Menu_background_color = {r=0.6, g=0.8, b=0.6}
Menu_border_color = {r=0.6, g=0.7, b=0.6}
Menu_command_color = {r=0.2, g=0.2, b=0.2}
Menu_highlight_color = {r=0.5, g=0.7, b=0.3}
function source.draw_menu_bar()
  if App.run_tests then return end  -- disable in tests
  App.color(Menu_background_color)
  love.graphics.rectangle('fill', 0,0, App.screen.width, Menu_status_bar_height)
  App.color(Menu_border_color)
  love.graphics.rectangle('line', 0,0, App.screen.width, Menu_status_bar_height)
  App.color(Menu_command_color)
  Menu_cursor = 5
  if Show_file_navigator then
    source.draw_file_navigator()
    return
  end
  add_hotkey_to_menu('ctrl+e: run')
  if Focus == 'edit' then
    add_hotkey_to_menu('ctrl+g: switch file')
    if Show_log_browser_side then
      add_hotkey_to_menu('ctrl+l: hide log browser')
    else
      add_hotkey_to_menu('ctrl+l: show log browser')
    end
    if Editor_state.expanded then
      add_hotkey_to_menu('ctrl+b: collapse debug prints')
    else
      add_hotkey_to_menu('ctrl+b: expand debug prints')
    end
    add_hotkey_to_menu('ctrl+d: create/edit debug print')
    add_hotkey_to_menu('ctrl+f: find in file')
    add_hotkey_to_menu('alt+left alt+right: prev/next word')
  elseif Focus == 'log_browser' then
    -- nothing yet
  else
    assert(false, 'unknown focus "'..Focus..'"')
  end
  add_hotkey_to_menu('ctrl+z ctrl+y: undo/redo')
  add_hotkey_to_menu('ctrl+x ctrl+c ctrl+v: cut/copy/paste')
  add_hotkey_to_menu('ctrl+= ctrl+- ctrl+0: zoom')
end
function add_hotkey_to_menu(s)
  if Text_cache[s] == nil then
    Text_cache[s] = App.newText(love.graphics.getFont(), s)
  end
  local width = App.width(Text_cache[s])
  if Menu_cursor + width > App.screen.width - 5 then
    return
  end
  App.color(Menu_command_color)
  App.screen.draw(Text_cache[s], Menu_cursor,5)
  Menu_cursor = Menu_cursor + width + 30
end
function source.draw_file_navigator()
  for i,file in ipairs(File_navigation.candidates) do
    if file == 'source' then
      App.color(Menu_border_color)
      love.graphics.line(Menu_cursor-10,2, Menu_cursor-10,Menu_status_bar_height-2)
    end
    add_file_to_menu(file, i == File_navigation.index)
  end
end
function add_file_to_menu(s, cursor_highlight)
  if Text_cache[s] == nil then
    Text_cache[s] = App.newText(love.graphics.getFont(), s)
  end
  local width = App.width(Text_cache[s])
  if Menu_cursor + width > App.screen.width - 5 then
    return
  end
  if cursor_highlight then
    App.color(Menu_highlight_color)
    love.graphics.rectangle('fill', Menu_cursor-5,5-2, App.width(Text_cache[s])+5*2,Editor_state.line_height+2*2)
  end
  App.color(Menu_command_color)
  App.screen.draw(Text_cache[s], Menu_cursor,5)
  Menu_cursor = Menu_cursor + width + 30
end
function keychord_pressed_on_file_navigator(chord, key)
  if chord == 'escape' then
    Show_file_navigator = false
  elseif chord == 'return' then
    local candidate = guess_source(File_navigation.candidates[File_navigation.index]..'.lua')
    source.switch_to_file(candidate)
    Show_file_navigator = false
  elseif chord == 'left' then
    if File_navigation.index > 1 then
      File_navigation.index = File_navigation.index-1
    end
  elseif chord == 'right' then
    if File_navigation.index < #File_navigation.candidates then
      File_navigation.index = File_navigation.index+1
    end
  end
end

Menu_background_color = {r=0.6, g=0.8, b=0.6}
Menu_border_color = {r=0.6, g=0.7, b=0.6}
Menu_command_color = {r=0.2, g=0.2, b=0.2}
Menu_highlight_color = {r=0.5, g=0.7, b=0.3}
function source.draw_menu_bar()
  if App.run_tests then return end  -- disable in tests
  App.color(Menu_background_color)
  love.graphics.rectangle('fill', 0,0, App.screen.width, Menu_status_bar_height)
  App.color(Menu_border_color)
  love.graphics.rectangle('line', 0,0, App.screen.width, Menu_status_bar_height)
  App.color(Menu_command_color)
  Menu_cursor = 5
  if Show_file_navigator then
    source.draw_file_navigator()
    return
  end
  add_hotkey_to_menu('ctrl+u: run')
  if Focus == 'edit' then
    add_hotkey_to_menu('ctrl+g: switch file')
    if Show_log_browser_side then
      add_hotkey_to_menu('ctrl+l: hide log browser')
    else
      add_hotkey_to_menu('ctrl+l: show log browser')
    end
    if Editor_state.expanded then
      add_hotkey_to_menu('ctrl+b: collapse debug prints')
    else
      add_hotkey_to_menu('ctrl+b: expand debug prints')
    end
    add_hotkey_to_menu('ctrl+d: create/edit debug print')
    add_hotkey_to_menu('ctrl+f: find in file')
    add_hotkey_to_menu('alt+left alt+right: prev/next word')
  elseif Focus == 'log_browser' then
    -- nothing yet
  else
    assert(false, 'unknown focus "'..Focus..'"')
  end
  add_hotkey_to_menu('ctrl+z ctrl+y: undo/redo')
  add_hotkey_to_menu('ctrl+x ctrl+c ctrl+v: cut/copy/paste')
  add_hotkey_to_menu('ctrl+= ctrl+- ctrl+0: zoom')
end
function add_hotkey_to_menu(s)
  if Text_cache[s] == nil then
    Text_cache[s] = App.newText(love.graphics.getFont(), s)
  end
  local width = App.width(Text_cache[s])
  if Menu_cursor + width > App.screen.width - 5 then
    return
  end
  App.color(Menu_command_color)
  App.screen.draw(Text_cache[s], Menu_cursor,5)
  Menu_cursor = Menu_cursor + width + 30
end
function source.draw_file_navigator()
  for i,file in ipairs(File_navigation.candidates) do
    if file == 'source' then
      App.color(Menu_border_color)
      love.graphics.line(Menu_cursor-10,2, Menu_cursor-10,Menu_status_bar_height-2)
    end
    add_file_to_menu(file, i == File_navigation.index)
  end
end
function add_file_to_menu(s, cursor_highlight)
  if Text_cache[s] == nil then
    Text_cache[s] = App.newText(love.graphics.getFont(), s)
  end
  local width = App.width(Text_cache[s])
  if Menu_cursor + width > App.screen.width - 5 then
    return
  end
  if cursor_highlight then
    App.color(Menu_highlight_color)
    love.graphics.rectangle('fill', Menu_cursor-5,5-2, App.width(Text_cache[s])+5*2,Editor_state.line_height+2*2)
  end
  App.color(Menu_command_color)
  App.screen.draw(Text_cache[s], Menu_cursor,5)
  Menu_cursor = Menu_cursor + width + 30
end
function keychord_pressed_on_file_navigator(chord, key)
  if chord == 'escape' then
    Show_file_navigator = false
  elseif chord == 'return' then
    local candidate = guess_source(File_navigation.candidates[File_navigation.index]..'.lua')
    source.switch_to_file(candidate)
    Show_file_navigator = false
  elseif chord == 'left' then
    if File_navigation.index > 1 then
      File_navigation.index = File_navigation.index-1
    end
  elseif chord == 'right' then
    if File_navigation.index < #File_navigation.candidates then
      File_navigation.index = File_navigation.index+1
    end
  end
end

  love.window.setTitle('lines.love - source')

  love.window.setTitle('pensieve.love - source')

  love.window.setTitle('lines.love - source')

  love.window.setTitle('pensieve.love - source')

function find(s, pat, i, plain)

  return s:find(pat, i, plain)

function rfind(s, pat, i, plain)

  local rendpos = rs:find(rpat, ri, plain)

Column_header_color = {r=0.7, g=0.7, b=0.7}
Pane_title_color = {r=0.5, g=0.5, b=0.5}
Pane_title_background_color = {r=0, g=0, b=0, a=0.1}
Pane_background_color = {r=0.7, g=0.7, b=0.7, a=0.1}
Grab_background_color = {r=0.7, g=0.7, b=0.7}
Cursor_pane_background_color = {r=0.7, g=0.7, b=0, a=0.1}
Menu_background_color = {r=0.6, g=0.8, b=0.6}
Menu_border_color = {r=0.6, g=0.7, b=0.6}
Menu_command_color = {r=0.2, g=0.2, b=0.2}
Command_palette_background_color = Menu_background_color
Command_palette_border_color = Menu_border_color
Command_palette_command_color = Menu_command_color
Command_palette_alternatives_background_color = Menu_background_color
Command_palette_highlighted_alternative_background_color = {r=0.5, g=0.7, b=0.3}
Command_palette_alternatives_color = {r=0.3, g=0.5, b=0.3}
Crosslink_color={r=0, g=0.7, b=0.7}
Crosslink_background_color={r=0, g=0, b=0, a=0.1}

-- The note-taking app has a few differences with the baseline editor it's
-- forked from:
--  - most notes are read-only
--  - the editor operates entirely in viewport-relative coordinates; 0,0 is
--    the top-left corner of the window. However the note-taking app in
--    read-only mode largely operates in absolute coordinates; a potentially
--    large 2D space that the window is just a peephole into.
--
-- We'll use the rendering logic in the editor, but only use its event loop
-- when a window is being edited (there can only be one all over the entire
-- surface)
--
-- Most of the time the viewport affects each pane's top and screen_top. An
-- exception is when you're editing a pane and you scroll the cursor inside
-- it. In that case we want to affect the viewport (for all panes) based on
-- the editable pane's screen_top.

