<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
</head>
<body>
<p><br>
</p>
<div class="moz-cite-prefix">On 1/2/24 13:12, Peter Constable wrote:<br>
</div>
<blockquote type="cite"
cite="mid:DS7PR21MB3367EA286C482F8D81AF3592DE612@DS7PR21MB3367.namprd21.prod.outlook.com">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<meta name="Generator"
content="Microsoft Word 15 (filtered medium)">
<style>@font-face
{font-family:Wingdings;
panose-1:5 0 0 0 0 0 0 0 0 0;}@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}@font-face
{font-family:Aptos;}@font-face
{font-family:"Segoe UI";
panose-1:2 11 5 2 4 2 4 2 2 3;}@font-face
{font-family:Consolas;
panose-1:2 11 6 9 2 2 4 3 2 4;}p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
font-size:12.0pt;
font-family:"Aptos",sans-serif;}a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}pre
{mso-style-priority:99;
mso-style-link:"HTML Preformatted Char";
margin:0in;
font-size:10.0pt;
font-family:"Courier New";}p.MsoListParagraph, li.MsoListParagraph, div.MsoListParagraph
{mso-style-priority:34;
margin-top:0in;
margin-right:0in;
margin-bottom:0in;
margin-left:.5in;
font-size:12.0pt;
font-family:"Aptos",sans-serif;}span.HTMLPreformattedChar
{mso-style-name:"HTML Preformatted Char";
mso-style-priority:99;
mso-style-link:"HTML Preformatted";
font-family:Consolas;}span.EmailStyle25
{mso-style-type:personal-compose;
font-family:"Aptos",sans-serif;
color:windowtext;}.MsoChpDefault
{mso-style-type:export-only;
font-size:10.0pt;
mso-ligatures:none;}div.WordSection1
{page:WordSection1;}ol
{margin-bottom:0in;}ul
{margin-bottom:0in;}</style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
<div class="WordSection1">
<p class="MsoNormal"><span style="font-size:11.0pt">Happy 2024,
all!<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">> </span>My
worry about using dmap for multi-language/region support…<o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">First, let
me repeat: multi-language/region support is not the only
reason for creating TTCs / not the only motivation for a
dmap table.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">As for
handling multi-language/region support…<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">If I
understand correctly your line of reasoning, you’re OK with
the idea that distinct font resources (bundled in a TTC for
de-duplication of data) can be used as the means given to
the user for selecting language-/region-specific glyphs. But
instead of cmap/dmap as the implementation mechanism to get
different glyphs according to the font resource that is
selected, you want to a mechanism that instead integrates
with GSUB/GPOS.<o:p></o:p></span></p>
</div>
</blockquote>
<p>Yes<br>
</p>
<blockquote type="cite"
cite="mid:DS7PR21MB3367EA286C482F8D81AF3592DE612@DS7PR21MB3367.namprd21.prod.outlook.com">
<div class="WordSection1">
<p class="MsoNormal"><span style="font-size:11.0pt"><b>Please
note that dmap is really orthogonal to your line of
reasoning</b>. Ignore dmap for a moment: today, a TTC can
bundle language-/region-specific font resources with
distinct cmaps as the mechanism for selecting distinct
glyphs.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">So, your
suggestion is that, instead of distinct cmaps, that we could
provide a way for the fonts in a TTC to share a common cmap
and instead have some distinct data that triggers different
GSUB/GPOS actions in each font resulting in selecting
language-/region-specific glyphs. Like the dmap proposal,
this would avoid a lot of duplication in cmap data, and the
size savings in each case would likely be comparable. The
key difference between these is<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<ul style="margin-top:0in" type="disc">
<li class="MsoListParagraph"
style="margin-left:0in;mso-list:l0 level1 lfo5"><span
style="font-size:11.0pt">Integration into initial
character-to-glyph mapping<o:p></o:p></span></li>
</ul>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">versus<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<ul style="margin-top:0in" type="disc">
<li class="MsoListParagraph"
style="margin-left:0in;mso-list:l0 level1 lfo5"><span
style="font-size:11.0pt">Integration into OT Layout glyph
actions that occur after initial character-to-glyph
mapping (which is typically done in a shaping engine).<o:p></o:p></span></li>
</ul>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Now, I said
earlier that TTCs can be created for reasons other than <b>multi-language/region
support. We could generalize the latter to cover any
situation provided the mechanism doesn’t require use of
registered script/langsys tags.</b><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
</div>
</blockquote>
<p>I think that it's an overstatement to say that they're
"orthogonal". The only reason I can see for adding dmap is to
reduce file size -- otherwise you could just have separate maps.
