             mat4.copyArray @sst, @HMD.stageParameters.sittingToStandingTransform
             mat4.invert @sst_inverse, @sst
             mat3.fromMat4 @sst3, @sst
+        @head_is_tracking = false
         # @to_Z_up = mat4.new 1,0,0,0, 0,0,1,0, 0,-1,0,0, 0,0,0,1
         # left eye viewport
         camera = left_cam = @scene.active_camera.clone()

            behaviour.on_exit_vr?()
        return

    exit: -> @destroy()

    pre_draw: ->
        {HMD} = this

            if @use_unpredict
                quat.slerp r0, @left_orientation, r0, unpredict
            quat.copy @left_orientation, r0
            # TODO: Test with other headsets.
            @head_is_tracking =
                not (p0.x == m4.m12 and p0.y == m4.m13 and p0.z == m4.m14)
            vec3.set p0, m4.m12, m4.m13, m4.m14

            mat4.copyArray m4, rightViewMatrix
