Teletext separated mosaic graphics

[Harriet Riddle]

It's worth pointing out that the control codes for showing mosaic characters as separated are also used in at least some formats to switch alphabetical characters to underlined display.

See for example the definitions for SPL and STL here: https://www.itscj.ipsj.or.jp/iso-ir/056.pdf (that document details the C1 control codes for Data Syntax 2 Serial Videotex—which would seem to be the Teletext set but as a C1 set, and as such with CSI rather than ESC).

Essentially, the expectation seems to be that an emphasised variant of a font would display mosaic characters separated, while a regular variant of a font would display them connected.

--Har.

________________________________
From: Unicode <unicode-bounces at unicode.org> on behalf of William_J_G Overington via Unicode <unicode at unicode.org>
Sent: 01 October 2020 18:44
To: unicode at unicode.org <unicode at unicode.org>
Subject: Re: Teletext separated mosaic graphics


The 1976 Teletext Specification has three meanings for sixty-four of the character code points - lowercase letters and a few others, contiguous graphics, separated graphics.


The Unicode Standard at present has the "lowercase letters and a few others" encoded and the "contiguous graphics" encoded separately, although, alas, all sixty-four contiguous graphic characters are not encoded as one block. My opinion is that that one-to-one directly mapped approach would have been preferable, but the situation is as it is.

The twenty-seven teletext control characters have not been encoded at this time.


I opine that these twenty-seven codes could be encoded within a block of thirty-two code points as characters that display as visual glyphs in most circumstances, yet are control codes in teletext apps.


For example, Alphanumerics Green would have a visible glyph of an A above a G on a pale.


That way, teletext pages from long ago and new designs could be recorded elegantly and conserved as the control codes in the teletext page would not conflict with the usual control codes of computing.


If those twenty-seven teletext control characters were encoded separately, would that help in developing your app, or are you using a different approach?


William Overington


Thursday 1 October 2020


http://www.users.globalnet.co.uk/~ngo/




------ Original Message ------
From: "Rob H via Unicode" <unicode at unicode.org>
To: unicode at unicode.org
Sent: Thursday, 2020 Oct 1 At 13:46
Subject: Teletext separated mosaic graphics

Hi,

I've started to develop a teletext app and plan to use the recently added graphic mosaic characters in the legacy computing block (the sextets). I see that Unicode includes the contiguous mosaics characters and not the separated form of those characters. I'm wondering if that was intentional? On one hand, that matches the teletext spec, which has one set of byte codes for the graphics, and uses control codes to switch between contiguous or separated. On the other hand it means I'll need to use styling tricks or a different font or glyph variations to recreate the separated graphics. It also means a simple text-only file of just the characters won't recreate a screen as the control codes to switch between contiguous/separated won't work.

A font I've found which maps these characters uses the new codepoints for the contiguous graphics and a private codepoints for separated, which seems awkward to me.

If having just the contiguous graphics was intentional, that's fine, but I just wanted to check.

Regards,
Rob.

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