It's true the reasoning I've offered for a GSUB/GPOS mechanism is
based in multi-language/region support, but as (I think) you imply
here, it could be extended to other cases via the use of reserved
or otherwise non-conforming langsys tags. <br>
</p>
<p>Generally speaking, distinct cmaps (whether achieved via separate
tables or dmap) will either be upstream of distinct GSUB tables or
(rarely) upstream of a font without a GSUB. (Constructing a GSUB
that will work correctly downstream from different cmaps is a
strange thing to even attempt.) So in practice, by enshrining dmap
one more or gives up saving the duplicate GSUB space. A typical
such GSUB may be smaller, in that more of the mapping will be
sorted out in the dmap, but the work of any optional features will
be duplicated. So how orthogonal the topics are depends in part on
what degree of file size savings is desired or expected.<br>
</p>
<blockquote type="cite"
cite="mid:DS7PR21MB3367EA286C482F8D81AF3592DE612@DS7PR21MB3367.namprd21.prod.outlook.com">
<div class="WordSection1">
<p class="MsoNormal"></p>
<p class="MsoNormal"><span style="font-size:11.0pt">I’ll digress
for a moment to point out that this situation is not
entirely unlike the need to handle Unicode variation
sequences: given a triggering condition (presence of a VS
character / user selection of a particular font resource)
some characters need to be mapped to different glyphs. It
was about 15 years ago that Adobe approached Microsoft to
work on a solution. In that case, those of us at MS thought
this could simply be handled in GSUB without needing to
design any new table formats. But Adobe pushed strongly, and
convinced us, to create a new table format, cmap subtable
format 14. While I forget all of the details, part of their
argument was that this should really be handled in the
initial character-to-glyph mapping, not in OT Layout glyph
processing that comes later.<o:p></o:p></span></p>
</div>
</blockquote>
<p>I can't speak to past Adobe positions beyond observing that
companies change their positions all the time. As far as this
specific issue is concerned, the point that Adobe may have been
making then and the point I'm making now aren't necessarily in
conflict. cmap, and thus dmap, are creatures of Unicode mappings,
and are accordingly a context for working out various complex
issues of <i>identity</i>. In some cases whether a question
relates to identity or to, say, "style" is a matter of opinion,
and people may have strongly felt that for the format 14 stuff it
was the former. <br>
</p>
<p>In any case, when there are questions of identity but no
subsequent questions of style, one can just map in cmap and be
done with it. When there are further questions of style -- and the
decision by Unicode to use a common subset of codepoints for
different CJK languages and regions effectively <i>classifies</i>
those distinctions as matters of style, broadly speaking -- one
needs to treat the GID initially cmapped-to as "symbolic", in a
sense, in order to support multiple such languages/regions in the
same (sfnt) font. Doing more of that work up front with dmap is
more of a "you won't have to bother with all that" sort of thing,
there's no big conceptual leap.<br>
</p>
<blockquote type="cite"
cite="mid:DS7PR21MB3367EA286C482F8D81AF3592DE612@DS7PR21MB3367.namprd21.prod.outlook.com">
<div class="WordSection1">
<p class="MsoNormal"><span style="font-size:11.0pt">Returning to
the main topic…<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">></span>
Ideally we want fonts that support different scripts and
languages via [OT Layout]…<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Is your
preference for OTL integration because you focused on TTCs
for multi-language/region support and OTL already has
script/langsys mechanisms? Or would you prefer OTL
integration even for TTCs not providing
multi-language/region support?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">If the
former, then (i) I’d counter that (again)
multi-language/region support isn’t the only reason for
creating TTCs.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">In either
case, I’ll ask: Why is OTL integration the ideal approach?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p><br>
</o:p></span></p>
</div>
</blockquote>
<p>I think there are virtues to doing either at the OTL level
because it will further minimize file size, which is the only
plausible goal of dmap. So it seems like the argument for dmap
would therefore be that it fits better into existing toolchains,
which is probably true. If that's right then the question boils
down the balance between how much reward we want from tool
development vs how much we think we can ask of it.</p>
<blockquote type="cite"
cite="mid:DS7PR21MB3367EA286C482F8D81AF3592DE612@DS7PR21MB3367.namprd21.prod.outlook.com">
<div class="WordSection1">
<p class="MsoNormal"><span style="font-size:11.0pt">For VSs,
Adobe argued the other way around: relying on OTL was less
preferable to initial character-to-glyph mapping. One
argument against OTL integration involves character-palette
UI: today that can be handled using cmap data alone. With
OTL integration, there’s all of the GSUB formats that need
to be processed—effectively invoking shaping logic. And this
applies not just to character-palette UIs: platform APIs
that return the initial character-to-glyph mapping (which
are independently needed) also need to route through code
that, to now, has been designed for use only after initial
character-to-glyph mapping.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">It’s mixing
layers that, for some implementations, could be kept cleanly
separated. For example, in the GDI text stack, the
<a
href="https://learn.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-getglyphindicesw"
moz-do-not-send="true">
GetGlyphIndices()</a> implementation would read cmap data
directly without calling into Uniscribe for OTL processing.
