end
function test_up_arrow_scrolls_up_by_one_line_skipping_drawing()
  -- display lines 3/4/5 with a drawing just off screen at line 2
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', '```lines', '```', 'def', 'ghi', 'jkl'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=3, pos=1}
  Editor_state.screen_top1 = {line=3, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'def', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'baseline/screen:3')
  -- after hitting the up arrow the screen scrolls up to previous text line
  edit.run_after_keychord(Editor_state, 'up')
  check_eq(Editor_state.screen_top1.line, 1, 'screen_top')
  check_eq(Editor_state.cursor1.line, 1, 'cursor')
end
function test_up_arrow_scrolls_up_by_one_screen_line()

      State.cursor1 = {
          line=State.screen_bottom1.line,
          pos=Text.to_pos_on_line(State, State.screen_bottom1.line, State.right-5, App.screen.height-5),
      }
    end
  end
end
-- slightly expensive since it redraws the screen
function Text.cursor_out_of_screen(State)
  App.draw()
  return State.cursor_y == nil
  -- this approach is cheaper and almost works, except on the final screen
  -- where file ends above bottom of screen
--?   local botpos = Text.pos_at_start_of_screen_line(State, State.cursor1)
--?   local botline1 = {line=State.cursor1.line, pos=botpos}
--?   return Text.lt1(State.screen_bottom1, botline1)
end
    return {line=loc2.line-1, screen_line=#State.line_cache[loc2.line-1].screen_line_starting_pos, screen_pos=1}
  end
end
    local l = State.lines[loc2.line-1]
    Text.populate_screen_line_starting_pos(State, loc2.line-1)
  elseif State.lines[loc2.line-1].mode == 'drawing' then
    return {line=loc2.line-1, screen_line=1, screen_pos=1}
  else
  return a.pos <= b.pos
end
  if a.line > b.line then
    return false
  end
  return a.pos < b.pos
end
function Text.le1(a, b)
  if a.line < b.line then
    return true
  end
function Text.eq1(a, b)
  return a.line == b.line and a.pos == b.pos
end
function Text.lt1(a, b)
  if a.line < b.line then
    return true
  end
  if a.line > b.line then
    return false
  end
      local s = string.sub(line.data, screen_line_starting_byte_offset)
--?       print('return', mx, Text.nearest_cursor_pos(s, mx, State.left), '=>', screen_line_starting_pos + Text.nearest_cursor_pos(s, mx, State.left) - 1)
      return screen_line_starting_pos + Text.nearest_cursor_pos(s, mx, State.left) - 1
    end
    y = nexty
  end
  assert(false)
end
function Text.screen_line_width(State, line_index, i)
  local line = State.lines[line_index]
  local line_cache = State.line_cache[line_index]
  local start_pos = line_cache.screen_line_starting_pos[i]
  local start_offset = Text.offset(line.data, start_pos)
  local screen_line
  if i < #line_cache.screen_line_starting_pos then
    local past_end_pos = line_cache.screen_line_starting_pos[i+1]
    local past_end_offset = Text.offset(line.data, past_end_pos)
    screen_line = string.sub(line.data, start_offset, past_end_offset-1)
  else
    screen_line = string.sub(line.data, start_pos)
  end
  local screen_line_text = App.newText(love.graphics.getFont(), screen_line)
  return App.width(screen_line_text)
end
        return line_cache.screen_line_starting_pos[screen_line_index+1]-1
      end
      if screen_line_index < #line_cache.screen_line_starting_pos and mx > State.left + Text.screen_line_width(State, line_index, screen_line_index) then
--?         print('past end of non-final line; return')
  local start_screen_line_index = Text.screen_line_index(line_cache.screen_line_starting_pos, line_cache.startpos)
  for screen_line_index = start_screen_line_index,#line_cache.screen_line_starting_pos do
    local screen_line_starting_pos = line_cache.screen_line_starting_pos[screen_line_index]
    local screen_line_starting_byte_offset = Text.offset(line.data, screen_line_starting_pos)
--?     print('iter', y, screen_line_index, screen_line_starting_pos, string.sub(line.data, screen_line_starting_byte_offset))
    local nexty = y + State.line_height
    if my < nexty then
      -- On all wrapped screen lines but the final one, clicks past end of
      -- line position cursor on final character of screen line.
      -- (The final screen line positions past end of screen line as always.)
  Text.populate_screen_line_starting_pos(State, line_index)
  return y < line_cache.starty + State.line_height*(#line_cache.screen_line_starting_pos - Text.screen_line_index(line_cache.screen_line_starting_pos, line_cache.startpos) + 1)
end
-- convert mx,my in pixels to schema-1 coordinates
--?   print('snap =>', State.screen_top1.line, State.screen_top1.pos, State.cursor1.line, State.cursor1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)
  Text.redraw_all(State)  -- if we're scrolling, reclaim all fragments to avoid memory leaks
--?     print(y, 'top2:', top2.line, top2.screen_line, top2.screen_pos)
    if top2.line == 1 and top2.screen_line == 1 then break end
  top2.screen_pos = 1  -- start of screen line
--?   print('snap', State.screen_top1.line, State.screen_top1.pos, State.cursor1.line, State.cursor1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)
--?   print('cursor pos '..tostring(State.cursor1.pos)..' is on the #'..tostring(top2.screen_line)..' screen line down')
  local y = App.screen.height - State.line_height
  -- duplicate some logic from love.draw
  while true do
--?   print('to2: =>', top2.line, top2.screen_line, top2.screen_pos)
  -- slide to start of screen line
--?   print('to2:', State.cursor1.line, State.cursor1.pos)
  local top2 = Text.to2(State, State.cursor1)
  return screen_lines[#screen_lines] <= State.cursor1.pos
end
function Text.move_cursor_down_to_next_text_line_while_scrolling_again_if_necessary(State)
  assert(State.lines[State.cursor1.line].mode == 'text')
    State.screen_top1 = {
      line=State.cursor1.line,
      pos=Text.pos_at_start_of_screen_line(State, State.cursor1),
    }
    Text.redraw_all(State)  -- if we're scrolling, reclaim all fragments to avoid memory leaks
  end
end
  if State.cursor1.pos > 1 then
    State.cursor1.pos = State.cursor1.pos-1
  if Text.cursor_out_of_screen(State) then
    Text.snap_cursor_to_bottom_of_screen(State)
  end
end
function Text.match(s, pos, pat)
  local start_offset = Text.offset(s, pos)
  assert(start_offset)
  local end_offset = Text.offset(s, pos+1)
  assert(end_offset > start_offset)
  local curr = s:sub(start_offset, end_offset-1)
  return curr:match(pat)
end
function Text.left(State)
function Text.word_right(State)
  -- skip some whitespace
  while true do
    if State.cursor1.pos > utf8.len(State.lines[State.cursor1.line].data) then
      break
    end
    if Text.match(State.lines[State.cursor1.line].data, State.cursor1.pos, '%S') then
      break
    end
    Text.right_without_scroll(State)
  end
  -- skip some non-whitespace
  while true do
  -- skip some whitespace
  while true do
    if State.cursor1.pos == 1 then
      break
    end
    if Text.match(State.lines[State.cursor1.line].data, State.cursor1.pos-1, '%S') then
      break
    end
    Text.left(State)
  end
  State.cursor1.pos = utf8.len(State.lines[State.cursor1.line].data) + 1
  if Text.cursor_out_of_screen(State) then
    Text.snap_cursor_to_bottom_of_screen(State)
  end
end
function Text.word_left(State)
    State.screen_top1 = {line=State.cursor1.line, pos=State.cursor1.pos}  -- copy
  end
end
function Text.end_of_line(State)
  State.cursor1.pos = 1
  if Text.lt1(State.cursor1, State.screen_top1) then
  else
    -- move down one screen line in current line
    local scroll_down = Text.le1(State.screen_bottom1, State.cursor1)
--?     print('cursor is NOT at final screen line of its line')
    local screen_line_starting_pos, screen_line_index = Text.pos_at_start_of_screen_line(State, State.cursor1)
    Text.populate_screen_line_starting_pos(State, State.cursor1.line)
    local new_screen_line_starting_pos = State.line_cache[State.cursor1.line].screen_line_starting_pos[screen_line_index+1]
--?     print('switching pos of screen line at cursor from '..tostring(screen_line_starting_pos)..' to '..tostring(new_screen_line_starting_pos))
    local new_screen_line_starting_byte_offset = Text.offset(State.lines[State.cursor1.line].data, new_screen_line_starting_pos)
    local s = string.sub(State.lines[State.cursor1.line].data, new_screen_line_starting_byte_offset)
    State.cursor1.pos = new_screen_line_starting_pos + Text.nearest_cursor_pos(s, State.cursor_x, State.left) - 1
--?     print('cursor pos is now', State.cursor1.line, State.cursor1.pos)
    if scroll_down then
--?       print('scroll up preserving cursor')
      Text.snap_cursor_to_bottom_of_screen(State)
--?       print('screen top after:', State.screen_top1.line, State.screen_top1.pos)
  State.cursor1 = {line=State.screen_top1.line, pos=State.screen_top1.pos}
    State.screen_top1 = {
      line=State.cursor1.line,
      pos=Text.pos_at_start_of_screen_line(State, State.cursor1),
    }
    Text.redraw_all(State)  -- if we're scrolling, reclaim all fragments to avoid memory leaks
  end
end
  Text.move_cursor_down_to_next_text_line_while_scrolling_again_if_necessary(State)
--?   print('top now', State.screen_top1.line)
  Text.redraw_all(State)  -- if we're scrolling, reclaim all fragments to avoid memory leaks
--?   print('pagedown end')
end
function Text.up(State)
    State.screen_top1 = {line=State.screen_bottom1.line, pos=State.screen_bottom1.pos}
  end
--?   print('setting top to', State.screen_top1.line, State.screen_top1.pos)
  if bot2.screen_line > 1 then
    bot2.screen_line = math.max(bot2.screen_line-10, 1)
  end
  local new_top1 = Text.to1(State, bot2)
  if Text.lt1(State.screen_top1, new_top1) then
    State.screen_top1 = new_top1
  else
  -- If a line/paragraph gets to a page boundary, I often want to scroll
  -- before I get to the bottom.
  -- However, only do this if it makes forward progress.
  local bot2 = Text.to2(State, State.screen_bottom1)
  State.cursor1 = {line=State.screen_top1.line, pos=State.screen_top1.pos}
  Text.move_cursor_down_to_next_text_line_while_scrolling_again_if_necessary(State)
--?   print(State.cursor1.line, State.cursor1.pos, State.screen_top1.line, State.screen_top1.pos)
--?   print('pageup end')
end
function Text.pagedown(State)
--?   print('pagedown')
    if State.screen_top1.line == 1 and State.screen_top1.pos == 1 then break end
    if State.lines[State.screen_top1.line].mode == 'text' then
      y = y - State.line_height
    elseif State.lines[State.screen_top1.line].mode == 'drawing' then
      y = y - Drawing_padding_height - Drawing.pixels(State.lines[State.screen_top1.line].h, State.width)
    end
  local byte_offset = Text.offset(State.lines[State.cursor1.line].data, State.cursor1.pos)
  table.insert(State.lines, State.cursor1.line+1, {mode='text', data=string.sub(State.lines[State.cursor1.line].data, byte_offset)})
  table.insert(State.line_cache, State.cursor1.line+1, {})
  State.lines[State.cursor1.line].data = string.sub(State.lines[State.cursor1.line].data, 1, byte_offset-1)
  Text.clear_screen_line_cache(State, State.cursor1.line)
  State.cursor1 = {line=State.cursor1.line+1, pos=1}
end
function Text.pageup(State)
--?   print('pageup')
  -- duplicate some logic from love.draw
  local top2 = Text.to2(State, State.screen_top1)
--?   print(App.screen.height)
  local y = App.screen.height - State.line_height
  while y >= State.top do
--?     print(y, top2.line, top2.screen_line, top2.screen_pos)
      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos}
    end
      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos}
    end
      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos}
    end
      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos}
    end
      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos}
    end
      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos}
    end
      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos}
    end
      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos}
    end
      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos}
    end
      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos}
    end
    if State.cursor1.pos <= utf8.len(State.lines[State.cursor1.line].data) then
      local byte_start = utf8.offset(State.lines[State.cursor1.line].data, State.cursor1.pos)
      local byte_end = utf8.offset(State.lines[State.cursor1.line].data, State.cursor1.pos+1)
      if byte_start then
        if byte_end then
          State.lines[State.cursor1.line].data = string.sub(State.lines[State.cursor1.line].data, 1, byte_start-1)..string.sub(State.lines[State.cursor1.line].data, byte_end)
        else
          State.lines[State.cursor1.line].data = string.sub(State.lines[State.cursor1.line].data, 1, byte_start-1)
        end
        -- no change to State.cursor1.pos
      end
    if State.cursor1.pos <= utf8.len(State.lines[State.cursor1.line].data) then
      before = snapshot(State, State.cursor1.line)
    else
      before = snapshot(State, State.cursor1.line, State.cursor1.line+1)
    end
    if State.cursor1.pos > 1 then
      State.screen_top1 = {
        line=State.cursor1.line,
        pos=Text.pos_at_start_of_screen_line(State, State.cursor1),
      }
      Text.redraw_all(State)  -- if we're scrolling, reclaim all fragments to avoid memory leaks
    end
    Text.clear_screen_line_cache(State, State.cursor1.line)
    assert(Text.le1(State.screen_top1, State.cursor1))
    schedule_save(State)
    record_undo_event(State, {before=before, after=snapshot(State, State.cursor1.line)})
  elseif chord == 'delete' then
      before = snapshot(State, State.cursor1.line)
      local byte_start = utf8.offset(State.lines[State.cursor1.line].data, State.cursor1.pos-1)
      local byte_end = utf8.offset(State.lines[State.cursor1.line].data, State.cursor1.pos)
      if byte_start then
        if byte_end then
          State.lines[State.cursor1.line].data = string.sub(State.lines[State.cursor1.line].data, 1, byte_start-1)..string.sub(State.lines[State.cursor1.line].data, byte_end)
        else
          State.lines[State.cursor1.line].data = string.sub(State.lines[State.cursor1.line].data, 1, byte_start-1)
        end
        State.cursor1.pos = State.cursor1.pos-1
  local byte_offset = Text.offset(State.lines[State.cursor1.line].data, State.cursor1.pos)
  State.lines[State.cursor1.line].data = string.sub(State.lines[State.cursor1.line].data, 1, byte_offset-1)..t..string.sub(State.lines[State.cursor1.line].data, byte_offset)
  Text.clear_screen_line_cache(State, State.cursor1.line)
  State.cursor1.pos = State.cursor1.pos+1
end
  return y, screen_line_starting_pos
end
function Text.draw_cursor(State, x, y)
  -- blink every 0.5s
  if math.floor(Cursor_time*2)%2 == 0 then
    App.color(Cursor_color)
    love.graphics.rectangle('fill', x,y, 3,State.line_height)
  end
  State.cursor_x = x
  State.cursor_y = y+State.line_height
end
function Text.populate_screen_line_starting_pos(State, line_index)
  local line = State.lines[line_index]
  if Focus == 'edit' and not hide_cursor and State.search_term == nil then
    if line_index == State.cursor1.line and State.cursor1.pos == pos then
      Text.draw_cursor(State, x, y)
    end
      if line_index == State.cursor1.line then
        if pos <= State.cursor1.pos and pos + frag_len > State.cursor1.pos then
          if State.search_term then
            if State.lines[State.cursor1.line].data:sub(State.cursor1.pos, State.cursor1.pos+utf8.len(State.search_term)-1) == State.search_term then
              local lo_px = Text.draw_highlight(State, line, x,y, pos, State.cursor1.pos, State.cursor1.pos+utf8.len(State.search_term))
              App.color(Text_color)
              love.graphics.print(State.search_term, x+lo_px,y)
            end
          elseif Focus == 'edit' then
            Text.draw_cursor(State, x+Text.x(frag, State.cursor1.pos-pos+1), y)
            App.color(Text_color)
          end
        end
      end
      x = x + frag_width
    end
    pos = pos + frag_len
  end
          return y, screen_line_starting_pos
        end
        screen_line_starting_pos = pos
        x = State.left
function ends_with(s, suffix)
  if #s < #suffix then
    return false
  end
  for i=0,#suffix-1 do
    if s:sub(#s-i,#s-i) ~= suffix:sub(#suffix-i,#suffix-i) then
      return false
    end
  end
  return true
end
  -- wrap long lines
  local x = State.left
  local pos = 1
  local screen_line_starting_pos = startpos
  Text.compute_fragments(State, line_index)
  local pos = 1
  initialize_color()
  for _, f in ipairs(line_cache.fragments) do
    App.color(Text_color)
    local frag, frag_text = f.data, f.text
    select_color(frag)
    local frag_len = utf8.len(frag)
--?     print('text.draw:', frag, 'at', line_index,pos, 'after', x,y)
    if pos < startpos then
      -- render nothing
--?       print('skipping', frag)
    else
      -- render fragment
      local frag_width = App.width(frag_text)
      if x + frag_width > State.right then
        assert(x > State.left)  -- no overfull lines
        y = y + State.line_height
        if y + State.line_height > App.screen.height then
-- return the final y, and position of start of final screen line drawn
function Text.draw(State, line_index, y, startpos, hide_cursor)
  local line = State.lines[line_index]
  local line_cache = State.line_cache[line_index]
  line_cache.starty = y
  line_cache.startpos = startpos
function starts_with(s, prefix)
  if #s < #prefix then
    return false
  end
  for i=1,#prefix do
    if s:sub(i,i) ~= prefix:sub(i,i) then
      return false
    end
  end
  return true
end

