BulletSim: add BSPhysObject code to manage registrations of preStep events. Use same to implement setForce and setTorque so the values are restored at the beginning of each step (since Bullet zeros forces applied last step). Simplify implementation of AddForce and AddTorque by relying on the addition of forces in Bullet.

OpenSim/Region/Physics/BulletSPlugin/BSPhysObject.cs

@@ -45,6 +45,16 @@ namespace OpenSim.Region.Physics.BulletSPlugin
  *      ForceVariableName: direct reference (store and fetch) to the value in the physics engine.
  *  The last two (and certainly the last one) should be referenced only 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              
+ */
+
 public abstract class BSPhysObject : PhysicsActor
 {
     protected BSPhysObject()
@@ -69,6 +79,12 @@ public abstract class BSPhysObject : PhysicsActor
         CollidingGroundStep = 0;
     }
 
+    // Tell the object to clean up.
+    public virtual void Destroy()
+    {
+        UnRegisterAllPreStepActions();
+    }
+
     public BSScene PhysicsScene { get; protected set; }
     // public override uint LocalID { get; set; } // Use the LocalID definition in PhysicsActor
     public string PhysObjectName { get; protected set; }
@@ -130,9 +146,6 @@ public abstract class BSPhysObject : PhysicsActor
     // Update the physical location and motion of the object. Called with data from Bullet.
     public abstract void UpdateProperties(EntityProperties entprop);
 
-    // Tell the object to clean up.
-    public abstract void Destroy();
-
     public abstract OMV.Vector3 RawPosition { get; set; }
     public abstract OMV.Vector3 ForcePosition { get; set; }
 
@@ -280,11 +293,48 @@ public abstract class BSPhysObject : PhysicsActor
 
     #endregion // Collisions
 
+    #region Per Simulation Step actions
+    // There are some actions that must be performed for a physical object before each simulation step.
+    // These actions are optional so, rather than scanning all the physical objects and asking them
+    //     if they have anything to do, a physical object registers for an event call before the step is performed.
+    // This bookkeeping makes it easy to add, remove and clean up after all these registrations.
+    private Dictionary<string, BSScene.PreStepAction> RegisteredActions = new Dictionary<string, BSScene.PreStepAction>();
+    protected void RegisterPreStepAction(string op, uint id, BSScene.PreStepAction actn)
+    {
+        string identifier = op + "-" + id.ToString();
+        RegisteredActions[identifier] = actn;
+        PhysicsScene.BeforeStep += actn;
+    }
+
+    // Unregister a pre step action. Safe to call if the action has not been registered.
+    protected void UnRegisterPreStepAction(string op, uint id)
+    {
+        string identifier = op + "-" + id.ToString();
+        if (RegisteredActions.ContainsKey(identifier))
+        {
+            PhysicsScene.BeforeStep -= RegisteredActions[identifier];
+            RegisteredActions.Remove(identifier);
+        }
+    }
+
+    protected void UnRegisterAllPreStepActions()
+    {
+        foreach (KeyValuePair<string, BSScene.PreStepAction> kvp in RegisteredActions)
+        {
+            PhysicsScene.BeforeStep -= kvp.Value;
+        }
+        RegisteredActions.Clear();
+    }
+
+    
+    #endregion // Per Simulation Step actions
+
     // High performance detailed logging routine used by the physical objects.
     protected void DetailLog(string msg, params Object[] args)
     {
         if (PhysicsScene.PhysicsLogging.Enabled)
             PhysicsScene.DetailLog(msg, args);
     }
+
 }
 }