Using OTL integration to de-dup cmap data in TTCs would
require the GetGlyphIndices implementation to call into
Uniscribe.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">So, I remain
unconvinced this is ideal and would like to understand more
why you think it is.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">></span>
<span style="font-size:11.0pt">
4. However, after thinking about how GSUB tables are
structured one realizes one can probably accomplish the same
thing without any spec changes…<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Except you
haven’t proposed any way to trigger a font-specific required
glyph substitution as part of the initial character-to-glyph
mapping, which it seems to me is _<i>the essence of what is
required</i>_.
</span></p>
</div>
</blockquote>
<p>The mechanism I discussed is allowing the lookup table associated
with DFLT/dflt to be distinct for each TTC entry. After thinking
about it a bit more one might also want to influence the dflt
entries for non-DFLT scripts to "match", but this is just a matter
of a bit more "duplicated" material. This GSUB mechanism does
raise some further questions about switching between language
systems in TTCs built this way, but distinct cmaps raise similar
questions. If a font can't support it it can just leave every TTC
slot as, in effect, DFLT-dflt-only. <br>
</p>
<p>Skef<br>
</p>
<blockquote type="cite"
cite="mid:DS7PR21MB3367EA286C482F8D81AF3592DE612@DS7PR21MB3367.namprd21.prod.outlook.com">
<div class="WordSection1">
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">A simple way
to do that could be a small, font-specific table that
provides an index into the GSUB lookup list, with the
constraint that the lookup must be a type 1(single
substitution) lookup (else it will be ignored). But I’m
still not sure this is ideal and preferable to a dmap table.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Peter
Constable<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<div>
<div
style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif">
mpeg-otspec <a class="moz-txt-link-rfc2396E" href="mailto:mpeg-otspec-bounces@lists.aau.at"><mpeg-otspec-bounces@lists.aau.at></a>
<b>On Behalf Of </b>Skef Iterum<br>
<b>Sent:</b> Wednesday, December 27, 2023 4:19 AM<br>
<b>To:</b> Ken Lunde <a class="moz-txt-link-rfc2396E" href="mailto:lunde@unicode.org"><lunde@unicode.org></a><br>
<b>Cc:</b> <a class="moz-txt-link-abbreviated" href="mailto:mpeg-otspec@lists.aau.at">mpeg-otspec@lists.aau.at</a><br>
<b>Subject:</b> [EXTERNAL] [MPEG-OTSPEC] Shared
GSUB/GPOS notes, was Re: dmap proposal<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<table class="MsoNormalTable" style="width:100.0%" width="100%"
cellspacing="0" cellpadding="0" border="0" align="left">
<tbody>
<tr>
<td
style="background:#A6A6A6;padding:5.25pt 1.5pt 5.25pt 1.5pt"><br>
</td>
<td
style="width:100.0%;background:#EAEAEA;padding:5.25pt 3.75pt 5.25pt 11.25pt"
width="100%">
<div>
<p class="MsoNormal"
style="mso-element:frame;mso-element-frame-hspace:2.25pt;mso-element-wrap:around;mso-element-anchor-vertical:paragraph;mso-element-anchor-horizontal:column;mso-height-rule:exactly">
<span
style="font-size:9.0pt;font-family:"Segoe UI",sans-serif;color:#212121">You
don't often get email from
<a href="mailto:skef@skef.org"
moz-do-not-send="true"
class="moz-txt-link-freetext">skef@skef.org</a>.