  -- tests currently mostly clear their own state

  -- stuff we paginate over is organized as follows:
  --  - there are multiple columns
  --  - each column contains panes
  --  - each pane contains editor state as in lines.love
  Surface = {}
  -- The surface may show the same file in multiple panes. This cache tries to
  -- share data between such aliases:
  --   line contents when panes are not editable (editable panes can diverge)
  --   links between files (never in Surface, can never diverge between panes)
  Cache = {}
  -- LÖVE renders N frames per second like any game engine, but we don't
  -- really need that. The only thing that animates in this app is the cursor.
  --
  -- Until I fix that, the architecture of this app will be to plan what to
  -- draw only when something changes. That way we minimize the amount of
  -- computation/power wasted on each of those frames.
  Panes_to_draw = {}  -- array of panes from surface
  Column_headers_to_draw = {}  -- strings with x coordinates
  Display_settings = {
    mode='normal',
      -- valid modes:
      --   normal (show full surface)
      --   maximize (show just a single note; focus mode)
      --   search (notes currently on surface)
      --   search_all (notes in directory)
      --   searching_all (search in progress)
    x=0, y=0,  -- <==== Top-left corner of the viewport into the surface
    column_width=400,
    show_palette=false,
    palette_command='',
    palette_command_text=App.newText(love.graphics.getFont(), ''),
    palette_alternative_index=1, palette_candidates=nil,
    search_term='', search_text=nil,
    search_backup_x=nil, search_backup_y=nil, search_backup_cursor_pane=nil,
    search_all_query=nil, search_all_query_text=nil, search_all_terms=nil,
    search_all_progress_indicator=nil,
    search_all_pane=nil, search_all_state=nil,
  }
  -- display settings that are constants
  Font_height = 20
  Line_height = math.floor(Font_height*1.3)
  -- space saved for headers
  -- this is only on the screen, not used on the surface itself
  Menu_status_bar_height = 5 + Line_height + 5
--?   print('menu height', Menu_status_bar_height)
  Column_header_height = 5 + Line_height + 5
--?   print('column header height', Column_header_height)
  Header_height = Menu_status_bar_height + Column_header_height
  -- padding is the space between panes on the surface
  Padding_vertical = 20  -- space between panes
  Padding_horizontal = 20
  -- margins are extra space inside the borders of panes on the surface
  Margin_above = 10
  Margin_below = 10
  Pan_step = 10
  Pan = {}
  Cursor_pane = {col=0, row=1}  -- surface column and row index, along with some cached data
  -- occasional secondary cursor
  Grab_pane = nil

  -- where we store our notes (pane id is also a relative path under there)
  Directory = 'data/'
  Settings_file = 'config'
  -- This little bit of state ensures we don't mess with a pane's screen_top
  -- if it was just used to update the viewport.
  Editable_cursor_pane_updated_screen_top = false

  Editor_state = nil  -- not used outside editor tests

  if Settings then
    run.load_settings()
  else
    run.initialize_default_settings()

  assert(#arg <= 1)
  if #arg > 0 then
    Directory = 'data.'..arg[1]..'/'
    Settings_file = 'config.'..arg[1]

  if #arg > 0 then
    Editor_state.filename = arg[1]
    load_from_disk(Editor_state)
    Text.redraw_all(Editor_state)
    Editor_state.screen_top1 = {line=1, pos=1}
    Editor_state.cursor1 = {line=1, pos=1}
    edit.fixup_cursor(Editor_state)

  love.window.setTitle('pensieve.love')
  print('reading notes from '..love.filesystem.getSaveDirectory()..'/'..Directory)
  print('put any notes there (and make frequent backups)')
  if love.filesystem.getInfo(Settings_file) then
    load_settings()

    load_from_disk(Editor_state)
    Text.redraw_all(Editor_state)
    if Editor_state.cursor1.line > #Editor_state.lines or Editor_state.lines[Editor_state.cursor1.line].mode ~= 'text' then
      edit.fixup_cursor(Editor_state)
    end

    initialize_default_settings()
  end
  if Display_settings.column_width > App.screen.width - Padding_horizontal - Margin_left - Margin_right - Padding_horizontal then
    Display_settings.column_width = math.max(200, App.screen.width - Padding_horizontal - Margin_left - Margin_right - Padding_horizontal)

  love.window.setTitle('lines.love - '..Editor_state.filename)

  if #arg > 1 then
    print('ignoring commandline args after '..arg[1])

  Cursor_pane.col = math.min(Cursor_pane.col, #Surface)
  if Cursor_pane.col >= 1 then
    Cursor_pane.row = math.min(Cursor_pane.row, #Surface[Cursor_pane.col])

  plan_draw()

function run.load_settings()
  love.graphics.setFont(love.graphics.newFont(Settings.font_height))

function load_settings()
  local settings = json.decode(love.filesystem.read(Settings_file))

  love.window.setMode(0, 0)  -- maximize

--?   print('max height', App.screen.height)

  App.screen.width, App.screen.height = Settings.width, Settings.height

  App.screen.width, App.screen.height = settings.width, settings.height

  love.window.setPosition(Settings.x, Settings.y, Settings.displayindex)
  Editor_state = edit.initialize_state(Margin_top, Margin_left, App.screen.width-Margin_right, Settings.font_height, math.floor(Settings.font_height*1.3))
  Editor_state.filename = Settings.filename
  Editor_state.screen_top1 = Settings.screen_top
  Editor_state.cursor1 = Settings.cursor

  love.window.setPosition(settings.x, settings.y, settings.displayindex)
  Font_height = settings.font_height
  Line_height = math.floor(Font_height*1.3)
  love.graphics.setFont(love.graphics.newFont(Font_height))
  Em = App.newText(love.graphics.getFont(), 'm')
  Display_settings.column_width = settings.column_width
  for _,column_name in ipairs(settings.columns) do
    create_column(column_name)
  end
  Cursor_pane.col = settings.cursor_col
  Cursor_pane.row = settings.cursor_row
  Display_settings.x = settings.surface_x
  Display_settings.y = settings.surface_y

function run.initialize_default_settings()
  local font_height = 20
  love.graphics.setFont(love.graphics.newFont(font_height))
  local em = App.newText(love.graphics.getFont(), 'm')
  run.initialize_window_geometry(App.width(em))
  Editor_state = edit.initialize_state(Margin_top, Margin_left, App.screen.width-Margin_right)
  Editor_state.font_height = font_height
  Editor_state.line_height = math.floor(font_height*1.3)
  Editor_state.em = em
  Settings = run.settings()

function initialize_default_settings()
  initialize_window_geometry()
  love.graphics.setFont(love.graphics.newFont(Font_height))
  Em = App.newText(love.graphics.getFont(), 'm')
  Display_settings.column_width = 40*App.width(Em)
  -- initialize surface with a single column
  command.recently_modified()

function run.initialize_window_geometry(em_width)

function initialize_window_geometry()

  App.screen.width = 40*em_width

  App.screen.width = App.screen.width-100

--?   print(("Window resized to width: %d and height: %d."):format(w, h))

  Text.redraw_all(Editor_state)
  Editor_state.selection1 = {}  -- no support for shift drag while we're resizing
  Editor_state.right = App.screen.width-Margin_right
  Editor_state.width = Editor_state.right-Editor_state.left
  Text.tweak_screen_top_and_cursor(Editor_state, Editor_state.left, Editor_state.right)

--?   print('resize:', App.screen.width, App.screen.height)
  plan_draw()
end
function initialize_cache_if_necessary(id)
  if Cache[id] then return end
--?   print('init:', id)
  Cache[id] = {id=id, filename=Directory..id, left=0, right=Display_settings.column_width, lines={}, line_cache={}}
  load_from_disk(Cache[id])
  Cache[id].links = load_links(id)
end
function load_pane(id)
--?   print('load pane from file', id)
  initialize_cache_if_necessary(id)
  local result = edit.initialize_state(0, 0, math.min(Display_settings.column_width, App.screen.width-Margin_right), Font_height, Line_height)
  result.id = id
  result.filename = Directory..id
  result.lines = Cache[id].lines
  result.line_cache = deepcopy(Cache[id].line_cache)  -- should be tiny; deepcopy is just to eliminate any chance of aliasing
  result.font_height = Font_height
  result.line_height = Line_height
  result.em = Em
  result.editable = false
  edit.fixup_cursor(result)
  return result

function run.filedropped(file)
  -- first make sure to save edits on any existing file
  if Editor_state.next_save then
    save_to_disk(Editor_state)

function height(pane)
  if pane._height == nil then
    refresh_pane_height(pane)
  end
  return pane._height
end
-- keep the structure of this function sync'd with plan_draw
function refresh_pane_height(pane)
--?   print('refresh pane height')
  local y = 0
  if pane.title then
    y = y + 5+Line_height+5
  end
  for i=1,#pane.lines do
    local line = pane.lines[i]
    if pane.line_cache[i] == nil then
      pane.line_cache[i] = {}
    end
    if line.mode == 'text' then
      pane.line_cache[i].fragments = nil
      pane.line_cache[i].screen_line_starting_pos = nil
      Text.compute_fragments(pane, i)
      Text.populate_screen_line_starting_pos(pane, i)
      y = y + Line_height*#pane.line_cache[i].screen_line_starting_pos
      Text.clear_screen_line_cache(pane, i)
    elseif line.mode == 'drawing' then
      -- nothing
      y = y + Drawing.pixels(line.h, Display_settings.column_width) + Drawing_padding_height
    else
      print(line.mode)
      assert(false)
    end
  end
  if Cache[pane.id].links and not empty(Cache[pane.id].links) then
    y = y + 5+Line_height+5  -- for crosslinks

  -- clear the slate for the new file
  App.initialize_globals()
  Editor_state.filename = file:getFilename()
  file:open('r')
  Editor_state.lines = load_from_file(file)
  file:close()
  Text.redraw_all(Editor_state)
  edit.fixup_cursor(Editor_state)
  love.window.setTitle('lines.love - '..Editor_state.filename)

  pane._height = y
end
-- titles are optional and so affect the height of the pane
function add_title(pane, title)
  pane.title = title
  pane._height = nil
end
-- keep the structure of this function sync'd with refresh_pane_height
function plan_draw(options)
--?   print('update pane bounds')
--?   print(#Surface, 'columns;', num_panes(), 'panes')
  Panes_to_draw = {}
  Column_headers_to_draw = {}
  local sx = Padding_horizontal + Margin_left
  for column_index, column in ipairs(Surface) do
    if should_show_column(sx) then
      table.insert(Column_headers_to_draw, {name=('%d. %s'):format(column_index, column.name), x = sx-Display_settings.x})
      local sy = Padding_vertical
      for pane_index, pane in ipairs(column) do
        if sy > Display_settings.y + App.screen.height - Header_height then
          break
        end
--?         print('bounds:', column_index, pane_index, sx,sy)
        if should_show_pane(pane, sy) then
          table.insert(Panes_to_draw, pane)
          -- stash some short-lived variables
          pane.column_index = column_index
          pane.pane_index = pane_index
          local y_offset = 0
          local body_sy = sy
          if column[pane_index].title then
            body_sy = body_sy + 5+Line_height+5
          end
          if should_update_screen_top(column_index, pane_index, pane, options) then
            if body_sy < Display_settings.y then
              pane.screen_top1, y_offset = schema1_of_y(pane, Display_settings.y - body_sy)
            else
              pane.screen_top1 = {line=1, pos=1}
            end
          end
          if body_sy < Display_settings.y then
            pane.top = Margin_above
          else
            pane.top = body_sy - Display_settings.y + Margin_above
          end
          pane.top = Header_height + pane.top - y_offset
--?           print('bounds: =>', pane.top)
          pane.left = sx - Display_settings.x
          pane.right = pane.left + Display_settings.column_width
          pane.width = pane.right - pane.left
        else
          -- clear bounds to catch issues early
          pane.top = nil
--?           print('bounds: =>', pane.top)
        end
        sy = sy + Margin_above + height(pane) + Margin_below + Padding_vertical
      end
    else
      -- clear bounds to catch issues early
      for _, pane in ipairs(column) do
        pane.top = nil
      end
    end
    sx = sx + Margin_right + Display_settings.column_width + Padding_horizontal + Margin_left
  end

function should_update_screen_top(column_index, pane_index, pane, options)
  if column_index ~= Cursor_pane.col then return true end
  if pane_index ~= Cursor_pane.row then return true end
  -- update the cursor pane either if it's not editable, or
  -- if it was explicitly requested
  if not pane.editable then return true end
  if options == nil then return true end
  if not options.ignore_editable_cursor_pane then return true end
  if not Editable_cursor_pane_updated_screen_top then return true end
  return false
end

  edit.draw(Editor_state)

