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Re: Vim on OS X, (no)macatsui problem

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  • björn
    ... Hi Ken, I have looked into why MacVim fails to render the deseret glyphs and I now have an answer, but unfortunately no solution. The problem is that one
    Message 1 of 17 , Oct 13, 2007
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      > > He also reports that mapping numbers `:map 3 ...` doesn't work. I
      > > can't reproduce this.
      >
      > I got this one wrong. See the other thread for Kenneth's
      > clarification. Sorry.

      Hi Ken,

      I have looked into why MacVim fails to render the deseret glyphs and I
      now have an answer, but unfortunately no solution.

      The problem is that one deseret character for some reason takes up
      _two_ characters when put in the text storage (I guess this have
      something to do with Unicode?). Specifically, calling "length" on an
      NSString containing one deseret character returns 2 instead of 1, as I
      would expect.

      Now, I do know how to fix this problem, but since Jiang is working on
      moving his drawing code to MacVim I don't really want to spend any
      time doing this, since the problem will disappear as soon as he is
      finished. I'm sorry about that.


      /Björn


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    • Tony Mechelynck
      ... UTF-8 uses: 1 byte for each codepoint in the range U+0000 - U+007F 2 bytes for each codepoint in the range U+0080 - U+07FF 3 bytes for each codepoint in
      Message 2 of 17 , Oct 13, 2007
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        björn wrote:
        >>> He also reports that mapping numbers `:map 3 ...` doesn't work. I
        >>> can't reproduce this.
        >> I got this one wrong. See the other thread for Kenneth's
        >> clarification. Sorry.
        >
        > Hi Ken,
        >
        > I have looked into why MacVim fails to render the deseret glyphs and I
        > now have an answer, but unfortunately no solution.
        >
        > The problem is that one deseret character for some reason takes up
        > _two_ characters when put in the text storage (I guess this have
        > something to do with Unicode?). Specifically, calling "length" on an
        > NSString containing one deseret character returns 2 instead of 1, as I
        > would expect.
        >
        > Now, I do know how to fix this problem, but since Jiang is working on
        > moving his drawing code to MacVim I don't really want to spend any
        > time doing this, since the problem will disappear as soon as he is
        > finished. I'm sorry about that.
        >
        >
        > /Björn

        UTF-8 uses:
        1 byte for each codepoint in the range U+0000 - U+007F
        2 bytes for each codepoint in the range U+0080 - U+07FF
        3 bytes for each codepoint in the range U+0800 - U+FFFF
        4 bytes for each codepoint in the range U+10000 - U+1FFFFF
        Actually, current standards mandate that no codepoints higher than U+10FFFD
        will "ever" be used. (Vim supports up to U+3FFFFFFF, with up to 6 bytes per
        codepoint, following an earlier draft of the standard.)

        Unicode also has the notion of "composing characters", which are characters
        which are "superimposed" on the preceding character, possibly changing its
        shape. These are usually diacritics: most of the accents of Latin can be
        either precomposed or spacing-non-accented + composing-accent, but the
        optional vowel marks of Hebrew and Arabic exist only as composing characters.

        Since your Deseret characters are outside the BMP, each of them requires 4
        bytes in UTF-8 (also two 16-bit words in UTF-16 and one 32-bit doubleword in
        UTF-32); but maybe that's not what your measured "length" means? Does your
        NSString include a final null (as C strings do) or an initial bytecount (as
        Pascal strings do)? Or do your Deseret characters include "composing" elements?


        Best regards,
        Tony.
        --
        hundred-and-one symptoms of being an internet addict:
        55. You ask your doctor to implant a gig in your brain.

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      • björn
        ... I m sorry about the confusion with posting this thread separately on vim_multibyte and vim_mac...I ll try to bring the diverging threads together by
        Message 3 of 17 , Oct 14, 2007
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          > > The problem is that one deseret character for some reason takes up
          > > _two_ characters when put in the text storage (I guess this have
          > > something to do with Unicode?). Specifically, calling "length" on an
          > > NSString containing one deseret character returns 2 instead of 1, as I
          > > would expect.
          > >
          > UTF-8 uses:
          > 1 byte for each codepoint in the range U+0000 - U+007F
          > 2 bytes for each codepoint in the range U+0080 - U+07FF
          > 3 bytes for each codepoint in the range U+0800 - U+FFFF
          > 4 bytes for each codepoint in the range U+10000 - U+1FFFFF
          > Actually, current standards mandate that no codepoints higher than U+10FFFD
          > will "ever" be used. (Vim supports up to U+3FFFFFFF, with up to 6 bytes per
          > codepoint, following an earlier draft of the standard.)
          >
          > Unicode also has the notion of "composing characters", which are characters
          > which are "superimposed" on the preceding character, possibly changing its
          > shape. These are usually diacritics: most of the accents of Latin can be
          > either precomposed or spacing-non-accented + composing-accent, but the
          > optional vowel marks of Hebrew and Arabic exist only as composing characters.
          >
          > Since your Deseret characters are outside the BMP, each of them requires 4
          > bytes in UTF-8 (also two 16-bit words in UTF-16 and one 32-bit doubleword in
          > UTF-32); but maybe that's not what your measured "length" means? Does your
          > NSString include a final null (as C strings do) or an initial bytecount (as
          > Pascal strings do)? Or do your Deseret characters include "composing" elements?

