Does not respect unicode RIGHT-TO-LEFT OVERRIDE, for some glyphs

[lcnbr]

U+2A74 has Bidi_Mirrored=Yes, so it should be mirrored when its resolved direction is R, but it does not have a mirrored counterpart encoded (no Bidi_Mirroring_Glyph), so it is up to the font to provide a mirrored version and substitute it in rtlm feature.

I.e. these two glyphs should be different:

⩴ | ‮‮⩴

[cormullion]

Interesting. I'll see if Glyphs lets me add them easily - if it's a lot of extra work, it might not happen...

[cormullion]

According to this document - http://www.unicode.org/Public/UNIDATA/BidiMirroring.txt - I'd need to create the following new glyphs:

# The following characters have no appropriate mirroring character.
# For these characters it is up to the rendering system
#   to provide mirrored glyphs.

# 2140; DOUBLE-STRUCK N-ARY SUMMATION
# 2201; COMPLEMENT
# 2202; PARTIAL DIFFERENTIAL
# 2203; THERE EXISTS
# 2204; THERE DOES NOT EXIST
# 2211; N-ARY SUMMATION
# 2216; SET MINUS
# 221A; SQUARE ROOT
# 221B; CUBE ROOT
# 221C; FOURTH ROOT
# 221D; PROPORTIONAL TO
# 2226; NOT PARALLEL TO
# 222B; INTEGRAL
# 222C; DOUBLE INTEGRAL
# 222D; TRIPLE INTEGRAL
# 222E; CONTOUR INTEGRAL
# 222F; SURFACE INTEGRAL
# 2230; VOLUME INTEGRAL
# 2231; CLOCKWISE INTEGRAL
# 2232; CLOCKWISE CONTOUR INTEGRAL
# 2233; ANTICLOCKWISE CONTOUR INTEGRAL
# 2239; EXCESS
# 223B; HOMOTHETIC
# 223E; INVERTED LAZY S
# 223F; SINE WAVE
# 2240; WREATH PRODUCT
# 2241; NOT TILDE
# 2242; MINUS TILDE
# 2244; NOT ASYMPTOTICALLY EQUAL TO
# 2246; APPROXIMATELY BUT NOT ACTUALLY EQUAL TO
# 2247; NEITHER APPROXIMATELY NOR ACTUALLY EQUAL TO
# 2248; ALMOST EQUAL TO
# 2249; NOT ALMOST EQUAL TO
# 224A; ALMOST EQUAL OR EQUAL TO
# 224B; TRIPLE TILDE
# 225F; QUESTIONED EQUAL TO
# 2260; NOT EQUAL TO
# 2262; NOT IDENTICAL TO
# 228C; MULTISET
# 22A7; MODELS
# 22AA; TRIPLE VERTICAL BAR RIGHT TURNSTILE
# 22AC; DOES NOT PROVE
# 22AD; NOT TRUE
# 22AE; DOES NOT FORCE
# 22AF; NEGATED DOUBLE VERTICAL BAR DOUBLE RIGHT TURNSTILE
# 22BE; RIGHT ANGLE WITH ARC
# 22BF; RIGHT TRIANGLE
# 22F5; ELEMENT OF WITH DOT ABOVE
# 22F8; ELEMENT OF WITH UNDERBAR
# 22F9; ELEMENT OF WITH TWO HORIZONTAL STROKES
# 22FF; Z NOTATION BAG MEMBERSHIP
# 2320; TOP HALF INTEGRAL
# 2321; BOTTOM HALF INTEGRAL
# 27C0; THREE DIMENSIONAL ANGLE
# 27CC; LONG DIVISION
# 27D3; LOWER RIGHT CORNER WITH DOT
# 27D4; UPPER LEFT CORNER WITH DOT
# 299C; RIGHT ANGLE VARIANT WITH SQUARE
# 299D; MEASURED RIGHT ANGLE WITH DOT
# 299E; ANGLE WITH S INSIDE
# 299F; ACUTE ANGLE
# 29A2; TURNED ANGLE
# 29A6; OBLIQUE ANGLE OPENING UP
# 29A7; OBLIQUE ANGLE OPENING DOWN
# 29C2; CIRCLE WITH SMALL CIRCLE TO THE RIGHT
# 29C3; CIRCLE WITH TWO HORIZONTAL STROKES TO THE RIGHT
# 29C9; TWO JOINED SQUARES
# 29CE; RIGHT TRIANGLE ABOVE LEFT TRIANGLE
# 29DC; INCOMPLETE INFINITY
# 29E1; INCREASES