--?   print(Display_settings.y)
  if Display_settings.mode == 'normal' then
    draw_normal_mode()
  elseif Display_settings.mode == 'search' then
    draw_normal_mode()
    -- hack: pass in an unexpected object and pun some attributes
    Text.draw_search_bar(Display_settings, --[[force show cursor]] true)
  elseif Display_settings.mode == 'search_all' then
    draw_normal_mode()
    -- only difference is in command palette below
  elseif Display_settings.mode == 'searching_all' then
    draw_normal_mode()
    -- only difference is in command palette below
  elseif Display_settings.mode == 'maximize' then
    if Cursor_pane.col >= 1 then
      local pane = Surface[Cursor_pane.col][Cursor_pane.row]
      if pane then
        pane.top = Header_height + Margin_above
        pane.left = App.screen.width/2 - 20*App.width(Em)
        pane.right = App.screen.width/2 + 20*App.width(Em)
        pane.width = pane.right - pane.left
        edit.draw(pane)
      end
    end
  else
    print(Display_settings.mode)
    assert(false)
  end
  if Grab_pane then
    local old_top, old_left, old_right = Grab_pane.top, Grab_pane.left, Grab_pane.right
    local old_screen_top = Grab_pane.screen_top1
    Grab_pane.screen_top1 = {line=1, pos=1}
    Grab_pane.top = App.screen.height - 10*Line_height
    Grab_pane.left = App.screen.width - Display_settings.column_width - Margin_right - Padding_horizontal
    Grab_pane.right = Grab_pane.left + Display_settings.column_width
    Grab_pane.width = Grab_pane.right - Grab_pane.left
    App.color(Grab_background_color)
    love.graphics.rectangle('fill', Grab_pane.left-Margin_left,Grab_pane.top-Margin_above, Grab_pane.width+Margin_left+Margin_right, App.screen.height-Grab_pane.top+Margin_above)
    edit.draw(Grab_pane)
    Grab_pane.top, Grab_pane.left, Grab_pane.right = old_top, old_left, old_right
    Grab_pane.screen_top1 = old_screen_top
  end
  draw_menu_bar()
  if Display_settings.mode == 'search_all' or Display_settings.mode == 'searching_all' then
    draw_command_palette_for_search_all()
  elseif Display_settings.show_palette then
    draw_command_palette()
  end
end
function draw_normal_mode()
  assert(Cursor_pane.col)
  assert(Cursor_pane.row)
--?   print('draw', Display_settings.x, Display_settings.y)
  for _,pane in ipairs(Panes_to_draw) do
    assert(pane.top)
--?     if Surface[pane.column_index].name == 'search: donate' then
--?       print('draw: search: donate', pane, Display_settings.search_all_pane)
--?       print(#pane.lines, #pane.line_cache, pane._height)
--?       print(pane.lines[1].data)
--?     end
    if pane.title and eq(pane.screen_top1, {line=1, pos=1}) then
      draw_title(pane)
    end
    edit.draw(pane)
    if pane_drew_to_bottom(pane) then
      draw_links(pane)
    end
    if pane.column_index == Cursor_pane.col and pane.pane_index == Cursor_pane.row then
      App.color(Cursor_pane_background_color)
      if pane.editable and Surface.cursor_on_screen_check then
        assert(pane.cursor_y, 'cursor went off screen; this should never happen')
        Surface.cursor_on_screen_check = false
      end
    else
      App.color(Pane_background_color)
    end
    love.graphics.rectangle('fill', pane.left-Margin_left,pane.top-Margin_above, pane.width+Margin_left+Margin_right, pane.bottom-pane.top+Margin_above+Margin_below)
  end
  for _,header in ipairs(Column_headers_to_draw) do
    -- column header
    App.color(Column_header_color)
    love.graphics.rectangle('fill', header.x - Margin_left, Menu_status_bar_height, Margin_left + Display_settings.column_width + Margin_right, Column_header_height)
    App.color(Text_color)
    love.graphics.print(header.name, header.x, Menu_status_bar_height+5)
  end
end
function pane_drew_to_bottom(pane)
  return pane.bottom < App.screen.height - Line_height
end
function should_show_column(sx)
  return overlap(sx-Margin_left, sx+Display_settings.column_width+Margin_right, Display_settings.x, Display_settings.x + App.screen.width)
end
function should_show_pane(pane, sy)
  return overlap(sy, sy + Margin_above + height(pane) + Margin_below, Display_settings.y, Display_settings.y + App.screen.height - Header_height)
end
function draw_title(pane)
  assert(pane.title)
  if Text_cache[pane.title] == nil then
    Text_cache[pane.title] = App.newText(love.graphics.getFont(), pane.title)
  end
  App.color(Pane_title_color)
  App.screen.draw(Text_cache[pane.title], pane.left, pane.top-Margin_above -5-Line_height)
  App.color(Pane_title_background_color)
  love.graphics.rectangle('fill', pane.left-Margin_left, pane.top-Margin_above-5-Line_height-5, Margin_left+Display_settings.column_width+Margin_right, 5+Line_height+5)
end
function draw_links(pane)
  local links = Cache[pane.id].links
  if links == nil then return end
  if empty(links) then return end
  local x = pane.left
  for _,label in ipairs(Edge_list) do
    if Text_cache[label] == nil then
      Text_cache[label] = App.newText(love.graphics.getFont(), label)
    end
    if links[label] then
      draw_link(label, x, pane.bottom)
    end
    x = x + App.width(Text_cache[label]) + 10 + 10
  end
  -- links we don't know about, just in case
  for link,_ in pairs(links) do
    if not Opposite[link] then
      if Text_cache[link] == nil then
        Text_cache[link] = App.newText(love.graphics.getFont(), link)
      end
      draw_link(link, x, pane.bottom)
      x = x + App.width(Text_cache[link]) + 10 + 10
    end
  end
  pane.bottom = pane.bottom + 5+Line_height+5
end
function draw_link(label, x,y)
  App.color(Crosslink_color)
  love.graphics.draw(Text_cache[label], x, y+5)
  App.color(Crosslink_background_color)
  love.graphics.rectangle('fill', x-5, y+3, App.width(Text_cache[label])+10, 2+Line_height+2)
end
-- assumes intervals are half-open: [lo, hi)
-- https://en.wikipedia.org/wiki/Interval_(mathematics)
function overlap(lo1,hi1, lo2,hi2)
  --     lo2       hi2
  --      |         |
  --    |     |
  --    |             |
  if lo1 <= lo2 and hi1 > lo2 then
    return true
  end
  --     lo2       hi2
  --      |         |
  --          |       |
  if lo1 < hi2 and hi1 >= hi2 then
    return true
  end
  --     lo2       hi2
  --      |         |
  --          |   |
  return lo1 >= lo2 and hi1 <= hi2

  edit.update(Editor_state, dt)

  if App.mouse_y() < Header_height then
    -- column header
    love.mouse.setCursor(love.mouse.getSystemCursor('arrow'))
  elseif in_pane(App.mouse_x(), App.mouse_y()) then
    love.mouse.setCursor(love.mouse.getSystemCursor('arrow'))
  else
    love.mouse.setCursor(love.mouse.getSystemCursor('hand'))
  end
  if Pan.x then
    Display_settings.x = math.max(Pan.x-App.mouse_x(), 0)
    Display_settings.y = math.max(Pan.y-(App.mouse_y()-Header_height), 0)
  end
  if Cursor_pane.col >= 1 then
    local pane = Surface[Cursor_pane.col][Cursor_pane.row]
    if pane and pane.editable then
      edit.update(pane, dt)
    end
  end
  if not Display_settings.show_palette and (Display_settings.mode == 'normal' or Display_settings.mode == 'search') and App.mouse_down(1) then
    -- pan the surface by dragging
    plan_draw()
  end
  if Display_settings.mode == 'searching_all' then
    resume_search_all()
  end
end
function in_pane(x,y)
  -- duplicate some logic from App.draw
  local sx,sy = to_surface(x,y)
  local x = Padding_horizontal
  for column_idx, column in ipairs(Surface) do
    if sx < x then
      return false
    end
    if sx < x + Margin_left + Display_settings.column_width + Margin_right then
      local y = Padding_vertical
      for pane_idx, pane in ipairs(column) do
        if sy < y then
          return false
        end
        if sy < y + Margin_above + height(pane) + Margin_below then
          return true
        end
        y = y + Margin_above + height(pane) + Margin_below + Padding_vertical
      end
    end
    x = x + Margin_left + Display_settings.column_width + Margin_right + Padding_horizontal
  end
  return false
end
function to_pane(sx,sy)
  -- duplicate some logic from App.draw
  local x = Padding_horizontal
  for column_idx, column in ipairs(Surface) do
    if sx < x then
      return nil
    end
    if sx < x + Margin_left + Display_settings.column_width + Margin_right then
      local y = Padding_vertical
      for pane_idx, pane in ipairs(column) do
        if sy < y then
          return nil
        end
        if sy < y + Margin_above + height(pane) + Margin_below then
          return {col=column_idx, row=pane_idx}
        end
        y = y + Margin_above + height(pane) + Margin_below + Padding_vertical
      end
    end
    x = x + Margin_left + Display_settings.column_width + Margin_right + Padding_horizontal
  end
  return nil

function to_surface(x, y)
  return x+Display_settings.x, y+Display_settings.y-Header_height
end

  edit.quit(Editor_state)

  if Cursor_pane.col >= 1 then
    local pane = Surface[Cursor_pane.col][Cursor_pane.row]
    if pane and pane.editable then
      edit.quit(pane)
    end
  end

function run.settings()

function settings()

  local filename = Editor_state.filename
  if filename:sub(1,1) ~= '/' then
    filename = love.filesystem.getWorkingDirectory()..'/'..filename  -- '/' should work even on Windows

  local column_names = {}
  for _,column in ipairs(Surface) do
    table.insert(column_names, column.name)

    font_height=Editor_state.font_height,
    filename=filename,
    screen_top=Editor_state.screen_top1, cursor=Editor_state.cursor1

    font_height=Font_height,
    column_width=Display_settings.column_width,
    surface_x=Display_settings.x,
    surface_y=Display_settings.y,
    cursor_col=Cursor_pane.col,
    cursor_row=Cursor_pane.row,
    columns=column_names,

