editing source code from within the app

integrated from pong.love via text.love:
  https://merveilles.town/@akkartik/108933336531898243

1 files changed, 1561 insertions, 0 deletions

diff --git a/source_text.lua b/source_text.lua
new file mode 100644
index 0000000..e491dac
--- /dev/null
+++ b/source_text.lua
@@ -0,0 +1,1561 @@
+-- text editor, particularly text drawing, horizontal wrap, vertical scrolling
+Text = {}
+AB_padding = 20  -- space in pixels between A side and B side
+
+-- draw a line starting from startpos to screen at y between State.left and State.right
+-- return the final y, and pos,posB of start of final screen line drawn
+function Text.draw(State, line_index, y, startpos, startposB)
+  local line = State.lines[line_index]
+  local line_cache = State.line_cache[line_index]
+  line_cache.starty = y
+  line_cache.startpos = startpos
+  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 State.search_term == nil 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 Foo then
+--?     print('draw:', State.lines[line_index].data, "=====", State.lines[line_index].dataB, 'starting from x', x+AB_padding)
+--?   end
+  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 State.search_term == nil 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..'$')
+  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 --[[screen filled]] true, x,y, pos, screen_line_starting_pos
+        end
+        screen_line_starting_pos = pos
+        x = State.left
+      end
+      App.screen.draw(frag_text, x,y)
+      -- render cursor if necessary
+      if State.cursor1.pos and 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 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
+      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
+    end
+    pos = pos + frag_len
+  end
+  return false, x,y, pos, 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]
+  local line_cache = State.line_cache[line_index]
+  if line_cache.screen_line_starting_pos then
+    return
+  end
+  -- duplicate some logic from Text.draw
+  Text.compute_fragments(State, line_index)
+  line_cache.screen_line_starting_pos = {1}
+  local x = State.left
+  local pos = 1
+  for _, f in ipairs(line_cache.fragments) 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_pos, pos)
+    end
+    x = x + frag_width
+    local frag_len = utf8.len(frag)
+    pos = pos + frag_len
+  end
+end
+
+function Text.compute_fragments(State, line_index)
+--?   print('compute_fragments', line_index, 'between', State.left, State.right)
+  local line = State.lines[line_index]
+  local line_cache = State.line_cache[line_index]
+  if line_cache.fragments then
+    return
+  end
+  line_cache.fragments = {}
+  local x = State.left
+  -- try to wrap at word boundaries
+  for frag in line.data:gmatch('%S*%s*') do
+    local frag_text = App.newText(love.graphics.getFont(), frag)
+    local frag_width = App.width(frag_text)
+--?     print('x: '..tostring(x)..'; frag_width: '..tostring(frag_width)..'; '..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.fragments, {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.fragments, {data=frag, text=frag_text})
+    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)
+    end
+    x = x + frag_width
+    local frag_len = utf8.len(frag)
+    pos = pos + frag_len
+  end
+end
+
+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
+
+function Text.textinput(State, t)
+  if App.mouse_down(1) then return end
+  if App.ctrl_down() or App.alt_down() or App.cmd_down() then return end
+  local before = snapshot(State, State.cursor1.line)
+--?   print(State.screen_top1.line, State.screen_top1.pos, State.cursor1.line, State.cursor1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)
+  Text.insert_at_cursor(State, t)
+  if State.cursor_y > App.screen.height - State.line_height then
+    Text.populate_screen_line_starting_pos(State, State.cursor1.line)
+    Text.snap_cursor_to_bottom_of_screen(State, State.left, State.right)
+  end
+  record_undo_event(State, {before=before, after=snapshot(State, State.cursor1.line)})
+end
+
+function Text.insert_at_cursor(State, t)
+  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
+end
+
+-- Don't handle any keys here that would trigger love.textinput above.