<a
href="https://aka.ms/LearnAboutSenderIdentification"
moz-do-not-send="true">
Learn why this is important</a><o:p></o:p></span></p>
</div>
</td>
<td
style="width:56.25pt;background:#EAEAEA;padding:5.25pt 3.75pt 5.25pt 3.75pt;align:left"
width="75">
<br>
</td>
</tr>
</tbody>
</table>
<p>Some preliminary notes on an idea I'm looking info, starting
from this line of reasoning:<o:p></o:p></p>
<ol type="1" start="1">
<li class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo1">
My worry about using dmap for multi-language/region support
is that the solution is separate from the script/language
GSUB/GPOS mechanism. Ideally we want fonts that support
different scripts and languages via the latter, and doing so
while starting with different initial cmaps is a lot of work
and QA.<o:p></o:p></li>
<li class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo1">
This leads to the idea of allowing a TTC slot to pick a
script and language to serve as the default that I brought
up last week, but that will face the objection that it
violates the current semantic properties of the TTC font
collection spec: TTC currently works only at the SFNT level,
not below.<o:p></o:p></li>
<li class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo1">
That leads naturally to the prospect of "DSUB": the
metaphorical equivalent of dmap but at the GSUB level. All
this would need to do is specify a "pseudo-default" for
GSUB: act like this script and this language were the
defaults so they're used unless one is specified. <o:p></o:p></li>
<li class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level1 lfo1">
However, after thinking about how GSUB tables are structured
one realizes one can probably accomplish the same thing
without any spec changes.
<o:p></o:p></li>
</ol>
<p>Why? In GSUB and GPOS all offset fields below the header are
"hierarchical" -- each is relative to the start of the
subtable it appears in. And the header is basically a short
list of offsets (relative to the start of the table). Together
this means that one should be able to do the following with
(e.g.) GSUB:<o:p></o:p></p>
<ol type="1" start="1">
<li class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l2 level1 lfo2">
Move the table, and those below it, a bit further down in
the font file<o:p></o:p></li>
<li class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l2 level1 lfo2">
Add a new GSUB header above the existing one pointing to
(literally) the same featureList, lookupList and, if
relevant, featureVariations tables. (Each offset being
increased by the difference in start of the two headers.<o:p></o:p></li>
<li class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l2 level1 lfo2">
Add a new top-level ScriptList table below the new header,
with all offsets adjusted similarly except those for DFLT,
which points to a new Script table below it.
<o:p></o:p></li>
<li class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l2 level1 lfo2">
Add the new ScriptList table, with all offsets adjusted
similarly except those for defaultLangSys, which is adjusted
to point to the LangSys table of a different language
(within the original GSUB table).<o:p></o:p></li>
</ol>
<p>Now, with a very modest amount of added memory, you have two
GSUB tables -- one with the original mapping for DFLT dflt and
one with a new mapping for those. The latter will include some
"junk" bytes (the former's header, ScriptList and DFLT Script
tables) but nothing in it will make any use of those areas. (I
haven't yet tested whether ots and such will complain about
that.) And you can do this for more languages by adding more
such table combinations, limited only by the Offset16 fields
in the header. (One could, of course, repeat the whole GSUB
table to buy more overlapping table sets if needed.)<o:p></o:p></p>
<p>With similar modifications to GPOS (when needed), I think all
that one needs to build out the language-specific TTC slots
is:<o:p></o:p></p>
<ol type="1" start="1">
<li class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l4 level1 lfo3">
Per-slot head tables (to get the checksums right -- would be
nice if this wasn't required)<o:p></o:p></li>
<li class="MsoNormal"
style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l4 level1 lfo3">
Per-slot name tables (although for this one could add the
font-specific name strings to the end of the string data and
do something similar to GSUB with the NameRecord array,
sharing the string storage)<o:p></o:p></li>
</ol>
