code: def set_stencil_mask(self, mask=8, face='front_and_back'):
          
          self.glir.command('FUNC', 'glStencilMaskSeparate', face, int(mask))
docs: Control the front or back writing of individual bits in the stencil
      
          Parameters
          ----------
          mask : int
              Mask that is ANDed with ref and stored stencil value.
          face : str
              Can be 'front', 'back', or 'front_and_back'.