+function Text.keychord_pressed(State, chord)
+--?   print('chord', chord)
+  --== shortcuts that mutate text
+  if chord == 'return' then
+    local before_line = State.cursor1.line
+    local before = snapshot(State, before_line)
+    Text.insert_return(State)
+    if State.cursor_y > App.screen.height - State.line_height 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)})
+  elseif chord == 'tab' then
+    local before = snapshot(State, State.cursor1.line)
+--?     print(State.screen_top1.line, State.screen_top1.pos, State.cursor1.line, State.cursor1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)
+    Text.insert_at_cursor(State, '\t')
+    if State.cursor_y > App.screen.height - State.line_height then
+      Text.populate_screen_line_starting_pos(State, State.cursor1.line)
+      Text.snap_cursor_to_bottom_of_screen(State, State.left, State.right)
+--?       print('=>', State.screen_top1.line, State.screen_top1.pos, State.cursor1.line, State.cursor1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)
+    end
+    schedule_save(State)
+    record_undo_event(State, {before=before, after=snapshot(State, State.cursor1.line)})
+  elseif chord == 'backspace' then
+    local before
+    if State.cursor1.pos and State.cursor1.pos > 1 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
+      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
+      end
+    elseif State.cursor1.line > 1 then
+      before = snapshot(State, State.cursor1.line-1, State.cursor1.line)
+      -- join lines
+      State.cursor1.pos = utf8.len(State.lines[State.cursor1.line-1].data)+1
+      State.lines[State.cursor1.line-1].data = State.lines[State.cursor1.line-1].data..State.lines[State.cursor1.line].data
+      table.remove(State.lines, State.cursor1.line)
+      table.remove(State.line_cache, State.cursor1.line)
+      State.cursor1.line = State.cursor1.line-1
+    end
+    if State.screen_top1.line > #State.lines then
+      Text.populate_screen_line_starting_pos(State, #State.lines)
+      local line_cache = State.line_cache[#State.line_cache]
+      State.screen_top1 = {line=#State.lines, pos=line_cache.screen_line_starting_pos[#line_cache.screen_line_starting_pos]}
+    elseif Text.lt1(State.cursor1, State.screen_top1) then
+      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)
+      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
+    local before
+    if State.cursor1.posB or 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 and 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
+    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
+      end
+    elseif State.cursor1.line < #State.lines then
+      -- join lines
+      State.lines[State.cursor1.line].data = State.lines[State.cursor1.line].data..State.lines[State.cursor1.line+1].data
+      -- delete side B on first line
+      State.lines[State.cursor1.line].dataB = State.lines[State.cursor1.line+1].dataB
+      table.remove(State.lines, State.cursor1.line+1)
+      table.remove(State.line_cache, State.cursor1.line+1)
+    end
+    Text.clear_screen_line_cache(State, State.cursor1.line)
+    schedule_save(State)
+    record_undo_event(State, {before=before, after=snapshot(State, State.cursor1.line)})
+  --== shortcuts that move the cursor
+  elseif chord == 'left' then
+    Text.left(State)
+  elseif chord == 'right' then
+    Text.right(State)
+  elseif chord == 'S-left' then
+    Text.left(State)
+  elseif chord == 'S-right' then
+    Text.right(State)
+  -- C- hotkeys reserved for drawings, so we'll use M-
+  elseif chord == 'M-left' then
+    Text.word_left(State)
+  elseif chord == 'M-right' then
+    Text.word_right(State)
+  elseif chord == 'M-S-left' then
+    Text.word_left(State)
+  elseif chord == 'M-S-right' then
+    Text.word_right(State)
+  elseif chord == 'home' then
+    Text.start_of_line(State)
+  elseif chord == 'end' then
+    Text.end_of_line(State)
+  elseif chord == 'S-home' then
+    Text.start_of_line(State)
+  elseif chord == 'S-end' then
+    Text.end_of_line(State)
+  elseif chord == 'up' then
+    Text.up(State)
+  elseif chord == 'down' then
+    Text.down(State)
+  elseif chord == 'S-up' then
+    Text.up(State)
+  elseif chord == 'S-down' then
+    Text.down(State)
+  elseif chord == 'pageup' then
+    Text.pageup(State)
+  elseif chord == 'pagedown' then
+    Text.pagedown(State)
+  elseif chord == 'S-pageup' then
+    Text.pageup(State)
+  elseif chord == 'S-pagedown' then
+    Text.pagedown(State)
+  end
+end
+
+function Text.insert_return(State)
+  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, {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
+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)
+    if State.screen_top1.line == 1 and State.screen_top1.pos and State.screen_top1.pos == 1 then break end
+    y = y - State.line_height
+    top2 = Text.previous_screen_line(State, top2)