          I'm sorry about the confusion with posting this thread separately on
          vim_multibyte and vim_mac...I'll try to bring the diverging threads
          together by posting this reply to both groups.

          Tim Allen replied to the vim_mac thread saying that NSString uses
          utf-16 internally and this is indeed why it says one deseret char has
          length 2 (since it needs two 16 bit chars to store one deseret char,
          as has been pointed out already).

          I was under the mistaken impression that NSString always returned
          length 1 for one character (not counting composing characters), which
          is why I thought MacVim would work in all situations except when
          composing characters were used. Again, this can be fixed by getting
          rid of the assumption that each line in the text storage has the same
          length (as returned by NSString), but this is a rather big code
          change.

          Thanks to Tony and Tim for educating me on the finer points of Unicode... :-)


          /Björn

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        • Tony Mechelynck
          björn wrote: [...] ... Yes, obviously (if one thinks about it) one UTF-16 16-bit word cannot represent anything above U+FFFF. For codepoints U+10000 to
          Message 4 of 17 , Oct 14, 2007
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            björn wrote:
            [...]
            > I'm sorry about the confusion with posting this thread separately on
            > vim_multibyte and vim_mac...I'll try to bring the diverging threads
            > together by posting this reply to both groups.
            >
            > Tim Allen replied to the vim_mac thread saying that NSString uses
            > utf-16 internally and this is indeed why it says one deseret char has
            > length 2 (since it needs two 16 bit chars to store one deseret char,
            > as has been pointed out already).

            Yes, obviously (if one thinks about it) one UTF-16 16-bit word cannot
            represent anything above U+FFFF. For codepoints U+10000 to U+10FFFF (including
            Deseret, among others), two "surrogate characters" are used -- two 16-bit
            words, one in the range 0xD800-0xDBFF and the other in the range 0xDC00-0xDFFF
            : see
            http://en.wikipedia.org/wiki/UTF-16#Encoding_of_characters_outside_the_BMP for
            details. Unlike UTF-8 and UTF-32, UTF-16 inherently cannot, even with
            surrogates, represent anything above U+10FFFF, and (I suppose) that's (one of
            the reasons) why it was decided to bring the "upper range" of Unicode down
            from U+7FFFFFFF to U+10FFFF (and even U+10FFFD since for other reasons, the
            last two codepoints of every plane -- U+xxFFFE and U+xxFFFF -- are "invalid").

            >
            > I was under the mistaken impression that NSString always returned
            > length 1 for one character (not counting composing characters), which
            > is why I thought MacVim would work in all situations except when
            > composing characters were used. Again, this can be fixed by getting
            > rid of the assumption that each line in the text storage has the same
            > length (as returned by NSString), but this is a rather big code
            > change.
            >
            > Thanks to Tony and Tim for educating me on the finer points of Unicode... :-)

            My pleasure. :-)

            >
            >
            > /Björn

            Best regards,
            Tony.
            --
            Court, n.:
            A place where they dispense with justice.
            -- Arthur Train

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          • Kenneth Beesley
            Hi Bjôrn, Many thanks for the message. Yeah, the term Character is a technical term in Unicode, and each Unicode character has a code point value that ranges
            Message 5 of 17 , Oct 15, 2007
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              Hi Bjôrn,

              Many thanks for the message.

              Yeah, the term Character is a technical term in Unicode, and each
              Unicode character has a code point value that ranges from 0x0 to
              0x10FFFF.

              In the original vision of Unicode, code point values ranged from 0x0
              to 0xFFFF, allowing just 64k distinct characters. This old limited
              range
              is now known as the Basic Multilingual Plane (BMP). The current
              vision of Unicode, now 10 years old, allows about a million characters,
              and the characters with code point values beyond 0xFFFF are known
              as supplementary characters.

              Many software applications still haven't caught up with supplementary
              characters. They're still stuck in the BMP.