    screen_top1 = {line=1, pos=1},  -- position of start of screen line at top of screen
    cursor1 = {line=1, pos=1},  -- position of cursor
    screen_bottom1 = {line=1, pos=1},  -- position of start of screen line at bottom of screen
    State.cursor1 = {line=#State.lines, pos=utf8.len(State.lines[#State.lines].data)+1}
  elseif chord == 'C-c' then
    local s = Text.selection(State)
    if s then
      App.setClipboardText(s)
    end
  elseif chord == 'C-x' then
    for _,line_cache in ipairs(State.line_cache) do line_cache.starty = nil end  -- just in case we scroll
    local s = Text.cut_selection(State, State.left, State.right)
    if s then
      App.setClipboardText(s)
    end
    schedule_save(State)
  elseif chord == 'C-v' then
    for _,line_cache in ipairs(State.line_cache) do line_cache.starty = nil end  -- just in case we scroll
    -- We don't have a good sense of when to scroll, so we'll be conservative
    -- and sometimes scroll when we didn't quite need to.
    local before_line = State.cursor1.line
    local before = snapshot(State, before_line)
    local clipboard_data = App.getClipboardText()
    for _,code in utf8.codes(clipboard_data) do
      local c = utf8.char(code)
      if c == '\n' then
        Text.insert_return(State)
      else
        Text.insert_at_cursor(State, c)
      end
    end
    if Text.cursor_out_of_screen(State) then
      Text.snap_cursor_to_bottom_of_screen(State, State.left, State.right)
    end
    schedule_save(State)
    record_undo_event(State, {before=before, after=snapshot(State, before_line, State.cursor1.line)})
      cursor={line=State.cursor1.line, pos=State.cursor1.pos},
      screen_top={line=State.screen_top1.line, pos=State.screen_top1.pos},
    }
    assert(State.search_text == nil)
      State.cursor1.pos = State.cursor1.pos+1
      Text.search_next(State)
    elseif chord == 'up' then
      Text.search_previous(State)
    end
    return
  elseif chord == 'C-f' then
    State.search_term = ''
    State.search_backup = {
          State.cursor1 = {
              line=line_index,
              pos=Text.to_pos_on_line(State, line_index, x, y),
          }
--?           print('cursor', State.cursor1.line, State.cursor1.pos)
          if State.mousepress_shift then
            if State.old_selection1.line == nil then
              State.selection1 = State.old_cursor1
            else
              State.selection1 = State.old_selection1
            end
          end
          State.old_cursor1, State.old_selection1, State.mousepress_shift = nil
          if eq(State.cursor1, State.selection1) then
            State.selection1 = {}
          end
          break
        end
      end
    end
--?     print('selection:', State.selection1.line, State.selection1.pos)
        State.selection1 = {
            line=line_index,
            pos=Text.to_pos_on_line(State, line_index, x, y),
        }
--?         print('selection', State.selection1.line, State.selection1.pos)
        break
      end
    elseif line.mode == 'drawing' then
      local line_cache = State.line_cache[line_index]
      if Drawing.in_drawing(line, line_cache, x, y, State.left,State.right) then
        State.lines.current_drawing_index = line_index
        State.lines.current_drawing = line
        Drawing.before = snapshot(State, line_index)
      y, State.screen_bottom1.pos = Text.draw(State, line_index, y, startpos, hide_cursor)
      y = y + State.line_height
--?       print('=> y', y)
    elseif line.mode == 'drawing' then
      y = y+Drawing_padding_top
      Drawing.draw(State, line_index, y)
      y = y + Drawing.pixels(line.h, State.width) + Drawing_padding_bottom
    else
      print(line.mode)
      assert(false)
        startpos = State.screen_top1.pos
      end
      if line.data == '' then
        -- button to insert new drawing
        button(State, 'draw', {x=4,y=y+4, w=12,h=12, color={1,1,0},
          icon = icon.insert_drawing,
          onpress1 = function()
                       Drawing.before = snapshot(State, line_index-1, line_index)
                       table.insert(State.lines, line_index, {mode='drawing', y=y, h=256/2, points={}, shapes={}, pending={}})
                       table.insert(State.line_cache, line_index, {})
                       if State.cursor1.line >= line_index then
                         State.cursor1.line = State.cursor1.line+1
                       end
                       schedule_save(State)
                       record_undo_event(State, {before=Drawing.before, after=snapshot(State, line_index-1, line_index+1)})
                     end,
        })
--?       print('text.draw', y, line_index)
      local startpos = 1
      if line_index == State.screen_top1.line then
    State.screen_bottom1 = {line=line_index, pos=nil}
    if line.mode == 'text' then
--?     print('draw:', y, line_index, line)
    if y + State.line_height > App.screen.height then break end
    print(State.screen_top1.line, State.screen_top1.pos, State.cursor1.line, State.cursor1.pos)
    assert(false)
  end
  State.cursor_x = nil
  State.cursor_y = nil
  local y = State.top
--?   print('== draw')
  for line_index = State.screen_top1.line,#State.lines do
    local line = State.lines[line_index]
    selection1 = {},
    -- some extra state to compute selection between mouse press and release
    old_cursor1 = nil,
    old_selection1 = nil,
    mousepress_shift = nil,
    -- when selecting text, avoid recomputing some state on every single frame
    recent_mouse = {},
    lines = {{mode='text', data=''}},  -- array of lines
    -- Lines can be too long to fit on screen, in which case they _wrap_ into
    -- multiple _screen lines_.
    -- rendering wrapped text lines needs some additional short-lived data per line:
    --   startpos, the index of data the line starts rendering from, can only be >1 for topmost line on screen
    --   starty, the y coord in pixels the line starts rendering from
    --   fragments: snippets of rendered love.graphics.Text, guaranteed to not straddle screen lines
    --   screen_line_starting_pos: optional array of grapheme indices if it wraps over more than one screen line
    line_cache = {},
    -- Given wrapping, any potential location for the text cursor can be described in two ways:
    -- * schema 1: As a combination of line index and position within a line (in utf8 codepoint units)
    -- * schema 2: As a combination of line index, screen line index within the line, and a position within the screen line.
    -- a line is either text or a drawing
    -- a text is a table with:
    --    mode = 'text',
    --    string data,
--?   print('press', State.selection1.line, State.selection1.pos)
  if mouse_press_consumed_by_any_button_handler(State, x,y, mouse_button) then
    -- press on a button and it returned 'true' to short-circuit
    return
  end
  for line_index,line in ipairs(State.lines) do
    -- give some time for the OS to flush everything to disk
    love.timer.sleep(0.1)
  end
end
    left = math.floor(left),
    right = math.floor(right),
    width = right-left,
    if State.font_height > 2 then
      edit.update_font_settings(State, State.font_height-2)
      Text.redraw_all(State)
    end
  elseif chord == 'C-0' then
    edit.update_font_settings(State, 20)
    Text.redraw_all(State)
  -- undo
  elseif chord == 'C-z' then
    for _,line_cache in ipairs(State.line_cache) do line_cache.starty = nil end  -- just in case we scroll
    local event = undo_event(State)
    if event then
      local src = event.before
      State.screen_top1 = deepcopy(src.screen_top)
      State.cursor1 = deepcopy(src.cursor)