+  end
+  State.screen_top1 = Text.to1(State, top2)
+  State.cursor1 = {line=State.screen_top1.line, pos=State.screen_top1.pos, posB=State.screen_top1.posB}
+  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')
+  local bot2 = Text.to2(State, State.screen_bottom1)
+  local new_top1 = Text.to1(State, bot2)
+  if Text.lt1(State.screen_top1, new_top1) then
+    State.screen_top1 = new_top1
+  else
+    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)
+  State.cursor1 = {line=State.screen_top1.line, pos=State.screen_top1.pos, posB=State.screen_top1.posB}
+  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)
+  if State.cursor1.pos then
+    Text.upA(State)
+  else
+    Text.upB(State)
+  end
+end
+
+function Text.upA(State)
+--?   print('up', State.cursor1.line, State.cursor1.pos, State.screen_top1.line, State.screen_top1.pos)
+  local screen_line_starting_pos, screen_line_index = Text.pos_at_start_of_screen_line(State, State.cursor1)
+  if screen_line_starting_pos == 1 then
+--?     print('cursor is at first screen line of its line')
+    -- line is done; skip to previous text line
+    if State.cursor1.line > 1 then
+--?       print('found previous text line')
+      State.cursor1 = {line=State.cursor1.line-1, pos=nil}
+      Text.populate_screen_line_starting_pos(State, State.cursor1.line)
+      -- previous text line found, pick its final screen line
+--?       print('has multiple screen lines')
+      local screen_line_starting_pos = State.line_cache[State.cursor1.line].screen_line_starting_pos
+--?       print(#screen_line_starting_pos)
+      screen_line_starting_pos = screen_line_starting_pos[#screen_line_starting_pos]
+      local screen_line_starting_byte_offset = Text.offset(State.lines[State.cursor1.line].data, screen_line_starting_pos)
+      local s = string.sub(State.lines[State.cursor1.line].data, screen_line_starting_byte_offset)
+      State.cursor1.pos = screen_line_starting_pos + Text.nearest_cursor_pos(s, State.cursor_x, State.left) - 1
+    end
+  else
+    -- move up one screen line in current line
+    assert(screen_line_index > 1)
+    local new_screen_line_starting_pos = State.line_cache[State.cursor1.line].screen_line_starting_pos[screen_line_index-1]
+    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 '..tostring(State.cursor1.pos))
+  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
+
+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
+    if State.cursor1.line > 1 then
+      State.cursor1.line = State.cursor1.line-1
+      State.cursor1.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
+    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
+function Text.down(State)
+--?   print('down', State.cursor1.line, State.cursor1.pos, State.screen_top1.line, State.screen_top1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)
+  if Text.cursor_at_final_screen_line(State) then
+    -- line is done, skip to next text line
+--?     print('cursor at final screen line of its line')
+    if State.cursor1.line < #State.lines then
+      State.cursor1 = {
+        line = State.cursor1.line+1,
+        pos = Text.nearest_cursor_pos(State.lines[State.cursor1.line+1].data, State.cursor_x, State.left)
+      }
+--?       print(State.cursor1.pos)
+    end
+    if State.cursor1.line > State.screen_bottom1.line then
+--?       print('screen top before:', State.screen_top1.line, State.screen_top1.pos)
+--?       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)
+    end
+  elseif State.cursor1.pos then
+    -- move down one screen line (A side) 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)
+    end
+  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
+  end
+--?   print('=>', State.cursor1.line, State.cursor1.pos, State.screen_top1.line, State.screen_top1.pos, State.screen_bottom1.line, State.screen_bottom1.pos)
+end
+
+function Text.start_of_line(State)
+  if State.cursor1.pos then
+    State.cursor1.pos = 1
+  else
+    State.cursor1.posB = 1
+  end
+  if Text.lt1(State.cursor1, State.screen_top1) then
+    State.screen_top1 = {line=State.cursor1.line, pos=1}  -- copy
+  end
+end
+
+function Text.end_of_line(State)
+  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
+  if Text.cursor_out_of_screen(State) then
+    Text.snap_cursor_to_bottom_of_screen(State)
+  end
+end
+
+function Text.word_left(State)
+  -- 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)
+  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
+end
+
+function Text.skip_whitespace_leftB(State)
+  while true do
+    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
+    Text.left(State)
+  end
+end
+
+function Text.skip_non_whitespace_leftA(State)
+  while true do
+    if State.cursor1.pos == 1 then
+      break
+    end
+    assert(State.cursor1.pos > 1)
+    if Text.match(State.lines[State.cursor1.line].data, State.cursor1.pos-1, '%s') then
