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<div class="moz-cite-prefix">On 2015-08-28 at 11:25 Greg Hitchcock
<a class="moz-txt-link-abbreviated" href="mailto:gregh@microsoft.com">gregh@microsoft.com</a> [mpeg-OTspec] wrote:<br>
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<blockquote style="border-left: 2px solid #009900 !important;
border-right: 2px solid #009900 !important; padding: 0px 15px 0px
15px; margin: 8px 2px;"
cite="mid:BN1PR03MB1230C05CEEE0D0AB6F37085BE6E0@BN1PR03MB123.namprd03.prod.outlook.com"
type="cite">
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Sitka Text"">Re:
Shape and mapping of Glyph ID 0 (the .notdef glyph)<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Sitka Text"">This
sounds reasonable. I suspect that color support would also be
reasonable for Glyph ID 0. I agree that no mappings should
point to this glyph.</span></p>
</blockquote>
<br>
Perhaps I misunderstand what is meant by "no mappings should point
to" glyph ID 0, but it seems to me that the spec in some cases
requires and in other cases allows this.<br>
<br>
In format 4 cmaps (Segment mapping to delta values) we have the
requirement that character 0xFFFF be included to terminate the
search, with the suggestion -- only reasonable -- that it point to
glyph ID 0. <br>
<br>
Also, in format 4 cmaps, is this tricky phrase:<br>
<blockquote type="cite">If the value obtained from the indexing
operation is not 0 (which indicates missingGlyph), idDelta[i] is
added to it to get the glyph index</blockquote>
<br>
This sounds like the authors expected in some cases that the
indexing operation will return 0, resulting in a character code
mapping to glyph ID 0.<br>
<br>
Similarly for format 2 cmaps:<br>
<blockquote type="cite">Finally, if the value obtained from the
subarray is not 0 (which indicates the missing glyph), you should
...</blockquote>
<br>
And in format 0, the only way to indicate a character is not
supported by the font is by pointing to glyph ID 0.<br>
<br>
Regards,<br>
Bob<br>
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