--?   print('app mouse pressed', x,y)

  return edit.mouse_pressed(Editor_state, x,y, mouse_button)

  clear_selections()
  if Display_settings.mode == 'normal' or Display_settings.mode == 'search' or Display_settings.mode == 'search_all' or Display_settings.mode == 'searching_all' then
    mouse_pressed_in_normal_mode(x,y, mouse_button)
  elseif Display_settings.mode == 'maximize' then
    if Cursor_pane.col >= 1 then
      local pane = Surface[Cursor_pane.col][Cursor_pane.row]
      if pane then
        edit.mouse_pressed(pane, x,y, mouse_button)
      end
    end
  else
    print(Display_settings.mode)
    assert(false)
  end
end
function clear_selections()
  for _,column in ipairs(Surface) do
    for _,pane in ipairs(column) do
      pane.selection1 = {}
    end
  end
end
function mouse_pressed_in_normal_mode(x,y, mouse_button)
  Pan = {}
  if y < Header_height then
    -- column headers currently not interactable
    return
  end
  local sx,sy = to_surface(x,y)
  if in_pane(x,y) then
--?     print('click on pane')
    Cursor_pane = to_pane(sx,sy)
    if Cursor_pane.col >= 1 then
      local pane = Surface[Cursor_pane.col][Cursor_pane.row]
      if pane then
        edit.mouse_pressed(pane, x,y, mouse_button)
        pane._height = nil
      end
    end
  else
    Pan = {x=sx, y=sy}
  end

--?   print('app mouse released')

  return edit.mouse_released(Editor_state, x,y, mouse_button)

  if Cursor_pane.col >= 1 then
    edit.mouse_released(Surface[Cursor_pane.col][Cursor_pane.row], x,y, mouse_button)
  end
  Pan = {}

  return edit.textinput(Editor_state, t)

--?   print('textinput', t)
  -- hotkeys operating on the cursor pane
  if Display_settings.show_palette then
    Display_settings.palette_command = Display_settings.palette_command..t
    Display_settings.palette_command_text = App.newText(love.graphics.getFont(), Display_settings.palette_command)
    Display_settings.palette_alternative_index = 1
    Display_settings.palette_candidates = candidates()
  elseif Display_settings.mode == 'normal' then
    if Cursor_pane.col >= 1 then
      local pane = Surface[Cursor_pane.col][Cursor_pane.row]
      if pane then
        if not pane.editable then
          -- global hotkeys for normal mode
          if t == 'X' then
            command.wider_columns()
            return
          elseif t == 'x' then
            command.narrower_columns()
            return
          end
          -- send keys to the current pane
        else
          if pane.cursor_x >= 0 and pane.cursor_x < App.screen.width then
            if pane.cursor_y >= Header_height and pane.cursor_y < App.screen.height then
--?               print(('%s typed in editor pane'):format(t))
              local old_top = {line=pane.screen_top1.line, pos=pane.screen_top1.pos}
              edit.textinput(pane, t)
              maybe_update_screen_top_of_cursor_pane(pane, old_top)
              pane._height = nil
              plan_draw()
            end
          end
        end
      end
    end
  elseif Display_settings.mode == 'search' then
--?     print('insert', t)
    Display_settings.search_term = Display_settings.search_term..t
    Display_settings.search_text = nil
    -- reset search state
    clear_selections()
    Display_settings.x = Display_settings.search_backup_x
    Display_settings.y = Display_settings.search_backup_y
    Cursor_pane = Display_settings.search_backup_cursor_pane
    -- search again
    search_next()
    bring_cursor_of_cursor_pane_in_view('down')
    Surface.cursor_on_screen_check = true
    plan_draw()
  elseif Display_settings.mode == 'search_all' then
    Display_settings.search_all_query = Display_settings.search_all_query..t
    Display_settings.search_all_query_text = nil
  elseif Display_settings.mode == 'searching_all' then
    Display_settings.mode = 'normal'
    Display_settings.search_all_query_text = nil
  elseif Display_settings.mode == 'maximize' then
    if Cursor_pane.col >= 1 then
      local pane = Surface[Cursor_pane.col][Cursor_pane.row]
      if pane then
        if pane.editable then
          edit.textinput(pane, t)
        end
      end
    end
  else
    print(Display_settings.mode)
    assert(false)
  end

--?   print('keychord press', chord)

  return edit.keychord_pressed(Editor_state, chord, key)