              In Java, there is a type called "char" that has 16 bits and so can
              represent any code point value in the BMP, 0x0 to 0xFFFF. It is
              important
              not to confuse "char" with the Unicode notion of Character. In Java,
              to store a supplementary Unicode character, two "chars" are used, in a
              coding system known as UTF-16. It sounds like MacVim has a similar
              storage system, and that the length-in-chars is being confused with
              the length-in-Unicode-characters.

              Best wishes,

              Ken



              On 13 Oct 2007, at 12:45, björn wrote:

              >
              >>> He also reports that mapping numbers `:map 3 ...` doesn't work. I
              >>> can't reproduce this.
              >>
              >> I got this one wrong. See the other thread for Kenneth's
              >> clarification. Sorry.
              >
              > Hi Ken,
              >
              > I have looked into why MacVim fails to render the deseret glyphs and I
              > now have an answer, but unfortunately no solution.
              >
              > The problem is that one deseret character for some reason takes up
              > _two_ characters when put in the text storage (I guess this have
              > something to do with Unicode?). Specifically, calling "length" on an
              > NSString containing one deseret character returns 2 instead of 1, as I
              > would expect.
              >
              > Now, I do know how to fix this problem, but since Jiang is working on
              > moving his drawing code to MacVim I don't really want to spend any
              > time doing this, since the problem will disappear as soon as he is
              > finished. I'm sorry about that.
              >
              >
              > /Björn
              >
              >
              > >


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            • Kenneth Beesley
              Tony, Great message, as usual. I insert some friendly comments below. ... KRB: The current modern Unicode character set has code point values ranging from U+0
              Message 6 of 17 , Oct 15, 2007
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                Tony,

                Great message, as usual.
                I insert some friendly comments below.

                On 13 Oct 2007, at 18:30, Tony Mechelynck wrote:

                >
                > björn wrote:
                >>>> He also reports that mapping numbers `:map 3 ...` doesn't work. I
                >>>> can't reproduce this.
                >>> I got this one wrong. See the other thread for Kenneth's
                >>> clarification. Sorry.
                >>
                >> Hi Ken,
                >>
                >> I have looked into why MacVim fails to render the deseret glyphs
                >> and I
                >> now have an answer, but unfortunately no solution.
                >>
                >> The problem is that one deseret character for some reason takes up
                >> _two_ characters when put in the text storage (I guess this have
                >> something to do with Unicode?). Specifically, calling "length" on an
                >> NSString containing one deseret character returns 2 instead of 1,
                >> as I
                >> would expect.
                >>
                >> Now, I do know how to fix this problem, but since Jiang is working on
                >> moving his drawing code to MacVim I don't really want to spend any
                >> time doing this, since the problem will disappear as soon as he is
                >> finished. I'm sorry about that.
                >>
                >>
                >> /Björn
                >

                Tony responds:
                > UTF-8 uses:
                > 1 byte for each codepoint in the range U+0000 - U+007F
                > 2 bytes for each codepoint in the range U+0080 - U+07FF
                > 3 bytes for each codepoint in the range U+0800 - U+FFFF
                > 4 bytes for each codepoint in the range U+10000 - U+1FFFFF

                KRB: The current modern Unicode character set has code point
                values ranging from U+0 to U+10FFFF, allowing about a million
                distinct "characters". These Unicode Characters are slightly abstract
                and need to be distinguished carefully from how they are "encoded"
                in a file or in a programming language. In UTF-8 encoding, the "code
                unit"
                is one byte, and each Unicode character (each code point value) is
                stored in one
                to four bytes as you describe above. The conversion between code point
                values (integers) and the bit/byte representations requires some trivlal
                bit extraction and shifting.

                What Bjôrn describes sounds more like UTF-16, where each Unicode
                character (code point value) is stored in either one 16-bit "code unit"
                or in two 16-bit code units. Characters from the Basic Multilingual
                Plane,
                U+0 to U+FFFF, are stored in a single 16-bit code unit. Supplementary
                characters, those beyond the Basic Multilingual Plane, are stored in two
                16-bit code units. (Again there is some trivial bit manipulation
                involved
                in conversion between code point values and the bit representations
                in the 16-bit code units.)

                Perl stores Unicode strings internally as UTF-8, but you should
                hardly ever
                have to know that. If you ask for the length of a Perl Unicode
                string, Perl gives
                you the length in Unicode Characters. If you loop through the
                characters in
                a Perl Unicode string, it loops through Unicode Characters, taking
                care of
                the underlying UTF-8 encoding in the background. The underlying
                encoding
                in UTF-8 is effectively hidden from the programmer. At the
                programming level,
                you can always think of a Perl Unicode string as a sequence of Unicode
                Characters (including supplementary characters).