-- environment for a mutable file
-- TODO: some initialization is also happening in load_settings/initialize_default_settings. Clean that up.

  Editor_state.cursor1 = {line=line.line_number, pos=1}
  -- make sure it's visible
  -- TODO: handle extremely long lines
  Editor_state.screen_top1.line = math.max(0, Editor_state.cursor1.line-5)
  -- show cursor
  Focus = 'edit'
  Log_browser_state.cursor1 = {line=1, pos=1}
end
Section_stack = {}
Section_border_color = {r=0.7, g=0.7, b=0.7}
Cursor_line_background_color = {r=0.7, g=0.7, b=0, a=0.1}
Section_border_padding_horizontal = 30  -- TODO: adjust this based on font height (because we draw text vertically along the borders
Section_border_padding_vertical = 15  -- TODO: adjust this based on font height
log_browser = {}
function log_browser.parse(State)
  for _,line in ipairs(State.lines) do
    if line.data ~= '' then

end
function test_up_arrow_scrolls_up_by_one_line_skipping_drawing()
  -- display lines 3/4/5 with a drawing just off screen at line 2
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', '```lines', '```', 'def', 'ghi', 'jkl'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=3, pos=1}
  Editor_state.screen_top1 = {line=3, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'def', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'baseline/screen:3')
  -- after hitting the up arrow the screen scrolls up to previous text line
  edit.run_after_keychord(Editor_state, 'up')
  check_eq(Editor_state.screen_top1.line, 1, 'screen_top')
  check_eq(Editor_state.cursor1.line, 1, 'cursor')

end
function test_up_arrow_scrolls_up_by_one_line_skipping_drawing()
  -- display lines 3/4/5 with a drawing just off screen at line 2
  App.screen.init{width=120, height=60}
  Editor_state = edit.initialize_test_state()
  Editor_state.lines = load_array{'abc', '```lines', '```', 'def', 'ghi', 'jkl'}
  Text.redraw_all(Editor_state)
  Editor_state.cursor1 = {line=3, pos=1}
  Editor_state.screen_top1 = {line=3, pos=1}
  Editor_state.screen_bottom1 = {}
  edit.draw(Editor_state)
  local y = Editor_state.top
  App.screen.check(y, 'def', 'baseline/screen:1')
  y = y + Editor_state.line_height
  App.screen.check(y, 'ghi', 'baseline/screen:2')
  y = y + Editor_state.line_height
  App.screen.check(y, 'jkl', 'baseline/screen:3')
  -- after hitting the up arrow the screen scrolls up to previous text line
  edit.run_after_keychord(Editor_state, 'up')
  check_eq(Editor_state.screen_top1.line, 1, 'screen_top')
  check_eq(Editor_state.cursor1.line, 1, 'cursor')

AB_padding = 20  -- space in pixels between A side and B side

-- return the final y, and pos,posB of start of final screen line drawn
function Text.draw(State, line_index, y, startpos, startposB, hide_cursor)

-- return the final y, and position of start of final screen line drawn
function Text.draw(State, line_index, y, startpos, hide_cursor)

  line_cache.startposB = startposB
  -- draw A side
  local overflows_screen, x, pos, screen_line_starting_pos
  if startpos then
    overflows_screen, x, y, pos, screen_line_starting_pos = Text.draw_wrapping_line(State, line_index, State.left, y, startpos)
    if overflows_screen then
      return y, screen_line_starting_pos
    end
    if Focus == 'edit' and State.cursor1.pos then
      if not hide_cursor and not State.search_term then
        if line_index == State.cursor1.line and State.cursor1.pos == pos then
          Text.draw_cursor(State, x, y)
        end
      end
    end
  else
    x = State.left
  end
  -- check for B side
--?   if line_index == 8 then print('checking for B side') end
  if line.dataB == nil then
    assert(y)
    assert(screen_line_starting_pos)
--?     if line_index == 8 then print('return 1') end
    return y, screen_line_starting_pos
  end
  if not State.expanded and not line.expanded then
    assert(y)
    assert(screen_line_starting_pos)
--?     if line_index == 8 then print('return 2') end
    button(State, 'expand', {x=x+AB_padding, y=y+2, w=App.width(State.em), h=State.line_height-4, color={1,1,1},
      icon = function(button_params)
               App.color(Fold_background_color)
               love.graphics.rectangle('fill', button_params.x, button_params.y, App.width(State.em), State.line_height-4, 2,2)
             end,
      onpress1 = function()
                   line.expanded = true
                 end,
    })
    return y, screen_line_starting_pos
  end
  -- draw B side
--?   if line_index == 8 then print('drawing B side') end
  App.color(Fold_color)
  if startposB then
    overflows_screen, x, y, pos, screen_line_starting_pos = Text.draw_wrapping_lineB(State, line_index, x,y, startposB)
  else
    overflows_screen, x, y, pos, screen_line_starting_pos = Text.draw_wrapping_lineB(State, line_index, x+AB_padding,y, 1)
  end
  if overflows_screen then
    return y, nil, screen_line_starting_pos
  end
--?   if line_index == 8 then print('a') end
  if Focus == 'edit' and State.cursor1.posB then
--?     if line_index == 8 then print('b') end
    if not hide_cursor and not State.search_term then
--?       if line_index == 8 then print('c', State.cursor1.line, State.cursor1.posB, line_index, pos) end
      if line_index == State.cursor1.line and State.cursor1.posB == pos then
        Text.draw_cursor(State, x, y)
      end
    end
  end
  return y, nil, screen_line_starting_pos
end
-- Given an array of fragments, draw the subset starting from pos to screen
-- starting from (x,y).
-- Return:
--  - whether we got to bottom of screen before end of line
--  - the final (x,y)
--  - the final pos
--  - starting pos of the final screen line drawn
function Text.draw_wrapping_line(State, line_index, x,y, startpos)
  local line = State.lines[line_index]
  local line_cache = State.line_cache[line_index]
--?   print('== line', line_index, '^'..line.data..'$')