  -- global hotkeys
  if chord == 'C-=' then
    update_font_settings(Font_height+2)
  elseif chord == 'C--' then
    update_font_settings(Font_height-2)
  elseif chord == 'C-0' then
    update_font_settings(20)
  -- mode-specific hotkeys
  elseif Display_settings.show_palette then
    keychord_pressed_on_command_palette(chord, key)
  elseif Display_settings.mode == 'normal' then
    if chord == 'C-return' then
      Display_settings.show_palette = true
      Display_settings.palette_candidates = candidates()
    elseif chord == 'C-f' then
      command.commence_find_on_surface()
    elseif Cursor_pane.col >= 1 then
      local pane = Surface[Cursor_pane.col][Cursor_pane.row]
      if pane and pane.editable then
        keychord_pressed_on_editable_pane(pane, chord, key)
      else
        keychord_pressed_in_normal_mode_with_immutable_pane(pane, chord, key)
      end
      -- editable cursor pane will have already updated its screen_top, so don't clobber it here
      plan_draw{ignore_editable_cursor_pane=true}
    end
  elseif Display_settings.mode == 'search' then
    keychord_pressed_in_search_mode(chord, key)
  elseif Display_settings.mode == 'search_all' then
    keychord_pressed_in_search_all_mode(chord, key)
  elseif Display_settings.mode == 'searching_all' then
    interrupt_search_all()
  elseif Display_settings.mode == 'maximize' then
    if chord == 'C-return' then
      Display_settings.show_palette = true
      Display_settings.palette_candidates = candidates()
    else
      keychord_pressed_in_maximize_mode(chord, key)
    end
  else
    print(Display_settings.mode)
    assert(false)
  end
end
function update_font_settings(font_height)
  local column_width_in_ems = Display_settings.column_width / App.width(Em)
  Font_height = font_height
  love.graphics.setFont(love.graphics.newFont(Font_height))
  Line_height = math.floor(font_height*1.3)
  Em = App.newText(love.graphics.getFont(), 'm')
  Display_settings.column_width = column_width_in_ems*App.width(Em)
  for _,column in ipairs(Surface) do
    for _,pane in ipairs(column) do
      pane.font_height = Font_height
      pane.line_height = Line_height
      pane.em = Em
      pane.left = 0
      pane.right = Display_settings.column_width
    end
  end
  clear_all_pane_heights()
  plan_draw()
end
-- Scan all panes, while delegating as much work as possible to lines.love search.
-- * Text.search_next in lines.love scans from cursor while wrapping around
--   within the pane, so we need to work around that.
-- * Each pane's search_term field influences whether the search term at
--   cursor is highlighted, so we need to manage that as well. At any moment
--   we want the search_term and search_text to be set for at most a single
--   pane.
--
-- Side-effect: we perturb the cursor of panes as we scan them.
function search_next()
  if Cursor_pane.col < 1 then return end
  clear_all_search_terms()
  local pane = Surface[Cursor_pane.col][Cursor_pane.row]
  if pane == nil then
    return
  end
--?   print('search next', Cursor_pane.col, Cursor_pane.row, pane.cursor1.line, pane.cursor1.pos)
  local old_cursor_in_cursor_pane = {line=pane.cursor1.line, pos=pane.cursor1.pos}
  -- scan current pane down from cursor
  if search_next_in_pane(Surface[Cursor_pane.col][Cursor_pane.row]) then
--?     print('found in same pane', pane.cursor1.line, pane.cursor1.pos)
    return
  end
  pane.cursor1 = old_cursor_in_cursor_pane
  -- scan current column down from current pane
  for current_pane_index=Cursor_pane.row+1,#Surface[Cursor_pane.col] do
    local pane = Surface[Cursor_pane.col][current_pane_index]
    pane.cursor1 = {line=1, pos=1}
    edit.fixup_cursor(pane)
    pane.screen_top1 = {line=1, pos=1}
    if search_next_in_pane(pane) then
      Cursor_pane.row = current_pane_index
--?       print('found in same column', Cursor_pane.col, Cursor_pane.row, pane.cursor1.line, pane.cursor1.pos)
      return
    end
  end
  local current_column_index = 1 + Cursor_pane.col%#Surface  -- (i+1)%#Surface in the presence of 1-indexing
  -- scan columns past current, looping around
  while true do
    for current_pane_index,pane in ipairs(Surface[current_column_index]) do
      pane.cursor1 = {line=1, pos=1}
      edit.fixup_cursor(pane)
      pane.screen_top1 = {line=1, pos=1}
      if search_next_in_pane(pane) then
        Cursor_pane = {col=current_column_index, row=current_pane_index}
--?         print('found', Cursor_pane.col, Cursor_pane.row, pane.cursor1.line, pane.cursor1.pos)
        return
      end
    end
    -- loop update
    current_column_index = 1 + current_column_index%#Surface  -- i = (i+1)%#Surface in the presence of 1-indexing
    -- termination check
    if current_column_index == Cursor_pane.col then
      break
    end
  end
  -- scan current column until current pane
  for current_pane_index=1,Cursor_pane.row-1 do
    if search_next_in_pane(Surface[Cursor_pane.col][current_pane_index]) then
      Cursor_pane.row = current_pane_index
--?       print('found in same column', Cursor_pane.col, Cursor_pane.row, pane.cursor1.line, pane.cursor1.pos)
      return
    end
  end
  -- finally, scan the cursor pane until the cursor
  local pane = Surface[Cursor_pane.col][Cursor_pane.row]
  local old_cursor = pane.cursor1
  pane.cursor1 = {line=1, pos=1}
  edit.fixup_cursor(pane)
  pane.screen_top1 = {line=1, pos=1}
  if search_next_in_pane(pane) then
    if Text.lt1(pane.cursor1, old_cursor) then
      return
    end
  end
  -- nothing found
  pane.cursor1 = old_cursor_in_cursor_pane
end
-- returns whether it found an occurrence
function search_next_in_pane(pane)
  pane.search_term = Display_settings.search_term
  pane.search_text = Display_settings.search_text
  pane.search_backup = {cursor={line=pane.cursor1.line, pos=pane.cursor1.pos}, screen_top={line=pane.screen_top1.line, pos=pane.screen_top1.pos}}
  for i=1,#pane.lines do
    if pane.line_cache[i] == nil then
      pane.line_cache[i] = {}
    end
  end
  if Text.search_next(pane) then
    if Text.le1(pane.search_backup.cursor, pane.cursor1) then
      -- select this occurrence
      return true
    end
    -- Otherwise cursor wrapped around. Skip this pane.
  end
  -- Clean up this pane before moving on to the next one.
  pane.search_term = nil
  pane.search_text = nil
  pane.cursor1.line = pane.search_backup.cursor.line
  pane.cursor1.pos = pane.search_backup.cursor.pos
  pane.screen_top1.line = pane.search_backup.screen_top.line
  pane.screen_top1.pos = pane.search_backup.screen_top.pos
  pane.search_backup = nil
end
-- Scan all panes, while delegating as much work as possible to lines.love search.
function search_previous()
  if Cursor_pane.col < 1 then return end
  clear_all_search_terms()
  local pane = Surface[Cursor_pane.col][Cursor_pane.row]
  if pane == nil then
    return
  end
--?   print('search previous', Cursor_pane.col, Cursor_pane.row, pane.cursor1.line, pane.cursor1.pos)
  local old_cursor_in_cursor_pane = {line=pane.cursor1.line, pos=pane.cursor1.pos}
  -- scan current pane up from cursor
  if search_previous_in_pane(Surface[Cursor_pane.col][Cursor_pane.row]) then
--?     print('found in same pane', pane.cursor1.line, pane.cursor1.pos)
    return
  end
  pane.cursor1 = old_cursor_in_cursor_pane
  -- scan current column down from current pane
  for current_pane_index=Cursor_pane.row-1,1,-1 do
    local pane = Surface[Cursor_pane.col][current_pane_index]
    pane.cursor1 = edit.final_cursor(pane)
    if search_previous_in_pane(pane) then
      Cursor_pane.row = current_pane_index
--?       print('found in same column', Cursor_pane.col, Cursor_pane.row, pane.cursor1.line, pane.cursor1.pos)
      return
    end
  end
  local current_column_index = 1 + (Cursor_pane.col-2)%#Surface  -- (i-1)%#Surface in the presence of 1-indexing
  -- scan columns past current, looping around
  while true do
    for current_pane_index = #Surface[current_column_index],1,-1 do
      local pane = Surface[current_column_index][current_pane_index]
      pane.cursor1 = edit.final_cursor(pane)
      if search_previous_in_pane(pane) then
        Cursor_pane = {col=current_column_index, row=current_pane_index}
--?         print('found', Cursor_pane.col, Cursor_pane.row, pane.cursor1.line, pane.cursor1.pos)
        return
      end
    end
    -- loop update
    current_column_index = 1 + (current_column_index-2)%#Surface  -- i = (i-1)%#Surface in the presence of 1-indexing
    -- termination check
    if current_column_index == Cursor_pane.col then
      break
    end
  end
  -- scan current column from bottom current pane
  for current_pane_index=#Surface[Cursor_pane.col],Cursor_pane.row+1,-1 do
--?     print('same column', current_pane_index)
    if search_previous_in_pane(Surface[Cursor_pane.col][current_pane_index]) then
      Cursor_pane.row = current_pane_index
--?       print('found in same column', Cursor_pane.col, Cursor_pane.row, pane.cursor1.line, pane.cursor1.pos)
      return
    end
  end
  -- finally, scan the cursor pane from bottom until cursor
  local pane = Surface[Cursor_pane.col][Cursor_pane.row]
  local old_cursor = pane.cursor1
  pane.cursor1 = edit.final_cursor(pane)
  if search_previous_in_pane(pane) then
    if Text.lt1(old_cursor, pane.cursor1) then
      return
    end
  end
  -- nothing found
  pane.cursor1 = old_cursor_in_cursor_pane
end
-- returns whether it found an occurrence
function search_previous_in_pane(pane)
  pane.search_term = Display_settings.search_term
  pane.search_text = Display_settings.search_text
  pane.search_backup = {cursor={line=pane.cursor1.line, pos=pane.cursor1.pos}, screen_top={line=pane.screen_top1.line, pos=pane.screen_top1.pos}}
  for i=1,#pane.lines do
    if pane.line_cache[i] == nil then
      pane.line_cache[i] = {}
    end
  end
  if Text.search_previous(pane) then
    if Text.lt1(pane.cursor1, pane.search_backup.cursor) then
      -- select this occurrence
      return true
    end
    -- Otherwise cursor wrapped around. Skip this pane.
  end
  -- Clean up this pane before moving on to the previous one.
  pane.search_term = nil
  pane.search_text = nil
  pane.cursor1.line = pane.search_backup.cursor.line
  pane.cursor1.pos = pane.search_backup.cursor.pos
  pane.screen_top1.line = pane.search_backup.screen_top.line
  pane.screen_top1.pos = pane.search_backup.screen_top.pos
  pane.search_backup = nil
end
function bring_cursor_of_cursor_pane_in_view(dir)
  if Cursor_pane.col < 1 then
    return
  end
  local pane = Surface[Cursor_pane.col][Cursor_pane.row]
  if pane == nil then
    return
  end
--?   print('viewport before', Display_settings.x, Display_settings.y)
  local left_edge_sx = left_edge_sx(Cursor_pane.col)
  local cursor_sx = left_edge_sx + Text.x_of_schema1(pane, pane.cursor1)
  local vertically_ok = cursor_sx > Display_settings.x and cursor_sx < Display_settings.x + App.screen.width - App.width(Em)
--?   print(y_of_schema1(pane, pane.cursor1))
--?   print('viewport starts at', Display_settings.y)
--?   print('pane starts at', up_edge_sy(Cursor_pane.col, Cursor_pane.row))
--?   print('cursor line contains ^'..pane.lines[pane.cursor1.line].data..'$')
--?   print('cursor is at', y_of_schema1(pane, pane.cursor1), 'from top of pane')
  local cursor_sy = up_edge_sy(Cursor_pane.col, Cursor_pane.row) + y_of_schema1(pane, pane.cursor1)
--?   print('cursor is at', cursor_sy)
  local horizontally_ok = cursor_sy > Display_settings.y and cursor_sy < Display_settings.y + App.screen.height - Header_height - 2*Line_height  -- account for search bar along the bottom
  if vertically_ok and horizontally_ok then
    return
  end
  if dir == 'up' then
    if not vertically_ok then
      Display_settings.x = left_edge_sx - Margin_left - Padding_horizontal
    end
    if not horizontally_ok then
      Display_settings.y = cursor_sy - 3*Line_height
    end
  else
    assert(dir == 'down')
    if not vertically_ok then
      Display_settings.x = left_edge_sx + Display_settings.column_width + Margin_right + Padding_horizontal - App.screen.width
    end
    if not horizontally_ok then
--?       print('cursor used to be at ', cursor_sy - Display_settings.y)
--?       print('subtract', App.screen.height, App.screen.height-Header_height)
      Display_settings.y = cursor_sy + Text.search_bar_height(pane) - (App.screen.height - Header_height)
      -- Bah, temporarily giving up on debugging.
      Display_settings.y = Display_settings.y + Line_height
--?       print('=>', Display_settings.y)
--?       print('cursor now at ', cursor_sy - Display_settings.y)
--?       print('viewport height', App.screen.height)
--?       print('cursor row starts', App.screen.height - (cursor_sy-Display_settings.y), 'px above bottom of viewport')  -- totally wrong
      assert(App.screen.height - (cursor_sy-Display_settings.y) > 1.5*Line_height)
    end
  end
--?   print('viewport before clamp', Display_settings.x, Display_settings.y)
  Display_settings.x = math.max(Display_settings.x, 0)
  Display_settings.y = math.max(Display_settings.y, 0)
--?   print('viewport now', Display_settings.x, Display_settings.y)
end
function clear_all_search_terms()
  for col,column in ipairs(Surface) do
    for row,pane in ipairs(column) do
      pane.search_term = nil
      pane.search_text = nil
    end
  end
end
function keychord_pressed_in_maximize_mode(chord, key)
  if Cursor_pane.col < 1 then
    print('no current note to edit')
    return
  end
  local pane = Surface[Cursor_pane.col][Cursor_pane.row]
  if pane == nil then
    print('no current note to edit')
    return
  end
  if pane.editable then
    if chord == 'C-e' then
      command.exit_editing()
    else
      edit.keychord_pressed(pane, chord, key)
    end
  else
    if chord == 'C-e' then
      command.edit_note()
    elseif chord == 'C-c' then
      edit.keychord_pressed(pane, chord, key)
    end
  end
end
function keychord_pressed_on_editable_pane(pane, chord, key)
  -- ignore if cursor is not visible on screen
  if pane.cursor_x == nil then
    assert(pane.cursor_y == nil)
    panning_keychord_pressed(chord, key)
    return
  end
  if chord == 'C-e' then
    command.exit_editing()
  else
--?     print(('%s pressed in editor pane'):format(chord))
--?     print(pane.cursor_x, pane.cursor_y)
    local old_top = {line=pane.screen_top1.line, pos=pane.screen_top1.pos}
    edit.keychord_pressed(pane, chord, key)
    maybe_update_screen_top_of_cursor_pane(pane, old_top)
    pane._height = nil
  end
end
function maybe_update_screen_top_of_cursor_pane(pane, old_top)
  local cursor_sy = up_edge_sy(Cursor_pane.col, Cursor_pane.row) + y_of_schema1(pane, pane.cursor1)
--?   print(eq(old_top, pane.screen_top1), eq(old_top, {line=1, pos=1}), pane.top, cursor_sy, cursor_sy - Display_settings.y, App.screen.height - Header_height - Line_height)
