code: def line_pos_from_number(self, line_number):
          
          editor = self._editor
          block = editor.document().findBlockByNumber(line_number)
          if block.isValid():
              return int(editor.blockBoundingGeometry(block).translated(
                  editor.contentOffset()).top())
          if line_number <= 0:
              return 0
          else:
              return int(editor.blockBoundingGeometry(
                  block.previous()).translated(editor.contentOffset()).bottom())
docs: Computes line position on Y-Axis (at the center of the line) from line
          number.
  
          :param line_number: The line number for which we want to know the
                              position in pixels.
          :return: The center position of the line.