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Re: Display of undisplayable characters: \U01F3A8 instead of diamond

From: Richard Stallman
Subject: Re: Display of undisplayable characters: \U01F3A8 instead of diamond
Date: Tue, 30 Aug 2022 00:12:02 -0400

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  > No, because displaying a non-ASCII character on a text-mode terminal
  > requires to encode it.

Maybe the existing mechamisms will insist on encoring it, but I think
it won't be hard to bypass that step.  The user could specify the
encoded sequence to send, by putting that sequence in a variable as a
string or vector.

Then redisplay simply has to send the sequence of characters
from the vector, _as if_ they were the result of encoding something.

  > > but what is so bad about sending a glyph that the terminal can't
  > > display?  What bad results does it cause?

  > It could mess up the display, because sending commands to the terminal
  > driver also involves sequences of unprintable bytes.

In some cases, maybe there is a risk it could do that.  But if the
user uses the feature I propose just above, perse will be responsible
for specifying a sequence that displays as a character.  So that won't
mess up the display.

  > This arranges for all the characters beyond 255 to be displayed as the
  > diamond with a special face.  (You can, of course, adjust the range of
  > characters for which this is done according to your needs, or have
  > several disjoint ranges instead of just one.)

  > Would that be good enough for your use patterns?

With 255 specified, it would not be adequate.  The Linux console handles
the Greek alphabet, the Russian alphabet, and I am not sure what else.

Using several disjoint ranges could do the job, I suppose,
if someone can tell me how to determine what those ranges should be.

Could this be figured out automatically by calling char-displayable-p
on each character code?  Up to what number would that loop have to run?

Dr Richard Stallman (https://stallman.org)
Chief GNUisance of the GNU Project (https://gnu.org)
Founder, Free Software Foundation (https://fsf.org)
Internet Hall-of-Famer (https://internethalloffame.org)

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