code: def clipPolygons(self, polygons):
          
          if not self.plane: 
              return polygons[:]
  
          front = []
          back = []
          for poly in polygons:
              self.plane.splitPolygon(poly, front, back, front, back)
  
          if self.front: 
              front = self.front.clipPolygons(front)
  
          if self.back: 
              back = self.back.clipPolygons(back)
          else:
              back = []
  
          front.extend(back)
          return front
docs: Recursively remove all polygons in `polygons` that are inside this BSP
          tree.