print('cursor pos is now '..tostring(Cursor1.pos))

      print('cursor pos is now', Cursor1.line, Cursor1.pos)

  local cursor2 = Text.to2(Cursor1)
  print('cursor pos '..tostring(Cursor1.pos)..' is on the #'..tostring(cursor2.screen_line)..' screen line down')
  local y = Screen_height - cursor2.screen_pos*math.floor(15*Zoom)

  local top2 = Text.to2(Cursor1)
--?   print('cursor pos '..tostring(Cursor1.pos)..' is on the #'..tostring(top2.screen_line)..' screen line down')
  local y = Screen_height - math.floor(15*Zoom)

    if Screen_top1.line == 1 then break end
    print('y', y)
    local h = 0
    if Lines[Screen_top1.line-1].mode == 'drawing' then
      h = 20 + Drawing.pixels(Lines[Screen_top1.line-1].h)
    elseif Lines[Screen_top1.line-1].screen_line_starting_pos == nil then
      h = h + math.floor(15*Zoom)  -- text height

--?     print(y, 'top2:', top2.line, top2.screen_line, top2.screen_pos)
    if top2.line == 1 and top2.screen_line == 1 then break end
    if top2.screen_line > 1 or Lines[top2.line-1].mode == 'text' then
      local h = math.floor(15*Zoom)
      if y - h < 15 then  -- top margin = 15
        break
      end
      y = y - h

      local n = #Lines[Screen_top1.line-1].screen_line_starting_pos
      h = h + n*math.floor(15*Zoom)  -- text height
    end
    print('height:', h)
    if y - h < 0 then
      break
    end
    y = y - h
    if y < math.floor(15*Zoom) then
      break

      assert(top2.line > 1)
      assert(Lines[top2.line-1].mode == 'drawing')
      -- We currently can't draw partial drawings, so either skip it entirely
      -- or not at all.
      local h = 20 + Drawing.pixels(Lines[Screen_top1.line-1].h)
      if y - h < 15 then
        break
      end
--?       print('skipping drawing of height', h)
      y = y - h

    Screen_top1.line = Screen_top1.line - 1

    top2 = Text.previous_screen_line(top2)

--?   print('top2 finally:', top2.line, top2.screen_line, top2.screen_pos)
  Screen_top1 = Text.to1(top2)
--?   print('top1 finally:', Screen_top1.line, Screen_top1.pos)

  assert(Lines[pos1.line].mode == 'text')

      if spos <= Cursor1.pos then

      if spos <= pos1.pos then

        result.screen_pos = spos

        result.screen_pos = pos1.pos - spos + 1

    result.pos = Lines[pos2.line].screen_line_starting_pos[pos2.screen_line] + pos2.screen_pos

    result.pos = Lines[pos2.line].screen_line_starting_pos[pos2.screen_line] + pos2.screen_pos - 1

end
function Text.previous_screen_line(pos2)
  if pos2.screen_line > 1 then
    return {line=pos2.line, screen_line=pos2.screen_line-1, screen_pos=1}
  elseif pos2.line == 1 then
    return pos2
  elseif Lines[pos2.line-1].mode == 'drawing' then
    return {line=pos2.line-1, screen_line=1, screen_pos=1}
  else
    local l = Lines[pos2.line-1]
    if l.screen_line_starting_pos == nil then
      return {line=pos2.line-1, screen_line=1, screen_pos=1}
    else
      return {line=pos2.line-1, screen_line=#Lines[pos2.line-1].screen_line_starting_pos, screen_pos=1}
    end
  end