  -- wrap long lines
  local x = State.left
  local pos = 1

          return --[[screen filled]] true, x,y, pos, screen_line_starting_pos

          return y, screen_line_starting_pos

      if State.cursor1.pos and line_index == State.cursor1.line then

      if line_index == State.cursor1.line then

  return false, x,y, pos, screen_line_starting_pos
end
function Text.draw_wrapping_lineB(State, line_index, x,y, startpos)
  local line = State.lines[line_index]
  local line_cache = State.line_cache[line_index]
  local screen_line_starting_pos = startpos
  Text.compute_fragmentsB(State, line_index, x)
  local pos = 1
  for _, f in ipairs(line_cache.fragmentsB) do
    local frag, frag_text = f.data, f.text
    local frag_len = utf8.len(frag)
--?     print('text.draw:', frag, 'at', line_index,pos, 'after', x,y)
    if pos < startpos then
      -- render nothing
--?       print('skipping', frag)
    else
      -- render fragment
      local frag_width = App.width(frag_text)
      if x + frag_width > State.right then
        assert(x > State.left)  -- no overfull lines
        y = y + State.line_height
        if y + State.line_height > App.screen.height then
          return --[[screen filled]] true, x,y, pos, screen_line_starting_pos
        end
        screen_line_starting_pos = pos
        x = State.left
      end
      if State.selection1.line then
        local lo, hi = Text.clip_selection(State, line_index, pos, pos+frag_len)
        Text.draw_highlight(State, line, x,y, pos, lo,hi)
      end
      App.screen.draw(frag_text, x,y)
      -- render cursor if necessary
      if State.cursor1.posB and line_index == State.cursor1.line then
        if pos <= State.cursor1.posB and pos + frag_len > State.cursor1.posB then
          if State.search_term then
            if State.lines[State.cursor1.line].dataB:sub(State.cursor1.posB, State.cursor1.posB+utf8.len(State.search_term)-1) == State.search_term then
              local lo_px = Text.draw_highlight(State, line, x,y, pos, State.cursor1.posB, State.cursor1.posB+utf8.len(State.search_term))
              App.color(Fold_color)
              love.graphics.print(State.search_term, x+lo_px,y)
            end
          elseif Focus == 'edit' then
            Text.draw_cursor(State, x+Text.x(frag, State.cursor1.posB-pos+1), y)
            App.color(Fold_color)
          end
        end
      end
      x = x + frag_width

  if Focus == 'edit' and not hide_cursor and State.search_term == nil then
    if line_index == State.cursor1.line and State.cursor1.pos == pos then
      Text.draw_cursor(State, x, y)

    pos = pos + frag_len

  return false, x,y, pos, screen_line_starting_pos

  return y, screen_line_starting_pos

    end
    x = x + frag_width
  end
end
function Text.populate_screen_line_starting_posB(State, line_index, x)
  local line = State.lines[line_index]
  local line_cache = State.line_cache[line_index]
  if line_cache.screen_line_starting_posB then
    return
  end
  -- duplicate some logic from Text.draw
  Text.compute_fragmentsB(State, line_index, x)
  line_cache.screen_line_starting_posB = {1}
  local pos = 1
  for _, f in ipairs(line_cache.fragmentsB) do
    local frag, frag_text = f.data, f.text
    -- render fragment
    local frag_width = App.width(frag_text)
    if x + frag_width > State.right then
      x = State.left
      table.insert(line_cache.screen_line_starting_posB, pos)

    local frag_len = utf8.len(frag)
    pos = pos + frag_len

function Text.compute_fragmentsB(State, line_index, x)
--?   print('compute_fragmentsB', line_index, 'between', x, State.right)
  local line = State.lines[line_index]
  local line_cache = State.line_cache[line_index]
  if line_cache.fragmentsB then
    return
  end
  line_cache.fragmentsB = {}
  -- try to wrap at word boundaries
  for frag in line.dataB:gmatch('%S*%s*') do
    local frag_text = App.newText(love.graphics.getFont(), frag)
    local frag_width = App.width(frag_text)
--?     print('x: '..tostring(x)..'; '..tostring(State.right-x)..'px to go')
    while x + frag_width > State.right do
--?       print(('checking whether to split fragment ^%s$ of width %d when rendering from %d'):format(frag, frag_width, x))
      if (x-State.left) < 0.8 * (State.right-State.left) then
--?         print('splitting')
        -- long word; chop it at some letter
        -- We're not going to reimplement TeX here.
        local bpos = Text.nearest_pos_less_than(frag, State.right - x)
--?         print('bpos', bpos)
        if bpos == 0 then break end  -- avoid infinite loop when window is too narrow
        local boffset = Text.offset(frag, bpos+1)  -- byte _after_ bpos
--?         print('space for '..tostring(bpos)..' graphemes, '..tostring(boffset-1)..' bytes')
        local frag1 = string.sub(frag, 1, boffset-1)
        local frag1_text = App.newText(love.graphics.getFont(), frag1)
        local frag1_width = App.width(frag1_text)
--?         print('extracting ^'..frag1..'$ of width '..tostring(frag1_width)..'px')
        assert(x + frag1_width <= State.right)
        table.insert(line_cache.fragmentsB, {data=frag1, text=frag1_text})
        frag = string.sub(frag, boffset)
        frag_text = App.newText(love.graphics.getFont(), frag)
        frag_width = App.width(frag_text)
      end
      x = State.left  -- new line
    end
    if #frag > 0 then
--?       print('inserting ^'..frag..'$ of width '..tostring(frag_width)..'px')
      table.insert(line_cache.fragmentsB, {data=frag, text=frag_text})
    end
    x = x + frag_width
  end
end

  if State.cursor1.pos then
    local byte_offset = Text.offset(State.lines[State.cursor1.line].data, State.cursor1.pos)
    State.lines[State.cursor1.line].data = string.sub(State.lines[State.cursor1.line].data, 1, byte_offset-1)..t..string.sub(State.lines[State.cursor1.line].data, byte_offset)
    Text.clear_screen_line_cache(State, State.cursor1.line)
    State.cursor1.pos = State.cursor1.pos+1
  else
    assert(State.cursor1.posB)
    local byte_offset = Text.offset(State.lines[State.cursor1.line].dataB, State.cursor1.posB)
    State.lines[State.cursor1.line].dataB = string.sub(State.lines[State.cursor1.line].dataB, 1, byte_offset-1)..t..string.sub(State.lines[State.cursor1.line].dataB, byte_offset)
    Text.clear_screen_line_cache(State, State.cursor1.line)
    State.cursor1.posB = State.cursor1.posB+1
  end

  local byte_offset = Text.offset(State.lines[State.cursor1.line].data, State.cursor1.pos)
  State.lines[State.cursor1.line].data = string.sub(State.lines[State.cursor1.line].data, 1, byte_offset-1)..t..string.sub(State.lines[State.cursor1.line].data, byte_offset)
  Text.clear_screen_line_cache(State, State.cursor1.line)
  State.cursor1.pos = State.cursor1.pos+1

    if State.cursor1.pos and State.cursor1.pos > 1 then

    if State.cursor1.pos > 1 then

      end
    elseif State.cursor1.posB then
      if State.cursor1.posB > 1 then
        before = snapshot(State, State.cursor1.line)
        local byte_start = utf8.offset(State.lines[State.cursor1.line].dataB, State.cursor1.posB-1)
        local byte_end = utf8.offset(State.lines[State.cursor1.line].dataB, State.cursor1.posB)
        if byte_start then
          if byte_end then
            State.lines[State.cursor1.line].dataB = string.sub(State.lines[State.cursor1.line].dataB, 1, byte_start-1)..string.sub(State.lines[State.cursor1.line].dataB, byte_end)
          else
            State.lines[State.cursor1.line].dataB = string.sub(State.lines[State.cursor1.line].dataB, 1, byte_start-1)
          end
          State.cursor1.posB = State.cursor1.posB-1
        end
      else
        -- refuse to delete past beginning of side B

      local top2 = Text.to2(State, State.screen_top1)
      top2 = Text.previous_screen_line(State, top2, State.left, State.right)
      State.screen_top1 = Text.to1(State, top2)