  if not eq(old_top, pane.screen_top1) and eq(old_top, {line=1, pos=1}) and pane.top > Header_height and cursor_sy - Display_settings.y > App.screen.height - Header_height  - Line_height then
    -- pan the surface instead of scrolling within the pane
    pane.screen_top1 = old_top
    bring_cursor_of_cursor_pane_in_view('down')
    Surface.cursor_on_screen_check = true  -- cursor was on screen before keystroke, so it should remain on screen after
    return
  end
  Editable_cursor_pane_updated_screen_top = not eq(old_top, pane.screen_top1)
  if Editable_cursor_pane_updated_screen_top then
--?     print(('screen top changed from (%d,%d) to (%d,%d)'):format(old_top.line, old_top.pos, pane.screen_top1.line, pane.screen_top1.pos))
--?     print('updating viewport based on screen top')
--?     print('from', Display_settings.y, y_of_schema1(pane, pane.screen_top1))
    Display_settings.y = up_edge_sy(Cursor_pane.col, Cursor_pane.row) + y_of_schema1(pane, pane.screen_top1)
--?     print('to', Display_settings.y)
    Surface.cursor_on_screen_check = true  -- cursor was on screen before keystroke, so it should remain on screen after
  end
end
function keychord_pressed_in_normal_mode_with_immutable_pane(pane, chord, key)
  -- return if no part of cursor pane is visible
  local left_sx = left_edge_sx(Cursor_pane.col)
  if not should_show_column(left_sx) then
    panning_keychord_pressed(chord, key)
    return
  end
  local up_sy = up_edge_sy(Cursor_pane.col, Cursor_pane.row)
  if not should_show_pane(pane, up_sy) then
    panning_keychord_pressed(chord, key)
    return
  end
  if chord == 'C-e' then
    command.edit_note()
  elseif chord == 'C-c' then
    edit.keychord_pressed(pane, chord, key)
  else
    panning_keychord_pressed(chord, key)
  end
end
-- y offset of a given (line, pos)
function y_of_schema1(pane, loc)
--?   print(('updating viewport y; cursor pane starts at %d; screen top is at %d,%d'):format(result, loc.line, loc.pos))
  local result = 0
  if pane.title then
    result = result + 5+Line_height+5
  end
  result = result + Margin_above
  if loc.line == 1 and loc.pos == 1 then
    return result
  end
  for i=1,loc.line-1 do
--?   print('', 'd', i, result)
    Text.populate_screen_line_starting_pos(pane, i)
--?     print('', '', #pane.line_cache[i].screen_line_starting_pos, pane.left, pane.right)
    result = result + line_height(pane, i, pane.left, pane.right)
  end
  if pane.lines[loc.line].mode == 'text' then
    Text.populate_screen_line_starting_pos(pane, loc.line)
    for i,screen_line_starting_pos in ipairs(pane.line_cache[loc.line].screen_line_starting_pos) do
      if screen_line_starting_pos >= loc.pos then
        break
      end
      result = result + Line_height
    end
  end
--?   print(('viewport at %d'):format(result))
  return result
end
function keychord_pressed_in_search_mode(chord, key)
  if chord == 'escape' then
    Display_settings.mode = 'normal'
    clear_all_search_terms()
    clean_up_panes()
    -- go back to old viewport
--?     print('esc; exiting search mode')
    Display_settings.x = Display_settings.search_backup_x
    Display_settings.y = Display_settings.search_backup_y
    Cursor_pane = Display_settings.search_backup_cursor_pane
    -- don't forget search text
  elseif chord == 'return' then
    Display_settings.mode = 'normal'
    clear_all_search_terms()
    clean_up_panes()
    -- forget old viewport
--?     print('return; exiting search mode')
    Display_settings.search_backup_x = nil
    Display_settings.search_backup_y = nil
    Display_settings.search_backup_cursor_pane = nil
    -- don't forget search text
  elseif chord == 'backspace' then
    local len = utf8.len(Display_settings.search_term)
    local byte_offset = Text.offset(Display_settings.search_term, len)
    Display_settings.search_term = string.sub(Display_settings.search_term, 1, byte_offset-1)
    Display_settings.search_text = nil
    -- reset search state
    clear_selections()
    Display_settings.x = Display_settings.search_backup_x
    Display_settings.y = Display_settings.search_backup_y
    Cursor_pane = Display_settings.search_backup_cursor_pane
    -- search again
    search_next()
    bring_cursor_of_cursor_pane_in_view('down')
    Surface.cursor_on_screen_check = true
    plan_draw()
--?     print('backspace; search term is now', Display_settings.search_term)
  elseif chord == 'C-v' then
    Display_settings.search_term = Display_settings.search_term..App.getClipboardText()
    Display_settings.search_text = nil
    -- reset search state
    clear_selections()
    Display_settings.x = Display_settings.search_backup_x
    Display_settings.y = Display_settings.search_backup_y
    Cursor_pane = Display_settings.search_backup_cursor_pane
    -- search again
    search_next()
    bring_cursor_of_cursor_pane_in_view('down')
    Surface.cursor_on_screen_check = true
    plan_draw()
--?     print('paste; search term is now', Display_settings.search_term)
  elseif chord == 'up' then
    if Cursor_pane.col >= 1 then
      local pane = Surface[Cursor_pane.col][Cursor_pane.row]
      if pane then
        search_previous()
        bring_cursor_of_cursor_pane_in_view('up')
        Surface.cursor_on_screen_check = true
        plan_draw()
      end
    end
  elseif chord == 'down' then
    if Cursor_pane.col >= 1 then
      local pane = Surface[Cursor_pane.col][Cursor_pane.row]
      if pane then
        pane.cursor1.pos = pane.cursor1.pos+1
        search_next()
        bring_cursor_of_cursor_pane_in_view('down')
        Surface.cursor_on_screen_check = true
        plan_draw()
      end
    end
  -- things from normal mode we still want
  elseif chord == 'C-c' then
    if Cursor_pane.col >= 1 then
      local pane = Surface[Cursor_pane.col][Cursor_pane.row]
      if pane then
        edit.keychord_pressed(pane, chord, key)
      end
    end
  end
end
function keychord_pressed_in_search_all_mode(chord, key)
  if chord == 'escape' then
    Display_settings.mode = 'normal'
    -- don't forget search text
    Display_settings.search_all_state = nil
  elseif chord == 'return' then
    finalize_search_all_pane()
    add_search_all_pane_to_right_of_cursor()
    Display_settings.mode = 'searching_all'
    plan_draw()
  elseif chord == 'backspace' then
    local len = utf8.len(Display_settings.search_all_query)
    local byte_offset = Text.offset(Display_settings.search_all_query, len)
    Display_settings.search_all_query = string.sub(Display_settings.search_all_query, 1, byte_offset-1)
    Display_settings.search_all_query_text = nil
--?     print('backspace; search_all term is now', Display_settings.search_all_query)
  elseif chord == 'C-v' then
    Display_settings.search_all_query = Display_settings.search_all_query..App.getClipboardText()
    Display_settings.search_all_query_text = nil
--?     print('paste; search_all term is now', Display_settings.search_all_query)
  end
end
-- return (line, pos) of the screen line starting near a given y offset, and
--        y_offset remaining after the calculation
--          invariants:
--            - 0 <= y_offset <= Line_height if line is text
--            - let loc, y_offset = schema1_of_y(pane, y)
--              y - y_offset == y_of_schema1(pane, loc)
function schema1_of_y(pane, y)
  assert(y >= 0)
  local y_offset = y
  for i=1,#pane.lines do
--?     print('--', y_offset)
    Text.populate_screen_line_starting_pos(pane, i)
    local height = line_height(pane, i, pane.left, pane.right)
    if y_offset < height then
      local line = pane.lines[i]
      if line.mode ~= 'text' then
        return {line=i, pos=1}, y_offset
      else
        local nlines = math.floor(y_offset/pane.line_height)
--?         print(y_offset, pane.line_height, nlines)
        assert(nlines >= 0 and nlines < #pane.line_cache[i].screen_line_starting_pos)
        local pos = pane.line_cache[i].screen_line_starting_pos[nlines+1]  -- switch to 1-indexing
        y_offset = y_offset - nlines*pane.line_height
        return {line=i, pos=pos}, y_offset
      end
    end
    y_offset = y_offset - height
  end
  -- y is below the pane
  return {line=#pane.lines+1, pos=1}, y_offset
end
function line_height(State, line_index, left, right)
  local line = State.lines[line_index]
  local line_cache = State.line_cache[line_index]
  if line.mode == 'text' then
    return Line_height*#line_cache.screen_line_starting_pos
  else
    return Drawing.pixels(line.h, right-left) + Drawing_padding_height
  end
end
function stop_editing_all()
  local edit_count = 0
  for _,column in ipairs(Surface) do
    for _,pane in ipairs(column) do
      if pane.editable then
        stop_editing(pane)
        edit_count = edit_count+1
      end
    end
  end
  assert(edit_count <= 1)
end
function stop_editing(pane)
  edit.quit(pane)
  -- save symmetric links
  for rel,target in pairs(Cache[pane.id].links) do
    initialize_cache_if_necessary(target)
    save_links(target)
  end
  if Display_settings.mode ~= 'maximize' then
    refresh_panes(pane)
  end
  pane.editable = false
end
function panning_keychord_pressed(chord, key)
  if chord == 'up' then
    Display_settings.y = math.max(Display_settings.y - Pan_step, 0)
    local up_sy = up_edge_sy(Cursor_pane.col, Cursor_pane.row)
    local up_py = up_sy - Display_settings.y
    if up_py > 2/3*App.screen.height then
      Cursor_pane.row = math.min(#Surface[Cursor_pane.col], row(Cursor_pane.col, Display_settings.y + App.screen.height/3))
    end
  elseif chord == 'down' then
    local visible_column_max_y = most(column_height, visible_columns())
    if visible_column_max_y - Display_settings.y > App.screen.height/2 then
      Display_settings.y = Display_settings.y + Pan_step
    end
    local down_sx = down_edge_sx(Cursor_pane.col, Cursor_pane.row)
    local down_px = down_sx - Display_settings.y
    if down_px < App.screen.height/3 then
      Cursor_pane.row = math.min(#Surface[Cursor_pane.col], row(Cursor_pane.col, Display_settings.y + App.screen.height/3))
    end
  elseif chord == 'left' then
    Display_settings.x = math.max(Display_settings.x - Pan_step, 0)
    local left_sx = left_edge_sx(Cursor_pane.col)
    local left_px = left_sx - Display_settings.x
    if left_px > App.screen.width - Margin_right - Display_settings.column_width/2 then
      Cursor_pane.col = math.min(#Surface, col(Display_settings.x + App.screen.width - Margin_right - Display_settings.column_width/2))
      Cursor_pane.row = math.min(#Surface[Cursor_pane.col], Cursor_pane.row)
    end
  elseif chord == 'right' then
    if Display_settings.x < (#Surface-1) * (Padding_horizontal + Margin_left + Display_settings.column_width + Margin_right) then
      Display_settings.x = Display_settings.x + Pan_step
    end
    local right_sx = left_edge_sx(Cursor_pane.col) + Display_settings.column_width
    local right_px = right_sx - Display_settings.x
    if right_px < Margin_left + Display_settings.column_width/2 then
      Cursor_pane.col = math.min(#Surface, col(Display_settings.x + Margin_left + Display_settings.column_width/2))
      Cursor_pane.row = math.min(#Surface[Cursor_pane.col], Cursor_pane.row)
    end
  elseif chord == 'pageup' or chord == 'S-up' then
    Display_settings.y = math.max(Display_settings.y - App.screen.height + Line_height*2, 0)
    local up_sy = up_edge_sy(Cursor_pane.col, Cursor_pane.row)
    local up_py = up_sy - Display_settings.y
    if up_py > 2/3*App.screen.height then
      Cursor_pane.row = math.min(#Surface[Cursor_pane.col], row(Cursor_pane.col, Display_settings.y + App.screen.height/3))
    end
  elseif chord == 'pagedown' or chord == 'S-down' then
--?     print('pagedown')
    local visible_column_max_y = most(column_height, visible_columns())
    if visible_column_max_y - Display_settings.y > App.screen.height then
--?       print('updating viewport')
      Display_settings.y = Display_settings.y + App.screen.height - Line_height*2
    end
    local down_sx = down_edge_sx(Cursor_pane.col, Cursor_pane.row)
    local down_px = down_sx - Display_settings.y
    if down_px < App.screen.height/3 then
--?       print('updating row')
      Cursor_pane.row = math.min(#Surface[Cursor_pane.col], row(Cursor_pane.col, Display_settings.y + App.screen.height/3))
--?       print('=>', Cursor_pane.row)
    end
  elseif chord == 'S-left' then
    Display_settings.x = math.max(Display_settings.x - Margin_left - Display_settings.column_width - Margin_right - Padding_horizontal, 0)
    local left_sx = left_edge_sx(Cursor_pane.col)
    local left_px = left_sx - Display_settings.x
    if left_px > App.screen.width - Margin_right - Display_settings.column_width/2 then
      Cursor_pane.col = math.min(#Surface, col(Display_settings.x + App.screen.width - Margin_right - Display_settings.column_width/2))
      Cursor_pane.row = math.min(#Surface[Cursor_pane.col], Cursor_pane.row)
    end
  elseif chord == 'S-right' then
    if Display_settings.x < (#Surface-1) * (Padding_horizontal + Margin_left + Display_settings.column_width + Margin_right) then
      Display_settings.x = Display_settings.x + Margin_left + Display_settings.column_width + Margin_right + Padding_horizontal
      local right_sx = left_edge_sx(Cursor_pane.col) + Display_settings.column_width
      local right_px = right_sx - Display_settings.x
      if right_px < Margin_left + Display_settings.column_width/2 then
        Cursor_pane.col = math.min(#Surface, col(Display_settings.x + Margin_left + Display_settings.column_width/2))
        Cursor_pane.row = math.min(#Surface[Cursor_pane.col], Cursor_pane.row)
      end
    end
  elseif chord == 'C-down' then
    command.down_one_pane()
  elseif chord == 'C-up' then
    command.up_one_pane()
  elseif chord == 'C-end' then
    command.bottom_pane_of_column()
  elseif chord == 'C-home' then
    command.top_pane_of_column()
  end
--?   print('after', Cursor_pane.col, Cursor_pane.row)
end
function visible_columns()
  local result = {}
  local col = col(Display_settings.x)
  local x = left_edge_sx(col) - Display_settings.x
  while col <= #Surface do
    x = x + Padding_horizontal
    table.insert(result, col)
    x = x + Margin_left + Display_settings.column_width + Margin_right + Padding_horizontal
    if x > App.screen.width then
      break
    end
    col = col+1
  end
  return result
end
function refresh_panes(pane)
--?   print('refreshing')
  Cache[pane.id].lines = pane.lines
  for x,col in ipairs(Surface) do
    for y,p in ipairs(col) do
      if p.id == pane.id then
--?         print(x,y)
        p.lines = pane.lines
        p._height = nil
        Text.redraw_all(p)
      end
    end
  end
  plan_draw()