                Java from the very beginning took Unicode very seriously. But Java
                emerged
                in the olden days of Unicode, when code point values ranged only from
                U+0 to
                U+FFFF, so every original Unicode character could be stored in a single
                16-bit "char". The length of a Unicode string was simply the number
                of chars.
                Easy and clean.
                The introduction of supplementary Unicode characters 10 years ago
                created
                quite a challenge for Java and other programming languages that wanted
                to take Unicode seriously. Instead of accommodating the New Unicode by
                making char 32 bits (which would allow each New Unicode character to be
                stored straightforwardly in a single 32-bit char) the Java gurus
                opted to keep "char" at 16-bits
                and use UTF-16 to store Unicode strings. If you ask for the "length"
                of a Unicode
                string in Java, it still returns the length in chars rather than the
                length in Unicode
                Characters. This is (arguably) quite a mess, and you have to be very
                aware of it
                as a programmer if you want to handle Supplementary Unicode Characters.

                The way that Python handles Unicode strings internally depends on how
                it is configured/built. If configured for "ucs2", Python stores
                Unicode strings as
                UTF-16, returns the "length" of strings as the number of 16-bit code
                units, and
                if you try to loop through the elements of a string, it loops through
                16-bit
                values, which creates a mess if your string contains supplementary
                characters.
                This is comparable to the situation in Java.

                If you configure Python for "ucs4", then each Unicode string is
                stored internally as
                a string of 32-bit code units, "length" is returned as the number of
                Unicode characters, and if you loop through the characters in a
                string, you
                get one Unicode character (code point value) at a time, even for
                supplementary
                characters. This "ucs4" option is now formally termed UTF-32 in Unicode
                circles.



                > Actually, current standards mandate that no codepoints higher than U
                > +10FFFD
                > will "ever" be used. (Vim supports up to U+3FFFFFFF, with up to 6
                > bytes per
                > codepoint, following an earlier draft of the standard.)
                >
                > Unicode also has the notion of "composing characters", which are
                > characters
                > which are "superimposed" on the preceding character, possibly
                > changing its
                > shape. These are usually diacritics: most of the accents of Latin
                > can be
                > either precomposed or spacing-non-accented + composing-accent, but the
                > optional vowel marks of Hebrew and Arabic exist only as composing
                > characters.

                Quite right. "Character" is a technical term in Unicode, and
                includes spaces,
                punctuation and these Composing Diacritical Marks (block starting U
                +0300)
                that might not fall under the everyday notion of character. An
                acute-accented é,
                for example, can be represented in Unicode either as a single character,

                U+00E9

                which has the name LATIN SMALL LETTER E WITH ACUTE

                You can alternatively represent é as a sequence of two Unicode
                characters

                U+0065 LATIN SMALL LETTER E
                U+0301 COMBINING ACUTE ACCENT

                The Unicode gods have explicitly decreed that these two
                representations are
                equivalent, which means that any proper Unicode-capable editor should
                handle and display them equivalently.

                In Hopi (spoken in Arizona) orthography (as defined at the University of
                Arizona), you have some double-accented graphemes like o with both
                diaeresis and an acute, grave or circumflex accent. In Unicode you
                can represent o with diaeresis and acute (the acute accent is rendered
                above the diaeresis) as either the three-character sequence

                U+006F UNICODE SMALL LETTER O
                U+0308 COMBINING DIAERESIS
                U+0301 COMBINING ACUTE ACCENT

                or as the two-character sequence

                U+00F6 LATIN SMALL LETTER O WITH DIAERESIS
                U+0301 COMBINING ACUTE ACCENT

                But there is no single "pre-composed" Unicode character for this
                purpose.

                This whole issue of Combining Diacritical Marks is separate from the
                issue
                of encoding (UTF-8, UTF-16 or UTF-32). Some conversion between "pre-
                composed"
                and "decomposed" representations can be done using "Normalization"
                routines
                available in Perl, Python, Java, ICU, etc.

                These Combining Diacritical Marks need to be rendered above or below,
                or attached in particular places, as appropriate, to any letter
                character. For
                that to work properly, you need a font (e.g. Doulos SIL or Charis
                SIL) that
                contains the diacritic-positioning information, and you need a
                sophisticated rendering
                engine (as in XeTeX) that reads and uses that diacritic-positioning
                information.

                Most software, including text editors, still do a poor job of handling
                Combining Diacritical Marks and supplementary characters in general.

