text: # ----------------------------------------------------------------------------
  # pyglet
  # Copyright (c) 2006-2008 Alex Holkner
  # Copyright (c) 2008-2020 pyglet contributors
  # All rights reserved.
  #
  # Redistribution and use in source and binary forms, with or without
  # modification, are permitted provided that the following conditions
  # are met:
  #
  #  * Redistributions of source code must retain the above copyright
  #    notice, this list of conditions and the following disclaimer.
  #  * Redistributions in binary form must reproduce the above copyright
  #    notice, this list of conditions and the following disclaimer in
  #    the documentation and/or other materials provided with the
  #    distribution.
  #  * Neither the name of pyglet nor the names of its
  #    contributors may be used to endorse or promote products
  #    derived from this software without specific prior written
  #    permission.
  #
  # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  # "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  # LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  # FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
  # COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  # INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
  # BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  # LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  # CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  # LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
  # ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  # POSSIBILITY OF SUCH DAMAGE.
  # ----------------------------------------------------------------------------
  from abc import ABCMeta, abstractmethod
  
  from pyglet.compat import with_metaclass
  
  
  class AbstractListener(with_metaclass(ABCMeta, object)):
      """The listener properties for positional audio.
  
      You can obtain the singleton instance of this class by calling
      :meth:`AbstractAudioDriver.get_listener`.
      """
  
      _volume = 1.0
      _position = (0, 0, 0)
      _forward_orientation = (0, 0, -1)
      _up_orientation = (0, 1, 0)
  
      @abstractmethod
      def _set_volume(self, volume):
          pass
  
      volume = property(lambda self: self._volume,
                        lambda self, volume: self._set_volume(volume),
                        doc="""The master volume for sound playback.
  
          All sound volumes are multiplied by this master volume before being
          played.  A value of 0 will silence playback (but still consume
          resources).  The nominal volume is 1.0.
  
          :type: float
          """)
  
      @abstractmethod
      def _set_position(self, position):
          pass
  
      position = property(lambda self: self._position,
                          lambda self, position: self._set_position(position),
                          doc="""The position of the listener in 3D space.
  
          The position is given as a tuple of floats (x, y, z).  The unit
          defaults to meters, but can be modified with the listener
          properties.
  
          :type: 3-tuple of float
          """)
  
      @abstractmethod
      def _set_forward_orientation(self, orientation):
          pass
  
      forward_orientation = property(lambda self: self._forward_orientation,
                                 lambda self, o: self._set_forward_orientation(o),
                                 doc="""A vector giving the direction the
          listener is facing.
  
          The orientation is given as a tuple of floats (x, y, z), and has
          no unit.  The forward orientation should be orthagonal to the
          up orientation.
  
          :type: 3-tuple of float
          """)
  
      @abstractmethod
      def _set_up_orientation(self, orientation):
          pass
  
      up_orientation = property(lambda self: self._up_orientation,
                                lambda self, o: self._set_up_orientation(o),
                                doc="""A vector giving the "up" orientation
          of the listener.
  
          The orientation is given as a tuple of floats (x, y, z), and has
          no unit.  The up orientation should be orthagonal to the
          forward orientation.
  
          :type: 3-tuple of float
          """)
  
  