+      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
+      break
+    end
+    Text.left(State)
+  end
+end
+
+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)
+  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
+end
+
+function Text.skip_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)
+  end
+end
+
+function Text.skip_non_whitespace_rightA(State)
+  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
+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)
+  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)
+  if State.cursor1.pos then
+    Text.leftA(State)
+  else
+    Text.leftB(State)
+  end
+end
+
+function Text.leftA(State)
+  if State.cursor1.pos > 1 then
+    State.cursor1.pos = State.cursor1.pos-1
+  elseif State.cursor1.line > 1 then
+    State.cursor1 = {
+      line = State.cursor1.line-1,
+      pos = utf8.len(State.lines[State.cursor1.line-1].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
+
+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
+
+function Text.right(State)
+  Text.right_without_scroll(State)
+  if Text.cursor_out_of_screen(State) then
+    Text.snap_cursor_to_bottom_of_screen(State)
+  end
+end
+
+function Text.right_without_scroll(State)
+  if State.cursor1.pos then
+    Text.right_without_scrollA(State)
+  else
+    Text.right_without_scrollB(State)
+  end
+end
+
+function Text.right_without_scrollA(State)
+  if State.cursor1.pos <= utf8.len(State.lines[State.cursor1.line].data) then
+    State.cursor1.pos = State.cursor1.pos+1
+  elseif State.cursor1.line <= #State.lines-1 then
+    State.cursor1 = {line=State.cursor1.line+1, pos=1}
+  end
+end
+
+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
+  elseif State.cursor1.line <= #State.lines-1 then
+    -- overflow back into A side
+    State.cursor1 = {line=State.cursor1.line+1, pos=1}
+  end
+end
+
+function Text.pos_at_start_of_screen_line(State, loc1)
+  Text.populate_screen_line_starting_pos(State, loc1.line)
+  local line_cache = State.line_cache[loc1.line]
+  for i=#line_cache.screen_line_starting_pos,1,-1 do
+    local spos = line_cache.screen_line_starting_pos[i]
+    if spos <= loc1.pos then
+      return spos,i
+    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
+    end
+  end
+  assert(false)
+end
+
+function Text.cursor_at_final_screen_line(State)
+  Text.populate_screen_line_starting_pos(State, State.cursor1.line)
+  local line = State.lines[State.cursor1.line]
+  local screen_lines = State.line_cache[State.cursor1.line].screen_line_starting_pos
+--?   print(screen_lines[#screen_lines], State.cursor1.pos)
+  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
+end
+
+function Text.move_cursor_down_to_next_text_line_while_scrolling_again_if_necessary(State)
+  if State.top > App.screen.height - State.line_height then
+--?     print('scroll up')
+    Text.snap_cursor_to_bottom_of_screen(State)
+  end
+end
+
+-- should never modify State.cursor1
+function Text.snap_cursor_to_bottom_of_screen(State)
+--?   print('to2:', State.cursor1.line, State.cursor1.pos, State.cursor1.posB)
+  local top2 = Text.to2(State, State.cursor1)
+--?   print('to2: =>', top2.line, top2.screen_line, top2.screen_pos, top2.screen_lineB, top2.screen_posB)
+  -- slide to start of screen line
+  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)
+--?   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(y, 'top2:', State.lines[top2.line].data, top2.line, top2.screen_line, top2.screen_pos, top2.screen_lineB, top2.screen_posB)
+    if top2.line == 1 and top2.screen_line == 1 then break end
+    local h = State.line_height
+    if y - h < State.top then
+      break
+    end
+    y = y - h
+    top2 = Text.previous_screen_line(State, top2)
+  end
+--?   print('top2 finally:', top2.line, top2.screen_line, top2.screen_pos)
+  State.screen_top1 = Text.to1(State, top2)
+--?   print('top1 finally:', State.screen_top1.line, State.screen_top1.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)
+  Text.redraw_all(State)  -- if we're scrolling, reclaim all fragments to avoid memory leaks
+  Foo = true
+end
+
+function Text.in_line(State, line_index, x,y)
+  local line = State.lines[line_index]
+  local line_cache = State.line_cache[line_index]
+  if line_cache.starty == nil then return false end  -- outside current page
+  if y < line_cache.starty then return false end
+  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
+end
+
+-- convert mx,my in pixels to schema-1 coordinates
+-- 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
+function Text.to_pos_on_line(State, line_index, mx, my)
+  local line = State.lines[line_index]
+  local line_cache = State.line_cache[line_index]
+  assert(my >= line_cache.starty)
+  -- duplicate some logic from Text.draw
+  local y = line_cache.starty
+--?   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 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.)