                >
                > Since your Deseret characters are outside the BMP, each of them
                > requires 4
                > bytes in UTF-8 (also two 16-bit words in UTF-16 and one 32-bit
                > doubleword in
                > UTF-32); but maybe that's not what your measured "length" means?
                > Does your
                > NSString include a final null (as C strings do) or an initial
                > bytecount (as
                > Pascal strings do)? Or do your Deseret characters include
                > "composing" elements?

                Because the "length" of each Deseret Character is being returned as 2
                rather
                than 1, it sounds like the MacVim code is using a Java-like UTF-16
                internal representation
                for storing Unicode characters (including supplementary characters).

                There are no Combining Diacritical Marks required in the traditional
                Deseret Alphabet, per se,
                although proper rendering software _should_ allow you to associate
                one or more Combining
                Diacritics Marks with any letter character and have it rendered
                acceptably. (Handling
                combining diacritical marks with Deseret Alphabet is very low priority.)

                Each Deseret Alphabet letter is a single Unicode character, with a
                single code
                point value in the supplementary area (block starting U+10400). The
                Shavian alphabet is
                much the same (in the block starting U+10450). The glyphs are
                straightforward, rendered
                left-to-right, requiring no ligatures, and could be forced into a
                fixed-pitch (mono) font about
                as easily as Roman glyphs.

                Ken



                >
                >
                > Best regards,
                > Tony.
                > --
                > hundred-and-one symptoms of being an internet addict:
                > 55. You ask your doctor to implant a gig in your brain.
                >
                > >


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              • Tony Mechelynck
                ... Vim doesn t use UTF-16 internally, because the many intervening nulls would wreak havoc with the C requirement of null-terminated strings. If you set
                Message 7 of 17 , Oct 16, 2007
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                  Kenneth Beesley wrote:
                  > Hi Bjôrn,
                  >
                  > Many thanks for the message.
                  >
                  > Yeah, the term Character is a technical term in Unicode, and each
                  > Unicode character has a code point value that ranges from 0x0 to
                  > 0x10FFFF.
                  >
                  > In the original vision of Unicode, code point values ranged from 0x0
                  > to 0xFFFF, allowing just 64k distinct characters. This old limited
                  > range
                  > is now known as the Basic Multilingual Plane (BMP). The current
                  > vision of Unicode, now 10 years old, allows about a million characters,
                  > and the characters with code point values beyond 0xFFFF are known
                  > as supplementary characters.
                  >
                  > Many software applications still haven't caught up with supplementary
                  > characters. They're still stuck in the BMP.
                  >
                  > In Java, there is a type called "char" that has 16 bits and so can
                  > represent any code point value in the BMP, 0x0 to 0xFFFF. It is
                  > important
                  > not to confuse "char" with the Unicode notion of Character. In Java,
                  > to store a supplementary Unicode character, two "chars" are used, in a
                  > coding system known as UTF-16. It sounds like MacVim has a similar
                  > storage system, and that the length-in-chars is being confused with
                  > the length-in-Unicode-characters.
                  >
                  > Best wishes,
                  >
                  > Ken

                  Vim doesn't use UTF-16 internally, because the many intervening nulls would
                  wreak havoc with the C requirement of null-terminated strings. If you set
                  'encoding' to UCS-4, UTF-16 or UTF-32 (of any endianness), Vim will actually
                  use UTF-8 internally, because 0x00 in UTF-8 is the NULL character (codepoint
                  U+0000), nothing else, and Vim already knows how to handle that.

                  When you set 'fileencoding' to UTF-16, the internal UTF-8 representation of
                  the text will be converted to and from UTF-16 when writing or reading
                  (respectively), using surrogate pairs for any codepoint above U+FFFF, so that,
                  _on disk_, they take two UTF-16 words rather than one.

                  I don't know what function you used to count characters, but the Vim
                  string-length function, strlen(), gives a string's length in _bytes_ in the
                  current internal representation: for Unicode, "a" (U+0061) is one, "é"
                  (e-acute, U+00E9) is two, "†" (dagger, U+2020) is three and any Deseret
                  character is four. (Under ":help strlen()" you can see how to count
                  "characters" in a string, as opposed to "bytes".)