AS
# 29E3; EQUALS SIGN AND SLANTED PARALLEL
# 29E4; EQUALS SIGN AND SLANTED PARALLEL WITH TILDE ABOVE
# 29E5; IDENTICAL TO AND SLANTED PARALLEL
# 29F4; RULE-DELAYED
# 29F6; SOLIDUS WITH OVERBAR
# 29F7; REVERSE SOLIDUS WITH HORIZONTAL STROKE
# 2A0A; MODULO TWO SUM
# 2A0B; SUMMATION WITH INTEGRAL
# 2A0C; QUADRUPLE INTEGRAL OPERATOR
# 2A0D; FINITE PART INTEGRAL
# 2A0E; INTEGRAL WITH DOUBLE STROKE
# 2A0F; INTEGRAL AVERAGE WITH SLASH
# 2A10; CIRCULATION FUNCTION
# 2A11; ANTICLOCKWISE INTEGRATION
# 2A12; LINE INTEGRATION WITH RECTANGULAR PATH AROUND POLE
# 2A13; LINE INTEGRATION WITH SEMICIRCULAR PATH AROUND POLE
# 2A14; LINE INTEGRATION NOT INCLUDING THE POLE
# 2A15; INTEGRAL AROUND A POINT OPERATOR
# 2A16; QUATERNION INTEGRAL OPERATOR
# 2A17; INTEGRAL WITH LEFTWARDS ARROW WITH HOOK
# 2A18; INTEGRAL WITH TIMES SIGN
# 2A19; INTEGRAL WITH INTERSECTION
# 2A1A; INTEGRAL WITH UNION
# 2A1B; INTEGRAL WITH OVERBAR
# 2A1C; INTEGRAL WITH UNDERBAR
# 2A1E; LARGE LEFT TRIANGLE OPERATOR
# 2A1F; Z NOTATION SCHEMA COMPOSITION
# 2A20; Z NOTATION SCHEMA PIPING
# 2A21; Z NOTATION SCHEMA PROJECTION
# 2A24; PLUS SIGN WITH TILDE ABOVE
# 2A26; PLUS SIGN WITH TILDE BELOW
# 2A29; MINUS SIGN WITH COMMA ABOVE
# 2A3E; Z NOTATION RELATIONAL COMPOSITION
# 2A57; SLOPING LARGE OR
# 2A58; SLOPING LARGE AND
# 2A6A; TILDE OPERATOR WITH DOT ABOVE
# 2A6B; TILDE OPERATOR WITH RISING DOTS
# 2A6C; SIMILAR MINUS SIMILAR
# 2A6D; CONGRUENT WITH DOT ABOVE
# 2A6F; ALMOST EQUAL TO WITH CIRCUMFLEX ACCENT
# 2A70; APPROXIMATELY EQUAL OR EQUAL TO
# 2A73; EQUALS SIGN ABOVE TILDE OPERATOR
# 2A74; DOUBLE COLON EQUAL
# 2AA3; DOUBLE NESTED LESS-THAN WITH UNDERBAR
# 2ADC; FORKING
# 2AE2; VERTICAL BAR TRIPLE RIGHT TURNSTILE
# 2AE6; LONG DASH FROM LEFT MEMBER OF DOUBLE VERTICAL
# 2AF3; PARALLEL WITH TILDE OPERATOR
# 2AFB; TRIPLE SOLIDUS BINARY RELATION
# 2AFD; DOUBLE SOLIDUS OPERATOR
# 1D6DB; MATHEMATICAL BOLD PARTIAL DIFFERENTIAL
# 1D715; MATHEMATICAL ITALIC PARTIAL DIFFERENTIAL
# 1D74F; MATHEMATICAL BOLD ITALIC PARTIAL DIFFERENTIAL
# 1D789; MATHEMATICAL SANS-SERIF BOLD PARTIAL DIFFERENTIAL
# 1D7C3; MATHEMATICAL SANS-SERIF BOLD ITALIC PARTIAL DIFFERENTIAL

This many new glyphs aren't going to be added any time soon. Perhaps, if there are any really important ones, they could be prioritized.🤔

[cormullion]

So I did one, which appears to work (if this hb-view test command is correct):

[lcnbr]

Yup thats the correct symbol! Thanks for looking into it!

[cormullion]

Do you happen know what, for example, 221B; CUBE ROOT should look like when reversed:

Like this:

or like this:

[lcnbr]

I think Noto sans Math has these symbols implemented correctly. It gives the first version. In general, RLO only reverses directional glyphs, not letters: https://xkcd.com/1137/

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