<p>All other tables, including cmap, would be shared in the
normal way.<o:p></o:p></p>
<p>To be clear, unless a picky client-side validator barfs on
these conventions I suspect one could build a cross-language
TTC font collection in this way
<i>today</i>, minimizing the memory cost of the additional
slots. I'm currently poking at constructing an example to make
this more concrete, but, of course, existing tools aren't
designed with this sort of thing in mind. I'll send another
note if and when I make progress.<o:p></o:p></p>
<p>Skef<o:p></o:p></p>
<div>
<p class="MsoNormal">On 12/21/23 23:58, Skef Iterum wrote:<o:p></o:p></p>
</div>
<p>I stand dystopianed. <o:p></o:p></p>
<p>However, to not yet give up entirely on this line of thinking
...<o:p></o:p></p>
<p>What is on the table in these messages is a further extension
of an existing table, in this case cmap. Which at least
suggests that the problem here isn't "system-level" support --
we think we can get those changes. What you describe is,
loosely speaking, "application level" support -- allowing the
context that the user interacts with to specify the needed
parameters, and then educating the user to do so.<o:p></o:p></p>
<p>I agree that's hopeless for the foreseeable future. <o:p></o:p></p>
<p>These dmap ideas do have the benefit of being <i>somewhat</i>
general (although one might worry about unusual cases). Maybe
other compelling use cases, or just the value of generality
itself, justify such an extension. Still, if the fundamental
problems are what you describe, we might also consider
addressing them directly and specifically. Instead of
extending cmap, and building region- or language-specific
fonts via a separate mechanism, we should at least consider
extending TTC to associate a named subfont with the missing
parameters. Basically: "render this set of tables using this
script and this language by default". Done a bit subtly, one
could just ship every cross-language font file with a "base"
font with just the name, and some entries for other scripts
and language, suitably named, and otherwise sharing TTC
data-structures. <o:p></o:p></p>
<p>From the perspective of the font engineer that seems more
productive than building a cross-language font with one set of
mechanisms and then building multiple data-sharing individual
language fonts using a different mechanism (assuming we still
want engineers to do the former).<o:p></o:p></p>
<p>Skef<o:p></o:p></p>
<div>
<p class="MsoNormal">On 12/21/23 18:15, Ken Lunde wrote:<o:p></o:p></p>
</div>
<pre>Skef,<o:p></o:p></pre>
<pre><o:p> </o:p></pre>
<pre>I might be the only one in this discussion who clearly remembers that Version 1.000 of Source Han Sans and Noto Sans CJK, which were released on 2014-07-15, *was* utopian in that the fonts with the full set of 64K glyphs, meaning genuine Pan-CJK, expected that language tagging would be used to access the desired non-default region-specific glyphs, with the default glyphs being for Japan. Reality quickly taught us that expecting language tagging alone to solve this was completely unrealistic for the following three reasons:<o:p></o:p></pre>
<pre><o:p> </o:p></pre>
<pre>1) The app must support language tagging<o:p></o:p></pre>
<pre>2) The app must support language tagging for the appropriate East Asian languages, which is now up to five for these Pan-CJK fonts<o:p></o:p></pre>
<pre>3) Assuming #1 and #2 work, the user must then language-tag the text<o:p></o:p></pre>
<pre><o:p> </o:p></pre>
<pre>Going on 10 years later, not much has changed for #1 and #2.<o:p></o:p></pre>
<pre><o:p> </o:p></pre>
<pre>Modern browsers supported the 'locl' GSUB feature way back in 2014, but support in authoring apps is still severely lacking today.<o:p></o:p></pre>
<pre><o:p> </o:p></pre>
<pre>I use Adobe InDesign to get full language-tagging support for these fonts, which is still about the only game in town. Adobe Illustrator silently added East Asian language-tagging in the 2018 release (in 2017), but it was a "close but no cigar" outcome in that they added only "Chinese" (that turned out to be Traditional Chinese for Taiwan) and Japanese, and despite filing bugs over five years ago, Adobe Illustrator 2024 (in 2023) is still unchanged in this regard. What makes the current support even less useful for mainstream users, ignoring that three of the five East Asian regions are not supported at all, is that the two supported East Asian regions are visible only when creating Character or Paragraph styles. They are not shown in the list of languages in the Character or Properties panels. Adobe Photoshop 2024 (in 2023) still does not support language tagging for East Asian languages.<o:p></o:p></pre>