                  >
                  >
                  >
                  > On 13 Oct 2007, at 12:45, björn wrote:
                  >
                  >>>> He also reports that mapping numbers `:map 3 ...` doesn't work. I
                  >>>> can't reproduce this.
                  >>> I got this one wrong. See the other thread for Kenneth's
                  >>> clarification. Sorry.
                  >> Hi Ken,
                  >>
                  >> I have looked into why MacVim fails to render the deseret glyphs and I
                  >> now have an answer, but unfortunately no solution.
                  >>
                  >> The problem is that one deseret character for some reason takes up
                  >> _two_ characters when put in the text storage (I guess this have
                  >> something to do with Unicode?). Specifically, calling "length" on an
                  >> NSString containing one deseret character returns 2 instead of 1, as I
                  >> would expect.
                  >>
                  >> Now, I do know how to fix this problem, but since Jiang is working on
                  >> moving his drawing code to MacVim I don't really want to spend any
                  >> time doing this, since the problem will disappear as soon as he is
                  >> finished. I'm sorry about that.
                  >>
                  >>
                  >> /Björn


                  Best regards,
                  Tony.
                  --
                  During a grouse hunt in North Carolina two intrepid sportsmen
                  were blasting away at a clump of trees near a stone wall. Suddenly a
                  red-faced country squire popped his head over the wall and shouted,
                  "Hey, you almost hit my wife."
                  "Did I?" cried the hunter, aghast. "Terribly sorry. Have a
                  shot at mine, over there."

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                • Tony Mechelynck
                  ... Hm. I guess I ll stay with Vim and vim-script, where I know what to expect. ... also control characters (carriage return, line feed, form feed, horizontal
                  Message 8 of 17 , Oct 16, 2007
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                    Kenneth Beesley wrote:
                    >
                    > Tony,
                    >
                    > Great message, as usual.
                    > I insert some friendly comments below.
                    >
                    > On 13 Oct 2007, at 18:30, Tony Mechelynck wrote:
                    >
                    >> björn wrote:
                    >>>>> He also reports that mapping numbers `:map 3 ...` doesn't work. I
                    >>>>> can't reproduce this.
                    >>>> I got this one wrong. See the other thread for Kenneth's
                    >>>> clarification. Sorry.
                    >>> Hi Ken,
                    >>>
                    >>> I have looked into why MacVim fails to render the deseret glyphs
                    >>> and I
                    >>> now have an answer, but unfortunately no solution.
                    >>>
                    >>> The problem is that one deseret character for some reason takes up
                    >>> _two_ characters when put in the text storage (I guess this have
                    >>> something to do with Unicode?). Specifically, calling "length" on an
                    >>> NSString containing one deseret character returns 2 instead of 1,
                    >>> as I
                    >>> would expect.
                    >>>
                    >>> Now, I do know how to fix this problem, but since Jiang is working on
                    >>> moving his drawing code to MacVim I don't really want to spend any
                    >>> time doing this, since the problem will disappear as soon as he is
                    >>> finished. I'm sorry about that.
                    >>>
                    >>>
                    >>> /Björn
                    >
                    > Tony responds:
                    >> UTF-8 uses:
                    >> 1 byte for each codepoint in the range U+0000 - U+007F
                    >> 2 bytes for each codepoint in the range U+0080 - U+07FF
                    >> 3 bytes for each codepoint in the range U+0800 - U+FFFF
                    >> 4 bytes for each codepoint in the range U+10000 - U+1FFFFF
                    >
                    > KRB: The current modern Unicode character set has code point
                    > values ranging from U+0 to U+10FFFF, allowing about a million
                    > distinct "characters". These Unicode Characters are slightly abstract
                    > and need to be distinguished carefully from how they are "encoded"
                    > in a file or in a programming language. In UTF-8 encoding, the "code
                    > unit"
                    > is one byte, and each Unicode character (each code point value) is
                    > stored in one
                    > to four bytes as you describe above. The conversion between code point
                    > values (integers) and the bit/byte representations requires some trivlal
                    > bit extraction and shifting.
                    >
                    > What Bjôrn describes sounds more like UTF-16, where each Unicode
                    > character (code point value) is stored in either one 16-bit "code unit"
                    > or in two 16-bit code units. Characters from the Basic Multilingual
                    > Plane,
                    > U+0 to U+FFFF, are stored in a single 16-bit code unit. Supplementary
                    > characters, those beyond the Basic Multilingual Plane, are stored in two
                    > 16-bit code units. (Again there is some trivial bit manipulation
                    > involved
                    > in conversion between code point values and the bit representations
                    > in the 16-bit code units.)
                    >
                    > Perl stores Unicode strings internally as UTF-8, but you should
                    > hardly ever
                    > have to know that. If you ask for the length of a Perl Unicode
                    > string, Perl gives
                    > you the length in Unicode Characters. If you loop through the
                    > characters in
                    > a Perl Unicode string, it loops through Unicode Characters, taking
                    > care of
                    > the underlying UTF-8 encoding in the background. The underlying
                    > encoding
                    > in UTF-8 is effectively hidden from the programmer. At the
                    > programming level,
                    > you can always think of a Perl Unicode string as a sequence of Unicode
                    > Characters (including supplementary characters).
                    >
                    > Java from the very beginning took Unicode very seriously. But Java
                    > emerged
                    > in the olden days of Unicode, when code point values ranged only from
                    > U+0 to
                    > U+FFFF, so every original Unicode character could be stored in a single
                    > 16-bit "char". The length of a Unicode string was simply the number
                    > of chars.
                    > Easy and clean.
                    > The introduction of supplementary Unicode characters 10 years ago
                    > created
                    > quite a challenge for Java and other programming languages that wanted
                    > to take Unicode seriously. Instead of accommodating the New Unicode by
                    > making char 32 bits (which would allow each New Unicode character to be
                    > stored straightforwardly in a single 32-bit char) the Java gurus
                    > opted to keep "char" at 16-bits
                    > and use UTF-16 to store Unicode strings. If you ask for the "length"
                    > of a Unicode
                    > string in Java, it still returns the length in chars rather than the
                    > length in Unicode
                    > Characters. This is (arguably) quite a mess, and you have to be very
                    > aware of it
                    > as a programmer if you want to handle Supplementary Unicode Characters.

