Friday, 3 July 2020

ZX81 Characters in Unicode 13.0

Almost exactly ten years ago, in an earlier post, I bemoaned the fact that a few glyphs from the ZX81 character set were missing from the Unicode standard. However, whilst researching seven-segment displays, I came across a reference to part of Unicode 13.0 named "Symbols for Legacy Computing". This obviously piqued my interest.



Within the upcoming release of the Unicode standard are:
214 graphic characters that provide compatibility with various home computers from the mid-1970s to the mid-1980s and with early teletext broadcasting standards.
Lo and behold, characters U+1FBF0 to U+1FBF9 are the ten seven-segment digits that first brought my attention to this block, whilst four other codepoints provide the missing ZX81 glyphs:

 ZX81Unicode Description 
 0x09 U+1FB8F LOWER HALF MEDIUM SHADE
 0x0A U+1FB8E UPPER HALF MEDIUM SHADE
 0x89 U+1FB91 UPPER HALF BLOCK AND LOWER HALF INVERSE MEDIUM SHADE
 0x8A U+1FB92 UPPER HALF INVERSE MEDIUM SHADE AND LOWER HALF BLOCK

Someone has even updated the Wikipedia page. Marvellous.

The ZX81 was launched in March 1981, but its character set was evolved from that used in the ZX80 which launched in January 1980. Then, in March 2020, Unicode was extended with characters that finally filled in the blanks. Forty years later? Crikey!

By the way, the eagle-eyed may have noticed that U+1FB94 ("LEFT HALF INVERSE MEDIUM SHADE AND RIGHT HALF BLOCK") does not have a mirrored twin ("LEFT HALF BLOCK AND RIGHT HALF INVERSE MEDIUM SHADE") which looks like it should fit at U+1FB93 (currently flagged "<reserved>"). However, the fascinating Working Group Proposal explains that
One code point, U+1FB93, was left unassigned in this proposal as a placeholder for the as-yet unattested *LEFT HALF BLOCK AND RIGHT HALF INVERSE MEDIUM SHADE, which would be the reverse-video equivalent of U+1FB8D RIGHT HALF MEDIUM SHADE from the Aquarius.
After briefly investigating the Aquarius character set, I feel Unicode 13.1 may be imminent.

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