-- display lines starting from the second screen line of line 3

  -- display lines starting from second screen line of a line

  -- after hitting the up arrow the screen scrolls up by one line

  -- after hitting the up arrow the screen scrolls up to first screen line

function test_up_arrow_scrolls_up_to_final_screen_line()
  print('test_up_arrow_scrolls_up_to_final_screen_line')
  -- display lines starting just after a long line
  App.screen.init{width=25+30, height=60}
  Lines = load_array{'abc def', 'ghi', 'jkl', 'mno'}
  Line_width = App.screen.width
  Cursor1 = {line=2, pos=1}
  Screen_top1 = {line=2, pos=1}
  Screen_bottom1 = {}
  Zoom = 1
  local screen_top_margin = 15  -- pixels
  local line_height = math.floor(15*Zoom)  -- pixels
  App.draw()
  local y = screen_top_margin
  App.screen.check(y, 'ghi', 'F - test_up_arrow_scrolls_up_to_final_screen_line/baseline/screen:1')
  y = y + line_height
  App.screen.check(y, 'jkl', 'F - test_up_arrow_scrolls_up_to_final_screen_line/baseline/screen:2')
  y = y + line_height
  App.screen.check(y, 'mno', 'F - test_up_arrow_scrolls_up_to_final_screen_line/baseline/screen:3')
  -- after hitting the up arrow the screen scrolls up to final screen line of previous line
  App.run_after_keychord('up')
  y = screen_top_margin
  App.screen.check(y, 'def', 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen:1')
  y = y + line_height
  App.screen.check(y, 'ghi', 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen:2')
  y = y + line_height
  App.screen.check(y, 'jkl', 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen:3')
  check_eq(Screen_top1.line, 1, 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen_top')
  check_eq(Screen_top1.pos, 5, 'F - test_up_arrow_scrolls_up_to_final_screen_line/screen_top')
  check_eq(Cursor1.line, 1, 'F - test_up_arrow_scrolls_up_to_final_screen_line/cursor')
  check_eq(Cursor1.pos, 5, 'F - test_up_arrow_scrolls_up_to_final_screen_line/cursor')
end

--?           print('found previous text line')

          Text.populate_screen_line_starting_pos(Cursor1.line)

--?           print('has multiple screen lines')

--?           print(#screen_line_starting_pos)

          if Screen_top1.line == Cursor1.line and Screen_top1.pos == screen_line_starting_pos then

          if Screen_top1.line > Cursor1.line then
            Screen_top1.line = Cursor1.line

function Text.populate_screen_line_starting_pos(line_index)
  -- duplicate some logic from Text.draw
  local line = Lines[line_index]
  if line.fragments == nil then
    Text.compute_fragments(line, Line_width)
  end
  local x = 25
  local pos = 1
  for _, f in ipairs(line.fragments) do
    local frag, frag_text = f.data, f.text
--?     print(x, frag)
    -- render fragment
    local frag_width = math.floor(App.width(frag_text)*Zoom)
    if x + frag_width > Line_width then
      x = 25
      if line.screen_line_starting_pos == nil then
        line.screen_line_starting_pos = {1, pos}
      else
        table.insert(line.screen_line_starting_pos, pos)
      end
    end
    x = x + frag_width
    local frag_len = utf8.len(frag)
    pos = pos + frag_len
  end
end

--?   print('checking for "'..expected_contents..'" at y '..tostring(y))