                    Hm. I guess I'll stay with Vim and vim-script, where I know what to expect.

                    >
                    > The way that Python handles Unicode strings internally depends on how
                    > it is configured/built. If configured for "ucs2", Python stores
                    > Unicode strings as
                    > UTF-16, returns the "length" of strings as the number of 16-bit code
                    > units, and
                    > if you try to loop through the elements of a string, it loops through
                    > 16-bit
                    > values, which creates a mess if your string contains supplementary
                    > characters.
                    > This is comparable to the situation in Java.
                    >
                    > If you configure Python for "ucs4", then each Unicode string is
                    > stored internally as
                    > a string of 32-bit code units, "length" is returned as the number of
                    > Unicode characters, and if you loop through the characters in a
                    > string, you
                    > get one Unicode character (code point value) at a time, even for
                    > supplementary
                    > characters. This "ucs4" option is now formally termed UTF-32 in Unicode
                    > circles.
                    >
                    >
                    >
                    >> Actually, current standards mandate that no codepoints higher than U
                    >> +10FFFD
                    >> will "ever" be used. (Vim supports up to U+3FFFFFFF, with up to 6
                    >> bytes per
                    >> codepoint, following an earlier draft of the standard.)
                    >>
                    >> Unicode also has the notion of "composing characters", which are
                    >> characters
                    >> which are "superimposed" on the preceding character, possibly
                    >> changing its
                    >> shape. These are usually diacritics: most of the accents of Latin
                    >> can be
                    >> either precomposed or spacing-non-accented + composing-accent, but the
                    >> optional vowel marks of Hebrew and Arabic exist only as composing
                    >> characters.
                    >
                    > Quite right. "Character" is a technical term in Unicode, and
                    > includes spaces,
                    > punctuation and these Composing Diacritical Marks (block starting U
                    > +0300)
                    > that might not fall under the everyday notion of character. An

                    also control characters (carriage return, line feed, form feed, horizontal
                    tab, soft hyphen, byte-order mark, zero-width joiner, etc.), which also might
                    not all fall under the everyday notion of "character".

                    > acute-accented é,
                    > for example, can be represented in Unicode either as a single character,
                    >
                    > U+00E9
                    >
                    > which has the name LATIN SMALL LETTER E WITH ACUTE
                    >
                    > You can alternatively represent é as a sequence of two Unicode
                    > characters
                    >
                    > U+0065 LATIN SMALL LETTER E
                    > U+0301 COMBINING ACUTE ACCENT
                    >
                    > The Unicode gods have explicitly decreed that these two
                    > representations are
                    > equivalent, which means that any proper Unicode-capable editor should
                    > handle and display them equivalently.
                    >
                    > In Hopi (spoken in Arizona) orthography (as defined at the University of
                    > Arizona), you have some double-accented graphemes like o with both
                    > diaeresis and an acute, grave or circumflex accent. In Unicode you
                    > can represent o with diaeresis and acute (the acute accent is rendered
                    > above the diaeresis) as either the three-character sequence
                    >
                    > U+006F UNICODE SMALL LETTER O
                    > U+0308 COMBINING DIAERESIS
                    > U+0301 COMBINING ACUTE ACCENT
                    >
                    > or as the two-character sequence
                    >
                    > U+00F6 LATIN SMALL LETTER O WITH DIAERESIS
                    > U+0301 COMBINING ACUTE ACCENT
                    >
                    > But there is no single "pre-composed" Unicode character for this
                    > purpose.
                    >
                    > This whole issue of Combining Diacritical Marks is separate from the
                    > issue
                    > of encoding (UTF-8, UTF-16 or UTF-32). Some conversion between "pre-
                    > composed"
                    > and "decomposed" representations can be done using "Normalization"
                    > routines
                    > available in Perl, Python, Java, ICU, etc.

