BulletSim: remove friction calcuation from BSMotor and move linear and

angular friction computation into linear and angular movement code.
The friction wasn't being applied properly. This will make it so vehicles
don't drift as much and the drift is tunable by changing the friction
timescales.

1 files changed, 31 insertions, 13 deletions

diff --git a/OpenSim/Region/Physics/BulletSPlugin/BSDynamics.cs b/OpenSim/Region/Physics/BulletSPlugin/BSDynamics.cs
index 0dd2aa5..272a162 100644
--- a/OpenSim/Region/Physics/BulletSPlugin/BSDynamics.cs
+++ b/OpenSim/Region/Physics/BulletSPlugin/BSDynamics.cs
@@ -235,7 +235,6 @@ namespace OpenSim.Region.Physics.BulletSPlugin
                 // set all of the components to the same value
                 case Vehicle.ANGULAR_FRICTION_TIMESCALE:
                     m_angularFrictionTimescale = new Vector3(pValue, pValue, pValue);
-                    m_angularMotor.FrictionTimescale = m_angularFrictionTimescale;
                     break;
                 case Vehicle.ANGULAR_MOTOR_DIRECTION:
                     m_angularMotorDirection = new Vector3(pValue, pValue, pValue);
@@ -244,7 +243,6 @@ namespace OpenSim.Region.Physics.BulletSPlugin
                     break;
                 case Vehicle.LINEAR_FRICTION_TIMESCALE:
                     m_linearFrictionTimescale = new Vector3(pValue, pValue, pValue);
-                    m_linearMotor.FrictionTimescale = m_linearFrictionTimescale;
                     break;
                 case Vehicle.LINEAR_MOTOR_DIRECTION:
                     m_linearMotorDirection = new Vector3(pValue, pValue, pValue);
@@ -265,7 +263,6 @@ namespace OpenSim.Region.Physics.BulletSPlugin
             {
                 case Vehicle.ANGULAR_FRICTION_TIMESCALE:
                     m_angularFrictionTimescale = new Vector3(pValue.X, pValue.Y, pValue.Z);
-                    m_angularMotor.FrictionTimescale = m_angularFrictionTimescale;
                     break;
                 case Vehicle.ANGULAR_MOTOR_DIRECTION:
                     // Limit requested angular speed to 2 rps= 4 pi rads/sec
@@ -278,7 +275,6 @@ namespace OpenSim.Region.Physics.BulletSPlugin
                     break;
                 case Vehicle.LINEAR_FRICTION_TIMESCALE:
                     m_linearFrictionTimescale = new Vector3(pValue.X, pValue.Y, pValue.Z);
-                    m_linearMotor.FrictionTimescale = m_linearFrictionTimescale;
                     break;
                 case Vehicle.LINEAR_MOTOR_DIRECTION:
                     m_linearMotorDirection = new Vector3(pValue.X, pValue.Y, pValue.Z);
@@ -559,14 +555,10 @@ namespace OpenSim.Region.Physics.BulletSPlugin
                     break;
             }
 
-            m_linearMotor = new BSVMotor("LinearMotor", m_linearMotorTimescale,
-                                m_linearMotorDecayTimescale, m_linearFrictionTimescale,
-                                1f);
+            m_linearMotor = new BSVMotor("LinearMotor", m_linearMotorTimescale, m_linearMotorDecayTimescale, 1f);
             m_linearMotor.PhysicsScene = m_physicsScene;  // DEBUG DEBUG DEBUG (enables detail logging)
 
-            m_angularMotor = new BSVMotor("AngularMotor", m_angularMotorTimescale,
-                                m_angularMotorDecayTimescale, m_angularFrictionTimescale,
-                                1f);
+            m_angularMotor = new BSVMotor("AngularMotor", m_angularMotorTimescale, m_angularMotorDecayTimescale, 1f);
             m_angularMotor.PhysicsScene = m_physicsScene;  // DEBUG DEBUG DEBUG (enables detail logging)
 
             /*  Not implemented
@@ -574,7 +566,6 @@ namespace OpenSim.Region.Physics.BulletSPlugin
                                 BSMotor.Infinite, BSMotor.InfiniteVector,
                                 m_verticalAttractionEfficiency);
             // Z goes away and we keep X and Y
-            m_verticalAttractionMotor.FrictionTimescale = new Vector3(BSMotor.Infinite, BSMotor.Infinite, 0.1f);
             m_verticalAttractionMotor.PhysicsScene = PhysicsScene;  // DEBUG DEBUG DEBUG (enables detail logging)
              */
 
@@ -1050,8 +1041,13 @@ namespace OpenSim.Region.Physics.BulletSPlugin
             // Add this correction to the velocity to make it faster/slower.
             VehicleVelocity += linearMotorVelocityW;
 
-            VDetailLog("{0},  MoveLinear,velocity,origVelW={1},velV={2},correctV={3},correctW={4},newVelW={5}",
-                        ControllingPrim.LocalID, origVelW, currentVelV, linearMotorCorrectionV, linearMotorVelocityW, VehicleVelocity);
+            // Friction reduces vehicle motion
+            Vector3 frictionFactor = ComputeFrictionFactor(m_linearFrictionTimescale, pTimestep);
+            VehicleVelocity -= (VehicleVelocity * frictionFactor);
+
+            VDetailLog("{0},  MoveLinear,velocity,origVelW={1},velV={2},correctV={3},correctW={4},newVelW={5},fricFact={6}",
+                        ControllingPrim.LocalID, origVelW, currentVelV, linearMotorCorrectionV,
+                        linearMotorVelocityW, VehicleVelocity, frictionFactor);
         }
 
         public void ComputeLinearTerrainHeightCorrection(float pTimestep)
@@ -1342,6 +1338,11 @@ namespace OpenSim.Region.Physics.BulletSPlugin
           //  }
 
             VehicleRotationalVelocity += angularMotorContributionV * VehicleOrientation;
+
+            // Reduce any velocity by friction.
+            Vector3 frictionFactor = ComputeFrictionFactor(m_angularFrictionTimescale, pTimestep);
+            VehicleRotationalVelocity -= (VehicleRotationalVelocity * frictionFactor);
+
             VDetailLog("{0},  MoveAngular,angularTurning,angularMotorContrib={1}", ControllingPrim.LocalID, angularMotorContributionV);
         }
 
@@ -1629,6 +1630,23 @@ namespace OpenSim.Region.Physics.BulletSPlugin
 
         }
 
+        // Given a friction vector (reduction in seconds) and a timestep, return the factor to reduce
+        //     some value by to apply this friction.
+        private Vector3 ComputeFrictionFactor(Vector3 friction, float pTimestep)
+        {
+            Vector3 frictionFactor = Vector3.Zero;
+            if (friction != BSMotor.InfiniteVector)
+            {
+                // frictionFactor = (Vector3.One / FrictionTimescale) * timeStep;
+                // Individual friction components can be 'infinite' so compute each separately.
+                frictionFactor.X = (friction.X == BSMotor.Infinite) ? 0f : (1f / friction.X);
+                frictionFactor.Y = (friction.Y == BSMotor.Infinite) ? 0f : (1f / friction.Y);
+                frictionFactor.Z = (friction.Z == BSMotor.Infinite) ? 0f : (1f / friction.Z);
+                frictionFactor *= pTimestep;
+            }
+            return frictionFactor;
+        }
+
         private float ClampInRange(float low, float val, float high)
         {
             return Math.Max(low, Math.Min(val, high));