function clean_up_panes()
  for x,col in ipairs(Surface) do
    for y,p in ipairs(col) do
      p._height = nil
      Text.redraw_all(p)
    end
  end
  plan_draw()
end

--?   print('key release', key)

  return edit.key_released(Editor_state, key, scancode)

  if Cursor_pane.col < 1 then
    return
  end
  local pane = Surface[Cursor_pane.col][Cursor_pane.row]
  if pane and pane.editable then
    edit.key_released(pane, key, scancode)
  end
end
function clear_all_pane_heights()
  Text_cache = {}
  for _,column in ipairs(Surface) do
    for _,pane in ipairs(column) do
      pane._height = nil
    end
  end
end
-- convert x surface pixel coordinate into column index
function col(x)
  return 1 + math.floor(x / (Padding_horizontal + Display_settings.column_width))
end
-- col is 1-indexed
-- returns x surface pixel coordinate of left edge of column col
function left_edge_sx(col)
  return (col-1)*(Padding_horizontal + Margin_left + Display_settings.column_width + Margin_right) + Padding_horizontal + Margin_left
end
function row(col, y)
  local sy = Padding_vertical
  for i,pane in ipairs(Surface[col]) do
--?     print('', i, y, sy, next_sy)
    local next_sy = sy + Margin_above + height(pane) + Margin_below + Padding_vertical
    if next_sy > y then
      return i
    end
    sy = next_sy
  end
  return #Surface[col]
end
function up_edge_sy(col, row)
  local result = Padding_vertical
  for i=1,row-1 do
    local pane = Surface[col][i]
    result = result + Margin_above + height(pane) + Margin_below + Padding_vertical
  end
  return result
end
function down_edge_sx(col, row)
  local result = Padding_vertical
  for i=1,row do
    local pane = Surface[col][i]
    result = result + Margin_above + height(pane) + Margin_below + Padding_vertical
  end
  return result - Padding_vertical
end
function column_height(col)
  local result = Padding_vertical
  for pane_index, pane in ipairs(Surface[col]) do
    result = result + Margin_above + height(pane) + Margin_below + Padding_vertical
  end
  return result
end
function most(f, arr)
  local result = nil
  for _,x in ipairs(arr) do
    local curr = f(x)
    if result == nil or result < curr then
      result = curr
    end
  end
  return result

end
function num_panes()
  local result = 0
  for _,column in ipairs(Surface) do
    result = result+#column
  end
  return result

require 'commands'

Column_header_color = {r=0.7, g=0.7, b=0.7}
Pane_title_color = {r=0.5, g=0.5, b=0.5}
Pane_title_background_color = {r=0, g=0, b=0, a=0.1}
Pane_background_color = {r=0.7, g=0.7, b=0.7, a=0.1}
Grab_background_color = {r=0.7, g=0.7, b=0.7}
Cursor_pane_background_color = {r=0.7, g=0.7, b=0, a=0.1}
Menu_background_color = {r=0.6, g=0.8, b=0.6}
Menu_border_color = {r=0.6, g=0.7, b=0.6}
Menu_command_color = {r=0.2, g=0.2, b=0.2}
Command_palette_background_color = Menu_background_color
Command_palette_border_color = Menu_border_color
Command_palette_command_color = Menu_command_color
Command_palette_alternatives_background_color = Menu_background_color
Command_palette_highlighted_alternative_background_color = {r=0.5, g=0.7, b=0.3}
Command_palette_alternatives_color = {r=0.3, g=0.5, b=0.3}
Crosslink_color={r=0, g=0.7, b=0.7}
Crosslink_background_color={r=0, g=0, b=0, a=0.1}
-- The note-taking app has a few differences with the baseline editor it's
-- forked from:
--  - most notes are read-only
--  - the editor operates entirely in viewport-relative coordinates; 0,0 is
--    the top-left corner of the window. However the note-taking app in
--    read-only mode largely operates in absolute coordinates; a potentially
--    large 2D space that the window is just a peephole into.
--
-- We'll use the rendering logic in the editor, but only use its event loop
-- when a window is being edited (there can only be one all over the entire
-- surface)
--
-- Most of the time the viewport affects each pane's top and screen_top. An
-- exception is when you're editing a pane and you scroll the cursor inside
-- it. In that case we want to affect the viewport (for all panes) based on
-- the editable pane's screen_top.

  -- stuff we paginate over is organized as follows:
  --  - there are multiple columns
  --  - each column contains panes
  --  - each pane contains editor state as in lines.love
  Surface = {}
  -- The surface may show the same file in multiple panes. This cache tries to
  -- share data between such aliases:
  --   line contents when panes are not editable (editable panes can diverge)
  --   links between files (never in Surface, can never diverge between panes)
  Cache = {}
  -- LÖVE renders N frames per second like any game engine, but we don't
  -- really need that. The only thing that animates in this app is the cursor.
  --
  -- Until I fix that, the architecture of this app will be to plan what to
  -- draw only when something changes. That way we minimize the amount of
  -- computation/power wasted on each of those frames.
  Panes_to_draw = {}  -- array of panes from surface
  Column_headers_to_draw = {}  -- strings with x coordinates

  Display_settings = {
    mode='normal',
      -- valid modes:
      --   normal (show full surface)
      --   maximize (show just a single note; focus mode)
      --   search (notes currently on surface)
      --   search_all (notes in directory)
      --   searching_all (search in progress)
    x=0, y=0,  -- <==== Top-left corner of the viewport into the surface
    column_width=400,
    show_palette=false,
    palette_command='',
    palette_command_text=App.newText(love.graphics.getFont(), ''),
    palette_alternative_index=1, palette_candidates=nil,
    search_term='', search_text=nil,
    search_backup_x=nil, search_backup_y=nil, search_backup_cursor_pane=nil,
    search_all_query=nil, search_all_query_text=nil, search_all_terms=nil,
    search_all_progress_indicator=nil,
    search_all_pane=nil, search_all_state=nil,
  }
  -- display settings that are constants
  Font_height = 20
  Line_height = math.floor(Font_height*1.3)
  -- space saved for headers
  -- this is only on the screen, not used on the surface itself
  Menu_status_bar_height = 5 + Line_height + 5
--?   print('menu height', Menu_status_bar_height)
  Column_header_height = 5 + Line_height + 5
--?   print('column header height', Column_header_height)
  Header_height = Menu_status_bar_height + Column_header_height
  -- padding is the space between panes on the surface
  Padding_vertical = 20  -- space between panes
  Padding_horizontal = 20
  -- margins are extra space inside the borders of panes on the surface
  Margin_above = 10
  Margin_below = 10
  Pan_step = 10
  Pan = {}
  Cursor_pane = {col=0, row=1}  -- surface column and row index, along with some cached data
  -- occasional secondary cursor
  Grab_pane = nil
  -- where we store our notes (pane id is also a relative path under there)
  Directory = 'data/'
  Settings_file = 'config'
  -- This little bit of state ensures we don't mess with a pane's screen_top
  -- if it was just used to update the viewport.
  Editable_cursor_pane_updated_screen_top = false
  -- a few text objects we can avoid recomputing unless the font changes
  Text_cache = {}