      State.screen_top1 = {
        line=State.cursor1.line,
        pos=Text.pos_at_start_of_screen_line(State, State.cursor1),
      }

    if State.cursor1.posB or State.cursor1.pos <= utf8.len(State.lines[State.cursor1.line].data) then

    if State.cursor1.pos <= utf8.len(State.lines[State.cursor1.line].data) then

    if State.cursor1.pos and State.cursor1.pos <= utf8.len(State.lines[State.cursor1.line].data) then

    if State.cursor1.pos <= utf8.len(State.lines[State.cursor1.line].data) then

      end
    elseif State.cursor1.posB then
      if State.cursor1.posB <= utf8.len(State.lines[State.cursor1.line].dataB) then
        local byte_start = utf8.offset(State.lines[State.cursor1.line].dataB, State.cursor1.posB)
        local byte_end = utf8.offset(State.lines[State.cursor1.line].dataB, State.cursor1.posB+1)
        if byte_start then
          if byte_end then
            State.lines[State.cursor1.line].dataB = string.sub(State.lines[State.cursor1.line].dataB, 1, byte_start-1)..string.sub(State.lines[State.cursor1.line].dataB, byte_end)
          else
            State.lines[State.cursor1.line].dataB = string.sub(State.lines[State.cursor1.line].dataB, 1, byte_start-1)
          end
          -- no change to State.cursor1.pos
        end
      else
        -- refuse to delete past end of side B

        -- delete side B on first line
        State.lines[State.cursor1.line].dataB = State.lines[State.cursor1.line+1].dataB

      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos, posB=State.cursor1.posB}

      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos}

      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos, posB=State.cursor1.posB}

      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos}

      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos, posB=State.cursor1.posB}

      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos}

      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos, posB=State.cursor1.posB}

      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos}

      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos, posB=State.cursor1.posB}

      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos}

      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos, posB=State.cursor1.posB}

      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos}

      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos, posB=State.cursor1.posB}

      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos}

      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos, posB=State.cursor1.posB}

      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos}

      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos, posB=State.cursor1.posB}

      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos}

      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos, posB=State.cursor1.posB}

      State.selection1 = {line=State.cursor1.line, pos=State.cursor1.pos}

  if State.cursor1.pos then
    -- when inserting a newline, move any B side to the new line
    local byte_offset = Text.offset(State.lines[State.cursor1.line].data, State.cursor1.pos)
    table.insert(State.lines, State.cursor1.line+1, {mode='text', data=string.sub(State.lines[State.cursor1.line].data, byte_offset), dataB=State.lines[State.cursor1.line].dataB})
    table.insert(State.line_cache, State.cursor1.line+1, {})
    State.lines[State.cursor1.line].data = string.sub(State.lines[State.cursor1.line].data, 1, byte_offset-1)
    State.lines[State.cursor1.line].dataB = nil
    Text.clear_screen_line_cache(State, State.cursor1.line)
    State.cursor1 = {line=State.cursor1.line+1, pos=1}
  else
    -- disable enter when cursor is on the B side
  end

  local byte_offset = Text.offset(State.lines[State.cursor1.line].data, State.cursor1.pos)
  table.insert(State.lines, State.cursor1.line+1, {mode='text', data=string.sub(State.lines[State.cursor1.line].data, byte_offset)})
  table.insert(State.line_cache, State.cursor1.line+1, {})
  State.lines[State.cursor1.line].data = string.sub(State.lines[State.cursor1.line].data, 1, byte_offset-1)
  Text.clear_screen_line_cache(State, State.cursor1.line)
  State.cursor1 = {line=State.cursor1.line+1, pos=1}

    if State.screen_top1.line == 1 and State.screen_top1.pos and State.screen_top1.pos == 1 then break end

    if State.screen_top1.line == 1 and State.screen_top1.pos == 1 then break end

  State.cursor1 = {line=State.screen_top1.line, pos=State.screen_top1.pos, posB=State.screen_top1.posB}

  State.cursor1 = {line=State.screen_top1.line, pos=State.screen_top1.pos}

  -- If a line/paragraph gets to a page boundary, I often want to scroll
  -- before I get to the bottom.
  -- However, only do this if it makes forward progress.

  if bot2.screen_line > 1 then
    bot2.screen_line = math.max(bot2.screen_line-10, 1)
  end

    State.screen_top1 = {line=State.screen_bottom1.line, pos=State.screen_bottom1.pos, posB=State.screen_bottom1.posB}

    State.screen_top1 = {line=State.screen_bottom1.line, pos=State.screen_bottom1.pos}

  State.cursor1 = {line=State.screen_top1.line, pos=State.screen_top1.pos, posB=State.screen_top1.posB}

  State.cursor1 = {line=State.screen_top1.line, pos=State.screen_top1.pos}

  if State.cursor1.pos then
    Text.upA(State)
  else
    Text.upB(State)
  end
end
function Text.upA(State)

    local top2 = Text.to2(State, State.screen_top1)
    top2 = Text.previous_screen_line(State, top2)
    State.screen_top1 = Text.to1(State, top2)

    State.screen_top1 = {
      line=State.cursor1.line,
      pos=Text.pos_at_start_of_screen_line(State, State.cursor1),
    }
    Text.redraw_all(State)  -- if we're scrolling, reclaim all fragments to avoid memory leaks

function Text.upB(State)
  local line_cache = State.line_cache[State.cursor1.line]
  local screen_line_starting_posB, screen_line_indexB = Text.pos_at_start_of_screen_lineB(State, State.cursor1)
  assert(screen_line_indexB >= 1)
  if screen_line_indexB == 1 then
    -- move to A side of previous line
    local new_cursor_line = State.cursor1.line
    while new_cursor_line > 1 do
      new_cursor_line = new_cursor_line-1
      if State.lines[new_cursor_line].mode == 'text' then
        State.cursor1 = {line=new_cursor_line, posB=nil}
        Text.populate_screen_line_starting_pos(State, State.cursor1.line)
        local prev_line_cache = State.line_cache[State.cursor1.line]
        local prev_screen_line_starting_pos = prev_line_cache.screen_line_starting_pos[#prev_line_cache.screen_line_starting_pos]
        local prev_screen_line_starting_byte_offset = Text.offset(State.lines[State.cursor1.line].data, prev_screen_line_starting_pos)
        local s = string.sub(State.lines[State.cursor1.line].data, prev_screen_line_starting_byte_offset)
        State.cursor1.pos = prev_screen_line_starting_pos + Text.nearest_cursor_pos(s, State.cursor_x, State.left) - 1
        break
      end
    end
  elseif screen_line_indexB == 2 then
    -- all-B screen-line to potentially A+B screen-line
    local xA = Margin_left + Text.screen_line_width(State, State.cursor1.line, #line_cache.screen_line_starting_pos) + AB_padding
    if State.cursor_x < xA then
      State.cursor1.posB = nil
      Text.populate_screen_line_starting_pos(State, State.cursor1.line)
      local new_screen_line_starting_pos = line_cache.screen_line_starting_pos[#line_cache.screen_line_starting_pos]
      local new_screen_line_starting_byte_offset = Text.offset(State.lines[State.cursor1.line].data, new_screen_line_starting_pos)
      local s = string.sub(State.lines[State.cursor1.line].data, new_screen_line_starting_byte_offset)
      State.cursor1.pos = new_screen_line_starting_pos + Text.nearest_cursor_pos(s, State.cursor_x, State.left) - 1
    else
      Text.populate_screen_line_starting_posB(State, State.cursor1.line)
      local new_screen_line_starting_posB = line_cache.screen_line_starting_posB[screen_line_indexB-1]
      local new_screen_line_starting_byte_offsetB = Text.offset(State.lines[State.cursor1.line].dataB, new_screen_line_starting_posB)
      local s = string.sub(State.lines[State.cursor1.line].dataB, new_screen_line_starting_byte_offsetB)
      State.cursor1.posB = new_screen_line_starting_posB + Text.nearest_cursor_pos(s, State.cursor_x-xA, State.left) - 1
    end
  else
    assert(screen_line_indexB > 2)
    -- all-B screen-line to all-B screen-line
    Text.populate_screen_line_starting_posB(State, State.cursor1.line)
    local new_screen_line_starting_posB = line_cache.screen_line_starting_posB[screen_line_indexB-1]
    local new_screen_line_starting_byte_offsetB = Text.offset(State.lines[State.cursor1.line].dataB, new_screen_line_starting_posB)
    local s = string.sub(State.lines[State.cursor1.line].dataB, new_screen_line_starting_byte_offsetB)
    State.cursor1.posB = new_screen_line_starting_posB + Text.nearest_cursor_pos(s, State.cursor_x, State.left) - 1
  end
  if Text.lt1(State.cursor1, State.screen_top1) then
    local top2 = Text.to2(State, State.screen_top1)
    top2 = Text.previous_screen_line(State, top2)
    State.screen_top1 = Text.to1(State, top2)
  end
end
-- cursor on final screen line (A or B side) => goes to next screen line on A side
-- cursor on A side => move down one screen line (A side) in current line
-- cursor on B side => move down one screen line (B side) in current line

  elseif State.cursor1.pos then
    -- move down one screen line (A side) in current line

  else
    -- move down one screen line in current line

  else
    -- move down one screen line (B side) in current line
    local scroll_down = false
    if Text.le1(State.screen_bottom1, State.cursor1) then
      scroll_down = true
    end
    local cursor_line = State.lines[State.cursor1.line]
    local cursor_line_cache = State.line_cache[State.cursor1.line]
    local cursor2 = Text.to2(State, State.cursor1)
    assert(cursor2.screen_lineB < #cursor_line_cache.screen_line_starting_posB)
    local screen_line_starting_posB, screen_line_indexB = Text.pos_at_start_of_screen_lineB(State, State.cursor1)
    Text.populate_screen_line_starting_posB(State, State.cursor1.line)
    local new_screen_line_starting_posB = cursor_line_cache.screen_line_starting_posB[screen_line_indexB+1]
    local new_screen_line_starting_byte_offsetB = Text.offset(cursor_line.dataB, new_screen_line_starting_posB)
    local s = string.sub(cursor_line.dataB, new_screen_line_starting_byte_offsetB)
    State.cursor1.posB = new_screen_line_starting_posB + Text.nearest_cursor_pos(s, State.cursor_x, State.left) - 1
    if scroll_down then
      Text.snap_cursor_to_bottom_of_screen(State)
    end

  if State.cursor1.pos then
    State.cursor1.pos = 1
  else
    State.cursor1.posB = 1
  end

