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SVGT 1.2: Font matching

From: Kalle Raita <kraita@nvidia.com>
Date: Sat, 19 Jan 2008 02:28:03 +0100
Message-ID: <85DD8D3F1695004A8A9A5AC16CE584BE04CC18A0@deemmail01.nvidia.com>
To: <www-svg@w3c.org>

Hi all,
 
A couple of questions relating to font matching. 
 
1) When using external SVG font, how are the two descriptors 
interpreted? What is their precedence or is the other just ignored?
In file a.svg:
... 
 <font-face font-family="foo-family" font-style="normal">
   <font-face-src>
     <font-face-uri xlink:href="b.svg#font" />
   </font-face-src>
 </font-face>
 
In file b.svg:
 <font id="font">
   <font-face font-family="foo-family" font-style="italic"> 
   </font-face>
   <glyph...
 </font>

So, a uses font from b and both present descriptors. What happens if 
the info is contradictory? What if some values are in their default 
in either or both descriptors?


2) When is the UA allowed to synthetize a font? 
I'm using the font-style as an example here as well. When the UA can 
synthesize oblique font from given font?

a1) If font-style is not specified in otherwise matching font-face? 
    (This seems to be the assumption in the conformance tests)
a2) If font-style is all or contains normal? (Based on the fact 
    that there is only one set of glyphs, see below)
b)  When font-face for that style has not been defined, 
    e.g., close match with font-style="normal" exists?

This also involves the question whether omitting equals really 'all' 
and whether 'all' equals listing 'normal','oblique','italic'. 

It is also worth noting that the glyphs in the SVG font cannot separate 
between style inside a single font. On the other hand, some 
other font format might be able to contain different glyphs for
different styles.

There may be situations where a font does not suit well for 
synthesis and the designed may want exclude the possibility. 
How is this communicated?

This issue can be seen in, e.g., conformance test text-area-220-t.
i)   font-face of the test file does not define font-style
ii)  font-face in SVGSansFree.svg referenced does not define font-style
iii) Text "THE END" is requested in italic SVGFreeSans.
iv)  The reference image shows text in italic. 

Basically the test assumes that the UA is capable of synthesizing the
italic 
form from the normal font. 

Reading the Font section in both SVGT 1.2 and CSS2 specs didn't help me
answer 
these questions. Any pointers or interpretations of the CSS2 descriptor
matching algorithm?

Yours,
   - Kalle Raita

Kalle Raita 
NVIDIA Corporation 
Tel. +358 40 723 1441 
kraita@nvidia.com 
http://eu.nvidia.com <http://eu.nvidia.com/>  

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Received on Saturday, 19 January 2008 01:28:49 GMT

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