private void UpdatePhysics( float deltaTime )
        {
            const float timeStep = 0.0016666f;
            
            /*
            accumulator += deltaTime;

            while( accumulator > timeStep )
            {
                testEnt.Update( timeStep );
                accumulator -= timeStep;
            }*/


            //  Apply some gravity.
            /*
            for( int i = 0; i < testEnt.PointMassSystem.Points.Count; i++ )
            {
                testEnt.PointMassSystem.Points[ i ].AddForce( new Vector2( 0.0f, 0.98f ) );
            }
            */
            
            testEnt.Update( timeStep );
        }