<pre><o:p> </o:p></pre>
<pre>Getting back to Source Han Sans and Noto Sans CJK, Version 1.001 was released on 2014-09-12, which added separate 64K-glyph fonts for each of the four (at the time) supported East Asian regions. The 'locl' feature is still included for the benefit of those environments that support language tagging. All five regions were not supported until Version 2.000, which was released on 2018-11-19, which meant five separate sets of 64K-glyph fonts. The fifth region, of course, was Hong Kong SAR.<o:p></o:p></pre>
<pre><o:p> </o:p></pre>
<pre>In other words, we are quite far from Utopia, and we are unlikely to arrive there anytime soon.<o:p></o:p></pre>
<pre><o:p> </o:p></pre>
<pre>Regards...<o:p></o:p></pre>
<pre><o:p> </o:p></pre>
<pre>-- Ken<o:p></o:p></pre>
<pre><o:p> </o:p></pre>
<pre>On Dec 21, 2023, at 17:04, Skef Iterum <a
href="mailto:skef@skef.org" moz-do-not-send="true"><skef@skef.org></a> wrote:<o:p></o:p></pre>
<pre><o:p> </o:p></pre>
<pre>More stuff after hitting send too fast:<o:p></o:p></pre>
<pre>I can see a set of arguments against trying to deal with these regional problems within a single mega-font grounded one way or another in GIDs being a limited resource. But we've already decided to overcome that problem. So, for example, if we need to spend a GID to, in effect, abstractly represent a given codepoint to bridge from cmap into the shaping tables, we have GIDs to spend now. (And, as implied in my other messages today, wouldn't necessarily have to pay the typical file overhead for them.)<o:p></o:p></pre>
<pre>As I understand it that's how regional variations in, e.g., Cyrillic are handled now. So I guess, other than the large number of glyphs in CJK fonts I'm not understanding what requirements are pushing the solution in such a different (and seemingly ad hoc) direction.<o:p></o:p></pre>
<pre>Skef<o:p></o:p></pre>
<pre>On 12/21/23 16:49, Skef Iterum wrote:<o:p></o:p></pre>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<pre>Maybe I'm being utopian but I can't help thinking that either there's some token ("dialect"?) that Unicode should be tracking and formalizing but isn't, or Unicode is doing that and we haven't tilted the font specifications enough in its direction to use it. There's already all of that script and language infrastructure there that is meant for this flavor of need, and it seems like a much better place to be solving these problems than rapping stuff up in a TTC and having the client side pick out the sub-font by name or whatever.<o:p></o:p></pre>
<pre>Skef<o:p></o:p></pre>
<pre>On 12/21/23 15:00, Peter Constable wrote:<o:p></o:p></pre>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<pre>During the recent AHG meeting, I mentioned that Apple, Adobe and Microsoft, some years ago, had started discussing a ‘dmap’ (delta character map) table proposal. This was in late fall of 2016; the focus was on pan-CJK fonts, and in that timeframe Ken Lunde has submitted a proposal to UTC (L2/16-063 Proposal to accept the submission to register the “PanCJKV” IVD collection) to define variation sequences for ideographs that designated a range of variation selector characters to correspond to several regions for which regional glyph variants of CJK ideographs might need to be supported. I managed to find an archive of some emails from discussions at the time, so can summarize:<o:p></o:p></pre>
<pre> The aim was to be able to support distinct fonts for regional CJK variants without duplication of data. A TTC could allow de-duplication of glyph data, but there would be other duplication. We agreed the biggest concern was with ‘cmap’ data: If any one of the regional variant fonts in the collection were taken as a point of reference, then any of the other regional variants would have many of the same mappings (perhaps most), though not all the same mappings. But there wasn’t any existing means to share common mappings across fonts while there were also some different mappings. Dwane Robinson suggested that we define a new ‘dmap’ table that uses ‘cmap’ formats but is just used to describe the differences in mappings from a common ‘cmap’. We agreed that a ‘dmap’ table doesn’t need the duplication of different platforms/encodings, and that we can converge on only one platform/encoding (hence, no encoding records are necessary). We discussed format 4 versus 12, and agreed to allow either, but that both are never required. Now, we had teleconfs between Apple and MS, but the emails I found indicate that Behdad was also kept informed: one of the emails records that Behdad requested that format 13 also be allowed.<o:p></o:p></pre>