  State.cursor1.pos = 1

    State.screen_top1 = {line=State.cursor1.line, pos=State.cursor1.pos, posB=State.cursor1.posB}  -- copy

    State.screen_top1 = {line=State.cursor1.line, pos=State.cursor1.pos}  -- copy

  if State.cursor1.pos then
    State.cursor1.pos = utf8.len(State.lines[State.cursor1.line].data) + 1
  else
    State.cursor1.posB = utf8.len(State.lines[State.cursor1.line].dataB) + 1
  end

  State.cursor1.pos = utf8.len(State.lines[State.cursor1.line].data) + 1

  -- we can cross the fold, so check side A/B one level down
  Text.skip_whitespace_left(State)
  Text.left(State)
  Text.skip_non_whitespace_left(State)
end
function Text.word_right(State)
  -- we can cross the fold, so check side A/B one level down
  Text.skip_whitespace_right(State)
  Text.right(State)
  Text.skip_non_whitespace_right(State)
  if Text.cursor_out_of_screen(State) then
    Text.snap_cursor_to_bottom_of_screen(State)
  end
end
function Text.skip_whitespace_left(State)
  if State.cursor1.pos then
    Text.skip_whitespace_leftA(State)
  else
    Text.skip_whitespace_leftB(State)
  end
end
function Text.skip_non_whitespace_left(State)
  if State.cursor1.pos then
    Text.skip_non_whitespace_leftA(State)
  else
    Text.skip_non_whitespace_leftB(State)
  end
end
function Text.skip_whitespace_leftA(State)

  -- skip some whitespace

end
function Text.skip_whitespace_leftB(State)

  -- skip some non-whitespace

    if State.cursor1.posB == 1 then
      break
    end
    if Text.match(State.lines[State.cursor1.line].dataB, State.cursor1.posB-1, '%S') then
      break
    end

  end
end
function Text.skip_non_whitespace_leftA(State)
  while true do

      break
    end
    Text.left(State)
  end
end
function Text.skip_non_whitespace_leftB(State)
  while true do
    if State.cursor1.posB == 1 then
      break
    end
    assert(State.cursor1.posB > 1)
    if Text.match(State.lines[State.cursor1.line].dataB, State.cursor1.posB-1, '%s') then

    Text.left(State)

function Text.skip_whitespace_right(State)
  if State.cursor1.pos then
    Text.skip_whitespace_rightA(State)
  else
    Text.skip_whitespace_rightB(State)
  end
end
function Text.skip_non_whitespace_right(State)
  if State.cursor1.pos then
    Text.skip_non_whitespace_rightA(State)
  else
    Text.skip_non_whitespace_rightB(State)
  end
end
function Text.skip_whitespace_rightA(State)

function Text.word_right(State)
  -- skip some whitespace

end
function Text.skip_whitespace_rightB(State)

    if State.cursor1.posB > utf8.len(State.lines[State.cursor1.line].dataB) then
      break
    end
    if Text.match(State.lines[State.cursor1.line].dataB, State.cursor1.posB, '%S') then
      break
    end

  end
end
function Text.skip_non_whitespace_rightA(State)
  while true do

    Text.right_without_scroll(State)

end
function Text.skip_non_whitespace_rightB(State)
  while true do
    if State.cursor1.posB > utf8.len(State.lines[State.cursor1.line].dataB) then
      break
    end
    if Text.match(State.lines[State.cursor1.line].dataB, State.cursor1.posB, '%s') then
      break
    end
    Text.right_without_scroll(State)

  if Text.cursor_out_of_screen(State) then
    Text.snap_cursor_to_bottom_of_screen(State)

  if State.cursor1.pos then
    Text.leftA(State)
  else
    Text.leftB(State)
  end
end
function Text.leftA(State)

  assert(State.lines[State.cursor1.line].mode == 'text')

    local top2 = Text.to2(State, State.screen_top1)
    top2 = Text.previous_screen_line(State, top2)
    State.screen_top1 = Text.to1(State, top2)

    State.screen_top1 = {
      line=State.cursor1.line,
      pos=Text.pos_at_start_of_screen_line(State, State.cursor1),
    }
    Text.redraw_all(State)  -- if we're scrolling, reclaim all fragments to avoid memory leaks

function Text.leftB(State)
  if State.cursor1.posB > 1 then
    State.cursor1.posB = State.cursor1.posB-1
  else
    -- overflow back into A side
    State.cursor1.posB = nil
    State.cursor1.pos = utf8.len(State.lines[State.cursor1.line].data) + 1
  end
  if Text.lt1(State.cursor1, State.screen_top1) then
    local top2 = Text.to2(State, State.screen_top1)
    top2 = Text.previous_screen_line(State, top2)
    State.screen_top1 = Text.to1(State, top2)
  end
end

  if State.cursor1.pos then
    Text.right_without_scrollA(State)
  else
    Text.right_without_scrollB(State)
  end
end
function Text.right_without_scrollA(State)

function Text.right_without_scrollB(State)
  if State.cursor1.posB <= utf8.len(State.lines[State.cursor1.line].dataB) then
    State.cursor1.posB = State.cursor1.posB+1
  else
    -- overflow back into A side
    local new_cursor_line = State.cursor1.line
    while new_cursor_line <= #State.lines-1 do
      new_cursor_line = new_cursor_line+1
      if State.lines[new_cursor_line].mode == 'text' then
        State.cursor1 = {line=new_cursor_line, pos=1}
        break
      end
    end
  end
end

    end
  end
  assert(false)
end
function Text.pos_at_start_of_screen_lineB(State, loc1)
  Text.populate_screen_line_starting_pos(State, loc1.line)
  local line_cache = State.line_cache[loc1.line]
  local x = Margin_left + Text.screen_line_width(State, loc1.line, #line_cache.screen_line_starting_pos) + AB_padding
  Text.populate_screen_line_starting_posB(State, loc1.line, x)
  for i=#line_cache.screen_line_starting_posB,1,-1 do
    local sposB = line_cache.screen_line_starting_posB[i]
    if sposB <= loc1.posB then
      return sposB,i

  local line = State.lines[State.cursor1.line]

  if (not State.expanded and not line.expanded) or
      line.dataB == nil then
    return screen_lines[#screen_lines] <= State.cursor1.pos
  end
  if State.cursor1.pos then
    -- ignore B side
    return screen_lines[#screen_lines] <= State.cursor1.pos
  end
  assert(State.cursor1.posB)
  local line_cache = State.line_cache[State.cursor1.line]
  local x = Margin_left + Text.screen_line_width(State, State.cursor1.line, #line_cache.screen_line_starting_pos) + AB_padding
  Text.populate_screen_line_starting_posB(State, State.cursor1.line, x)
  local screen_lines = State.line_cache[State.cursor1.line].screen_line_starting_posB
  return screen_lines[#screen_lines] <= State.cursor1.posB

  return screen_lines[#screen_lines] <= State.cursor1.pos

--?   print('to2:', State.cursor1.line, State.cursor1.pos, State.cursor1.posB)

--?   print('to2:', State.cursor1.line, State.cursor1.pos)

--?   print('to2: =>', top2.line, top2.screen_line, top2.screen_pos, top2.screen_lineB, top2.screen_posB)

--?   print('to2: =>', top2.line, top2.screen_line, top2.screen_pos)

  if top2.screen_pos then
    top2.screen_pos = 1
  else
    assert(top2.screen_posB)
    top2.screen_posB = 1
  end
--?   print('snap', State.screen_top1.line, State.screen_top1.pos, State.screen_top1.posB, State.cursor1.line, State.cursor1.pos, State.cursor1.posB, State.screen_bottom1.line, State.screen_bottom1.pos, State.screen_bottom1.posB)

  top2.screen_pos = 1  -- start of screen line
--?   print('snap', State.screen_top1.line, State.screen_top1.pos, State.cursor1.line, State.cursor1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)

--?     print(y, 'top2:', State.lines[top2.line].data, top2.line, top2.screen_line, top2.screen_pos, top2.screen_lineB, top2.screen_posB)

--?     print(y, 'top2:', top2.line, top2.screen_line, top2.screen_pos)

--?   print('snap =>', State.screen_top1.line, State.screen_top1.pos, State.screen_top1.posB, State.cursor1.line, State.cursor1.pos, State.cursor1.posB, State.screen_bottom1.line, State.screen_bottom1.pos, State.screen_bottom1.posB)

--?   print('snap =>', State.screen_top1.line, State.screen_top1.pos, State.cursor1.line, State.cursor1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)

  local num_screen_lines = 0
  if line_cache.startpos then
    Text.populate_screen_line_starting_pos(State, line_index)
    num_screen_lines = num_screen_lines + #line_cache.screen_line_starting_pos - Text.screen_line_index(line_cache.screen_line_starting_pos, line_cache.startpos) + 1
  end
--?   print('#screenlines after A', num_screen_lines)
  if line.dataB and (State.expanded or line.expanded) then
    local x = Margin_left + Text.screen_line_width(State, line_index, #line_cache.screen_line_starting_pos) + AB_padding
    Text.populate_screen_line_starting_posB(State, line_index, x)
--?     print('B:', x, #line_cache.screen_line_starting_posB)
    if line_cache.startposB then
      num_screen_lines = num_screen_lines + #line_cache.screen_line_starting_posB - Text.screen_line_indexB(line_cache.screen_line_starting_posB, line_cache.startposB)  -- no +1; first screen line of B side overlaps with A side
    else
      num_screen_lines = num_screen_lines + #line_cache.screen_line_starting_posB - Text.screen_line_indexB(line_cache.screen_line_starting_posB, 1)  -- no +1; first screen line of B side overlaps with A side
    end
  end
--?   print('#screenlines after B', num_screen_lines)
  return y < line_cache.starty + State.line_height*num_screen_lines

