* Created a way that the OpenSimulator scene can ask the physics scene to do a raycast test safely.

* Test for prim obstructions between the avatar and camera.  If there are obstructions, inform the client to move the camera closer.  This makes it so that walls and objects don't obstruct your view while you're moving around.   Try walking inside a hollowed tori.   You'll see how much easier it is now because your camera automatically moves closer so you can still see.
* Created a way to know if the user's camera is alt + cammed or just following the avatar.
* Changes IClientAPI interface by adding SendCameraConstraint(Vector4 CameraConstraint)

OpenSim/Region/Physics/Manager/PhysicsScene.cs

@@ -36,6 +36,8 @@ namespace OpenSim.Region.Physics.Manager
 {
     public delegate void physicsCrash();
 
+    public delegate void RaycastCallback(bool hitYN, Vector3 collisionPoint, uint localid, float distance);
+
     public abstract class PhysicsScene
     {
         private static readonly ILog m_log = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);
@@ -152,6 +154,39 @@ namespace OpenSim.Region.Physics.Manager
 
         public abstract bool IsThreaded { get; }
 
+        /// <summary>
+        /// True if the physics plugin supports raycasting against the physics scene
+        /// </summary>
+        public virtual bool SupportsRayCast()
+        {
+            return false;
+        }
+
+        /// <summary>
+        /// Queue a raycast against the physics scene.  
+        /// The provided callback method will be called when the raycast is complete
+        /// 
+        /// Many physics engines don't support collision testing at the same time as 
+        /// manipulating the physics scene, so we queue the request up and callback 
+        /// a custom method when the raycast is complete.  
+        /// This allows physics engines that give an immediate result to callback immediately
+        /// and ones that don't, to callback when it gets a result back.
+        /// 
+        /// ODE for example will not allow you to change the scene while collision testing or
+        /// it asserts, 'opteration not valid for locked space'.  This includes adding a ray to the scene.
+        /// 
+        /// This is named RayCastWorld to not conflict with modrex's Raycast method.
+        /// </summary>
+        /// <param name="position">Origin of the ray</param>
+        /// <param name="direction">Direction of the ray</param>
+        /// <param name="length">Length of ray in meters</param>
+        /// <param name="retMethod">Method to call when the raycast is complete</param>
+        public virtual void RaycastWorld( Vector3 position, Vector3 direction, float length, RaycastCallback retMethod)
+        {
+            if (retMethod != null)
+                retMethod(false, Vector3.Zero, 0, 999999999999f);
+        }
+
         private class NullPhysicsScene : PhysicsScene
         {
             private static int m_workIndicator;
@@ -240,6 +275,7 @@ namespace OpenSim.Region.Physics.Manager
                 Dictionary<uint, float> returncolliders = new Dictionary<uint, float>();
                 return returncolliders;
             }
+            
         }
     }
     public delegate void JointMoved(PhysicsJoint joint);