  -- a few text objects we can avoid recomputing unless the font changes
  Text_cache = {}

  Editor_state = nil  -- not used outside editor tests

-- but some files we want to only load sometimes
function App.load()
  if love.filesystem.getInfo('config') then
    Settings = json.decode(love.filesystem.read('config'))
    Current_app = Settings.current_app
  end

  if Current_app == nil then
    Current_app = 'run'
  end

  assert(#arg <= 1)
  if #arg > 0 then
    Directory = 'data.'..arg[1]..'/'
    Settings_file = 'config.'..arg[1]

  if Current_app == 'run' then
    load_file_from_source_or_save_directory('file.lua')
    load_file_from_source_or_save_directory('run.lua')
      load_file_from_source_or_save_directory('commands.lua')
      load_file_from_source_or_save_directory('edit.lua')
      load_file_from_source_or_save_directory('text.lua')
        load_file_from_source_or_save_directory('search.lua')
        load_file_from_source_or_save_directory('select.lua')
        load_file_from_source_or_save_directory('undo.lua')
      load_file_from_source_or_save_directory('icons.lua')
      load_file_from_source_or_save_directory('text_tests.lua')
    load_file_from_source_or_save_directory('run_tests.lua')
    load_file_from_source_or_save_directory('drawing.lua')
      load_file_from_source_or_save_directory('geom.lua')
      load_file_from_source_or_save_directory('help.lua')
    load_file_from_source_or_save_directory('drawing_tests.lua')
  else
    load_file_from_source_or_save_directory('source_file.lua')
    load_file_from_source_or_save_directory('source.lua')
      load_file_from_source_or_save_directory('source_commands.lua')
      load_file_from_source_or_save_directory('source_edit.lua')
      load_file_from_source_or_save_directory('log_browser.lua')
      load_file_from_source_or_save_directory('source_text.lua')
        load_file_from_source_or_save_directory('search.lua')
        load_file_from_source_or_save_directory('select.lua')
        load_file_from_source_or_save_directory('source_undo.lua')
        load_file_from_source_or_save_directory('colorize.lua')
      load_file_from_source_or_save_directory('source_text_tests.lua')
    load_file_from_source_or_save_directory('source_tests.lua')

end

  love.window.setTitle('pensieve.love')
  print('reading notes from '..love.filesystem.getSaveDirectory()..'/'..Directory)
  print('put any notes there (and make frequent backups)')
-- but some files we want to only load sometimes
function App.load()
  if love.filesystem.getInfo(Settings_file) then
    load_settings()

function App.initialize_globals()
  if Current_app == 'run' then
    run.initialize_globals()
  elseif Current_app == 'source' then
    source.initialize_globals()

    initialize_default_settings()

    assert(false, 'unknown app "'..Current_app..'"')

  if Display_settings.column_width > App.screen.width - Padding_horizontal - Margin_left - Margin_right - Padding_horizontal then
    Display_settings.column_width = math.max(200, App.screen.width - Padding_horizontal - Margin_left - Margin_right - Padding_horizontal)

  -- for hysteresis in a few places
  Last_focus_time = App.getTime()  -- https://love2d.org/forums/viewtopic.php?p=249700
  Last_resize_time = App.getTime()
end
function App.initialize(arg)
  if Current_app == 'run' then
    run.initialize(arg)
  elseif Current_app == 'source' then
    source.initialize(arg)
  else
    assert(false, 'unknown app "'..Current_app..'"')

    Settings = json.decode(love.filesystem.read('config'))
    Current_app = Settings.current_app
  if Current_app == nil then
    Current_app = 'run'

end

function App.resize(w, h)
  App.screen.width, App.screen.height = w, h
--?   print('resize:', App.screen.width, App.screen.height)
  Last_resize_time = App.getTime()
  plan_draw()

function App.resize(w,h)
  if Current_app == 'run' then
    if run.resize then run.resize(w,h) end
  elseif Current_app == 'source' then
    if source.resize then source.resize(w,h) end
  else
    assert(false, 'unknown app "'..Current_app..'"')
  end
  Last_resize_time = App.getTime()
function App.filedropped(file)
  if Current_app == 'run' then
    if run.filedropped then run.filedropped(file) end
  elseif Current_app == 'source' then
    if source.filedropped then source.filedropped(file) end
  else
    assert(false, 'unknown app "'..Current_app..'"')
  end

end

function initialize_cache_if_necessary(id)
  if Cache[id] then return end
--?   print('init:', id)
  Cache[id] = {id=id, filename=Directory..id, left=0, right=Display_settings.column_width, lines={}, line_cache={}}
  load_from_disk(Cache[id])
  Cache[id].links = load_links(id)

function App.focus(in_focus)
  if in_focus then
    Last_focus_time = App.getTime()
  if Current_app == 'run' then
    if run.focus then run.focus(in_focus) end
  elseif Current_app == 'source' then
    if source.focus then source.focus(in_focus) end
  else
    assert(false, 'unknown app "'..Current_app..'"')
  end
  --
  if Current_app == 'run' then
    run.update(dt)
  elseif Current_app == 'source' then
    source.update(dt)
  else
    assert(false, 'unknown app "'..Current_app..'"')

  end

end
function App.draw()
  if Current_app == 'run' then
    run.draw()
  elseif Current_app == 'source' then
    source.draw()
  else
    assert(false, 'unknown app "'..Current_app..'"')
  end
end
function App.update(dt)
  -- some hysteresis while resizing
  if App.getTime() < Last_resize_time + 0.1 then
    return
  end

  end
end
function load_pane(id)
--?   print('load pane from file', id)
  initialize_cache_if_necessary(id)
  local result = edit.initialize_state(0, 0, math.min(Display_settings.column_width, App.screen.width-Margin_right), Font_height, Line_height)
  result.id = id
  result.filename = Directory..id
  result.lines = Cache[id].lines
  result.line_cache = deepcopy(Cache[id].line_cache)  -- should be tiny; deepcopy is just to eliminate any chance of aliasing
  result.font_height = Font_height
  result.line_height = Line_height
  result.em = Em
  result.editable = false
  edit.fixup_cursor(result)
  return result
end
function height(pane)
  if pane._height == nil then
    refresh_pane_height(pane)

  return pane._height

-- keep the structure of this function sync'd with plan_draw
function refresh_pane_height(pane)
--?   print('refresh pane height')
  local y = 0
  if pane.title then
    y = y + 5+Line_height+5
  end
  for i=1,#pane.lines do
    local line = pane.lines[i]
    if pane.line_cache[i] == nil then
      pane.line_cache[i] = {}
    end
    if line.mode == 'text' then
      pane.line_cache[i].fragments = nil
      pane.line_cache[i].screen_line_starting_pos = nil
      Text.compute_fragments(pane, i)
      Text.populate_screen_line_starting_pos(pane, i)
      y = y + Line_height*#pane.line_cache[i].screen_line_starting_pos
      Text.clear_screen_line_cache(pane, i)
    elseif line.mode == 'drawing' then
      -- nothing
      y = y + Drawing.pixels(line.h, Display_settings.column_width) + Drawing_padding_height
    else
      print(line.mode)
      assert(false)
    end
  end
  if Cache[pane.id].links and not empty(Cache[pane.id].links) then
    y = y + 5+Line_height+5  -- for crosslinks
  end
  pane._height = y

function App.keychord_pressed(chord, key)
  -- ignore events for some time after window in focus (mostly alt-tab)
  if App.getTime() < Last_focus_time + 0.01 then
    return
  end
  --

  if chord == 'C-e' then

  if chord == 'C-u' then

      Settings = run.settings()

      Settings = settings()

-- titles are optional and so affect the height of the pane
function add_title(pane, title)
  pane.title = title
  pane._height = nil
end
-- keep the structure of this function sync'd with refresh_pane_height
function plan_draw(options)
--?   print('update pane bounds')
--?   print(#Surface, 'columns;', num_panes(), 'panes')
  Panes_to_draw = {}
  Column_headers_to_draw = {}
  local sx = Padding_horizontal + Margin_left
  for column_index, column in ipairs(Surface) do
    if should_show_column(sx) then
      table.insert(Column_headers_to_draw, {name=('%d. %s'):format(column_index, column.name), x = sx-Display_settings.x})
      local sy = Padding_vertical
      for pane_index, pane in ipairs(column) do
        if sy > Display_settings.y + App.screen.height - Header_height then
          break
        end
--?         print('bounds:', column_index, pane_index, sx,sy)
        if should_show_pane(pane, sy) then
          table.insert(Panes_to_draw, pane)
          -- stash some short-lived variables
          pane.column_index = column_index
          pane.pane_index = pane_index
          local y_offset = 0
          local body_sy = sy
          if column[pane_index].title then
            body_sy = body_sy + 5+Line_height+5
          end
          if should_update_screen_top(column_index, pane_index, pane, options) then
            if body_sy < Display_settings.y then
              pane.screen_top1, y_offset = schema1_of_y(pane, Display_settings.y - body_sy)
            else
              pane.screen_top1 = {line=1, pos=1}
            end
          end
          if body_sy < Display_settings.y then
            pane.top = Margin_above
          else
            pane.top = body_sy - Display_settings.y + Margin_above
          end
          pane.top = Header_height + pane.top - y_offset
--?           print('bounds: =>', pane.top)
          pane.left = sx - Display_settings.x
          pane.right = pane.left + Display_settings.column_width
          pane.width = pane.right - pane.left
        else
          -- clear bounds to catch issues early
          pane.top = nil
--?           print('bounds: =>', pane.top)
        end
        sy = sy + Margin_above + height(pane) + Margin_below + Padding_vertical
      end
    else
      -- clear bounds to catch issues early
      for _, pane in ipairs(column) do
        pane.top = nil
      end
    end
    sx = sx + Margin_right + Display_settings.column_width + Padding_horizontal + Margin_left