<pre> We hadn’t settled, however, on what to do about format 14 subtables. It wasn’t a priority for Apple at the time, but it seemed like it would be incomplete if we ignored it. Knowing that Ken Lunde was dealing a lot with VSes and also working on pan CJK Source Han Sans CJK, we brought Adobe into our discussion at that point.<o:p></o:p></pre>
<pre> The issue with format 14 is that it divides variation sequences into two groups: (i) VSes that map to the same glyph already mapped in a format 4 or 12 subtable (DefaultUVS), and (ii) VSes that map to a different glyph. Certainly the default mappings would be different in the various regional variant fonts, and some of the non-default mappings could also be different. (Even if a given VS never mapped to different glyphs in the different fonts, the fonts could still differ in what VSes they need to support.) So it’s necessary to resolve how a dmap/14 subtable should interacts with a cmap/4 (or cmap/12) subtable, with a cmap/14 subtable, with a dmap/4 (or dmap/12) subtable, and with a dmap/14 subtable. One possible approach would be that the dmap/14 subtable completely supersedes the cmap/14 subtable (i.e., the latter is not used at all, and there is no de-duplication of that data). Another approach could be that a dmap/14 subtable complements the cmap/14 subtable by providing select replacement mappings (a delta—though there are still further details about how that would work exactly).<o:p></o:p></pre>
<pre> There were some useful points brought up along the way: <o:p></o:p></pre>
<pre> • Ned Holbrook pointed out that the format 14 DefaultUVS subtable is just a space-saving variant of the NonDevaultUVS subtable. A font doesn’t need to have any DefaultUVS table: the same sequences could be handled in NonDefaultUVS subtables — less efficiently… _in a single font_.<o:p></o:p></pre>
<pre> • For CJK, Ken Lunde pointed out that there are two kinds of UVSes to consider: <o:p></o:p></pre>
<pre> • “Standardized” VSs: these are defined in the Unicode Standard (see unicode.org/Public/UCD/latest/ucd/StandardizedVariants.txt) for CJK Compatibility Ideographs. They are defined in Unicode in a region-independent manner, but most represent region-specific glyphs.<o:p></o:p></pre>
<pre> • “Ideographic” VSes: these are VSes registered in the Ideographic Variation Database (Ideographic Variation Database (unicode.org)) in region-specific collections. <o:p></o:p></pre>
<pre>Because of the nature of each type, Ken thought there might be limited sharing across fonts. (E.g., at least some font developers would want to support a given IVS collection only in the one regional font for the corresponding region.) He did identify cases, however, in which the same SVS would need to map to different glyphs in different fonts.<o:p></o:p></pre>
<pre> • Again, for CJK, there would be cases in which different fonts would need to support the same VSes, but they would differ wrt DefaultUVS vs. NonDefaultUVS mappings.<o:p></o:p></pre>
<pre> Ken also called out some other uses in email exchanges. It all suggested that an ideal solution would make it possible to construct a collection file in which - two or more fonts can share some UVS mapping data while also having some font-specific mapping data; and<o:p></o:p></pre>
<pre>- it's also possible to have other fonts that do not share any UVS mapping data with other fonts.<o:p></o:p></pre>
<pre> That would allow the fonts to support only UVSs that are relevant for their respective markets, while also having an efficiency benefit from data-sharing between certain of the fonts.<o:p></o:p></pre>
<pre> That was in December 2016. We ran into end-of-year holidays and never resumed to closed on an approach that optimizes size of VS mapping data. The following is the last draft proposal that we exchanged. —-<o:p></o:p></pre>
<pre>dmap - Character to Glyph Index Differences Table<o:p></o:p></pre>
<pre> This table is an optional adjunct to the ‘cmap’ table defining differences from the nominal mappings in order to increase sharing of the ‘cmap’ itself across fonts in a TTC.<o:p></o:p></pre>