  Text.populate_screen_line_starting_pos(State, line_index)
  return y < line_cache.starty + State.line_height*(#line_cache.screen_line_starting_pos - Text.screen_line_index(line_cache.screen_line_starting_pos, line_cache.startpos) + 1)

-- returns: pos, posB
-- scenarios:
--   line without B side
--   line with B side collapsed
--   line with B side expanded
--   line starting rendering in A side (startpos ~= nil)
--   line starting rendering in B side (startposB ~= nil)
--   my on final screen line of A side
--     mx to right of A side with no B side
--     mx to right of A side but left of B side
--     mx to right of B side
-- preconditions:
--  startpos xor startposB
--  expanded -> dataB

--?   print('click', line_index, my, 'with line starting at', y, #line_cache.screen_line_starting_pos)  -- , #line_cache.screen_line_starting_posB)
  if line_cache.startpos then
    local start_screen_line_index = Text.screen_line_index(line_cache.screen_line_starting_pos, line_cache.startpos)
    for screen_line_index = start_screen_line_index,#line_cache.screen_line_starting_pos do
      local screen_line_starting_pos = line_cache.screen_line_starting_pos[screen_line_index]
      local screen_line_starting_byte_offset = Text.offset(line.data, screen_line_starting_pos)
--?       print('iter', y, screen_line_index, screen_line_starting_pos, string.sub(line.data, screen_line_starting_byte_offset))
      local nexty = y + State.line_height
      if my < nexty then
        -- On all wrapped screen lines but the final one, clicks past end of
        -- line position cursor on final character of screen line.
        -- (The final screen line positions past end of screen line as always.)
        if screen_line_index < #line_cache.screen_line_starting_pos and mx > State.left + Text.screen_line_width(State, line_index, screen_line_index) then
--?           print('past end of non-final line; return')
          return line_cache.screen_line_starting_pos[screen_line_index+1]-1
        end
        local s = string.sub(line.data, screen_line_starting_byte_offset)
--?         print('return', mx, Text.nearest_cursor_pos(s, mx, State.left), '=>', screen_line_starting_pos + Text.nearest_cursor_pos(s, mx, State.left) - 1)
        local screen_line_posA = Text.nearest_cursor_pos(s, mx, State.left)
        if line.dataB == nil then
          -- no B side
          return screen_line_starting_pos + screen_line_posA - 1
        end
        if not State.expanded and not line.expanded then
          -- B side is not expanded
          return screen_line_starting_pos + screen_line_posA - 1
        end
        local lenA = utf8.len(s)
        if screen_line_posA < lenA then
          -- mx is within A side
          return screen_line_starting_pos + screen_line_posA - 1
        end
        local max_xA = State.left+Text.x(s, lenA+1)
        if mx < max_xA + AB_padding then
          -- mx is in the space between A and B side
          return screen_line_starting_pos + screen_line_posA - 1
        end
        mx = mx - max_xA - AB_padding
        local screen_line_posB = Text.nearest_cursor_pos(line.dataB, mx, --[[no left margin]] 0)
        return nil, screen_line_posB
      end
      y = nexty
    end
  end
  -- look in screen lines composed entirely of the B side
  assert(State.expanded or line.expanded)
  local start_screen_line_indexB
  if line_cache.startposB then
    start_screen_line_indexB = Text.screen_line_indexB(line_cache.screen_line_starting_posB, line_cache.startposB)
  else
    start_screen_line_indexB = 2  -- skip the first line of side B, which we checked above
  end
  for screen_line_indexB = start_screen_line_indexB,#line_cache.screen_line_starting_posB do
    local screen_line_starting_posB = line_cache.screen_line_starting_posB[screen_line_indexB]
    local screen_line_starting_byte_offsetB = Text.offset(line.dataB, screen_line_starting_posB)
--?     print('iter2', y, screen_line_indexB, screen_line_starting_posB, string.sub(line.dataB, screen_line_starting_byte_offsetB))

  local start_screen_line_index = Text.screen_line_index(line_cache.screen_line_starting_pos, line_cache.startpos)
  for screen_line_index = start_screen_line_index,#line_cache.screen_line_starting_pos do
    local screen_line_starting_pos = line_cache.screen_line_starting_pos[screen_line_index]
    local screen_line_starting_byte_offset = Text.offset(line.data, screen_line_starting_pos)
--?     print('iter', y, screen_line_index, screen_line_starting_pos, string.sub(line.data, screen_line_starting_byte_offset))

--?       print('aa', mx, State.left, Text.screen_line_widthB(State, line_index, screen_line_indexB))
      if screen_line_indexB < #line_cache.screen_line_starting_posB and mx > State.left + Text.screen_line_widthB(State, line_index, screen_line_indexB) then

      if screen_line_index < #line_cache.screen_line_starting_pos and mx > State.left + Text.screen_line_width(State, line_index, screen_line_index) then

        return nil, line_cache.screen_line_starting_posB[screen_line_indexB+1]-1

        return line_cache.screen_line_starting_pos[screen_line_index+1]-1

      local s = string.sub(line.dataB, screen_line_starting_byte_offsetB)
--?       print('return', mx, Text.nearest_cursor_pos(s, mx, State.left), '=>', screen_line_starting_posB + Text.nearest_cursor_pos(s, mx, State.left) - 1)
      return nil, screen_line_starting_posB + Text.nearest_cursor_pos(s, mx, State.left) - 1

      local s = string.sub(line.data, screen_line_starting_byte_offset)
--?       print('return', mx, Text.nearest_cursor_pos(s, mx, State.left), '=>', screen_line_starting_pos + Text.nearest_cursor_pos(s, mx, State.left) - 1)
      return screen_line_starting_pos + Text.nearest_cursor_pos(s, mx, State.left) - 1

function Text.screen_line_widthB(State, line_index, i)
  local line = State.lines[line_index]
  local line_cache = State.line_cache[line_index]
  local start_posB = line_cache.screen_line_starting_posB[i]
  local start_offsetB = Text.offset(line.dataB, start_posB)
  local screen_line
  if i < #line_cache.screen_line_starting_posB then
--?     print('non-final', i)
    local past_end_posB = line_cache.screen_line_starting_posB[i+1]
    local past_end_offsetB = Text.offset(line.dataB, past_end_posB)
--?     print('between', start_offsetB, past_end_offsetB)
    screen_line = string.sub(line.dataB, start_offsetB, past_end_offsetB-1)
  else
--?     print('final', i)
--?     print('after', start_offsetB)
    screen_line = string.sub(line.dataB, start_offsetB)
  end
  local screen_line_text = App.newText(love.graphics.getFont(), screen_line)
--?   local result = App.width(screen_line_text)
--?   print('=>', result)
--?   return result
  return App.width(screen_line_text)
end

function Text.screen_line_indexB(screen_line_starting_posB, posB)
  if posB == nil then
    return 0
  end
  assert(screen_line_starting_posB)
  for i = #screen_line_starting_posB,1,-1 do
    if screen_line_starting_posB[i] <= posB then
      return i
    end
  end
end

  end
  if loc1.pos then
    return Text.to2A(State, loc1)
  else
    return Text.to2B(State, loc1)

end
function Text.to2A(State, loc1)

  return result
end
function Text.to2B(State, loc1)
  local result = {line=loc1.line}
  local line_cache = State.line_cache[loc1.line]
  Text.populate_screen_line_starting_pos(State, loc1.line)
  local x = Margin_left + Text.screen_line_width(State, loc1.line, #line_cache.screen_line_starting_pos) + AB_padding
  Text.populate_screen_line_starting_posB(State, loc1.line, x)
  for i=#line_cache.screen_line_starting_posB,1,-1 do
    local sposB = line_cache.screen_line_starting_posB[i]
    if sposB <= loc1.posB then
      result.screen_lineB = i
      result.screen_posB = loc1.posB - sposB + 1
      break
    end
  end
  assert(result.screen_posB)

  if loc2.screen_pos then
    return Text.to1A(State, loc2)
  else
    return Text.to1B(State, loc2)
  end
end
function Text.to1A(State, loc2)

function Text.to1B(State, loc2)
  local result = {line=loc2.line, posB=loc2.screen_posB}
  if loc2.screen_lineB > 1 then
    result.posB = State.line_cache[loc2.line].screen_line_starting_posB[loc2.screen_lineB] + loc2.screen_posB - 1
  end
  return result

function Text.eq1(a, b)
  return a.line == b.line and a.pos == b.pos

  -- A side < B side
  if a.pos and not b.pos then

  return a.pos < b.pos
end
function Text.le1(a, b)
  if a.line < b.line then

  if not a.pos and b.pos then

  if a.line > b.line then

  if a.pos then
    return a.pos < b.pos
  else
    return a.posB < b.posB
  end

  return a.pos <= b.pos

function Text.le1(a, b)
  return eq(a, b) or Text.lt1(a, b)
end

  if loc2.screen_pos then
    return Text.previous_screen_lineA(State, loc2)
  else
    return Text.previous_screen_lineB(State, loc2)
  end
end
function Text.previous_screen_lineA(State, loc2)

  elseif State.lines[loc2.line-1].mode == 'drawing' then
    return {line=loc2.line-1, screen_line=1, screen_pos=1}

    local l = State.lines[loc2.line-1]

