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<p class="MsoNormal">I was trying to clean up some terminology and format descriptions in the OT spec and discovered there was a greater terminology problem than I realized. (This applies equally to OFF.) I’d like to get input on how people are used to using
these terms / names of structures and the best remedy for clear and consistent usage in the spec.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">This is about those structures that are found at the start of a (non-collection) font file: an offset (sub)table / array of table records.
<i><span style="color:#C00000">Q: What terms are people used to using for these?</span><o:p></o:p></i></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Here’s the skivvy wrt Apple’s TrueType Reference Manual, and OT/OFF:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><a href="https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6.html">Apple’s TrueType Reference Manual</a> has terminology that’s similar to but slightly different to that currently in OT/OFF, and it has its own inconsistency.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<ul style="margin-top:0in" type="disc">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo2">The TT font begins with a “font directory”, which is a two-part entity comprised of the “offset subtable” that is followed directly by the “table directory”.
<o:p></o:p></li></ul>
<p class="MsoNormal"><o:p> </o:p></p>
<ul style="margin-top:0in" type="disc">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo2">“Offset subtable” refers to the five fields from sfntVersion to rangeShift.<o:p></o:p></li></ul>
<p class="MsoListParagraph"><o:p> </o:p></p>
<ul style="margin-top:0in" type="disc">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo2">“Table directory” is used inconsistently:<o:p></o:p></li></ul>
<p class="MsoListParagraph"><o:p> </o:p></p>
<ul style="margin-top:0in" type="disc">
<ul style="margin-top:0in" type="circle">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level2 lfo2">There’s a good usage, meaning an array of records (each record comprised of tag, checksum, offset, length fields).
<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level2 lfo2">The bad usage: the same term is also used as the name for that record.<o:p></o:p></li></ul>
</ul>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The <a href="https://docs.microsoft.com/en-us/typography/opentype/spec/otff#organization-of-an-opentype-font">
OT spec</a> / OFF refer to that four-member record as “Table Record”, though it inconsistently uses “Table Record entries” or “Table Record” to mean the array.
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The record part is easy to fix in OT/OFF and in Apple’s spec: That record should be called “TableRecord”, and that term should only be used for that structure (not the array).<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">But OT / OFF also have another inconsistency in that “Table Directory” is used with different meanings:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<ul style="margin-top:0in" type="disc">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo2">The table record array only (consistent with Apple’s good use of “table directory”)<o:p></o:p></li></ul>
<p class="MsoNormal"><o:p> </o:p></p>
<ul style="margin-top:0in" type="disc">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo2">The Offset Table, or the combination of offset table + table records array (= Apple’s “font directory”)<o:p></o:p></li></ul>
<p class="MsoListParagraph"><o:p> </o:p></p>
<p class="MsoNormal">This inconsistency dates back at least to Microsoft’s TrueType 1.66 spec.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">A simple fix would be to use “Offset Table” to mean the same thing that Apple calls the “font directory”, incorporating a
<span style="font-family:Consolas;color:black;background:#E7E6E6">tableRecords[]</span> member into that structure, then revise current instances of “Table Directory” changing to “Offset Table” or “tableRecords array” as appropriate.
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">But as these are such a basic part of every font file, it occurs to me that many implementers may have terminology engrained in their minds—or their code—that differs, and that this could be confusing / hard to adjust to.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">An alternative would be a clean-up of Apple’s terminology:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<ul style="margin-top:0in" type="disc">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo2">“<span style="font-family:Consolas">Font Directory</span>” is comprised of the “<span style="font-family:Consolas">Offset Table</span>” followed directly by the “<span style="font-family:Consolas">Table
Directory</span>”.<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo2">“<span style="font-family:Consolas">Offset Table</span>” is comprised of five members,
<span style="font-family:Consolas">sfntVersion</span> to <span style="font-family:Consolas">
rangeShift</span>.<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo2">“<span style="font-family:Consolas">Table Directory</span>” is comprised of an array of “<span style="font-family:Consolas">TableRecord</span>”. (This could be described as a struct
consisting of <span style="font-family:Consolas">tableRecords[]</span>.)<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo2">“<span style="font-family:Consolas">TableRecord</span>” is a structure comprised of tag, checksum, offset and length fields.<o:p></o:p></li></ul>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Yet another alternative would be to use “<span style="font-family:Consolas">Font Directory</span>” as a formal struct name that includes
<span style="font-family:Consolas">tableRecords[]</span> as a member, so “offset table” would not be used in the formal description.
<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Personally, I don’t care for either of these alternatives owing to the use of “font directory”: IMO, that would be better used in describing a collection-level structure, not a font-resource-level structure. (I.e., a collection file begins
with a font directory that provides offsets to “offset tables” (or whatever) for one or more font resources.)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Peter<o:p></o:p></p>
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