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Re: Cygwin fails to utilize Unicode replacement character

On Tue, 4 Sep 2018 23:43:16, Thomas Wolff wrote:
Traditionally, many terminals used to display the DEL character as a checkered block, which is more or less the MEDIUM SHADE.
This makes the glyph appear somewhat "erroneous" by convention.

I see - now that Unicode has some dedicated characters for this, it would make
sense to use them, especially since linux is already using them:

1. U+FFFD: http://unicode.org/charts/nameslist/n_FFF0.html
2. U+25A1: http://unicode.org/charts/nameslist/n_25A0.html

valid code point with no glyph in font -> .notdef glyph -> WHITE SQUARE

this is not true. "WHITE SQUARE" refers to U+25A1, which is an actual character
and different from the ".notdef" glyph. as has been discussed as length in this
thread, the ".notdef glyph" is not an actual character, but a glyph that exists
at position 0 in the font, and while its appearance is not strictly defined,
some recommendations exist:

- empty rectangle
- rectangle with a question mark
- rectangle with an X

Now if you switch to FFFD REPLACEMENT CHARACTER for invalid code point, and considering that it does not exist in most actual fonts and that the console does not apply font fallback, it will resolve to WHITE SQUARE, thus:
folding the two different use cases into the same appearance,
which is bad.

no again, it will resolve to ".notdef glyph", as I put above. otherwise yes, you
do have a point. in the case of a font without U+FFFD, you have ultimately:

invalid code point: .notdef glyph
missing character: .notdef glyph

several ideas have been proposed:

1. keep U+FFFD
2. go back to U+2592
3. use U+25A1 instead
4. use U+FFFD if possible else fallback to U+2592 or U+25A1

if we choose option 1, people not happy with the ambiguity can simply install
"dejavu-fonts" or similar, which Cygwin provides.

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