go through and fix similar issues

Dependencies

• [2] 4VKEE43Z bugfix
• [3] CUIV2LE5 some typos
• [4] 5FW7YOFT highlight selection while dragging
• [5] AYE2VEGJ extract a couple of methods
• [6] BOFNXP5G clicking now moves the cursor even on long, wrapped lines
• [7] PR4KIAZD first stab at equally hacky cursor down support
• [8] V5MJRFOZ bugfix: down arrow doesn't scroll up unnecessarily
• [9] ZPUQSPQP extract a few methods
• [10] 5L7K4GBD clicking to the right of a wrapped line
• [11] HOSPP2AN crisp font rendering
• [12] XNFTJHC4 split keyboard handling between Text and Drawing
• [*] BULPIBEG beginnings of a module for the text editor
• [*] BJ5X5O4A let's prevent the text cursor from ever getting on a drawing

Change contents

• replacement in text.lua at line 467
  [3.1520]→[3.1520:1601](∅→∅)
  − local s = string.sub(Lines[Cursor1.line].data, screen_line_starting_pos)
  [3.1520]

  [3.1601]
  + local screen_line_starting_byte_offset = utf8.offset(Lines[Cursor1.line].data, screen_line_starting_pos)

  + assert(screen_line_starting_byte_offset)

  + local s = string.sub(Lines[Cursor1.line].data, screen_line_starting_byte_offset)
• replacement in text.lua at line 487
  [3.2441]→[3.2441:2522](∅→∅)
  − local s = string.sub(Lines[Cursor1.line].data, new_screen_line_starting_pos)
  [3.2441]

  [3.2522]
  + local new_screen_line_starting_byte_offset = utf8.offset(Lines[Cursor1.line].data, new_screen_line_starting_pos)

  + assert(new_screen_line_starting_byte_offset)

  + local s = string.sub(Lines[Cursor1.line].data, new_screen_line_starting_byte_offset)
• replacement in text.lua at line 527
  [3.4338]→[3.4338:4419](∅→∅)
  − local s = string.sub(Lines[Cursor1.line].data, new_screen_line_starting_pos)
  [3.4338]

  [3.4419]
  + local new_screen_line_starting_byte_offset = utf8.offset(Lines[Cursor1.line].data, new_screen_line_starting_pos)

  + assert(new_screen_line_starting_byte_offset)

  + local s = string.sub(Lines[Cursor1.line].data, new_screen_line_starting_byte_offset)
• replacement in text.lua at line 698
  [3.133]→[2.1359:1478](∅→∅)
  − --? print('iter', y, screen_line_index, screen_line_starting_pos, string.sub(line.data, screen_line_starting_pos))
  [3.133]

  [3.3874]
  + local screen_line_starting_byte_offset = utf8.offset(line.data, screen_line_starting_pos)

  + assert(screen_line_starting_byte_offset)

  + --? print('iter', y, screen_line_index, screen_line_starting_pos, string.sub(line.data, screen_line_starting_byte_offset))
• edit in text.lua at line 710
  [3.538]→[2.1536:1679](∅→∅)
  − local screen_line_starting_byte_offset = utf8.offset(line.data, screen_line_starting_pos)

  − assert(screen_line_starting_byte_offset)
• edit in manual_tests at line 1
  [15.1]

  [15.2]
  + -- static properties of the code

  + All strings are UTF-8. Bytes within them are not characters.

  + I try to label byte offsets as _offset, and character positions as _pos.

  + For example, string.sub should never use a _pos to substring, only an _offset.

  + Wish I had some static typing here. We're not going to try to write tests to catch issues like this.

  +

  + -- manual tests