<pre> If a font production tool determines that the ‘cmap’ tables across the fonts in a TTC are largely but not entirely identical, it can choose one font to be used as the basis for the others in terms of character to glyph index mapping, expressing the mappings of the other fonts using only the mappings that are different from those of the former font. An example would be a CJK font family with region-specific fonts, where most characters would map to the same glyph index.<o:p></o:p></pre>
<pre> The ‘dmap’ table<o:p></o:p></pre>
<pre> Type Name Description<o:p></o:p></pre>
<pre>UInt16 version Set to 0.<o:p></o:p></pre>
<pre>UInt16 numTables Number of offset fields to follow.<o:p></o:p></pre>
<pre>UInt32 offset[numTables] Array of byte offsets from beginning of table to cmap subtables. All subtables are assumed to use Unicode. There can be at most one subtable of either format 4, 12, or 13.<o:p></o:p></pre>
<pre> As in the ‘cmap’ table, each ‘dmap’ subtable shall have the same structure as in ‘cmap’, starting with a format field that determines the remainder. The language field for a format 4, 12, or 13 subtable must be set to zero.<o:p></o:p></pre>
<pre> The steps for determining the glyph index for a given UVS consisting of a base character and optional variation selector are as follows:<o:p></o:p></pre>
<pre> <o:p></o:p></pre>
<pre> • Apply the Unicode ‘cmap’ subtable to the base character to get the nominal glyph index.<o:p></o:p></pre>
<pre> • If the font has a ‘dmap’ format 4 or 12 subtable that maps the base character to a non-zero glyph index, it will replace the nominal glyph index.<o:p></o:p></pre>
<pre> • If the ‘cmap’ has a format 14 subtable, apply it in this way: <o:p></o:p></pre>
<pre>3.1.If the Default UVS Table contains the base character, the final glyph index will the be one determined by the ‘cmap’.<o:p></o:p></pre>
<pre>3.2.Else if the Non-Default UVS Table contains the base character, it will determine the final glyph index.<o:p></o:p></pre>
<pre>3.3.Else the final glyph index will remain as it was after step 2.<o:p></o:p></pre>
<pre> Note: An earlier draft of this document allowed for a second subtable of format 14, which would allow redefinition of variation sequences. Owing to uncertainty about usefulness and the exact behavior of the Default UVS Table, however, it has been removed pending further discussion.<o:p></o:p></pre>
<pre> —<o:p></o:p></pre>
<pre> In the previous draft, a different set of steps for handling UVSes were considered:<o:p></o:p></pre>
<pre> —<o:p></o:p></pre>
<pre>The steps for determining the glyph index for a given UVS consisting of a base character and optional variation selector are as follows:<o:p></o:p></pre>
<pre> 1. Apply the ‘cmap’ to the base character to get the nominal glyph index.<o:p></o:p></pre>
<pre>2. If the font has a ‘dmap’ format 4 or 12 subtable that maps the base character to a non-zero glyph index, it will replace the nominal glyph index.<o:p></o:p></pre>
<pre>3. If the ‘dmap’ has a format 14 subtable, it will be used in place of the one in the ‘cmap’.<o:p></o:p></pre>
<pre>4. If there is a format 14 subtable, apply it in this way:<o:p></o:p></pre>
<pre>4.1.If the Default UVS Table contains the base character, the final glyph index will the be one determined by the ‘cmap’.<o:p></o:p></pre>
<pre>4.2.Else if the Non-Default UVS Table contains the base character, it will determine the final glyph index.<o:p></o:p></pre>
<pre>4.3.Else the final glyph index will remain as it was after step 2.<o:p></o:p></pre>
<pre> —<o:p></o:p></pre>
<pre> Peter<o:p></o:p></pre>
<pre> <o:p></o:p></pre>
<pre>_______________________________________________<o:p></o:p></pre>
<pre>mpeg-otspec mailing list<o:p></o:p></pre>
<pre><a href="mailto:mpeg-otspec@lists.aau.at"
moz-do-not-send="true" class="moz-txt-link-freetext">mpeg-otspec@lists.aau.at</a><o:p></o:p></pre>
<pre><a
href="https://lists.aau.at/mailman/listinfo/mpeg-otspec"
moz-do-not-send="true" class="moz-txt-link-freetext">https://lists.aau.at/mailman/listinfo/mpeg-otspec</a><o:p></o:p></pre>
<pre><o:p> </o:p></pre>
</blockquote>
</blockquote>
<pre>_______________________________________________<o:p></o:p></pre>
<pre>mpeg-otspec mailing list<o:p></o:p></pre>
<pre><a href="mailto:mpeg-otspec@lists.aau.at"
moz-do-not-send="true" class="moz-txt-link-freetext">mpeg-otspec@lists.aau.at</a><o:p></o:p></pre>
<pre><a href="https://lists.aau.at/mailman/listinfo/mpeg-otspec"
moz-do-not-send="true" class="moz-txt-link-freetext">https://lists.aau.at/mailman/listinfo/mpeg-otspec</a><o:p></o:p></pre>
</div>
</blockquote>
</body>
</html>