatarTerminalVelocity, 0, 255f);
+                    if (AvatarTerminalVelocity != avatarTerminalVelocity)
+                    {
+                        m_log.WarnFormat(
+                            "[ODE SCENE]: avatar_terminal_velocity of {0} is invalid.  Clamping to {1}",
+                            avatarTerminalVelocity, AvatarTerminalVelocity);
+                    }
+
                     worldHashspaceLow = physicsconfig.GetInt("world_hashspace_size_low", -4);
                     worldHashspaceHigh = physicsconfig.GetInt("world_hashspace_size_high", 128);
 

bin/OpenSimDefaults.ini

@@ -655,6 +655,11 @@
     world_gravityy = 0
     world_gravityz = -9.8
 
+    ; Terminal velocity of a falling avatar
+    ; This is the same http://en.wikipedia.org/wiki/Terminal_velocity#Examples
+    ; Max value is 255, min value is 0
+    avatar_terminal_velocity = 54
+
     ; World Step size. (warning these are dangerous.  Changing these will probably cause your scene to explode dramatically)
     ; reference: fps = (0.089/ODE_STEPSIZE) * 1000;
     world_stepsize = 0.0178