+--?       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
+--?         print('past end of non-final line; return')
+        return nil, line_cache.screen_line_starting_posB[screen_line_indexB+1]-1
+      end
+      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
+    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
+
+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_index(screen_line_starting_pos, pos)
+  for i = #screen_line_starting_pos,1,-1 do
+    if screen_line_starting_pos[i] <= pos then
+      return i
+    end
+  end
+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
+
+-- convert x pixel coordinate to pos
+-- oblivious to wrapping
+-- result: 1 to len+1
+function Text.nearest_cursor_pos(line, x, left)
+  if x < left then
+    return 1
+  end
+  local len = utf8.len(line)
+  local max_x = left+Text.x(line, len+1)
+  if x > max_x then
+    return len+1
+  end
+  local leftpos, rightpos = 1, len+1
+--?   print('-- nearest', x)
+  while true do
+--?     print('nearest', x, '^'..line..'$', leftpos, rightpos)
+    if leftpos == rightpos then
+      return leftpos
+    end
+    local curr = math.floor((leftpos+rightpos)/2)
+    local currxmin = left+Text.x(line, curr)
+    local currxmax = left+Text.x(line, curr+1)
+--?     print('nearest', x, leftpos, rightpos, curr, currxmin, currxmax)
+    if currxmin <= x and x < currxmax then
+      if x-currxmin < currxmax-x then
+        return curr
+      else
+        return curr+1
+      end
+    end
+    if leftpos >= rightpos-1 then
+      return rightpos
+    end
+    if currxmin > x then
+      rightpos = curr
+    else
+      leftpos = curr
+    end
+  end
+  assert(false)
+end
+
+-- return the nearest index of line (in utf8 code points) which lies entirely
+-- within x pixels of the left margin
+-- result: 0 to len+1
+function Text.nearest_pos_less_than(line, x)
+--?   print('', '-- nearest_pos_less_than', line, x)
+  local len = utf8.len(line)
+  local max_x = Text.x_after(line, len)
+  if x > max_x then
+    return len+1
+  end
+  local left, right = 0, len+1
+  while true do
+    local curr = math.floor((left+right)/2)
+    local currxmin = Text.x_after(line, curr+1)
+    local currxmax = Text.x_after(line, curr+2)
+--?     print('', x, left, right, curr, currxmin, currxmax)
+    if currxmin <= x and x < currxmax then
+      return curr
+    end
+    if left >= right-1 then
+      return left
+    end
+    if currxmin > x then
+      right = curr
+    else
+      left = curr
+    end
+  end
+  assert(false)
+end
+
+function Text.x_after(s, pos)
+  local offset = Text.offset(s, math.min(pos+1, #s+1))
+  local s_before = s:sub(1, offset-1)
+--?   print('^'..s_before..'$')
+  local text_before = App.newText(love.graphics.getFont(), s_before)
+  return App.width(text_before)
+end
+
+function Text.x(s, pos)
+  local offset = Text.offset(s, pos)
+  local s_before = s:sub(1, offset-1)
+  local text_before = App.newText(love.graphics.getFont(), s_before)
+  return App.width(text_before)
+end
+
+function Text.to2(State, loc1)
+  if loc1.pos then
+    return Text.to2A(State, loc1)
+  else
+    return Text.to2B(State, loc1)
+  end
+end
+
+function Text.to2A(State, loc1)
+  local result = {line=loc1.line}
+  local line_cache = State.line_cache[loc1.line]
+  Text.populate_screen_line_starting_pos(State, loc1.line)
+  for i=#line_cache.screen_line_starting_pos,1,-1 do
+    local spos = line_cache.screen_line_starting_pos[i]
+    if spos <= loc1.pos then
+      result.screen_line = i
+      result.screen_pos = loc1.pos - spos + 1
+      break
+    end
+  end
