def prev_column
      # TODO take care of multipliers
      _calculate_column_offsets unless @coffsets
      c = @column_pointer.previous
      cp = @coffsets[c]
      #$log.debug " prev #{c} , #{cp} "
      @curpos = cp if cp
      up() if c > @column_pointer.last_index
      fire_column_event :ENTER_COLUMN
    end
def prev_column
      # TODO take care of multipliers
      _calculate_column_offsets unless @coffsets
      c = @column_pointer.previous
      cp = @coffsets[c]
      #$log.debug " prev #{c} , #{cp} "
      @curpos = cp if cp
      up() if c > @column_pointer.last_index
      fire_column_event :ENTER_COLUMN
    end
jump cursor to previous column
 TODO : if cursor goes out of view, then pad should scroll right or left and down