    if State.lines[loc2.line-1].dataB == nil or
        (not State.expanded and not State.lines[loc2.line-1].expanded) then
--?       print('c1', loc2.line-1, State.lines[loc2.line-1].data, '==', State.lines[loc2.line-1].dataB, State.line_cache[loc2.line-1].fragmentsB)
      return {line=loc2.line-1, screen_line=#State.line_cache[loc2.line-1].screen_line_starting_pos, screen_pos=1}
    end
    -- try to switch to B
    local prev_line_cache = State.line_cache[loc2.line-1]
    local x = Margin_left + Text.screen_line_width(State, loc2.line-1, #prev_line_cache.screen_line_starting_pos) + AB_padding
    Text.populate_screen_line_starting_posB(State, loc2.line-1, x)
    local screen_line_starting_posB = State.line_cache[loc2.line-1].screen_line_starting_posB
--?     print('c', loc2.line-1, State.lines[loc2.line-1].data, '==', State.lines[loc2.line-1].dataB, '==', #screen_line_starting_posB, 'starting from x', x)
    if #screen_line_starting_posB > 1 then
--?       print('c2')
      return {line=loc2.line-1, screen_lineB=#State.line_cache[loc2.line-1].screen_line_starting_posB, screen_posB=1}
    else
--?       print('c3')
      -- if there's only one screen line, assume it overlaps with A, so remain in A
      return {line=loc2.line-1, screen_line=#State.line_cache[loc2.line-1].screen_line_starting_pos, screen_pos=1}
    end

    return {line=loc2.line-1, screen_line=#State.line_cache[loc2.line-1].screen_line_starting_pos, screen_pos=1}

function Text.previous_screen_lineB(State, loc2)
  if loc2.screen_lineB > 2 then  -- first screen line of B side overlaps with A side
    return {line=loc2.line, screen_lineB=loc2.screen_lineB-1, screen_posB=1}
  else
    -- switch to A side
    -- TODO: handle case where fold lands precisely at end of a new screen-line
    return {line=loc2.line, screen_line=#State.line_cache[loc2.line].screen_line_starting_pos, screen_pos=1}
  end
end

      local pos,posB = Text.to_pos_on_line(State, State.screen_bottom1.line, State.right-5, App.screen.height-5)
      State.cursor1 = {line=State.screen_bottom1.line, pos=pos, posB=posB}

      State.cursor1 = {
          line=State.screen_bottom1.line,
          pos=Text.to_pos_on_line(State, State.screen_bottom1.line, State.right-5, App.screen.height-5),
      }

  State.line_cache[line_index].fragmentsB = nil

  State.line_cache[line_index].screen_line_starting_posB = nil

function starts_with(s, sub)
  return s:find(sub, 1, --[[no escapes]] true) == 1

function starts_with(s, prefix)
  if #s < #prefix then
    return false
  end
  for i=1,#prefix do
    if s:sub(i,i) ~= prefix:sub(i,i) then
      return false
    end
  end
  return true

function ends_with(s, sub)
  return s:reverse():find(sub:reverse(), 1, --[[no escapes]] true) == 1

function ends_with(s, suffix)
  if #s < #suffix then
    return false
  end
  for i=0,#suffix-1 do
    if s:sub(#s-i,#s-i) ~= suffix:sub(#suffix-i,#suffix-i) then
      return false
    end
  end
  return true

Fold_color = {r=0, g=0.6, b=0}
Fold_background_color = {r=0, g=0.7, b=0}

    -- a line is either bifold text or a drawing
    -- a line of bifold text consists of an A side and an optional B side

    -- a line is either text or a drawing
    -- a text is a table with:

    --    string dataB,
    --    expanded: whether to show B side

    lines = {{mode='text', data='', dataB=nil, expanded=nil}},  -- array of lines

    lines = {{mode='text', data=''}},  -- array of lines

    -- Positions (and screen line indexes) can be in either the A or the B side.

    screen_top1 = {line=1, pos=1, posB=nil},  -- position of start of screen line at top of screen
    cursor1 = {line=1, pos=1, posB=nil},  -- position of cursor
    screen_bottom1 = {line=1, pos=1, posB=nil},  -- position of start of screen line at bottom of screen

    screen_top1 = {line=1, pos=1},  -- position of start of screen line at top of screen
    cursor1 = {line=1, pos=1},  -- position of cursor
    screen_bottom1 = {line=1, pos=1},  -- position of start of screen line at bottom of screen

    left = left,
    right = right,

    left = math.floor(left),
    right = math.floor(right),

    print(State.screen_top1.line, State.screen_top1.pos, State.screen_top1.posB, State.cursor1.line, State.cursor1.pos, State.cursor1.posB)

    print(State.screen_top1.line, State.screen_top1.pos, State.cursor1.line, State.cursor1.pos)

--?     print('draw:', y, line_index, line, line.mode)

--?     print('draw:', y, line_index, line)

    State.screen_bottom1 = {line=line_index, pos=nil, posB=nil}

    State.screen_bottom1 = {line=line_index, pos=nil}

--?     print('text.draw', y, line_index)
      local startpos, startposB = 1, nil

--?       print('text.draw', y, line_index)
      local startpos = 1

        if State.screen_top1.pos then
          startpos = State.screen_top1.pos
        else
          startpos, startposB = nil, State.screen_top1.posB
        end

        startpos = State.screen_top1.pos

      y, State.screen_bottom1.pos, State.screen_bottom1.posB = Text.draw(State, line_index, y, startpos, startposB, hide_cursor)

      y, State.screen_bottom1.pos = Text.draw(State, line_index, y, startpos, hide_cursor)

    -- give some time for the OS to flush everything to disk
    love.timer.sleep(0.1)

--?   print('press')

--?   print('press', State.selection1.line, State.selection1.pos)

        local pos,posB = Text.to_pos_on_line(State, line_index, x, y)
  --?       print(x,y, 'setting cursor:', line_index, pos, posB)
        State.selection1 = {line=line_index, pos=pos, posB=posB}
--?         print('selection', State.selection1.line, State.selection1.pos, State.selection1.posB)

        State.selection1 = {
            line=line_index,
            pos=Text.to_pos_on_line(State, line_index, x, y),
        }
--?         print('selection', State.selection1.line, State.selection1.pos)

          local pos,posB = Text.to_pos_on_line(State, line_index, x, y)
          State.cursor1 = {line=line_index, pos=pos, posB=posB}
--?           print('cursor', State.cursor1.line, State.cursor1.pos, State.cursor1.posB)

          State.cursor1 = {
              line=line_index,
              pos=Text.to_pos_on_line(State, line_index, x, y),
          }
--?           print('cursor', State.cursor1.line, State.cursor1.pos)

      if State.cursor1.pos then
        State.cursor1.pos = State.cursor1.pos+1
      else
        State.cursor1.posB = State.cursor1.posB+1
      end

      State.cursor1.pos = State.cursor1.pos+1

      cursor={line=State.cursor1.line, pos=State.cursor1.pos, posB=State.cursor1.posB},
      screen_top={line=State.screen_top1.line, pos=State.screen_top1.pos, posB=State.screen_top1.posB},

      cursor={line=State.cursor1.line, pos=State.cursor1.pos},
      screen_top={line=State.screen_top1.line, pos=State.screen_top1.pos},

  -- bifold text
  elseif chord == 'M-b' then
    State.expanded = not State.expanded
    Text.redraw_all(State)
    if not State.expanded then
      for _,line in ipairs(State.lines) do
        line.expanded = nil
      end
      edit.eradicate_locations_after_the_fold(State)
    end
  elseif chord == 'M-d' then
    if State.cursor1.posB == nil then
      local before = snapshot(State, State.cursor1.line)
      if State.lines[State.cursor1.line].dataB == nil then
        State.lines[State.cursor1.line].dataB = ''
      end
      State.lines[State.cursor1.line].expanded = true
      State.cursor1.pos = nil
      State.cursor1.posB = 1
      if Text.cursor_out_of_screen(State) then
        Text.snap_cursor_to_bottom_of_screen(State, State.left, State.right)
      end
      schedule_save(State)
      record_undo_event(State, {before=before, after=snapshot(State, State.cursor1.line)})
    end

    edit.update_font_settings(State, State.font_height-2)
    Text.redraw_all(State)

    if State.font_height > 2 then
      edit.update_font_settings(State, State.font_height-2)
      Text.redraw_all(State)
    end

    State.cursor1 = {line=#State.lines, pos=utf8.len(State.lines[#State.lines].data)+1, posB=nil}

    State.cursor1 = {line=#State.lines, pos=utf8.len(State.lines[#State.lines].data)+1}

function edit.eradicate_locations_after_the_fold(State)
  -- eradicate side B from any locations we track
  if State.cursor1.posB then
    State.cursor1.posB = nil
    State.cursor1.pos = utf8.len(State.lines[State.cursor1.line].data)
    State.cursor1.pos = Text.pos_at_start_of_screen_line(State, State.cursor1)
  end
  if State.screen_top1.posB then
    State.screen_top1.posB = nil
    State.screen_top1.pos = utf8.len(State.lines[State.screen_top1.line].data)
    State.screen_top1.pos = Text.pos_at_start_of_screen_line(State, State.screen_top1)
  end
end

-- environment for a mutable file of bifolded text

-- environment for a mutable file

  -- We currently start out with side B collapsed.
  -- Other options:
  --  * save all expanded state by line
  --  * expand all if any location is in side B

  edit.eradicate_locations_after_the_fold(Editor_state)

  -- convert any bifold files here

function source.convert_bifold_text(infilename, outfilename)
  local contents = love.filesystem.read(infilename)
  contents = contents:gsub('\u{1e}', ';')
  love.filesystem.write(outfilename, contents)
end

  Log_browser_state.cursor1 = {line=1, pos=nil}

  Log_browser_state.cursor1 = {line=1, pos=1}

  Editor_state.cursor1 = {line=line.line_number, pos=1, posB=nil}

  Editor_state.cursor1 = {line=line.line_number, pos=1}

  -- expand B side
  Editor_state.expanded = true

      or not Text.le1(State.screen_top1, State.cursor1) then
    State.screen_top1 = {line=1, pos=1}

  end
end
function edit.invalid1(State, loc1)
  return loc1.line > #State.lines
      or loc1.pos > #State.lines[loc1.line].data
end