+  assert(result.screen_pos)
+  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)
+  return result
+end
+
+function Text.to1(State, loc2)
+  if loc2.screen_pos then
+    return Text.to1A(State, loc2)
+  else
+    return Text.to1B(State, loc2)
+  end
+end
+
+function Text.to1A(State, loc2)
+  local result = {line=loc2.line, pos=loc2.screen_pos}
+  if loc2.screen_line > 1 then
+    result.pos = State.line_cache[loc2.line].screen_line_starting_pos[loc2.screen_line] + loc2.screen_pos - 1
+  end
+  return result
+end
+
+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
+end
+
+function Text.lt1(a, b)
+  if a.line < b.line then
+    return true
+  end
+  if a.line > b.line then
+    return false
+  end
+  -- A side < B side
+  if a.pos and not b.pos then
+    return true
+  end
+  if not a.pos and b.pos then
+    return false
+  end
+  if a.pos then
+    return a.pos < b.pos
+  else
+    return a.posB < b.posB
+  end
+end
+
+function Text.le1(a, b)
+  return eq(a, b) or Text.lt1(a, b)
+end
+
+function Text.offset(s, pos1)
+  if pos1 == 1 then return 1 end
+  local result = utf8.offset(s, pos1)
+  if result == nil then
+    print(pos1, #s, s)
+  end
+  assert(result)
+  return result
+end
+
+function Text.previous_screen_line(State, loc2)
+  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)
+  if loc2.screen_line > 1 then
+--?     print('a')
+    return {line=loc2.line, screen_line=loc2.screen_line-1, screen_pos=1}
+  elseif loc2.line == 1 then
+--?     print('b')
+    return loc2
+  else
+    Text.populate_screen_line_starting_pos(State, 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
+  end
+end
+
+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
+
+-- resize helper
+function Text.tweak_screen_top_and_cursor(State)
+  if State.screen_top1.pos == 1 then return end
+  Text.populate_screen_line_starting_pos(State, State.screen_top1.line)
+  local line = State.lines[State.screen_top1.line]
+  local line_cache = State.line_cache[State.screen_top1.line]
+  for i=2,#line_cache.screen_line_starting_pos do
+    local pos = line_cache.screen_line_starting_pos[i]
+    if pos == State.screen_top1.pos then
+      break
+    end
+    if pos > State.screen_top1.pos then
+      -- make sure screen top is at start of a screen line
+      local prev = line_cache.screen_line_starting_pos[i-1]
+      if State.screen_top1.pos - prev < pos - State.screen_top1.pos then
+        State.screen_top1.pos = prev
+      else
+        State.screen_top1.pos = pos
+      end
+      break
+    end
+  end
+  -- make sure cursor is on screen
+  if Text.lt1(State.cursor1, State.screen_top1) then
+    State.cursor1 = {line=State.screen_top1.line, pos=State.screen_top1.pos}
+  elseif State.cursor1.line >= State.screen_bottom1.line then
+--?     print('too low')
+    if Text.cursor_out_of_screen(State) then
+--?       print('tweak')
+      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}
+    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
+
+function Text.redraw_all(State)
+--?   print('clearing fragments')
+  State.line_cache = {}
+  for i=1,#State.lines do
+    State.line_cache[i] = {}
+  end
+end
+
+function Text.clear_screen_line_cache(State, line_index)
+  State.line_cache[line_index].fragments = nil
+  State.line_cache[line_index].fragmentsB = nil
+  State.line_cache[line_index].screen_line_starting_pos = nil
+  State.line_cache[line_index].screen_line_starting_posB = nil
+end
+
+function trim(s)
+  return s:gsub('^%s+', ''):gsub('%s+$', '')
+end
+
+function ltrim(s)
+  return s:gsub('^%s+', '')
+end
+
+function rtrim(s)
+  return s:gsub('%s+$', '')
+end