                    but not in Vim. AFAIK, the only "normalization" routines afforded by Vim
                    (other than not using a separate screen cell for composing character) are: (a)
                    the 'delcombine' option, which, if set, allows <BS> to erase one combining
                    character at a time, while when clear (default) it will erase one spacing
                    character together with any number of combining characters in the same screen
                    cell; and (b) the \Z pattern atom, which will ignore combining characters
                    anywhere in the text while matching. But AFAIK Vim will always treat "é"
                    (U+00E9 LATIN SMALL LETTER E WITH ACUTE) and "é" (U+0065 LATIN SMALL LETTER E
                    + U+0301 COMBINING ACUTE ACCENT) as different even if it displays them the same.

                    >
                    > These Combining Diacritical Marks need to be rendered above or below,
                    > or attached in particular places, as appropriate, to any letter
                    > character. For
                    > that to work properly, you need a font (e.g. Doulos SIL or Charis
                    > SIL) that
                    > contains the diacritic-positioning information, and you need a
                    > sophisticated rendering
                    > engine (as in XeTeX) that reads and uses that diacritic-positioning
                    > information.
                    >
                    > Most software, including text editors, still do a poor job of handling
                    > Combining Diacritical Marks and supplementary characters in general.

                    In Arabic, Vim handles combining vowels etc. ("harakaat" as Arabic grammarians
                    call them) quite well, including several per character as e.g. in (spacing)
                    seen (Arabic S) + combining shadda (geminated-consonant sign) + combining
                    fatha (Arabic short vowel a), a combination which appears in the fully
                    vocalized form of "as-salaam" (Peace). Starting recently (7.1.116), Vim can
                    now display (not only edit) any codepoint in the current 'guifont', not only
                    those in the BMP. From what you say above, it looks like Vim is ahead of "most
                    software including text editors", but I don't doubt that the situation will
                    get better as time goes on.

                    >
                    >> Since your Deseret characters are outside the BMP, each of them
                    >> requires 4
                    >> bytes in UTF-8 (also two 16-bit words in UTF-16 and one 32-bit
                    >> doubleword in
                    >> UTF-32); but maybe that's not what your measured "length" means?
                    >> Does your
                    >> NSString include a final null (as C strings do) or an initial
                    >> bytecount (as
                    >> Pascal strings do)? Or do your Deseret characters include
                    >> "composing" elements?
                    >
                    > Because the "length" of each Deseret Character is being returned as 2
                    > rather
                    > than 1, it sounds like the MacVim code is using a Java-like UTF-16
                    > internal representation
                    > for storing Unicode characters (including supplementary characters).

                    How do you compute that length? The strlen() function should return 4 for each
                    Deseret character, and the function (similar to that mentioned under ":help
                    strlen()")

                    strlen(substitute(string,'.','-'))

                    should return 1.

                    >
                    > There are no Combining Diacritical Marks required in the traditional
                    > Deseret Alphabet, per se,
                    > although proper rendering software _should_ allow you to associate
                    > one or more Combining
                    > Diacritics Marks with any letter character and have it rendered
                    > acceptably. (Handling
                    > combining diacritical marks with Deseret Alphabet is very low priority.)
                    >
                    > Each Deseret Alphabet letter is a single Unicode character, with a
                    > single code
                    > point value in the supplementary area (block starting U+10400). The
                    > Shavian alphabet is
                    > much the same (in the block starting U+10450). The glyphs are
                    > straightforward, rendered
                    > left-to-right, requiring no ligatures, and could be forced into a
                    > fixed-pitch (mono) font about
                    > as easily as Roman glyphs.
                    >
                    > Ken

                    and a lot more easily than Arabic, where a single letter (with a single code
                    point) may have to be shown in up to 4 different ways (not counting combining
                    characters), depending on its position in the word and on which letter (if
                    any) precedes it. Happily Vim (with +arabic) knows how to fetch the required
                    "presentation forms" from the Arabic fonts. Anyway, the beautiful cursive
                    shapes of Arabic still look ugly when rendered in any monospace font, but
                    that's because Arabic calligraphy, with its long flourishes at the end of
                    almost every word, was invented for the calame (i.e., the reed pen), not the
                    typewriter.


                    Best regards,
                    Tony.
                    --
                    Try to be the best of whatever you are, even if what you are is no
                    good.


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