The start rotation of the tween. When the PhysicsBody.TransformWriteTween.transformWriteMode is PhysicsBody.TransformWriteMode.Current, this is set to the last Transform._rotation but is not used. When the PhysicsBody.TransformWriteTween.transformWriteMode is PhysicsBody.TransformWriteMode.Interpolate, this is set to the last Transform._rotation. When the PhysicsBody.TransformWriteTween.transformWriteMode is PhysicsBody.TransformWriteMode.Extrapolate, this will be calculated from PhysicsBody.TransformWriteTween.physicsTransform. See Transform._rotation.