consider allowing custom X positioning of display characters

[Lx]

The hardware-based right justification is known to be buggy.

Given the existence of 1px-wide spaces (as discussed in #1), it is possible to fake right-justification (or indeed draw characters at any X position and with any desired spacing).

I prepared the following kludge to fix the right justification in a production environment:

_DISPLAY_WIDTH = 120
_CHARS_BY_WIDTH = {
 3: b'.',
 4: b'I1: ',
 5: b'0-',
 6: b'ABCDEFGHJKLMNOPQRSTUVWXYZ23456789',
}
_WIDTHS_BY_CHAR = {}
for width, chars in _CHARS_BY_WIDTH.items():
 for char in chars:
 _WIDTHS_BY_CHAR[char] = width


def pixel_width(string):
 width = 0
 for char in string:
 if char not in _WIDTHS_BY_CHAR:
 raise ValueError('unknown width for character "%s"' % char)
 width += _WIDTHS_BY_CHAR[char]
 return width


def fix_right_justification(bytestring):
 if rb'\R' not in bytestring:
 return bytestring
 left_start = 7
 left_end = bytestring.index(rb'\R', left_start)
 right_start = left_end + len(rb'\R')
 right_end = bytestring.index(
 b'\n', right_start
 ) if b'\n' in bytestring[right_start:] else bytestring.index(
 b'\r', right_start)
 left = bytestring[left_start:left_end]
 right = bytestring[right_start:right_end]
 left_width = pixel_width(left)
 right_width = pixel_width(right)
 padding_width = _DISPLAY_WIDTH - 2 - left_width - right_width
 padding = b''
 space_width = _WIDTHS_BY_CHAR[ord(' ')]
 while padding_width >= space_width:
 padding += b' '
 padding_width -= space_width
 while padding_width > 0:
 padding += b'\xff'
 padding_width -= 1
 return bytestring[:left_end] + padding + bytestring[right_start:]

fix_right_justification takes bytes as returned by DisplayMessage.to_bytes() and further modifies them.

Think about how best this could be incorporated into the library.